Identification of protein secretion systems in bacterial genomes

Bacteria with two cell membranes (diderms) have evolved complex systems for protein secretion. These systems were extensively studied in some model bacteria, but the characterisation of their diversity has lagged behind due to lack of standard annotation tools. We built models for accurate identification of protein secretion systems and related appendages in bacteria with LPS-containing outer membranes. They can be used with MacSyFinder (standalone program) or online (http://mobyle.pasteur.fr/cgi-bin/portal.py#forms::txsscan). They include protein profiles and information on the systems composition and genetic organisation. They can be used to search for T1SS-T6SS, T9SS, and accessorily for flagella, Type IV and Tad pili. We identified ~10,000 systems in bacterial genomes, where T1SS and T5SS were by far the most abundant and widespread. The recently described T6SSiii and T9SS were restricted to Bacteroidetes, and T6SSii to Francisella. T2SS, T3SS, and T4SS were frequently encoded in single-copy in one locus, whereas most T1SS were encoded in two loci. The secretion systems of diderm Firmicutes were similar to those found in other diderms. Novel systems may remain to be discovered, since some clades of environmental bacteria lacked all known protein secretion systems. Our models can be fully customized, which should facilitate the identification of novel systems.Introduction