Biology subjects

Kashtan, N.

Publications and source records attributed to Kashtan, N..

8 recordsLinked to original sources

bioRxiv2026

Microscale spatial fragmentation promotes bacterial survival under antibiotics

Most bacteria inhabit fragmented microscale environments rather than well-mixed systems in which antibiotic efficacy is typically defined. Here, we show that microscale spatial fragmentation alone can deterministically promote bacterial survival under antibiotic exposure. A coarse-grained theoretical model predicts that, at fixed bulk cell density and antibiotic concentration, fragmentation generates refuges through two coupled mechanisms: slower growth, which reduces susceptibility to growth-dependent antibiotics, and a finite antibiotic-per-cell constraint that lowers the effective intracellular antibiotic concentration. Using a microdroplet platform spanning five orders of magnitude in volume, we experimentally confirm these predictions for {beta}-lactams; we further demonstrate that the same fragmentation-mediated protection extends to antibiotics with distinct modes of action. Spatial fragmentation thus creates robust, non-genetic antibiotic refuges governed by physical constraints rather than resistance or collective protection, with implications for bacterial persistence in natural and clinical environments and for antibiotic design.

microbiology↗

bioRxiv2024

Hydration conditions as a critical factor in antibiotic-mediated bacterial competition outcomes

Antibiotic secretion plays a pivotal role in bacterial interference competition, yet the impact of environmental hydration conditions on such competition is not well-understood. Here, we investigate how hydration conditions affect interference competition among bacteria, studying the interactions between the antibiotic-producing Bacillus velezensis FZB42 and two bacterial strains susceptible to its antibiotics: Xanthomonas euvesicatoria 85-10 and Pseudomonas syringae DC3000. Our results show that wet-dry cycles significantly modify the response of the susceptible bacteria to both the supernatant and cells of the antibiotic-producing bacteria, compared to constantly wet conditions. Notably, X. euvesicatoria shows increased protection against both the cells and supernatants of B. velezensis under wet-dry cycles, while P. syringae cells become more susceptible under wet-dry cycles. In addition, we observed a reciprocal interaction between P. syringae and B. velezensis, where P. syringae inhibits B. velezensis under wet conditions. Our findings highlight the important role of hydration conditions in shaping bacterial interference competition, providing valuable insights into microbial ecology of water-unsaturated surfaces, with implications for applications such as biological control of plant pathogens and mitigating antibiotic resistance.

microbiology↗

bioRxiv2024

The impact of micro-habitat fragmentation on microbial populations growth dynamics

Microbial communities inhabit almost every habitat on Earth and are essential to the function of diverse ecosystems. Most microbial habitats are not spatially continuous and well-mixed, but rather composed, at the microscale, of many isolated or semi-isolated local patches, resulting in partitioning of microbial populations into discrete local populations. The impact of this spatial fragmentation on population dynamics is not well-understood. Here, we study how fragmentations affect the growth dynamics of clonal microbial populations and how dynamics in individual patches dictate those of the whole metapopulation. To investigate this, we developed the {micro}-SPLASH, a novel ecology-on-a-chip platform, enabling the culture of microbes in microscopic landscapes comprised of thousands of microdroplets, spanning a wide range of sizes. Using the {micro}-SPLASH, we cultured the model bacteria E. coli and based on time-lapse microscopy, analyzed the population dynamics within thousands of individual droplets at single-cell resolution. Our results reveal that growth curves vary dramatically with droplet size. While growth rates generally increase with drop size, reproductive success and the time to approach carrying capacity, display non-monotonic patterns. Combining {micro}-SPLASH experiments with computational modeling, we show that these patterns result from both stochastic and deterministic processes, and demonstrate the roles of initial population density, patchiness, and patch size distribution in dictating the local and metapopulation dynamics. This study reveals basic principles that elucidate the effects of habitat fragmentation and population partitioning on microbial population dynamics. These insights are imperative for a deeper understanding of natural microbial communities and have significant implications for microbiome engineering.

microbiology↗

bioRxiv2022

Droplet size and surface hydrophobicity enhance bacterial plasmid transfer rates in microscopic surface wetness

Conjugal plasmids constitute a major engine for horizontal gene transfer in bacteria, and are key drivers of the spread of antibiotic resistance, virulence, and metabolic functions. Bacteria in terrestrial habitats often inhabit surfaces that are not constantly water-saturated, where microscopic surface wetness (MSW), comprised of thin liquid films and microdroplets, permanently or intermittently occurs. How physical properties of microdroplets, and of the surfaces they reside on, affect plasmid transfer rates is not well understood. Here, building on microscopy-based microdroplet experiments, we examined the relation between droplet properties (size and spread) and plasmid transfer rates at single-cell and individual droplet resolution, using Pseudomonas putida as a model species. We show that transfer rates increase with droplet size, due to higher densities of cells on the surface in larger droplets, resulting from lower ratio between the area of the liquid-solid interface and droplet volumes. We further show that surface hydrophobicity promotes transfer rates via the same mechanism. Our results provide new insights into how physical properties of surfaces and MSW affect plasmid transfer rates, and more generally, interactions mediated by cell-to-cell contact, with important implications for our understanding of the ecology and evolution of bacteria in unsaturated environments.

