T6SS intraspecific competition orchestrates Vibrio cholerae genotypic diversity

Abstract

Vibrio cholerae is a diverse species that inhabits a wide range of environments from copepods in brackish water

to the intestines of humans. In order to remain competitive, V. cholerae uses the versatile type-VI secretion system (T6SS) to

secrete anti-prokaryotic and anti-eukaryotic effectors. In addition to competing with other bacterial species, V. cholerae strains

also compete with one another. Some strains are able to coexist, and are referred to as belonging to the same compatibility group.

Challenged by diverse competitors in various environments, different V. choleare strains secrete different combination of effectors

– presumably to best suit their niche. Interestingly, all pandemic V. cholerae strains encode the same three effectors. In addition

to the diversity displayed in the encoded effectors, the regulation of V. cholerae also differs between strains. Two main layers

of regulation appear to exist. One strategy connects T6SS activity with behavior that is suited to fighting eukaryotic cells, while

the other is linked with natural competence – the ability of the bacterium to acquire and incorporate extracellular DNA. This

relationship between bacterial killing and natural competence is potentially a source of diversification for V. cholerae as it has

been shown to incorporate the DNA of cells recently killed through T6SS activity. It is through this process that we hypothesize

the transfer of virulence factors, including T6SS effector modules, to happen. Switching of T6SS effectors has the potential to

change the range of competitors V. cholerae can kill and to newly define which strains V. cholerae can co-exist with, two important

parameters for survival in diverse environments.