Lactobacillus gasseri Gasser AM63(T) degrades oxalate in a multistage continuous culture simulator of the human colonic microbiota.

Colonic oxalate-degrading bacteria have been shown to play an important role in human kidney stone formation. In this study, molecular analysis of the Lactobacillus gasseri genome revealed a cluster of genes encoding putative formyl coenzyme A transferase (frc) and oxalyl coenzyme A decarboxylase (oxc) homologues, possibly involved in oxalate degradation. The ability of Lactobacillus gasseri Gasser AM63(T) to degrade oxalate was confirmed in vitro. Transcription of both genes was induced by oxalate, and reverse transcription-PCR confirmed that they were co-transcribed as an operon. A three-stage continuous culture system (CCS) inoculated with human fecal bacteria was used to model environmental conditions in the proximal and distal colons, at system retention times within the range of normal colonic transit rates (30 and 60 hours). A freeze-dried preparation of L. gasseri was introduced into the CCS under steady-state growth conditions. Short chain fatty acid analysis indicated that addition of L. gasseri to the CCS did not affect the equilibrium of the microbial ecosystem. Oxalate degradation was initiated in the first stage of the CCS, corresponding to the proximal colon, suggesting that this organism may have potential therapeutic use in managing oxalate kidney stone disease in humans.