Emerging from 2020… into 2022

Koskella lab retreat at the UC Berkeley Angelo Coast Reserve, March 2022

Where did 2021 go? I often ask myself that question, but here we are half way through 2022. Despite time moving in odd ways, we have been slowly regaining a sense of normalcy and sciencing away as always! Here is a brief taste of what we’ve been up to:

Britt has spent the 2021/2022 academic year as a fellow of the Wissenschaftskolleg zu Berlin (https://www.wiko-berlin.de). Her sabbatical has afforded her some amazing opportunities to read, think, reflect, dream, and plan. She has been working on, among other things, two projects relating to how phage ecology and evolution are shaped by the host (meta)communities in which they exist and a theoretical exploration of how host immune systems are shaped by the microbiome over evolutionary timescales. More on both soon! Britt is also excited to announce that she was selected as a CZ Biohub Investigator (https://www.czbiohub.org/investigator-program/). The unrestricted funds provided by this initiative will allow the group to explore new high-risk ideas on how phages might shape host health in unexpected ways, and she is thrilled to join this exciting network of researchers.

New arrivals! The lab has grown a lot over the last year. We have welcomed Dominique Holtappels as a new postdoctoral researcher to lead the Pear Project. He arrived from KU Leuven, where he completed his PhD in Bio-science Engineering with Prof Rob Lavigne. His previous research focused on the challenges and opportunities of phage therapy in agriculture (see more here) and he is now taking on a large-scale project, funded by our NSF/USDA CAREER award, to better understand how phage host range is shaped by and shapes bacterial community dynamics. We are also welcoming new NSF postdoctoral Fellow Milo Johnson. Milo is joining us from Michael Desai‘s lab at Harvard, where he recently completed his PhD exploring the molecular evolution of yeast (see more here) and developed new and improved ways to visualize scientific data. At Berkeley, he will be developing new ways to understand neutral evolutionary processes that occur over the course of pathogen infection. We also had two new PhD students join the group in 2021: Asa Conover and Claire Evensen. Asa is joining us as a Berkeley Fellow most recently from the labs of Drs. Gregory Gilbert and Ingrid Parker at UC Santa Cruz, where he was working as a research technician. Prior to that, Asa graduated Summa Cum Laude from the University of Southern California with a BS in Biological Sciences, where he worked on projects ranging from hydrothermal vent effects on protist biogeography to stable isotope probing (SIP) experiments in diazotrophic marine cyanobacteria (see here). Claire joined the Boots lab as a Berkeley fellow in 2021, and will be co-advised by Britt on projects relating to the development and testing of new theory on factors that shape microbial coexistence. Claire received her BS in Biochemistry and Mathematics at the University of Wisconsin-Madison, and then completed her MSc in Mathematical Modelling and Scientific Computing at Oxford. You can check out her work here. Finally, we were incredibly lucky to welcome recent UCB graduate Julia Sherman as our new lab manager, and UCB grads Sara A. and Fernando Diaz as NSF REPs fellows!

New papers! Despite all of the setbacks from lockdown and other pandemic-related challenges, the group has been pushing forward with some awesome new results:

Covers from the lab

Mehlferber, E. C., McCue, K. F., Ferrel, J. E., Koskella, B., & Khanna, R. (2022). Temporally Selective Modification of the Tomato Rhizosphere and Root Microbiome by Volcanic Ash Fertilizer Containing Micronutrients. Applied and Environmental Microbiology, e00049-22.

Meyer, K. M., Porch, R., Muscettola, I. E., Vasconcelos, A. L. S., Sherman, J. K., Metcalf, C. J. E., Lindow, S. E. & Koskella, B. (2022). Plant neighborhood shapes diversity and reduces interspecific variation of the phyllosphere microbiome. The ISME journal, 1-12.

Dewald-Wang, E. A., Parr, N., Tiley, K., Lee, A., & Koskella, B. (2022). Multiyear time-shift study of bacteria and phage dynamics in the phyllosphere. The American Naturalist, 199(1), 126-140.

Debray, R., Herbert, R. A., Jaffe, A. L., Crits-Christoph, A., Power, M. E., & Koskella, B. (2021). Priority effects in microbiome assembly. Nature Reviews Microbiology, 1-13.

Debray, R., Socolar, Y., Kaulbach, G., Guzman, A., Hernandez, C. A., Curley, R., Dhond, A., Bowles, T. & Koskella, B. (2021). Water stress and disruption of mycorrhizas induce parallel shifts in phyllosphere microbiome composition. New Phytologist.

What a year (2020) it’s been!

Sciencing during a global pandemic is no joke.

Image shows snippets from our year in lockdown, starting with some masked planting of tomato in our new field trail, followed by a basket of gifts from my lab for tenure, and then a group picture (on zoom of course). Next row is a picture of the pear trees that are now out in bloom, a group photo from our socially distanced lab retreat, and a row of tomatoes growing in the greenhouse.

Well, you need only look at how long it has been since our last news post to see that things have been…. unusual. As COVID-19 brought the University and our lab to a grinding halt, we all had to find new ways to continue meeting (thank you Zoom), teaching, and doing research. As we slowly return to a new normal, still wearing our masks and social distancing, we finally have time to reflect on our successes despite the circumstances.

The first news is that, since the last post, Britt got tenure this past July! It was a somewhat anticlimactic event given it was just a few months after we began lockdown, but the lab group put together a fantastic gift basket and we had a great time dreaming up the next phase of the lab. On that note, this past month we had our first ever virtual lab retreat. This three day event allowed us to get back together as a team, identify shared goals and values, share new tricks and hacks, discuss failures and successes, and – of course – have some fun too! It was incredibly refreshing and left us all with a renewed sense of purpose as a group.

