Efficient expression of a carbon starvation promoter activity under nutrient-limited chemostat culture

The promoter region of a carbon starvation gene isolated from Pseudomonas putida was cloned and analyzed for its potential use for in situ bioremediation and bioprocessing. We constructed a recombinant plasmid pMKD101 by cloning the 0.65 kb promoter region of the gene into the promoter proving vector, pMK301, which contains the lacZ for β-galactosidase activity as a reporter gene. pMKD101 was transformed into the wild-type P. putida MK1, resulting in P. putida RPD101, and analyzed for β-galactosidase activity under different culture conditions. When RPD101 was grown on the minimal medium plus 0.1% glucose as a sole carbon source in batch cultures, β-galactosidase activity was found to be 3.2-fold higher during the stationary phase than during the exponential phase. In chemostat cultures, β-galactosidase activity was found to be 3.1-fold higher at the minimal growth rate (dilution rate=0.05 h^-1) than at the maximal growth rate (dilution rate=0.173 h^-1). The results suggest that a carbon starvation promoter can be utilized to maximize the expression of a desired gene under nutrient limitation.