After enrichment cultivation, 38 strains were obtained, and 22 strains could grow in MBSM with 2% diesel oil as the sole carbon and energy source. The strains degraded between 16.4% and 91.6% of TPHs, and 11 strains degraded more than 70% of TPHs in diesel oil (Fig. 1A). The biomass of each isolate was proportional to degradation of TPHs (Fig. 1B). The Pearson correlation coefficient is 0.881 (p < 0.01), which indicates that the degradation of diesel oil is positive correlation to growth of the isolates. None of the controls showed growth of biomass and biodegradation of diesel oil.
Gas chromatography–mass spectroscopy peaks indicated that the bacteria, which could grow with diesel oil as the sole source of carbon and energy, degraded C12–C25 n-alkanes and other hydrocarbon fractions (data not shown). Since crude oil is a complex mixture of hydrocarbons and other compounds, the wide range of degradation substrates by the strains should be a significant advantage in bioremediation of oil-contaminated soils.