Evaluation of solvent tolerance of microorganisms by microcalorimetry

Solvent tolerance is important because it allows microorganisms to grow at high concentrations of organic solvents. Organisms capable of surviving under these extreme conditions have great application in bioremediation of contaminated sites. In our study, four strains of Pseudomonas sp. B1 and J2, Acinetobacter sp. B2 and J6 which were isolated from the activated sludge were used to evaluate the solvent tolerance by microcalorimetry. The strains B2 and J2 showed high tolerance to organic solvent as they could grow well in the medium containing 10 vol% of benzene and 70 vol% of toluene, respectively. The higher the growth rate constant, the higher the solvent tolerance of the strains isolated. The microbial growths obtained by microcalorimetry were in good agreement with the results determined by OD600. The decrease in growth rate constant and the change in total thermal effect in the presence of organic solvents were in agreement with the data reported in the literatures. Strains B1 and B2 degraded about 67% and 94% of 0.1 vol% benzene within 72 h in a medium with benzene as the sole carbon source, respectively. Strains J2 and J6 degraded approximately 92% and 85% of 0.1 vol% toluene within 72 h, respectively. The related degradation genes detected in previous study in these strains highlight an important potential use of those bacteria for the clean-up of benzene and toluene in the environment.