We have also welcomed some new lab members, including postdoctoral research fellow Kate Ennis, who is joining us from UC Santa Cruz. Kate received both a UC President’s fellowship and NSF postdoctoral fellowship to start up a new system exploring the role of phages in the floral microbiome. We were also joined by new graduate student, Emily Dewald-Wang, who came via Washington University in St Louis, and will be working on – among other things – bringing community ecology and disease ecology together using plant-microbiome interactions (including as part of the NSF CAREER – funded Pear tree project). Over the Summer and Fall, we were lucky to bring Ash Rosas onto the team as a NSURP fellow. And we can’t forget to mention to new lab mascots: Simba (a 95 pound shepherd mix who joined the lab last April) and Pili (a brand new puppy currently the size of Simba’s head but with fierce ambitions of someday taking him down.

As we said goodbye to (or prepare to say goodbye to) past members, we have lots of great news to share on their behalf: Cathy Hernandez will be wrapping up her PhD this Summer and is heading to Yale as a Donnelly fellow to work with Paul Turner on the ecology and evolution of viral thermal performance. Wenke Smets, who has been with us as a postdoctoral fellow for two years, will be returning to Belgium this Autumn to take up an independent research fellowship there, continuing to explore the phyllosphere. The undergraduate researchers in the lab are also kicking ass! Xuening Zhang graduating this past Spring and started her PhD at Cornell, working with Anurag Agrawal as a Presidential Life Science Fellow. Tristan Caro began his PhD at UC Boulder, and just received a NSF GRFP! Rachel Rovinsky received a SPUR grant to support her senior research project and will be graduating this coming Spring, after which she will be starting her PhD at UW Madison in the Microbiology Doctoral Training Program. Isabella Muscettola will be starting this Spring as a crewmember on the Grand Canyon National Park Fire Effects & Fire Monitoring Program, assisting on managed fires through data collection of fire behavior and firefighting and implementing prescribed burns. Previous AmGen summer student Nina De Luna (an undergraduate at Penn State) will be starting her PhD in the Immunology program at the University of Pennsylvania, and AmGen fellow Lina Ruiz (an undergraduate at Purchase College) will be starting her PhD at Columbia this Fall. Congratulations to you all!

In other news, graduate student Reena Debray received a Berkeley IB Summer Research Award and a Sigma Xi GIAR grant to support her work on the evolution (and loss) of phage resistance in bacterial pathogens. Graduate student Kama Chock received a UC Berkeley SMART fellowship to fund a mentored project in collaboration with an undergraduate researcher. The lab also received funding from the California Tomato Research Institute to run a set of field trials, lead by graduate student Elijah Mehlferber, this coming summer to test the role of disease protective symbionts in agricultural practice.

Finally, a few new publications to share:

  • McDonald, J. E., Marchesi, J. R., & Koskella, B. (2020). Application of ecological and evolutionary theory to microbiome community dynamics across systems.
  • Hernandez, C. A., Salazar, A. J., & Koskella, B. (2020). Bacteriophage-Mediated Reduction of Bacterial Speck on Tomato Seedlings. PHAGE1(4), 205-212.
  • Mutalik, V. K., Adler, B. A., Rishi, H. S., Piya, D., Zhong, C., Koskella, B., … & Arkin, A. P. (2020). High-throughput mapping of the phage resistance landscape in E. coli. PLoS biology18(10), e3000877.
  • Koskella, B. (2020). The phyllosphere. Current Biology30(19), R1143-R1146.
  • Koskella, B., & Bergelson, J. (2020). The study of host–microbiome (co) evolution across levels of selection. Philosophical Transactions of the Royal Society B375(1808), 20190604.
  • Simmons, E. L., Bond, M. C., Koskella, B., Drescher, K., Bucci, V., & Nadell, C. D. (2020). Biofilm structure promotes coexistence of phage-resistant and phage-susceptible bacteria. Msystems5(3).
  • Smets, W., & Koskella, B. (2020). Microbiome: Insect Herbivory Drives Plant Phyllosphere Dysbiosis. Current biology30(9), R412-R414.

As well as PhD student Kama Chock’s new papers from his Master’s work:

  • Chock, M. K., Hoyt, B., & Amend, A. S. (2021). Mycobiome transplant increases resistance to Austropuccinia psidii in an endangered Hawaiian plant. Phytobiomes Journal.
  • Chock, M. K. (2020). The global threat of Myrtle rust (Austropuccinia psidii): Future prospects for control and breeding resistance in susceptible hosts. Crop Protection, 105176.

