Degradation of naphthalene by Pseudomonas sp. strain KR3 investigated by flow calorimetry

Abstract

Abstract Biotic degradation techniques are gaining importance in decontaminating soils and waste water from organic pollutants. One class of organic pollutants of much interest are polyaromatic hydrocarbons (PAH), ubiquitous substances some of which show a high carcinogenic and mutagenic potential and acute toxicity. Although they usually possess a high thermodynamic stability they can be degraded by microorganisms. In our investigations of PAH degradation we used naphthalene as a model substance because of its high solubility. The degradation of naphthalene at 25°C in liquid culture by Pseudomonas sp. strain KR3 was observed with a Thermometric microcalorimeter equipped with a flow cell. Bacterial cultures from a fermentor were pumped through this measuring cell via tubing. Parallel to the microcalorimetric investigations the amount of degraded naphthalene and the generation of metabolites were observed by HPLC analysis, and biomass production and oxygen consumption were measured. On degrading naphthalene, Pseudomonas sp. strain KR3 generated various metabolites at the same time. Only some of the metabolites had their maximum concentration synchronous to the maximum heat flow rate. Anabolic processes were delayed compared to the consumption of the substrate. A good correlation between calorimetric results and oxygen consumption was found. A relationship between a strong decrease in heat production after the main heat flow rate peak and inhibition of metabolic processes by lack of oxygen could be excluded. Decrease in the heat flow rate is assumed to be due to lowered gas exchange in the calorimeter tubes, i.e. the inhibited degassing of carbon dioxide. Calculation of an envelope for the heat flow rate is useful to improve experimental results.