Glycogen-Degrading pullulanase a is variably present and correlated with lactic acid in vaginal samples from young african women

A healthy vaginal microbiome is dominated by Lactobacillus species that produce lactic acid, lowering vaginal pH and limiting pathogen colonization. Lactobacillus dominance is established during puberty, but is lost by many women, especially those of Black race, during later reproductive years. Glycogen is a key host nutrient that supports vaginal lactobacilli and we asked whether L. crispatus strains dominating young African women are directly accessing glycogen via secreted pullulanase. We biochemically segregated glycogen and glycogen-derived maltodextrin, as well as glycogen-degrading enzyme activities in vaginal samples from African women with limited sexual experience (N=17). We coupled biochemical measurements with metagenomic profiling to determine how glycogen catabolism relates to L. crispatus dominance. We further profiled allelic variation in pullulanase A (pulA) genes in L. crispatus genomes from this cohort and others around the world. The vaginal microbiota in most young African women (65%) was dominated by L. crispatus. Glycogen and pullulanase activity, but not maltodextrin and amylase activity were positively correlated with lactic acid. Pullulanase activity was 4-fold higher in L. crispatus-dominated samples, but 33% of dominant L. crispatus strains in our cohort lacked the pulA gene. pulA gene loss or inactivation was 3-fold more frequent in this cohort compared to other published cohorts. Our results indicate pullulanase activity may contribute to maximal lactic acid production by L. crispatus. However, a substantial proportion of young African women with dominant L. crispatus lacked a functional pulA gene, which could contribute to instability of this taxon after sexual debut.