AcrR and Rex control mannitol and sorbitol utilization through their cross-regulation of aldehyde-alcohol dehydrogenase (AdhE) in Lactobacillus plantarum .

Lactobacillus plantarum is a kind of versatile bacteria that occupies a wide range of environmental niches. In this study, we found a bifunctional aldehyde-alcohol dehydrogenase encoding gene adhE was responsible for L. plantarum to utilize mannitol and sorbitol through cross-regulation by two DNA-binding regulators. In L. plantarum NF92, adhE was greatly induced and the growth of adhE disrupted strain (ΔadhE) was repressed when sorbitol or mannitol instead of glucose was used as carbon source. The results of enzyme activity and metabolite assay demonstrated that AdhE could catalyze the synthesis of ethanol in L. plantarum NF92 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 of adhE DNase I footprinting assay results showed that they shared a similar binding site ( GTTCATTAATGAAC ) in adhE promoter. Over-expression and knock-out of AcrR showed that AcrR was a novel regulator to promote the transcription of adhE The activator AcrR and repressor Rex may cross-regulate adhE when L. plantarum NF92 utilizes sorbitol or mannitol. Thus a proposed model about the control of adhE by AcrR and Rex during L. plantarum NF92 utilizing mannitol or sorbitol was proposed. IMPORTANCE The function and regulation of AdhE are rarely reported in the important probiotic Lactobacillus Here we demonstrated that AdhE was responsible for sorbitol and mannitol utilization and cross-regulated by two transcriptional regulators in L. plantarum NF92, which had not been reported. This is important for L. plantarum to 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 of adhE , which was unknown before. The cross-regulation of adhE by AcrR and Rex is important to balance the level of NADH in the cell during sorbitol or mannitol utilization.