About

Joshua Weitz is a Professor and Clark Leadership Chair in Data Analytics at the University of Maryland, within the Department of Biology. His research centrally focuses on understanding how viruses influence human and environmental health. His group develops theories and computational models to study how viral infections affect the fates of individuals, populations, and communities, as well as their impact on ecosystem-scale functions. Weitz collaborates with a global network of experimentalists, field biologists, and public health experts to integrate models and data, aiming to advance fundamental understanding of living systems and inform science-driven actions. His research efforts are broadly organized around viruses of microbes, known as virus ecology, and viruses of humans, referred to as infectious disease dynamics. His team is interdisciplinary, including bioscientists, physicists, mathematicians, and biologists. Since joining the University of Maryland research community in Summer 2023, Weitz has actively sought to deepen understanding of viral spread principles and their applications to areas such as phage therapy, marine ecosystems, microbial ecology and evolution, and infectious disease dynamics. His ongoing and planned research initiatives in Quantitative Viral Dynamics encompass foundational viral ecology, marine viral impacts, bacteriophage therapy, microbial ecology and evolution, and infectious disease dynamics.

Research topics

• Computer Science
• Sociology
• Medicine
• Econometrics
• Environmental health
• Economics
• Data science
• Physics
• Geography
• Demography
• Psychology

Selected publications

• Viruses aren’t all bad: In the ocean, some help fuel the food web – a new study shows how

  2026-01-13

  articleOpen accessSenior author
  PublisherDOI

• Code for "The adaptive plasticity of temperate phage λ"

  Zenodo (CERN European Organization for Nuclear Research) · 2026-02-20

  otherOpen access

  This deposit contains the Jupyter Notebooks (with Julia code), R scripts and Python code neeeded to produce all figures of article The adaptive plasticity of temperate phage λ Sylvain Gandon , Tapan Goel , Joshua S. Weitz and Sébastien Lion Submitted to Virus Evolution (Feb 2026) ExplicitSimulations.zip contains all the code and data needed to generate Figures 1, S2, S3 and S5. This code was written by Tapan Goel and Joshua Weitz. An actively maintained version of the code can be found on Github. Data for figure 1 courtesy of Dr. Ido Golding - data from Zeng et al. 2010 (DOI: 10.1016/j.cell.2010.03.034). This data can also be found in the file Figure1.m in ExplicitSimulations.zip.

  PublisherDOI

• Density-dependent feedback and higher-order interactions enable coexistence in phage–bacteria community dynamics

  The ISME Journal · 2026-01-01 · 1 citations

  articleOpen accessSenior author

  Diverse phage-bacteria communities coexist at high densities in environmental, agricultural, and human-associated microbiomes. Phage-bacteria coexistence is often attributed to coevolutionary processes mediated by complex, pairwise infection networks. Here, using in vitro experiments and mathematical models, we explore how higher-order interactions function as a complementary, ecological feedback mechanism to stabilize phage-bacteria communities. To do so, we examine an environmentally derived, synthetic phage-bacteria community comprised of five marine heterotrophic bacteria (Cellulophaga baltica and Pseudoalteromonas strains) and five associated phage. We used Bayesian inference to reconstruct free phage production in one-step growth experiments and then forecasted pairwise phage-bacteria community dynamics over multiple infection cycles. In contrast to model predictions of rapid bacterial population collapse, each bacterial strain persisted in the community. We hypothesized and then experimentally validated the relevance of infection attenuation at relatively high viral densities. We extended models into a community context, corroborating complex coexistence of all phage and bacteria. Life-history traits inferred in community fits often differed from those inferred in a pairwise context, implicating higher-order interactions as an additional, ecological stabilization mechanism. Follow-up experiments confirm that phage traits (including burst size) can shift when infecting single versus multiple strains. More broadly, these findings suggest that complex community coexistence of phage and bacteria may be more common than anticipated when including feedback mechanisms outside of the growth-dominated regimes of fitted pairwise models that do not reflect the full scope of ecologically relevant contexts.

  PublisherDOI

• Coexistence of Photosynthetic Marine Microorganisms, Viruses and Grazers: Towards Integration in Ocean Ecosystem Models

  Environmental Microbiology · 2026-04-01

  articleOpen accessSenior authorCorresponding

  Photosynthetic microorganisms are responsible for primary production at the base of the marine food web and influence global biogeochemistry. Their growth is balanced by mortality processes, including zooplankton grazing and viral lysis. These predators coexist despite competing for the same microorganisms. Here, we develop a community model of photosynthetic microorganisms, grazers and viruses that incorporates elemental quotas and is suitable for ocean ecosystem models. We evaluate the extent to which coexistence is facilitated by: (i) explicit infected phytoplankton; (ii) heterogeneity in susceptibility to viral infection; and (iii) higher-order mortality for the predators. We show a trade-off between the virus latent period and virulence in facilitating coexistence. The latent period generates oscillations that reduce the growth rate of the free virus, promoting coexistence. Heterogeneity in susceptibility supports coexistence through resource partitioning, while higher-order mortality widens the coexistence regime. The model outcomes are sensitive to viral life history traits, including the percentage of infected cells and the balance between virally- and zooplankton-induced mortality. Leveraging algebraic model equilibria, we identify parameter combinations that yield realistic ecological properties in simplified epipelagic environments. Our models suggest that efforts to embed virus dynamics in ocean ecosystem models should include moderate to strong resistance to viral infection.

