Quorum Sensing and Type VI Secretion Dependent Genotypic Diversification in Aging V. cholerae Colonies

Abstract

Quorum sensing (QS) is a cell-cell communication process that allows bacterial populations to synchronize their gene expression patterns. In Vibrio cholerae, QS regulates expression of genes encoding the type VI secretion system (T6SS), an apparatus that enables inter-bacterial killing promoting survival in the presence of competing bacterial species. T6SS is activated at high cell densities by HapR, while it is repressed at low cell densities by LuxO. However, it is not known whether T6SS activity also affects the QS circuit. Here, I show that colonies of a V. cholerae isolate, with a constitutively active T6SS, spontaneously diversify into sub-populations that are QS and T6SS deficient. My data further suggest that T6SS activation may become maladaptive as colonies age because it makes them more vulnerable to self-intoxication. Thus, the emergence of these QS and T6SS inactive variants suggests that T6SS activation provides negative feedback to revert the system to a QS-inactive state, and this behavior may confer a fitness advantage to the new variant strains by lowering the risk of self-intoxication.