COMPETITION IN CHEMOSTAT CULTURE BETWEEN PSEUDOMONAS STRAINS THAT USEDIFFERENT PATHWAYS FOR THE DEGRADATION OF TOLUENE

Pseudomonas putida mt-2, P. cepacia G4, P. mendocina KR1, and P. putid a F1 degrade toluene through different pathways. In this study, we com pared the competition behaviors of these strains in chemostat culture at a low growth rate (D = 0.05 h(-1)), with toluene as the sole source of carbon and energy. Either toluene or oxygen was growth limiting. U nder toluene-limiting conditions, P. mendocina KR1, in which initial a ttack is by monooxgygenation of the aromatic nucleus at the para posit ion, outcompeted the other three strains. Under oxygen limitation, P. cepacia G4, which hydroxylates toluene in the ortho position, was the most competitive strain. P. putida mt-2, which metabolizes toluene via oxidation of the methyl group, was the least competitive strain under both growth conditions. The apparent superiority of strains carrying toluene degradation pathways that start degradation by hydroxylation o f the aromatic nucleus aas also found during competition experiments w ith pairs of strains of P. cepacia, P. fluorescence, and P. putida tha t were freshly isolated from contaminated soil.