Effect of temperature and additional carbon sources on phenol degradation by an indigenous soil Pseudomonad

A new indigenous soil bacterium Pseudomonas sp. growing on phenol and on a mixture of phenol, toluene, o-cresol, naphthalene and 1,2,3-trimethylbenzene (1,2,3-TMB) was isolated and characterized. Phylogenetic analysis suggested its classification to Pseudomonadaceae family and showed 99.8% DNA sequence identity to Pseudomonas pseudoalcaligenes species. The isolate was psychrotroph, with growth temperatures ranging from ca. 0 to 40 degrees C. The GC-MS structural analysis of metabolic products of phenol degradation by this microorganism indicated a possible ortho cleavage pathway for high concentrations (over 200 mg L(-1)) of phenol. Biodegradation rates by this species were found to be three times more effective than those previously reported by other Pseudomonas strains. The effect of temperature on phenol degradation was studied in batch cultures at temperatures ranging from 10 to 40 degrees C and different initial phenol concentrations (up to 500 mg L(-1)). Above 300 mg L(-1) of initial phenol concentration no considerable depletion was recorded at both 10 and 40 degrees C. Maximum degradation rates for phenol were recorded at 30 degrees C. The biodegradation rate of phenol was studied also in the presence of additional carbon sources (o-cresol, toluene, naphthalene, 1,2,3-TMB) at the optimum growth temperature and was found significantly lower by a factor of eight in respect to the strong competitive inhibition between the substrates and the more available sources of carbon and energy. The Haldane equation mu = mum S/(Ks + S + S2/K1) was found to best fit the experimental data at the optimum temperature of 30 degrees C than the Monod equation with kinetic constants mum = 0.27 h(-1), KS = 56.70 mg L(-1), KI = 249.08 mg L(-1).