Wrapping up 2019! Welcomes and new papers…

A subset of our group (it’s hard to get everyone together at the same time!), November 2019
(Newest members: Kama Chock (1st year PhD Student; 2nd from left), Wenke Smets (BAEF Postdoctoral Fellow; 9th from left), Emily Dewald-Wang (Research Technician, 5th from left), and Ana Luisa Soares de Vasconcelos (visiting PhD Student from the University of São Paulo; 3rd from right)

We’ve had a fun and productive 2019, with lots of new arrivals, new projects underway, and new papers. Here are just a few of the Fall 2019 highlights:

  • We welcomed many new lab members, including postdoctoral researcher Wenke Smets who is joining us from Belgium on a B.A.E.F. fellowship, new PhD student Mason Kamalani Chock arriving from Hawaii, visiting PhD student Ana Luisa Soares de Vasconcelos from the University of São Paulo, research technician Emily Dewald-Wang who recently graduated from Washington University in St. Louis, as well as many new fantastic undergraduate researchers.
  • We successfully completed not one, but three (!!!) summer field trials/experiments across sites in Berkeley, Davis, and Half Moon Bay (see pictures below). Stay tuned for data on above-belowground interactions, protective microbiomes in agriculture, and phyllosphere microbiome transmission in the next year.
  • We found out that our NSF CAREER award was recommended for funding, which means the Pear Tree Fire Blight project is official! Thanks to the hard work of 6 undergraduate researchers, we’ve performed monthly sampling of 24 Bradford Pear Trees around Berkeley for the last four years and can now compare our phage local adaptation and host range results to the full viral metagenomes from this natural disease system!
  • We had a number of publications resulting from the creativity and hard work of the group and our collaborators, including (only listing those not covered in earlier posts):

Spring news, updates, and congratulations                                                         June 2019

It has been a fantastic Spring in the lab, and we are launching into a busy summer of research, with three ongoing field trials (that’s right, we’re heading outdoors!) and a new cohort of summer undergraduate researchers. Stay tuned for more on their work soon.

First, a few congratulations:

1) Dr. Norma Morella has successfully completed her PhD! She is heading off to the Fred Hutchinson Cancer Research Center in Seattle to work in the lab of Neelendu Dey, studying the role of the human microbiome in gastrointestinal cancer. During her four years in the lab, Norma developed numerous tools (including the use of ddPCR for exploring bacteria-phage interactions) ran a series of pathbreaking experiments to explore how phages impact the microbiome and most recently how microbial communities in the phyllosphere adapt to hosts over successive passaging. She was also a fantastic mentor to undergraduate researchers in the lab, a wonderful collaborator, and a general joy to be around. We will miss her! But are all very excited to follow her career and future research.


2) First year PhD student Reena Debray was awarded the SSE Graduate Research Excellence Grant (R.C. Lewontin Early Award) to support her work using functional genomics to probe adaptation of commensal bacteria to their plant hosts.

3) Fourth year PhD student Cathy Hernandez received an outstanding abstract award For the upcoming ASM Microbe meeting. Make sure to catch her talk from 1:45pm – 1:55pm on Sat, Jun 22 if you are attending.

4) and our newest lab member (soon to be first year PhD student in the lab) Mason Kamalani Chock received a Ford Foundation Predoctoral Fellowship. He’ll be bringing his fungal community expertise to the lab, so stay tuned for a more complete picture of the microbiome!

and 5) Britt received a Hellman award from the Hellman Family Faculty Fund to support the lab’s work on microbiome-mediated protection against pathogens.

Next, a few new publications to share (most up on BioRxiv now, so please share your thoughts/comments with us!)

1) Morella, N. M., Zhang, X., & Koskella, B. (2019). Tomato seed-associated bacteria confer protection of seedlings against foliar speck caused by Pseudomonas syringae. Phytobiomes Journal, (ja). Online early here!

2) Morella, N. M., Weng, F. C. H., Joubert, P. M., Metcalf, C. J. E., Lindow, S., & Koskella, B. (2019). Successive passaging of a plant-associated microbiome reveals robust habitat and host genotype-dependent selection. bioRxiv, 627794. Found here.

3) C. Jessica Metcalf and Britt Koskella. (2019) Protective microbiomes can limit the evolution of host pathogen defense. bioRxiv 665265; doi: https://doi.org/10.1101/665265

(Now here: Metcalf, C.J.E. and Koskella, B. (2019), Protective microbiomes can limit the evolution of host pathogen defense. Evolution Letters, 3: 534-543.)

and 4) C. Jessica E. Metcalf, Lucas P Henry, Maria Rebolleda-Gomez, and Britt Koskella. (2019) Why evolve reliance on the microbiome for timing of ontogeny? bioRxiv 665182; doi: https://doi.org/10.1101/665182

(Now here: Metcalf, C. J. E., Henry, L. P., Rebolleda-Gómez, M., & Koskella, B. (2019). Why Evolve Reliance on the Microbiome for Timing of Ontogeny?. mBio, 10(5).)

And for those attending either ASM Microbe 2019 (San Francisco), ASPB 2019 (San Jose), the Microbial Population Biology GRC, or ESEB 2019 (Turku, Finland) – we hope to see you there!


Congratulations to previous PhD student Sean Meaden                             February 2019

A huge congratulations to Dr. Sean Meaden, who graduate from the lab in 2016, on his recent Marie Curie Fellowship award. I asked Sean to send a quick blurb on what he will be doing, and he responded:

I will be spending 2 years at the University of Otago working with Prof. Peter Fineran. The Fineran group are expert on studying both abortive infection and CRISPR immunity. I aim to combine experimental evolution with metagenomics to tease apart the relative contributions of ecological conditions on the maintenance or loss of bacterial immune systems. I will be investigating how ecological conditions shape bacterial immune systems. We know that phage defence systems such as CRISPR and abortive infection are highly variable between closely related bacterial species, which suggests rapid loss and acquisition. In turn, we predict that the maintenance or loss of these systems will be determined by ecological conditions. I will then return to Exeter for 1 year to continue this work with Dr. Edze Westra, an expert in CRISPR ecology and evoution.”

Congratulations again Sean, we can’t wait to hear about your new work and your life on the South Island!

