Microcalorimetric investigation of the toxic action of pyrene on the growth of PAH-degrading bacteria Acinetobacter junii

A multi-channel thermal activity microcalorimeter was used to determine the pyrene-induced toxic effect on two polycyclic aromatic hydrocarbon (PAH)-degrading bacteria Acinetobacter junii (A. junii) and Bacillus subtilis (B. subtilis). Power-time curves were analyzed and calorimetric parameters including growth rate constant (k), half inhibitory concentration (IC ₅₀) and total thermal effect (Q_T) were obtained. A. junii and B. subtilis were completely inhibited when the concentration of pyrene reached 400 and 160 μg mL^-1, respectively. The relationships between the calorimetric parameters and concentration of pyrene were studied. The growth rate of A. junii decreased with the increase in pyrene concentration at 50-200 μ g mL^-1. The growth of biomass for A. junii at various concentrations of pyrene was determined. The count of A. junii after 8 day's incubation reached maximum irrespective of the initial pyrene concentrations ranging from 50 to 200 μg mL^-1 and the smallest stimulative action of pyrene was at 200 μg mL^-1. The variations of biomass during the growth of A. junii were consistent with the microcalorimetric data, indicating that microcalorimetry can be an effective technique to investigate the effect of pyrene on microorganisms.