Comprehensive analysis of the type VI secretion system in Neisseria: identification, distribution, and evolutionary insights

The genus Neisseria, a gram-negative diplococcus, includes commensal and pathogenic species that infect mucosal tissues, causing diseases such as gonorrhea and meningitis. The type VI secretion system (T6SS), a multifunctional molecular machine that facilitates the ability of gram-negative bacteria to deliver effectors for bacterial competition, virulence, and interaction with host cells, has been widely studied across various bacterial taxa. However, research on the T6SS in the genus Neisseria remains limited. In this study, we employed comparative genomics and pangenomics, among other bioinformatics approaches, to characterize the distribution of the T6SS and its related proteins, including effectors, immunity proteins and regulators, across different species within the genus. Through an analysis of 5,067 Neisseria genomes, we identified two complete T6SS loci. We found that more than half of the Neisseria species possess at least one complete T6SS locus. Further investigation revealed multiple T6SS-related loci. We also applied a statistics-based method for identifying T6SS-associated orthologous groups and revealed 64 new T6SS-associated proteins within the genus. Our research provides a comprehensive analysis of the T6SS in Neisseria, advancing the understanding of T6SS-related mechanisms.