Genetic evidence of distinct physiological regulation mechanisms in the sigma(54) Pu promoter of Pseudomonas putida

The activity of the toluene-responsive sigma(54)Pu promoter of the pWW0 TOL plasmid of Pseudomonas putida is down-regulated in vivo during exponential growth in rich medium and also by the presence of glucose in the culture. Although the Pu promoter already performs poorly during log growth in minim al medium when amended,vith casamino acids, the addition of glucose further decreased by two- to threefold the accumulation of beta-galactosidase in a Pu-lacZ reporter P. putida strain. Since Pu was still down-regulated durin g exponential growth regardless of glucose addition, it appeared that the c arbohydrate separately influenced promoter activity. This notion was suppor ted by the growth-dependent induction pattern of Po in a ptsN mutant of P. putida, the loss of which makes Pu no longer responsive to repression by gl ucose. On the other hand, overexpression of the sigma factor sigma(54), kno wn to partially alleviate the exponential silencing of the promoter, did no t affect glucose inhibition of Pu. These data indicated that exponential si lencing and carbon source-dependent repression are two overlapping but gene tically distinguishable mechanisms that adapt Po to the physiological statu s of the cells and nutrient availability.