Genetic elements orchestrating Lactobacillus crispatus glycogen metabolism in the vagina

Abstract

Glycogen in the female lower reproductive tract is a major carbon source for vaginal colonization and acidification by common vaginal Lactobacillus species, such as Lactobacillus crispatus. Previously we identified the pullulanase gene pulA in Lactobacillus crispatus, correlating with its ability to autonomously utilize glycogen for growth. Here we further characterize genetic variation and differential regulation of pulA affecting the presence of its gene product on the outer surface layer. We show that alpha-glucan degrading activity dissipates when Lactobacilllus crispatus is grown on glucose, maltose and maltotriose, in agreement with carbon catabolite repression elements flanking the pulA gene. Proteome analysis of the S-layer confirmed that the pullulanase protein is highly abundant in an S-layer enriched fraction, but not in a strain with a defective pullulanase variant or in a pullulanase-sufficient strain grown on glucose. In addition, we provide evidence that Lactobacillus crispatus pulA mutants are relevant in vivo, as they are commonly observed in metagenome datasets of human vaginal microbial communities. Analysis of the largest publicly available human vaginal metagenome dataset indicates that 15 out of 272 samples, containing a Lactobacillus crispatus pulA gene, contain a defective variant of this gene. Another 23 out of 272 samples show large deletions or transposon insertions. Taken together, these results demonstrate that both environmental as well as genetic factors explain variation of Lactobacillus crispatus alpha-glucosidases in the vaginal environment.