The insecticidal toxin genes of Y ersinia enterocolitica are activated by the thermolabile LTTR ‐like regulator TcaR 2 at low temperatures

Summary Temperature‐dependent activation of bacterial virulence factors at 37° C is well investigated. The molecular mechanism underlying the expression of toxicity determinants at environmental temperatures, however, has not been characterized. The insecticidal activity of Y ersinia enterocolitica strain W 22703 requires the toxin complex subunit A ( TcaA ) encoded on the pathogenicity island T c‐ PAI Ye . Genes tcaA and tcaB encoding this subunit are maximally produced at low temperatures (10–20° C ), but repressed at body temperature. Two further insecticidal genes, tcaC (subunit B ) and tccC1 (subunit C ), are silent at both temperatures. A novel LysR ‐type transcriptional regulator ( LTTR ), TcaR 2, revealed to be autoregulated and essential for tcaA and tcaB expression in W 22703. Expression of tcaR2 is negatively controlled by a second LTTR ‐like regulator, TcaR 1. Gel mobility shift assays confirmed the interaction of TcaR 2 with the tcaR2 , tcaA and tcaB promoters. The activity of the tcaA promoter in heterologous hosts in the presence of TcaR 2 excludes the requirement of additional, Y ersinia ‐specific (co)factors for toxin gene expression. Overproduced TcaR 2 protein is shown to be unstable at 37° C , whereas the mRNA of tcaA and tcaR2 is equally stable at low and high temperature. Thus, TcaR 2 is a key player in the induction of insecticidal genes in Y . enterocolitica at low temperatures.