Papers, grants, and new postdoc arriving:                                                      January 2019

We wrapped up 2018 with the exciting announcement that our project was among those chosen for the new NSF Rules of Life program. Elijah Mehlferber, Jessica Metcalf, Steve Lindow and I will be testing whether and how knowledge of microbiome-mediated protection from one disease system can be used to generate predictions about protective microbial consortia in another. We are also working with Francis Weng, who published THIS fantastic paper and recently visited the lab on a fellowship from Taiwan, to develop and test the best computational methods for identifying protective consortia.

We are thrilled to welcome a new postdoctoral researcher, starting in March 2019, Kyle Meyer – joining us from the Bohannan lab at the University of Oregon. Kyle will be working with Britt, Jess Metcalf, and Steve Lindow to understand how microbiome transmission mode impacts upon community structure and function.

Britt recently contributed two opinion/review pieces, the first focused on new approaches in understanding bacteria-phage interactions, and the next on how host resistance against parasites might be gained and lost. She was also interviewed for a piece in Quanta magazine: “Should Evolution Treat Our Microbes as Part of Us?”

In collaboration with Justin Meyer and Katie Petrie at UCSD, and Jordan Moberg Parker at UCLA, we have been awarded a University of California Multicampus Research Programs and Initiatives (MRPI) award to explore the molecular mechanisms underpinning phage host range.

Finally, Britt was also recently chosen as a Winkler Faculty Fellow, and is incredibly appreciative of this support from the Winkler family, which will be used to further develop the Pear tree Fire Blight disease system we have been working on to track bacteria-phage dynamics in urban tree populations.

New papers and arrivals:                                                                             September 2018

We are welcoming Reena Debray, our newest graduate student, to the lab! Reena’s time in the lab is off to a great start as she seeks to quantify the impact of phages on plant resistance to pathogens. Stay tuned for some great science.

I am also happy to share two new papers from the lab:

1. Berg, M., & Koskella, B. (2018). Nutrient-and Dose-Dependent Microbiome-Mediated Protection against a Plant Pathogen. Current Biology, 28(15), 2487-2492.

During her final year of graduate school, Maureen Berg spent time in our lab to learn about plant microbiomes (to complement her amazing work on gut microbiota of C. elegans, as can be seen here: https://www.nature.com/articles/ismej2015253). Maureen and I set out to ask a very simple question: does the tomato phyllosphere protect against pathogen colonization. We used a new method we’ve been developing in the lab, where we transplant the microbiomes from field-grown tomato plants onto mostly sterile plants in the growth chamber. In this way, we can control host genotype, and other extrinsic factors, and examine how plants with these augmented microbiomes differ in phenotype from those without. Of course we had to add a twist, and in this case we thought we would ask how dose impacts microbiome-mediated protection. To make a long story short, the answer is that it does! But not always in the way we would have predicted – sometimes less was better. We then tested these patterns more explicitly using a constructed community of 12 culturable isolates from the tomato phyllosphere, and were able to confirm this counterintuitive result – which we are now following up on. Moreover, we accidentally discovered that fertilizing the plants before the experiment abolished the previously observed protection – a result we confirmed with a fully factorial experiment. When the plants were not fertilized, pathogen colonization depended critically on whether the phyllosphere had been colonized by commensal bacteria, but when they were fertilized, the phyllosphere no longer had any observable protective effects. See news coverage of the work here: http://news.berkeley.edu/2018/07/26/fertilizer-destroys-plant-microbiomes-ability-to-protect-against-disease/

2. Koskella, B., & Taylor, T. B. (2018). Multifaceted Impacts of Bacteriophages in the Plant Microbiome. Annual review of phytopathology, 56, 361-380.

In collaboration with Tiffany Taylor at Bath University, we spent some time thinking about the myriad ways in which phages might impact the plant microbiome. This blossoming field nicely complements work from the human microbiome (and other systems) suggesting that phages are key components of the microbiome, shaping composition, diversity, and function. This means there is plenty of work to be done in order to determine how and when such knowledge can be leveraged in human health and agriculture.

More papers, awards, and grants:                                                                          July 2018

Congratulations to graduate student Norma Morella, who received the College of Natural Resources M.J. Vlamis Award for high level of academic distinction!

It’s no surprise given the great new results she has published:

(1) Morella, N. M., Gomez, A. L., Wang, G., Leung, M. S., & Koskella, B. (2018). The impact of bacteriophages on phyllosphere bacterial abundance and composition. Molecular ecology, 27(8), 2025-2038.

We show that naturally occurring phage communities in the tomato phyllosphere have important impacts on both the abundance (short term) and diversity (longer term) of colonizing bacteria during phyllosphere microbiome establishment. Taking an experimental approach, we were able to ‘deplete’ phages from field collected microbiomes using filtration (see below) and then compare the initial establishment of microbial communities on leaves in the presence versus absence of these lytic phages. Our results suggest the presence of phages decreases abundance of total bacteria 24 hours after colonization on new plants, but increases bacterial diversity when measured a week later.


(2) Morella, N. M., Yang, S. C., Hernandez, C. A., & Koskella, B. (2018). Rapid Quantification of Bacteriophages and Their Bacterial Hosts in Vitro and in Vivo using Droplet Digital PCR. Journal of virological methods.