  PublisherDOI

• Phage infection fronts trigger early sporulation and viral entrapment in bacterial populations

  The ISME Journal · 2026-01-01

  articleOpen accessSenior author

  Bacteriophages (phages) infect, lyse, and propagate within bacterial populations. However, physiological changes in bacterial cell state can protect against infection even within genetically susceptible populations. One such example is the generation of endospores by Bacillus and its relatives, characterized by a reversible state of reduced metabolic activity that protects cells against stressors including desiccation, energy limitation, antibiotics, and infection by phage. Here we tested how sporulation at the cellular scale impacts phage dynamics at population scales when propagating amongst B. subtilis in spatially structured environments. Plaques resulting from infection and lysis were approximately three-fold smaller on lawns of spore-forming bacteria vs. non-spore-forming bacteria. Analysis of plaque growth revealed that final plaque size was reduced due to an early termination of expanding phage plaques rather than the reduction of plaque growth speed. Microscopic imaging of the plaques revealed "sporulation rings," i.e. spores enriched around plaque edges relative to phage-free regions. We developed a series of mathematical models of phage, bacteria, spores, and small molecules that recapitulate plaque dynamics. We show evidence that phage infections trigger the formation of sporulation rings that reduce the productivity of phage infections and halt plaque spread even when resources are available for infection and lysis further away from plaque centers. Moreover, sporulation rings are also enriched in viable virospores, suggesting that although dormancy limits phage infections at population scales in the near term, viruses may co-opt phage-avoidance strategies to re-emerge over the long term, opening new avenues to explore the entangled fates of phages and their bacterial hosts.

  PublisherDOI

• Code for "The adaptive plasticity of temperate phage λ"

  Zenodo (CERN European Organization for Nuclear Research) · 2026-02-20

  otherOpen access

  This deposit contains the Jupyter Notebooks (with Julia code), R scripts and Python code neeeded to produce all figures of article The adaptive plasticity of temperate phage λ Sylvain Gandon , Tapan Goel , Joshua S. Weitz and Sébastien Lion Submitted to Virus Evolution (Feb 2026) ExplicitSimulations.zip contains all the code and data needed to generate Figures 1, S2, S3 and S5. This code was written by Tapan Goel and Joshua Weitz. An actively maintained version of the code can be found on Github. Data for figure 1 courtesy of Dr. Ido Golding - data from Zeng et al. 2010 (DOI: 10.1016/j.cell.2010.03.034). This data can also be found in the file Figure1.m in ExplicitSimulations.zip.

  PublisherDOI

• The adaptive plasticity of temperate phage λ

  Virus Evolution · 2026-04-27

  articleOpen access

  Abstract When temperate phage $\lambda $ infects its host, the bacterium Escherichia coli, it can either replicate to form new progeny (lytic growth) or integrate its genome into the host chromosome (lysogenization). Crucially, the probability of lysis or lysogeny is tightly regulated and varies with phage and host genotypes and the environment. In particular, the number of viruses coinfecting the same host cell is known to have a strong effect on the outcome of the infection, leading to phenotypic plasticity: the probability of lysogenization is higher when the cellular multiplicity of infection (MOI) increases. However, the selective forces driving the evolution of plasticity in phage $\lambda $ remain unclear. Here we analyze the evolution of the plasticity of lysogenization and show that a MOI-varying strategy is adaptive when the abundance of susceptible cells fluctuates periodically. We study how the speed of these fluctuations and various within-host decision rules affect the evolution of viral plasticity. Our results suggest that the complex genetic regulation of lysogeny of temperate phages can be shaped by natural selection allowing viruses to use MOI as indirect information to persist in environments with fluctuating host densities.

