Host-independent synergism between Lactobacillus crispatus and other vaginal lactobacilli.

The human vagina is a unique microbiome, typically predominated by Lactobacillus species in healthy women. However, we currently lack an understanding of why lactobacilli predominate in this environment and how these bacteria interact, aspects that are crucial for developing microbiome-based therapeutics. In this study, we used cost-efficient synthetic communities (SynComs) to investigate the stability and dynamics of Lactobacillus-predominated vaginal communities from healthy women independent of host influence. Reproducible communities of Lactobacillus crispatus co-occurring with Limosilactobacillus species and Lactobacillus jensenii were established in top-down experiments. Co-occurrence was verified with compositional correlation patterns in metagenome sequencing data and reproduced through a bottom-up approach. This co-occurrence pattern was independent of strain selection, host factors, and inoculation ratio. Genome-scale metabolic models predicted potential cross-feeding involving amino acids (e.g., L-arginine, L-lysine, and γ-aminobutyric acid [GABA]) and vitamins as mechanisms mediating their co-occurrence. This study provides a framework for developing reproducible synthetic vaginal Lactobacillus communities and informs future microbiome-based therapies.