We have spent the last few years developing a new method to quantify bacterial and phage abundance and dynamics both in vitro and in vivo. Using droplet digital PCR, we are working to get more accurate measures of bacteria/phage densities in order to more precisely address questions of bacterial and phage fitness, phage-phage competition, and the impact of phages on their bacterial host populations. We are very happy with the method, especially as it is saving us a great deal of time and plastic that we used to spend on CFU (colony forming units) and PFU (plaque forming units) dilution plating.

Finally, we are also celebrating the receipt of an NSF grant from DEB to study the importance of microbiome transmission in shaping the evolution and ecology of (plant) host-microbiomes interactions. Stay tuned for a postdoctoral opportunity announcement.

P.s. we also discovered that Carrot Dogs are amazing!!! https://www.brandnewvegan.com/recipes/smoky-vegan-carrot-dogs


Papers and awards:                                                                                                 April 2018

It’s been a busy year so far! Among the recent exciting news:

(1) Fourth year graduate student Norma Morella, AmGen summer scholar Annika Gomez (now heading to MIT for her NSF-funded Phd), undergraduate researchers Grant Wang, Michelle Leung, and I have just published a paper in Molecular Ecology showing the impact that a naturally occurring phage community can have on microbiome colonization of new host plants. In short: phages reduce bacterial density overall and seem to shape both the alpha and beta diversity of the phyllosphere during initial establishment.

(2) Third year graduate student Cathy Hernandez was accepted into the 2018 Australia-Americas PhD Research Internship Program to spend the upcoming summer working with Jeremy Barr at Monash University. More to come soon on this exciting project!

(3) First year graduate student Elijah Mehlferber has been awarded honorable mention for his NSF GRFP proposal this year. He is seeking to better understand how competition within the phyllosphere can alter plant susceptibility to pathogens.

(4) Incoming graduate student, and former summer AmGen Scholar, Reena Debray has been awarded a NSF GRFP for her planned work to examine the role phages play in shaping bacterial adaptation to host plants. Welcome back to the lab Reena!

(5) Undergraduate researcher Callie Cuff, who is completing her honors thesis in the lab examining host range of naturally occurring phages from pear trees, has been awarded the Nutritional Sciences Department Citation Award in recognition of her distinguished undergraduate work.

(6) Undergraduate researcher Shirley Zhang has been awarded a 2018 ASPB Summer Undergraduate Research (SURF) Fellowship to continue her amazing work on seed-associated microbiota and disease.

(7) Undergraduate researcher Kore Lum has been awarded a URAP Summer Award to support her research on phage-mediated selection of the plant pathogen P. syringae.

Congratulations to all!

A few new papers from the lab:                                                                     February 2018

(1) The microbiome beyond the horizon of ecological and evolutionary theory published in Nature Ecology and Evolution. Britt’s coauthors, Jess Metcalf from Princeton and Lindsay Hall from the Quadrum Institute set out to ask where current evolutionary and ecological theory might fall short when being applied to microbiome research. It was a very challenging and fun piece to write! (found here: https://www.nature.com/articles/s41559-017-0340-2).

Figure 2_new

(2) Phd Student, Norma Morella, and Britt took a stab at figuring out what we might learn about the interaction between the immune system and the microbiome by looking across systems. This short opinion piece certainly got us thinking, and emphasized that there is still a lot of work to be done (The Value of a Comparative Approach to Understand the Complex Interplay between Microbiota and Host Immunity can be found here: https://www.frontiersin.org/articles/10.3389/fimmu.2017.01114/full).

(3) In collaboration with Derek Lin and Henry Lin in the Department of Medicine at University of New Mexico, we recently examined the promise of phage therapy and its complex history.  (Phage therapy: An alternative to antibiotics in the age of multi-drug resistance can be found here: chttps://www.ncbi.nlm.nih.gov/pmc/articles/PMC5547374/).

(4) As part of a large theoretical undertaking, Britt was coauthor on a paper examining when and how you can generate frequency dependent selection in host-parasite coevolution without the strict specificity for infection that is typically built into models. This work suggests that fluctuating selection (important in many theories, including the Red Queen Hypothesis for the maintenance of sex) might be far more common than predicted based on infection genetic mechanisms. Paper can be found here: http://rspb.royalsocietypublishing.org/content/284/1866/20171615

Also, if you’re interested, Britt partook in a QandA for Current Biology about everything from her career to the future of science. More here: http://www.cell.com/current-biology/pdf/S0960-9822(17)31395-7.pdf

Britt awarded the ASM Young Investigator Prize                                   September 2017

Britt is one of three recipients of the American Society for Microbiology’s Young Investigator Award, which “Recognizes and rewards early career scientists for research excellence and potential in microbiology and infectious disease.” She will be accepting the award, and giving a research seminar, at ASM Microbe in Atlanta this coming Summer.


Now out in the New Phytologist: exploring the relationship between tree health and the bark microbiome                                                                                                May 2017

Summary: Host susceptibility to pathogens can be shaped by genetic, ecological, and evolutionary factors. The ability to predict the spread of disease therefore requires an integrated understanding of these factors, including effects of pests on pathogen growth and competition between pathogens and commensal microbiota for host resources. We examined interactions between the leaf-mining moth Cameraria ohridella, the bacterial causal agent of bleeding canker disease Pseudomonas syringae pv aesculi, and the bark-associated microbiota of horse chestnut (Aesculus hippocastanum) trees. Through surveys of > 900 trees from 60 sites in the UK, we tested for ecological or life history predictors of leaf miner infestation, bleeding canker, or coinfection. Using culture-independent sequencing, we then compared the bark microbiomes from 46 trees to measure the association between microbiome composition and key ecological variables, including the severity of disease. Both pest and pathogen were found to respond to tree characteristics, but neither explained damage inflicted by the other. However, we found a clear loss of microbial diversity and associated shift in microbiome composition of trees as a function of disease. These results show a link between bark-associated microbiota and tree health that introduces the intriguing possibility that tree microbiota play key roles in the spread of disease.

