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Two acid‐inducible promoters from Lactococcus lactis require the cis‐acting ACiD‐box and the transcription regulator RcfB

We previously characterized three Lactococcus lactis promoters, P170, P1 and P3, which are induced by low pH. Here, we identified a novel 14 bp regulatory DNA region centred at around −41.5 and composed of three tetranucleotide sequences, boxes A, C and D. Boxes A and C contribute to P1 activity, whereas box D and the position of boxes ACD (renamed ACiD‐box) are essential to P1 activity and acid response. We also identified a trans ‐acting protein, RcfB, which is involved in P170 and P1 basal activity and is essential for their pH induction. The regulator belongs to the Crp‐Fnr family of transcription regulators. Overexpression of rcfB resulted in increased β‐galactosidase activities and lantibiotic lacticin 481 production from P170‐ and P1‐controlled genes, respectively, in acid condition. RcfB is thus probably activated when cells encounter an acid environment. rcfB is co‐transcribed with genes encoding an universal stress‐like protein and a multidrug transporter. RcfB plays a role in acid adaptation, as the survival rate of an rcfB mutant after a lethal acid challenge was 130‐fold lower than that of the wild‐type strain, when the bacteria were first grown in acidic medium. The groESL promoter includes a sequence resembling an ACiD‐box and the chaperone GroEL production is partly RcfB dependent in acid condition. Our results suggest that the ACiD‐box could be the DNA target site of RcfB.