GROWTH-KINETICS OF PSEUDOMONAS-PUTIDA G7 ON NAPHTHALENE AND OCCURRENCE OF NAPHTHALENE TOXICITY DURING NUTRIENT DEPRIVATION

The objectives of this work were (1) to demonstrate how the chemostat approach could be modified to allow determination of kinetic parameter s for a sparingly soluble, volatile substrate such as naphthalene and (2) to examine the influence of the interactions of various nutrients on possible growth-inhibitory effects of naphthalene. Pseudomonas puti da G7 was used as a model naphthalene-degrading microorganism. Naphtha lene was found to be toxic to P. putida G7 in the absence of a nitroge n source or oxygen. The death rate of cells grown on minimal medium pl us naphthalene and then exposed to naphthalene under anoxic conditions was higher than that observed under oxic conditions in the absence of a nitrogen source. The presence of necessary nutrients for the biodeg radation of PAH compounds is indicated to be important for the surviva l of microorganisms that are capable of PAH degradation. The amounts o f ammonia and oxygen necessary for naphthalene biodegradation and for suppression of naphthalene toxicity were calculated from growth yield coefficients. A chemostat culture of P. putida G7 using naphthalene as a carbon and energy source was accomplished by using a feed augmented with a methanol solution of naphthalene so as to provide sufficient g rowth to allow accurate evaluation of kinetic parameters. When naphtha lene was the growth-limiting substrate, the degradation of naphthalene followed Monod kinetics. Maximum specific growth rate (mu(m)) and Mon od constant (K-s) were 0.627 +/- 0.007 h(-1) and 0.234 +/- 0.0185 mg/L , respectively. The evaluation of biodegradation parameters will allow a mathematical model to be applied to predict the long-term behavior of PAH compounds in soil when combined with PAH transport parameters. (C) 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 59: 587-594, 1998.