Figure 2 cropped

New paper by Sean Meaden in Environmental Microbiology Reports examining the microbiota of English Oak in Wytham Woods                                         May 2016

Summary: Drivers of bacterial community assemblages associated with plants are diverse and include biotic factors, such as competitors and host traits, and abiotic factors, including environmental conditions and dispersal mechanisms. We examine the roles of spatial distribution and host size, as an approximation for age, in shaping the microbiome associated with Quercus robur woody tissue using culture-independent 16S rRNA gene amplicon sequencing. In addition to providing a baseline survey of the Q. robur microbiome, we screened for the pathogen of acute oak decline. Our results suggest that age is a predictor of bacterial community composition, demonstrating a surprising negative correlation between tree age and alpha diversity. We find no signature of dispersal limitation within the Wytham Woods plot sampled. Together, these results provide evidence for niche-based hypotheses of community assembly and the importance of tree age in bacterial community structure, as well as highlighting that caution must be applied when diagnosing dysbiosis in a long-lived plant host. Read more here!

Congratulations to Cathy Hernandez on her NSF graduate research fellowship!

Cathy’s first year in the lab is off to a great start, with plants in the greenhouse ready for her first multigenerational  bacteria – phage selection experiment. The funding from her GRFP will be used to take her research out into the field. Watch this space, and well done Cathy!

Congratulations to DR Sean Meaden! What a great few years it’s been, and best of luck with all of your future sciencing. We will miss you!!

Last week I traveled back across the sea and down the coast to the beautiful (but very rainy) Cornwall to celebrate the successful PhD viva (aka defense) of my first PhD student, Sean Meaden. A big thanks to external examiner Prof Martha Clokie for insightful comments and for hanging around to celebrate (despite my bailing early due to severe jet lag – and I can’t even blame the baby). The visit was bittersweet, as the joy of celebrating Sean’s success was coupled with the sadness of no longer having Sean in the lab. Sean impressed me every single day that he was part of the lab; whether it was learning how to develop bioinformatic pipelines to analyze microbiome datasets, sequencing and annotating phage genomes, running experiments in the greenhouse, or volunteering in Sierra Leone during the ebola outbreak, Sean’s work ethic, integrity, and love of science made him an absolute pleasure to work with. Oh yeah, and he happens to be one of the nicest, sincere, and well-balanced people I know. I have no doubt that Sean’s future scientific endeavors will be hugely successful and I look forward to following his continued growth as a scientist, as well as to our continued  collaborations. Congratulations Sean!

Phage (in tomato leaf) cake!


Dr Meaden
Dr. Meaden – all the wiser.

P.s. Thanks to Sarah Paul for baking and designing the amazing phage and tomato cakes!

New paper in AREES exploring microbial adaptation in nature (collaboration with Dr. Michiel Vos at the University of Exeter, ESI)              Dec 2015

Abstract: Although their diversity greatly exceeds that of plants and animals, microbial organisms have historically received less attention in ecology and evolutionary biology research. This knowledge gap is rapidly closing, owing to recent technological advances and an increasing appreciation for the role microbes play in shaping ecosystems and human health. In this review, we examine when and how the process and patterns of bacterial adaptation might fundamentally differ from those of macrobes, highlight methods used to measure adaptation in natural microbial populations, and discuss the importance of examining bacterial adaptation across multiple scales. We emphasize the need to consider the scales of adaptation as continua, in which the genetic makeup of bacteria blur boundaries between populations, species, and communities and with them concepts of ecological and evolutionary time. Finally, we examine current directions of the field as we move beyond the stamp-collecting phase and toward a better understanding of microbial adaptation in nature.

You can access the paper here!

Britt and Nicole have a new paper out exploring the generality of bacterial resistance to phage across time and space                July 2015 

Koskella, B., and N. Parr. 2015. The evolution of bacterial resistance against bacteriophages in the horse chestnut phyllosphere is general across both space and time. Philosophical Transactions of the Royal Society of London B: Biological Sciences 370. HERE

Abstract: Insight to the spatial and temporal scales of coevolution is key to predicting the outcome of host–parasite interactions and spread of disease. For bacteria infecting long-lived hosts, selection to overcome host defences is just one factor shaping the course of evolution; populations will also be competing with other microbial species and will themselves be facing infection by bacteriophage viruses. Here, we examine the temporal and spatial patterns of bacterial adaptation against natural phage populations from within leaves of horse chestnut trees. Using a time-shift experiment with both sympatric and allopatric phages from either contemporary or earlier points in the season, we demonstrate that bacterial resistance is higher against phages from the past, regardless of spatial sympatry or how much earlier in the season phages were collected. Similarly, we show that future bacterial hosts are more resistant to both sympatric and allopatric phages than contemporary bacterial hosts. Together, our results suggest the evolution of relatively general bacterial resistance against phages in nature and are contrasting to previously observed patterns of phage adaptation to bacteria from the same tree hosts over the same time frame, indicating a potential asymmetry in coevolutionary dynamics.

