Regulation and utilization of microsin promoter turn on in a chromosomal fusion

Prior work has demonstrated that the microsin antibiotics are produced by enteric bacteria when the growth medium is depleted of nutrients. Because the control loci could have biotechnical potential, and general stress-response phenomena are of importance to understanding how bacteria survive in natural and bioreactor environments, we examined further the growth rate dependence of gene expression under the control of the microsin B17 promoter. This work entailed performing batch and chemostat growth experiments with a strain of E. coli K-12 containing a mcbA-lacZ gene fusion in the chromosome. Our results indicate that when a culture is presented with excess respiratory substrate, a well defined growth rate exists, below which a significant induction event occurs. However, cultures that are fermenting or highly glycolytic tend to express poorly. Additionally, the utility of the fusion strain was examined by performing fed-batch cultivation experiments. We found that sustained production in a fed-batch reactor can be accomplished by using a straightforward, exponential nutrient feeding profile.