A CARBON STARVATION SURVIVAL GENE OF PSEUDOMONAS-PUTIDA IS REGULATED BY SIGMA(54)

By using mini-Tn5 transposon mutagenesis, two mutants of Pseudomonas p utida ATCC 12633 were isolated which showed a marked increase in their sensitivity to carbon starvation; these mutants are presumably affect ed in the Per type of proteins that P. putida induces upon carbon star vation (M. Givskov, L. Eberl, and S. Molin, J. Bacteriol. 176:4816-482 4, 1994). The affected genes in our mutants were induced about threefo ld upon carbon starvation. The promoter region of the starvation gene in the mutant MK107 possessed a strong sigma(54)-type promoter sequenc e, and deletion analysis suggested that this was the major promoter re gulating expression; this was confirmed by transcript mapping in rpoN( +) and rpoN mutant backgrounds. The deletion analysis implicated a seq uence upstream of the sigma(54) promoter, as well as a region downstre am of the transcription start site, in the functioning of the promoter . Two sigma(70)-type Pribnow boxes were also detected in the promoter region, but their transcriptional activity in the wild type was very w eak However, in a sigma(54)-deficient background, these promoters beca me stronger. The mechanism and possible physiological role of this phe nomenon and the possibility that the sequence upstream of the sigma(54 ) promoter may have a role in carbon sensing are discussed.