Figure 3

New paper by Sean exploring context-dependent nature of costs of resistance to phage now online in Evolution                April 2015

Meaden, S., Paszkiewicz, K., & Koskella, B. (2015). The cost of phage resistance in a plant pathogenic bacterium is context‐dependent. Evolution. HERE

Abstract: Parasites are ubiquitous features of living systems and many parasites severely reduce the fecundity or longevity of their hosts. This parasite-imposed selection on host populations should strongly favor the evolution of host resistance, but hosts typically face a trade-off between investment in reproductive fitness and investment in defense against parasites. The magnitude of such a trade-off is likely to be context-dependent, and accordingly costs that are key in shaping evolution in nature may not be easily observable in an artificial environment. We set out to assess the costs of phage resistance for a plant pathogenic bacterium in its natural plant host versus in a nutrient-rich, artificial medium. We demonstrate that mutants of Pseudomonas syringae that have evolved resistance via a single mutational step pay a substantial cost for this resistance when grown on their tomato plant hosts, but do not realize any measurable growth rate costs in nutrient-rich media. This work demonstrates that resistance to phage can significantly alter bacterial growth within plant hosts, and therefore that phage-mediated selection in nature is likely to be an important component of bacterial pathogenicity.

Evernote Snapshot 20140515 131242

Tomato leaf infected with Pseudomonas syringae pv tomato 48 hours previously. Credit: Alexander Rose.

Paper exploring the transition of the human-associated bacterium, Helicobacter pylori, now online and open access at Evolutionary Applications               Nov 2014

Lin, D., & Koskella, B. (2014). Friend and foe: factors influencing the movement of the bacterium Helicobacter pylori along the parasitism‐mutualism continuum. Evolutionary Applications. HERE

Figure 1Abstract: Understanding the transition of bacterial species from commensal to pathogen, or vice versa, is a key application of evolutionary theory to preventative medicine. This requires working knowledge of the molecular interaction between hosts and bacteria, ecological interactions among microbes, spatial variation in bacterial prevalence or host life history, and evolution in response to these factors. However, there are very few systems for which such broad datasets are available. One exception is the gram-negative bacterium, Helicobacter pylori, which infects upwards of 50% of the global human population. This bacterium is associated with a wide breadth of human gastrointestinal disease, including numerous cancers, inflammatory disorders, and pathogenic infections, but is also known to confer fitness benefits to its host both indirectly, through interactions with other pathogens, and directly. Outstanding questions are therefore why, when, and how this bacterium transitions along the parasitism–mutualism continuum. We examine known virulence factors, genetic predispositions of the host, and environmental contributors that impact progression of clinical disease and help define geographical trends in disease incidence. We also highlight the complexity of the interaction and discuss future therapeutic strategies for disease management and public health in light of the longstanding evolutionary history between the bacterium and its human host.

New book chapter in collaboration with Dr. Tiffany Taylor on the potential impacts of phages on plant-bacterial interactions

Koskella, B. and Taylor, T. B. The potential role of bacteriophages in shaping plant-bacterial interactions, in Plant-Bacterial Interactions, Murillo, J., Jackson, R. W., Arnold, D., and Vinatzer, B. (eds). Horizon Scientific Press, Norwich UK.

Table 1

The American Naturalist Vice Presidential Symposium issue is now online ahead of print, including Britt’s new work on phage adaptation through time and space, as well as open questions in disease ecology and evolution              (July 2014)

Check the papers out here:


and http://www.jstor.org/stable/10.1086/677032

(press release here: http://www.amnat.org/an/newpapers/VPKoskella.html)


Our work on phages in Horse chestnut trees highlighted in Current Biology                                                                                           (June 2014)

Check out this great piece on phage therapy for plants and people by Michael Gross in Current Biology:


Nice coverage of the work being done in the lab, especially by Sean Meaden.

New paper in collaboration with Prof Mike Brockhurst now online and open access                                                                           (March 2014)


“Bacteria-phage coevolution, the reciprocal evolution between bacterial hosts and the phages that infect them, is an important driver of ecological and evolutionary processes in microbial communities. There is growing evidence from both laboratory and natural populations that coevolution can maintain phenotypic and genetic diversity, increase the rate of bacterial and phage evolution and divergence, affect community structure, and shape the evolution of ecologically relevant bacterial traits. Although the study of bacteria phage coevolution is still in its infancy, with open questions remaining about the specificity of the interaction, the gene networks of coevolving partners, and the relative importance of the coevolving interaction in complex communities and environments, there have been some intriguing recent developments. In this review we sum up our current understanding of bacteria-phage coevolution both in the laboratory and in nature, discuss recent findings that demonstrate both the coevolutionary process itself and the impact of coevolution on bacterial phenotype, diversity and interactions with other species, particularly their eukaryotic hosts, and outline future directions for the field.”

Results of a PubMed search for keywords of studies focused on host and parasite genomics (black dashed line) and bacteria and phage genomics (grey dashed line) versus host-parasite coevolution (black solid line) and bacteria-phage coevolution (grey solid line). Exact search terms were combinations of genom*, host, parasit*, bacter*, *phage, and coevol* linked with “and” functions. The results illustrate that while bacteria-phage systems pioneered the early genomic studies of host-parasite interactions, they have been notably under-represented in studies of coevolution.
Results of a PubMed search for keywords of studies focused on host and parasite genomics (black dashed line) and bacteria and phage genomics (grey dashed line) versus host-parasite coevolution (black solid line) and bacteria-phage coevolution (grey solid line). Exact search terms were combinations of genom*, host, parasit*, bacter*, *phage, and coevol* linked with “and” functions. The results illustrate that while bacteria-phage systems pioneered the early genomic studies of host-parasite interactions, they have been notably under-represented in studies of coevolution.

