Identification of the transcription factor responsible for L-malate-dependent regulation in the marine Antarctic bacterium Pseudoalteromonas haloplanktis TAC125

Two-component systems are widespread in nature and constitute the most common mechanism of transmembrane signal transduction in bacteria. Recently, a functionally active two-component system consisting of malS and malR genes possibly involved in the expression of a C4-dicarboxylate transporter system (dctAB operon) was identified in the marine Antarctic bacterium Pseudoalteromonas haloplanktis TAC125. In this paper, we performed a functional analysis of the two-component system and demonstrated its involvement in the regulation of the expression of C4-dicarboxylate transporter genes. The expression of the C4- dicarboxylate transporter genes was induced by L-malate with the promoter element located upstream of the dctA gene being active only in the presence of the inducer. A s54 promoter responsible for the L-malate dependent transcription regulation was identified and functionally characterized. The molecular mechanism involves an inverted repeat sequence located upstream the s54 promoter that was shown to bind regulatory proteins only in the presence of L-malate. The protein factor responsible for the induction of the dctAB operon expression was eventually identified as the transcriptional regulatory protein MalR. MalR is the first transcriptional factor identified in P. haloplanktis TAC125 and one of the few transcriptional modulators reported so far in cold adapted bacteria.