AcrR and Rex Control Mannitol and Sorbitol Utilization through Their Cross-Regulation of Aldehyde-Alcohol Dehydrogenase (AdhE) inLactobacillus plantarum
ABSTRACTLactobacillus plantarumis a versatile bacterium that occupies a wide range of environmental niches. In this study, we found that a bifunctional aldehyde-alcohol dehydrogenase-encoding gene,adhE, was responsible forL. plantarumbeing able to utilize mannitol and sorbitol through cross-regulation by two DNA-binding regulators. InL. plantarumNF92,adhEwas greatly induced, and the growth of anadhE-disrupted (ΔadhE) strain was repressed when sorbitol or mannitol instead of glucose was used as a carbon source. The results of enzyme activity and metabolite assays demonstrated that AdhE could catalyze the synthesis of ethanol inL. plantarumNF92 when sorbitol or mannitol was used as the carbon source. AcrR and Rex were two transcriptional factors screened by an affinity isolation method and verified to regulate the expression ofadhE. DNase I footprinting assay results showed that they shared a binding site (GTTCATTAATGAAC) in theadhEpromoter. Overexpression and knockout of AcrR showed that AcrR was a novel regulator to promote the transcription ofadhE. The activator AcrR and repressor Rex may cross-regulateadhEwhenL. plantarumNF92 utilizes sorbitol or mannitol. Thus, a model of the control ofadhEby AcrR and Rex duringL. plantarumNF92 utilization of mannitol or sorbitol was proposed.IMPORTANCEThe function and regulation of AdhE in the important probiotic genusLactobacillusare rarely reported. Here we demonstrated that AdhE is responsible for sorbitol and mannitol utilization and is cross-regulated by two transcriptional regulators inL. plantarumNF92, which had not been reported previously. This is important forL. plantarumto compete and survive in some harsh environments in which sorbitol or mannitol could be used as carbon source. A novel transcriptional regulator AcrR was identified to be important to promote the expression ofadhE, which was unknown before. The cross-regulation ofadhEby AcrR and Rex is important to balance the level of NADH in the cell during sorbitol or mannitol utilization.