Use of starvation promoters to limit growth and select for trichloroethylene and phenol transformation activity in recombinant Escherichia coli

The expression of much useful bacterial activity is facilitated by rapid growth. This coupling can create problems in bacterial fermentations and in situ bioremediation. In the latter process, for example, it necessitates addition of large amounts of nutrients to contaminated environments, such as aquifers. This approach, termed biostimulation, can be technically difficult. Moreover, the resulting in situ bacterial biomass production can have undesirable consequences. In an attempt to minimize coupling between expression of biodegradative activity and growth, we used Escherichia coli starvation promoters to control toluene monooxygenase synthesis. This enzyme complex can degrade the environmental contaminants trichloroethylene (TCE) and phenol. Totally starving cell suspensions of such strains degraded phenol and TCE. Furthermore, rapid conversions occurred in the postexponential batch or very slow growth (dilution) rate chemostat cultures, and the nutrient demand and biomass formation for transforming a given amount of TCE or phenol were reduced by 60 to 90%. Strong starvation promoters have recently been cloned and characterized in environmentally relevant bacteria like Pseudomonas species; thus, starvation promoter-driven degradative systems can now be constructed in such bacteria and tested for in situ efficacy.