Genomic insights into Lactobacillus gasseri and Lactobacillus paragasseri

Abstract

Background Antimicrobial and antifungal species are essential members of the healthy human microbiota. Several different species of lactobacilli that naturally inhabit the human body have been explored for their probiotic capabilities including strains of the species Lactobacillus gasseri. However, L. gasseri (identified by 16S rRNA gene sequencing) has been associated with urogenital symptoms. Recently a new sister taxon of L. gasseri was described: L. paragasseri. L. paragasseri is also posited to have probiotic qualities. Methods Here, we present a genomic investigation of all (n = 79) publicly available genome assemblies for both species. These strains include isolates from the vaginal tract, gastrointestinal tract, urinary tract, oral cavity, wounds, and lungs. Results The two species cannot be distinguished from short-read sequencing of the 16S rRNA as the full-length gene sequences differ only by two nucleotides. Based upon average nucleotide identity (ANI), we identified 20 strains deposited as L. gasseri that are in fact representatives of L. paragasseri. Investigation of the genic content of the strains of these two species suggests recent divergence and/or frequent gene exchange between the two species. The genomes frequently harbored intact prophage sequences, including prophages identified in strains of both species. To further explore the antimicrobial potential associated with both species, genome assemblies were examined for biosynthetic gene clusters. Gassericin T and S were identified in 46 of the genome assemblies, with all L. paragasseri strains including one or both bacteriocins. This suggests that the properties once ascribed to L. gasseri may better represent the L. paragasseri species.