Understanding the probiotic potential of a healthy human vaginal flora, Lactobacillus gasseri K9: genomic and in vitro aspects

Lactobacillus gasseri K9, isolated from a healthy vaginal sample, underwent detailed genomic and phenotypic evaluation. The strain demonstrated strong stress tolerance, adhesion, aggregation, and biofilm formation, while ensuring safety with no mucin degradation or hemolysis. Antimicrobial compounds, pathogen inhibition, and resilience in simulated gastrointestinal conditions highlight its potential role in maintaining vaginal homeostasis and functioning as a safe, effective probiotic candidate. The entire genome sequence of L. gasseri K9, with an emphasis on studying its probiotic potential and safety profile. The complete genome of L. gasseri K9, with a genome size of 1,872,894 base pairs, comprises 1,779 genes, exhibiting an average G + C content of 34.83%. Comprehensive genomic analysis identified genes associated with stress adaptation, carbohydrate utilization, cell adhesion, secondary metabolite biosynthesis, and other probiotic traits through multiple annotation platforms, including RAST, KEGG, COG, CAZyme, BAGEL4, and AntiSMASH. The detection of CRISPR arrays with broad phage-targeting patterns suggests that this strain possesses robust phage defence capabilities. Additionally, the absence of virulence factors and antibiotic resistance determinants, verified using CARD, ResFinder, and VFDB, underscores the safety profile of K9 as a promising probiotic candidate. Pangenome analysis of 278 L. gasseri genomes identified 12 distinctive sequences shared only by the K9 and Q9001 strains, setting them apart from all other isolates. Most of these sequences encoded hypothetical proteins, with one linked to a phage-related HK97-gp10 family protein. This study presents detailed genomic and functional characterization of L. gasseri K9, revealing unique genetic traits, strong probiotic functions, and a robust safety profile. Its role in maintaining vaginal health suggests strong potential for incorporation into probiotic formulations targeting women’s wellness. Overall, these findings highlight K9 as a promising strain for next-generation vaginal probiotics.