Distribution of the putative type VI secretion system core genes in Klebsiella spp.

The type VI secretion system (t6ss) is a recently characterized secretion system which appears to be involved in bacterial pathogenesis as a potential nano-syringe for the translocation of effector proteins into the eukaryotic host cell cytoplasm. Until now no evidence was provided for the presence of t6ss in the genomes of the sequenced representatives of Klebsiella spp., including the human opportunistic pathogen Klebsiella pneumoniae. However, in a previous study by Lawlor et al. (2005), were revealed two insertion mutants in hypothetical proteins of K. pneumoniae with decreased ability to infect mouse spleen. Interestingly, these two putative proteins appear to be homologues with two characterized t6ss core proteins of Yersinia pestis. In order to investigate the presence of genes encoding for putative t6ss core components and putative effectors in Klebsiella spp., we have undertaken an in silico genome mining in three fully and one partially sequenced strains of K. pneumoniae, as well as a strain of the Klebsiella variicola. Moreover, we have investigated the phylogenetic relatedness of three core proteins of the Klebsiella t6ss with their orthologues of various bacteria species. Our analysis evidenced three distinguishable, conserved syntenies in Klebsiella spp. genomes that contain the recognised as putative t6ss genes. The results of our work taken together with the results on the functional analysis of insertion mutants, strongly suggest the existence of an organised t6ss mechanism that likely accounts of the host-pathogen interaction.