Impact of culture conditions on the transcriptional levels of oxc gene and the oxalate consumption in Bifidobacterium

Oxalate is a highly toxic compound ubiquitous in the plant kingdom and widely consumed in human diet. A number of pathological conditions can arise from oxalate accumulation. Oxalate-degrading gut bacteria may play a key role in oxalate-related diseases by catabolizing free oxalate, reducing its plasmatic and urinary levels. Thirteen Bifidobacterium strains were screened for their ability to degrade oxalate by a rapid and sensitive method based on capillary electrophoresis (CE). A 100% oxalate degrading capacity was observed only for B. animalis subsp. lactis, a species widely used in dairy and pharmaceutical probiotic products. Putative oxalyl-CoA decarboxylase (oxc) and predicted permease genes were identified in B. lactis BI07, one of the most active strains. B. lactis BI07 consumption of oxalate and carbon sources was evaluated by CE analysis of the culture broths recovered from batch fermentation processes carried out in different growth conditions. Transcriptional analysis, using reverse transcription-quantitative PCR, along with the kinetics of oxalate degradation revealed that acidic conditions were a fundamental prerequisite for oxc transcription and enzyme activity.