Parabacteroides vesiculifaciens sp. nov., a Novel Immunomodulatory, Vesicle-Producing Gut Commensal Isolated from the Human Gut

The genus <i>Parabacteroides</i> comprises widespread gastrointestinal commensals, known to produce immunomodulatory molecules and extracellular vesicles, yet its full diversity is incompletely cataloged. This study describes strain ASD2025^T, isolated from healthy child feces, using a polyphasic taxonomic approach including phenotypic profiling, chemotaxonomy, and comparative genomics. Cells were non-motile, polymorphic rods that produced extracellular vesicles. Phylogenomic analysis placed ASD2025^T within the genus <i>Parabacteroides</i> within a species complex consisting of <i>P. acidifaciens</i>, <i>P. hominis</i>, "<i>P. massiliensis</i>", <i>P. merdae,</i> and <i>P. johnsonii</i>, with average nucleotide identities to the type strains of 85.5-89.9%. The large genome (5.16 Mbp, 46.2% GC content) contained integrative conjugative elements harboring antibiotic resistance genes and hankyphage-related prophage. The strain produced succinate as the major metabolic end product, and its major fatty acids were anteiso-C_15:0, iso-C_17:0 3-OH, and C_15:0. Conditioned medium from ASD2025^T antagonized the interleukin-8 response caused by <i>E. coli</i> lipopolysaccharide in HT29 cells. The majority of related metagenome-assembled genomes originate from mouse microbiomes. Based on these distinct characteristics, strain ASD2025^T (=VKM B-3926^T = JCM 37967^T) represents a novel species of the genus <i>Parabacteroides</i>, for which the name <i>Parabacteroides vesiculifaciens</i> sp. nov. is proposed.