microbiology↗

bioRxiv2020

Inherent protection of bacteria from beta-lactam antibiotics by wet-dry cycles with microscopic surface wetness

A large portion of bacterial life occurs on surfaces that are not constantly saturated with water and experience recurrent wet-dry cycles. While soil, plant leaves and roots, and many indoor surfaces may appear dry when not saturated with water, they are in fact often covered by thin liquid films and microdroplets, invisible to the naked eye, known as microscopic surface wetness (MSW). Such MSW, resulting from the condensation of water vapor to hygroscopic salts, is ubiquitous yet largely underexplored. A wide variety of antibiotics are abundant in environments where MSW occurs, yet little is known about bacterial response to antibiotics in wet-dry cycles and under MSW conditions. Using E. coli as a model organism, we show, through a combination of experiments and computational modeling, that bacteria are considerably more protected from beta-lactams under wet-dry cycles with MSW phases, than they are under constantly wet conditions. This is due to the combined effect of several mechanisms, including tolerance triggered by inherent properties of MSW, i.e., high salt concentrations and slow cell growth, and the deactivation of antibiotics due to physicochemical properties of MSW. Remarkably, we also find evidence for a cross-protection effect, where addition of lethal doses of antibiotic before drying significantly increases cells survival under MSW. As wet-dry cycles with MSW and beta-lactams, as well as other antibiotics, are common in vast terrestrial microbial habitats, our findings are expected to have significant implications for how we understand antibiotic response, population dynamics, and interspecies interactions in these globally important microbial ecosystems.

microbiology↗

bioRxiv2020

Virus survival in evaporated saliva microdroplets deposited on inanimate surfaces

The novel coronavirus respiratory syndrome (COVID-19) has now spread worldwide. The relative contribution of viral transmission via fomites is still unclear. SARS-CoV-2 has been shown to survive on inanimate surfaces for several days, yet the factors that determine its survival on surfaces are not well understood. Here we combine microscopy imaging with virus viability assays to study survival of three bacteriophages suggested as good models for human respiratory pathogens: the enveloped Phi6 (a surrogate for SARS-CoV-2), and the non-enveloped PhiX174 and MS2. We measured virus viability in human saliva microdroplets, SM buffer, and water following deposition on glass surfaces at various relative humidities (RH). Although saliva microdroplets dried out rapidly at all tested RH levels (unlike SM that remained hydrated at RH [≥] 57%), survival of all three viruses in dry saliva microdroplets was significantly higher than in water or SM. Thus, RH and hydration conditions are not sufficient to explain virus survival, indicating that the suspended medium, and association with saliva components in particular, likely affect physicochemical properties that determine virus survival. The observed high virus survival in dry saliva deposited on surfaces, under a wide range of RH levels, can have profound implications for human public health, specifically the COVID-19 pandemic.

microbiology↗

bioRxiv2019

Microscale interactions between immigrant bacteria and plant leaf microbiota as revealed by live imaging

The phyllosphere - the aerial parts of plants - is an important microbial habitat that is home to diverse microbial communities. The spatial organization of bacterial cells on leaf surfaces is non-random, and correlates with leaf microscopic features. Yet, the role of microscale interactions between bacterial cells therein is not well understood. Here, we ask how interactions between immigrant bacteria and resident microbiota affect the spatial organization of the combined community. By means of live imaging in a simplified in vitro system, we studied the spatial organization, at the micrometer scale, of the bio-control agent Pseudomonas fluorescens A506 and the plant pathogen P. syringae B728a when introduced to pear and bean leaf microbiota (the corresponding native plants of these strains). We found significant co-localization of immigrant and resident microbial cells at distances of a few micrometers, for both strains. Interestingly, this co-localization was in part due to preferential attachment of microbiota cells near newly formed P. fluorescens aggregates. Our results indicate that two-way immigrant bacteria - resident microbiota interactions affect the leafs microscale spatial organization, and possibly that of other surface-related microbial communities.

microbiology↗

bioRxiv2019

Bacterial survival in microscopic droplets

Plant leaves constitute a huge microbial habitat of global importance. How microorganisms survive the dry daytime on leaves and avoid desiccation is not well-understood. There is evidence that microscopic wetness in the form of thin films and micrometer-sized droplets, invisible to the naked eye, persists on leaves during daytime due to deliquescence - the absorption of water until dissolution - of hygroscopic aerosols. Here we study how such microscopic wetness affects cell survival. We show that, on surfaces drying under moderate humidity, stable microdroplets form around bacterial aggregates due to deliquescence and capillary pinning. Notably, droplet-size increases with aggregate-size and the survival of cells is higher the larger the droplet. This phenomenon was observed for 13 different bacterial species, two of which - Pseudomonas fluorescens and P. putida - were studied in depth. Microdroplet formation around aggregates are likely key to bacterial survival in a variety of unsaturated microbial habitats, including leaf surfaces.

microbiology↗