Operating principles and consequences of T6SS mediated predation in microbial communities - Project Summary The D’Souza Lab investigates how bacterial antagonism shapes the ecological and evolutionary dynamics of microbial communities, with a special focus on the Type VI secretion system (T6SS). Beyond competition, our recent work shows that when autonomous growth is impossible, T6SS enables bacteria to lyse susceptible neighbors and grow on the released nutrients, akin to predation. We study two ecologically disparate communities: (i) a marine pair of isolates — T6SS⁺ Vibrio anguillarum with Vibrio cyclitrophicus prey, and (ii) a synthetically assembled pair — T6SS⁺ Vibrio cholerae with Escherichia coli prey. Although V. anguillarum and V. cholerae are pathogens, we use them strictly as tractable models to uncover operating principles of T6SS in nature, not to study pathogenesis. Much of what is known about T6SS comes from experiments often performed in nutrient-replete and static environments. Far less is known about how bacteria deploy T6SS and how it functions in structured, fluctuating, and multispecies habitats, situations that majority of bacteria in nature experience. To close this gap, we will couple realistic microfluidic microcosms with automated time-lapse microscopy, quantitative image analytics, targeted genetics, experimental evolution, and comparative genomics. This multipronged approach enables our work to connect dynamics across genes, cells, and communities and link lab findings to natural microbiomes. Over the next five years, we will pursue three fronts. First, we will define operating principles for predation in nutrient-poor and spatially structured landscapes, unraveling how predators find hotspots of prey growth, choose effectors, and control T6SS deployment to optimize nutritional payoff. Second, we will test whether species can share T6SS parts to complement antagonistic functions in multi-genotypic communities. This direction will introduce a new paradigm in which T6SS capacity becomes a communal and not purely genomic trait, explaining why incomplete loci persist in genomes and describing how T6SS functionality is maintained. Third, we will determine how repeated T6SS foraging reshapes genomic and metabolic capacity of predators, an evolutionary dimension often left unaddressed in antagonism research. Together, these studies will: i) establish general rules for T6SS functionality in fluctuating environments that toggle bacterial behavior between competition and predation, ii) elucidate how community-level complementation stabilizes antagonistic functions, and iii) reveal how antagonism steers the course of evolution. Beyond providing a fundamental understanding, these principles can be leveraged to curb pathogens that use T6SS for colonization, to repurpose T6SS for therapeutic delivery and ultimately engineer microbiomes.
