Intestinal microbial communities play major roles in the health of their hosts. Competition between bacterial species and bacterial perturbation of the host environment help shape community composition, but the ways in which these general mechanisms can be realized remain poorly understood. We consider here a specific bacterial machinery that affects both inter-bacterial and host-microbe interactions: the type VI secretion system (T6SS), a syringe-like apparatus found in many species that can inject toxins into adjacent cells. Using zebrafish, a model organism that allows the derivation of initially germ-free fish and the introduction of specific microbial species, and bacteria that include a Vibrio strain whose T6SS can attack both bacterial and eukaryotic cells, we examine the effects of Vibrio invasion on pre-established gut bacterial communities of varying complexity. Gut dissection and plating quantifies the abundance of bacterial species, and live imaging using light sheet fluorescence microscopy reveals the spatial dynamics of gut bacteria in situ. We find that all initially colonizing species and combinations of species examined were reduced in abundance following inoculation with Vibrio , but with differing magnitudes depending on the initial species, the number of species, and the T6SS type of the invader. These observations illuminate the ability of the T6SS to mediate inter-species competition and more generally help reveal factors, such as species diversity, that determine gut microbiome composition and stability.
Winkler et al. (Sun,) studied this question.