A global survey of bacterial type III secretion systems and their effectors

Abstract

The type III secretion system (T3SS) is an important genetic determinant that mediates interactions between Gram-negative bacteria and their eukaryotic hosts. Our understanding of the T3SS continues to expand, yet the availability of new bacterial genomes prompts questions about its diversity, distribution and evolution. Through a comprehensive survey of ∼20 000 bacterial genomes, we identified 174 non-redundant T3SSs from 109 genera and 5 phyla. Many of the bacteria are environmental strains that have not been reported to interact with eukaryotic hosts, while several species groups carry multiple T3SSs. Four ultra-conserved Microsynteny Blocks (MSBs) were defined within the T3SSs, facilitating comprehensive clustering of the T3SSs into 13 major categories, and establishing the largest diversity of T3SSs to date. We subsequently extended our search to identify type III effectors, resulting in 8740 candidate effectors. Lastly, an analysis of the key transcriptional regulators and circuits for the T3SS families revealed that low-level T3SS regulators were more conserved than higher-level regulators. This comprehensive analysis of the T3SSs and their protein effectors provides new insight into the diversity of systems used to facilitate host-bacterial interactions.

Edwardsiella piscicida: A versatile emerging pathogen of fish

“…Some T3SS effectors of plant and animal pathogens have common properties, suggesting that bacteria have evolved similar functions or inherited these genes through horizontal transfers to hijack host cells and disrupt host defense mechanisms [66]. Seventy percent of the T3SS effectors were estimated belonging to 91 families based on BLASTs results [67]. However, the remaining 30% of effectors appear to be species or strain specific, indicating a specific role in host cell/tissue tropism and host specificity [66,67].…”

Topological analysis of the type 3 secretion system translocon pore protein IpaC following its native delivery to the plasma membrane during infection

“…The type 3 secretion system is a specialized nanomachine required for the virulence of more than 30 bacterial pathogens (1). The T3SS translocates bacterial virulence proteins, known as effector proteins, from the bacterial cytosol into the cytosol of eukaryotic cells.…”

Comparative Genomics Reveals Metabolic Specificity of Endozoicomonas Isolated from a Marine Sponge and the Genomic Repertoire for Host-Bacteria Symbioses

“…It was located in different genomic regions as gene clusters encoding highly conserved genes responsible for T3SS apparatus. T3SS is a major genetic determinant of Gram-negative bacteria that facilitate the interaction between bacteria and eukaryotic hosts [93]. Besides secretion system apparatus genes encoding homologues of several effector molecules were also detected in the genome of Endozoicomonas sp.…”