Resistant Rhodococcus for Biodegradation of Diesel Fuel at High Concentration and Low Temperature

The resistance of 16 Rhodococcus strains to diesel fuel was studied. The minimal inhibitory concentrations of diesel fuel against Rhodococcus were 4.0-64.0 vol. % and 0.5-16.0 vol. % after 7 days of incubation in Luria-Bertani broth and a mineral "Rhodococcus-surfactant" medium, respectively. The three most resistant strains (R. ruber IEGM 231, IEGM 442 and Rhodococcus sp. IEGM 1276) capable of overcoming the toxicity of diesel fuel at a high (8.0 vol. %) concentration and at a low (4 °C) temperature were selected. Respiration activities, growth kinetics, and changes in the diesel fuel composition during the biodegradation process were elucidated using gas chromatography with mass spectrometry, respirometry, and Bradford analysis. Growth conditions were optimised for the improved biodegradation of diesel fuel by Rhodococcus cells using multifactor analysis. They included the simultaneous addition of 1.3 g·L^-1 of granular sugar and 0.25 g·L^-1 of yeast extract. The twofold stimulation of the biodegradation of individual hydrocarbons in diesel fuel (n-pentadecane, n-hexadecane and n-heptadecane) was demonstrated when glycolipid Rhodococcus-biosurfactants were added at a concentration of 1.4 g·L^-1. A total removal of 71-91% of diesel fuel was achieved in this work.