Multifaceted Interfaces of Bacterial Competition

Abstract

Microbial communities span many orders of magnitude, ranging in scale from hundreds of cells on a single particle of soil to billions of cells within the lumen of the gastrointestinal tract. Bacterial cells in all habitats are members of densely populated local environments that facilitate competition between neighboring cells. Accordingly, bacteria require dynamic systems to respond to the competitive challenges and the fluctuations in environmental circumstances that tax their fitness. The assemblage of bacteria into communities provides an environment where competitive mechanisms are developed into new strategies for survival. In this minireview, we highlight a number of mechanisms used by bacteria to compete between species. We focus on recent discoveries that illustrate the dynamic and multifaceted functions used in bacterial competition and discuss how specific mechanisms provide a foundation for understanding bacterial community development and function.

FIG 1

Mechanisms of bacterial competition. (A and B) Detection of patterns of SM production and degradation through imaging mass spectrometry. (A) False-colored extracted ion image showing the distribution of surfactin (blue) produced by B. subtilis and hydrolyzed surfactin (yellow) resulting from the activity of surfactin hydrolase secreted by Streptomyces sp. Mg1. (B) The extracted ion image from panel A overlaid onto a photograph of a culture of B. subtilis and Streptomyces sp. Mg1 to highlight the localization patterns of each SM during competition. (C and D) Revealing essential SM functions using predator-prey interactions. (C) Photograph of M. xanthus spotted onto the center of a wild-type B. subtilis NCIB 3610 colony. The colony is mostly opaque due to intact viable B. subtilis cells. (D) A mutant B. subtilis strain deficient in bacillaene production becomes transparent as it is consumed by M. xanthus, which forms fruiting bodies on the lysed remains of the B. subtilis colony. (E and F) Structural features of a contact-mediated competitive apparatus. (E) Cryo-electron micrographs of a T6SS apparatus inside an intact Vibrio cholerae cell. Scale bar = 100 nm. IM, inner membrane; OM, outer membrane. (F) Comparison of flagellum (F) and T6SS sheath (S) isolated from V. cholerae. Scale bar = 100 nm. Panels C and D were provided by John Kirby. Panels E and F were reproduced with permission from reference .

FIG 2

Summary of mechanisms used in bacterial competition. (A) Contact-mediated mechanisms involve either direct contact between cell envelopes (OME) or are facilitated by protein complexes (CDI and T6SS). In the case of CDI and T6SS, toxic effectors (square or wedged circle) are delivered into the target cell. (B) Bacteria compete at a distance using SMs (examples shown are bacillaene and streptomycin), secreted enzymes, and extracellular vesicles. CDI, contact-dependent inhibition; EVs, extracellular vesicles; M, membrane; M_T, target cell membrane; IM, inner membrane; OM, outer membrane; PG, peptidoglycan; T6SS, type VI secretion system.