  PublisherDOI

• Sub-daily virus sampling at the Bermuda Atlantic Time Series reveals diel and depth-structured population dynamics without community-level shifts

  PLoS Biology · 2026-03-06

  articleOpen access

  Ocean microbes contribute to biogeochemical cycles and ecosystem function, but they do so under top-down pressure imposed by viruses. While viruses are increasingly understood spatially and beginning to be incorporated into predictive modeling, high-frequency ocean virus dynamics remain understudied due to methodological challenges. Here we sampled stratified Bermuda Atlantic Time Series (BATS) waters for 112 hours at sub-daily 4- (surface) or 12- (deep chlorophyll maximum) hour intervals, purified viral particles from these samples, sequenced their metagenomes, and used the resulting data to characterize high-frequency virus community dynamics. Aggregated community diversity metrics changed with depth, but were not statistically significant temporally at a fixed location. However, finer-scale population-level analyses revealed both depth and temporal change, including physicochemical depth-driven differences and, in surface waters, thousands of viral populations that exhibited statistically significant diel rhythms. Statistical analyses revealed three main archetypes of temporal dynamics that themselves differed in abundance patterns, host predictions, viral taxonomy, and gene functions. Among these, highlights include viruses resembling an archetype with a night peaking pattern in activity that include an over-representation of viruses that putatively infect Prochlorococcus, a phototrophic cyanobacteria. Together, these efforts provide baseline community- and population-scale short-time-frame observations relevant to future climate state modeling.

  PublisherDOI

• Communicating the Economic Impact of Science Funding Cuts Changes Attitudes and Motivates Action

  2026-03-06

  articleOpen accessSenior author

  In the United States, recent cuts to federal science funding have widespread negative consequences for research, healthcare, and the economy. Scalable behavioral interventions that communicate the impact of science funding cuts could support informed policy-related decisions and bridge partisan divides. In two preregistered psychological experiments (N=5,342) with politically-representative samples of U.S. adults, we tested novel text, quiz, and map-based interventions that illustrated economic losses associated with National Institutes of Health (NIH) funding cuts. Across the political spectrum, the interventions robustly and reliably decreased approval of funding cuts, and increased perceived knowledge and negative local impact. Interactive interventions featuring quizzes and maps selectively motivated further action (e.g., contacting congressional representatives, sharing information). We scaled these interventions via a public website (https://scienceimpacts.org/); a third study analyzing naturalistic user data (N=24,028) revealed converging evidence of effectiveness. Overall, scalable interventions that interactively communicated economic impact changed attitudes and motivated action to support science funding.

  PublisherDOI

• Communicating the Economic Impact of Science Funding Cuts Changes Attitudes and Motivates Action

  PsyArXiv (OSF Preprints) · 2026-03-06

  preprintOpen access

  In the United States, recent cuts to federal science funding have widespread negative consequences for research, healthcare, and the economy. Scalable behavioral interventions that communicate the impact of science funding cuts could support informed policy-related decisions and bridge partisan divides. In two preregistered psychological experiments (N=5,342) with politically-representative samples of U.S. adults, we tested novel text, quiz, and map-based interventions that illustrated economic losses associated with National Institutes of Health (NIH) funding cuts. Across the political spectrum, the interventions robustly and reliably decreased approval of funding cuts, and increased perceived knowledge and negative local impact. Interactive interventions featuring quizzes and maps selectively motivated further action (e.g., contacting congressional representatives, sharing information). We scaled these interventions via a public website (https://scienceimpacts.org/); a third study analyzing naturalistic user data (N=24,028) revealed converging evidence of effectiveness. Overall, scalable interventions that interactively communicated economic impact changed attitudes and motivated action to support science funding.

  Publisher

Recent grants

• Collaborative Research: Inferring Cellular Lysis and Regeneration of Organic Matter by Marine Viruses

  NSF · $337k · 2018–2023

• Synergistic control of acute respiratory pathogens by bacteriophage and the innate immune response

  NIH · $1.9M · 2019–2025

• Collaborative Research: RAPID: Integrative Modeling of Intervention Serology and the Role of Shield Immunity in Reducing COVID-19 Epidemic Spread

  NSF · $99k · 2020–2021

• Synergistic control of acute respiratory pathogens by bacteriophage and the innate immune response

  NIH · $502k · 2019–2024

• Understanding the Effects of Complex Phage-Bacteria Infection Networks on Marine Ecosystems

  NSF · $471k · 2012–2017

Frequent coauthors

• Jonathan Dushoff

  McMaster University

  51 shared

• Stephen J. Beckett

  University of Maryland, College Park

  41 shared

• Bryan T. Grenfell

  Princeton Public Schools

  38 shared

• David Demory

  Sorbonne Université

  36 shared

• Rogelio A. Rodriguez-Gonzalez

  Quantitative BioSciences

  36 shared

• Laurent Debarbieux

  Université Paris Cité

  35 shared

• Sang Woo Park

  Princeton University

  31 shared

• Daniel Muratore

  Georgia Institute of Technology

  27 shared

Awards & honors

• Simons Foundation Investigator in Theoretical Physics of Liv…
• Chaire Blaise Pascal, Institut de Biologie of the ENS, Paris…
• Fellow of the American Academy of Microbiology, 2019
• Fellow of the American Association for the Advancement of Sc…
• Best Postgraduate Textbook Prize Awarded by the Royal Societ…