TheVibrioType III Secretion System 2 is not restricted to theVibrionaceaeand encodes differentially distributed repertoires of effector proteins

Abstract

Vibrio parahaemolyticus is the leading cause of seafood-borne gastroenteritis worldwide. A distinctive feature of the O3:K6 pandemic clone, and its derivatives, is the presence of a second, phylogenetically distinct, Type III Secretion System (T3SS2) encoded within the genomic island VPaI-7. The T3SS2 allows the delivery of effector proteins directly into the cytosol of infected eukaryotic cells to subvert key host cell processes, critical for V. parahaemolyticus to colonize and cause disease. Furthermore, the T3SS2 also increases the environmental fitness of V. parahaemolyticus in its interaction with bacterivorous protists; hence it has been proposed that it contributed to the global oceanic spread of the pandemic clone. Several reports have identified T3SS2-related genes in Vibrio and non-Vibrio species, suggesting that the T3SS2 gene cluster is not restricted to the Vibrionaceae and can mobilize through horizontal gene transfer events. In this work, we performed a large-scale genomic analysis to determine the phylogenetic distribution of the T3SS2 gene cluster and its repertoire of effector proteins. We identified putative T3SS2 gene clusters in 1130 bacterial genomes from eight bacterial genera and five bacterial families. A hierarchical clustering analysis allowed us to define six T3SS2 subgroups (I-VI) with different repertoires of T3SS2 effector proteins, redefining the concepts of T3SS2 core and accessory effector proteins. Finally, we identified a subset of T3SS2 gene clusters that lack most T3SS2 effector proteins described to date and provided a list of 10 novel effector candidates for this subgroup through bioinformatic analysis. Collectively, our findings indicate that the T3SS2 extends beyond the Vibrionaceae family and suggest that different effector protein repertories could have a differential impact on the pathogenic potential and environmental fitness of all the bacteria that have acquired the Vibrio T3SS2 gene cluster.

Genome Analysis Identifies a Novel Type III Secretion System (T3SS) Category in Vibrio Species

“…To clarify the true function of each protein, experimental evidence is essential. The number and type of effectors are known to differ even among the same species [ 3 ], and a recent report also indicates diversity of effectors in T3SS2 clusters [ 42 ]. Bioinformatics analysis can find many putative effectors as in our study, and their functional characterization through experiments is awaited [ 43 ].…”