Author(s)

A. Matin, D. Hahm & D. F. Ackerley

Abstract

Bacterial bioremediation is a safe and inexpensive means of decontaminating environmental pollution. However, low nutrient concentrations at polluted sites frequently limit bioremediating activity. Biostimulation by exogenous application of nutrients does not always promote effective transformation of pollutants, and the high levels of biomass that result can cause clogging around feeding ports, further constraining this strategy. To overcome these limitations we propose the application of starvation promoters to selectively express genes that are useful in bioremediation at maximal levels in nutrient-limited cells. Here we show that placing toluene monoxygenase (TMO) genes under control of the Pstarv1 starvation promoter in Pseudomonas putida MK1 brought about an 8-fold increase in the rate of phenol degradation by stationary-phase cells over exponentially growing cells. Under nutrient-limiting conditions these cells were also able to transform trichloroethylene with a conversion efficiency approximately 64-fold greater than unmodified cells, which only express appreciable levels of TMO in exponential phase. We also mapped and characterized the native promoter of chrR, a P. putida gene encoding a chromate-reducing enzyme, and show that it is likely to be under the transcriptional control of sigma 32, a heat shock and starvation regulated sigma factor. Consistent with this observation, P. putida cells grown at different dilution rates in a chemostat exhibited maximal chromate-reducing activity at low growth rates. These results are promising for maximizing the expression of chrR under field conditions for chromate bioremediation. Keywords: bioremediation, biostimulation, phenol, trichloroethylene, hexavalent chromium, toluene monoxygenase, chromate reductase, starvation promoter.

Keywords

bioremediation, biostimulation, phenol, trichloroethylene, hexavalent chromium, toluene monoxygenase, chromate reductase, starvation promoter.