Two Type VI Secretion Systems of Are Required for Bacterial Competition, Cell Adherence, and Intestinal Colonization.

has emerged as an opportunistic pathogen in healthcare-associated infections. Analysis of the genomic sequences of several strains revealed the presence of genes that code for expression of at least one type VI secretion system (T6SS). Here, we report that strain ATCC 13047 codes for two functional T6SS named T6SS-1 and T6SS-2. T6SS-1 and T6SS-2 were preferentially expressed in tryptic soy broth and tissue culture medium (DMEM), respectively. Mutants in T6SS-1-associated genes and significantly affected their ability of inter- and intra-bacterial killing indicating that T6SS-1 is required for bacterial competition. In addition, the Hcp effector protein was detected in supernatants of cultures and a functional T6SS-1 was required for the secretion of this protein. A mutant was impaired in both biofilm formation and adherence to epithelial cells, supporting the notion that these phenotypes are T6SS-2 dependent. data strongly suggest that both T6SSs are required for intestinal colonization because single and double mutants in and genes were defective in gut colonization in mice. We conclude that the two T6SSs are involved in the pathogenesis scheme of with specialized functions in the interaction with other bacteria and with host cells.