Transcriptional Regulator AcrR Increases Ethanol Tolerance through Regulation of Fatty Acid Synthesis in .

is a versatile bacterium with significant adaptability to harsh habitats containing excessive ethanol concentrations. It was found that the NF92-TetR/AcrR family regulator, AcrR, significantly enhanced the growth rate of this lactic acid bacterium in the presence of ethanol. Through screening 172 ethanol-resistant related genes by electrophoretic mobility shift and quantitative reverse transcription-PCR (RT-qPCR) assays, six genes were identified to be regulated by AcrR under ethanol stress. Among these was a gene coding for a 3-hydroxyacyl-ACP dehydratase () regulated by AcrR under ethanol stress. AcrR regulated under ethanol stress by binding to its promoter, P DNase I footprinting analysis indicated that there were two specific AcrR binding sites on P RT-PCR results showed could cotranscribe with its downstream 12 genes and conform a fatty acid biosynthesis () gene cluster under the control of P Both RT-qPCR of the gene cluster in knockout and overexpression strains and fatty acid methyl ester analysis of the knockout strain showed that AcrR could promote fatty acid synthesis in NF92. Membrane fluorescence anisotropy analysis of knockout and overexpression strains showed that AcrR could increase membrane fluidity under ethanol stress. Thus, AcrR could regulate fatty acid synthesis and membrane fluidity to promote the adaption of NF92 to a high ethanol concentration. Ethanol tolerance is essential for strains living in substances with more than 9% ethanol, such as wine and beer. The details regarding how adapts to ethanol are still lacking. This study demonstrates that AcrR regulates the synthesis of fatty acids in adapting to toxic levels of ethanol. We also identified the ability of the TetR/AcrR family regulator to bind to the fatty acid biosynthesis gene promoter, P , in and defined the binding sites. This finding facilitates the induction of the adaptation of strains to ethanol for food fermentation applications.