The effects of substrate exposure history and carbon starvation-induced stress on the EPS synthesis of TCE degrading toluene oxidizing soil bacteria

A series of batch experiments was undertaken to explore the influence of growth conditions on the extracellular polymeric substances (EPS) production of five representative strains of trichloroethylene (TCE) degrading toluene oxidizing bacteria of importance to in situ bioremediation. EPS production for three distinct carbon sources (i.e., lactate, glucose, and toluene) was examined under starvation and non-starvation conditions. EPS extraction was accomplished using DOWEX™ (cation exchange resin; CER), and total carbohydrate, protein, and uronic acid were quantified as the main EPS constituents. Experimental results reveal that most bacteria grown on toluene synthesized more EPS per colony forming unit (CFU) than those grown on other substrates and that EPS production is enhanced with increasing length of starvation. These observations suggest that EPS may be produced under conditions of environmental stress and may be linked to enzyme deactivation. The results from this work additionally indicate that the mutant strain of Ralstonia pickettii PKO1 with the lack of gene encoding TbuX (an outer membrane protein) is more hydrophobic due to less EPS synthesis ability. The relatively lower amount of EPS synthesis in the mutant strain of R. pickettii PKO1 suggests that TbuX, an outer membrane protein encoded a part of the toluene catabolic regulation of R. pickettii PKO1, has a role in bacterial EPS production.