Britt is now the research highlights associate editor for Evolutionary Applications                                                                                           (Jan 2014)

First research highlight available now: http://onlinelibrary.wiley.com/doi/10.1111/eva.12146/full

Evolutionary Applications is the only journal specializing specifically in publishing papers that make contributions to fundamental questions in evolutionary biology using study systems that are of practical or applied importance in topics including, but not limited to: agriculture, aquaculture, biomedicine, biotechnology, climate change, conservation biology, disease biology, forestry, invasion biology, and fisheries and wildlife management. As such, one of our main goals is to promote interest of applied evolution to a diverse audience including evolutionary biologists, ecologists, biomedical researchers, environmental consultants, and biologists within industry, government, and health care. Toward this end, this new series of research highlights will offer brief synopses of new work with direct relevance to readers of Evolutionary Applications from across other journals with the aim of exploring the breadth of potential applications of evolutionary theory from across fields and disciplines.”

If you’ve recently read or written a paper (from any journal) that exemplifies the application of evolutionary theory, please feel free to suggest it for a future highlight!

Sean’s new paper on the risks associated with phage biopesticide use in the environment is out now and open access                    (Nov 2013)


“Interest in using bacteriophages to control the growth and spread of bacterial pathogens is being revived in the wake of widespread antibiotic resistance. However, little is known about the ecological effects that high concentrations of phages in the environment might have on natural microbial communities. We review the current evidence suggesting phage-mediated environmental perturbation, with a focus on agricultural examples, and describe the potential implications for human health and agriculture. Specifically, we examine the known and potential consequences of phage application in certain agricultural practices, discuss the risks of evolved bacterial resistance to phages, and question whether the future of phage therapy will emulate that of antibiotic treatment in terms of widespread resistance. Finally, we propose some basic precautions that could preclude such phenomena and highlight existing methods for tracking bacterial resistance to phage therapeutic agents.”

My new paper on bacteria-phage coevolution within horse chestnut trees is now out and open access                  (July 2013)


“It is increasingly apparent that the dynamic microbial communities of long-lived hosts affect their phenotype, including resistance to disease. The host microbiota will change over time due to immigration of new species, interaction with the host immune system, and selection by bacteriophage viruses (phages), but the relative roles of each process are unclear. Previous metagenomic approaches confirm the presence of phages infecting host microbiota, and experimental coevolution of bacteria and phage populations in the laboratory has demonstrated rapid reciprocal change over time. The key challenge is to determine whether phages influence host-associated bacterial communities in nature, in the face of other selection pressures. I use a tree-bacteria-phage system to measure reciprocal changes in phage infectivity and bacterial resistance within microbial communities of tree hosts over one season. An experimental time shift shows that bacterial isolates are most resistant to lytic phages from the prior month and least resistant to those from the future month, providing clear evidence for both phage-mediated selection on bacterial communities and bacterial-mediated selection on phage communities in nature. These reciprocal changes suggest that phages indeed play a key role in shaping the microbiota of their eukaryotic hosts.”

P.s. I have also published the reviews for this paper and my response to these reviews in the “blog” tab here.

New paper on the power of experimental coevolution is now online at TREE                                  (March 2013)


“Coevolution, the process of reciprocal adaptation and counter-adaptation between ecologically interacting species, affects most organisms and is considered a key force structuring biological diversity. Our understanding of the pattern and process of coevolution, particularly of antagonistic species interactions, has been hugely advanced in recent years by an upsurge in experimental studies that directly observe coevolution in the laboratory. These experiments pose new questions by revealing novel facets of the coevolutionary process not captured by current theory, while also providing the first empirical tests of longstanding coevolutionary ideas, including the influential Red Queen hypothesis. In this article, we highlight emerging directions for this field, including experimental coevolution of mutualistic interactions and understanding how pairwise coevolutionary processes scale up within species-rich communities.”

-Brockhurst and Koskella 2013

Our new paper on the importance of understanding phage specificity in natural populations is out!                 (March 2013)

And it’s open access: http://www.mdpi.com/1999-4915/5/3/806

Why should we care about which bacteria are infected by what phages? Because the underlying specificity for infection is key to predicting if an how phages will effect the bacterial populations and communities in which they are found. We review what is known, what we need to learn, and why it matters. We also present the results from Sean’s masters project, where he tested whether natural phages have narrow or broad host ranges. The answer: both!

Network interaction among bacteria and phage collected from horse chestnut tree leaves
Interaction network for bacteria and phages collected from horse chestnut tree leaves

Welcome to new masters student, Amy McLeman      (March 2013)

Amy will be taking a novel approach to understanding if and how plants might benefit from phages in the environment. Although there is some evidence that viruses move around within plants, it has yet to be determined whether phages can play a role in hindering the establishment of infection by bacterial pathogens.

Watch this space!

Sean Meaden has joined the lab!           (Sept 2013)


Sean finished his masters project on characterizing the specificity of natural phages from the horse chestnut phyllosphere and has now begun his doctoral work. For his first project, Sean will be examining the costs associated with bacterial resistance to phages in their natural habitats.

There is good evidence that resisting parasites is costly, but most of this evidence comes from tests in the lab (e.g. our recent paper on resisting multiple phages: here). Sean is taking this a step further to determine what these costs might look like in terms of the bacteria’s ability to infect its plants hosts. Stay tuned for some great results!

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