Biodegradation of A-fuel oil in soil samples with bacterial mixtures of Rhodococcus and Gordonia strains under low temperature conditions.

Bioaugmentation is an effective treatment to clean up polluted sites using contaminant-degrading bacteria. However, this treatment is influenced by various environmental conditions, including temperature. In this study, an effective bioaugmentation system under low temperature condition was developed with three Rhodococcus (strains A, C, and D) and one Gordonia (strain B) oil-degraders, which are officially permitted for bioaugmentation applications in Japan. The oil-degrading ability of each strain and mixture was assessed in liquid culture and in model soils supplemented with A-fuel oil. In liquid culture, Rhodococcus strains A and C degraded the A-fuel oil in cold temperature conditions (15°C and 10°C) as well as in mesophilic condition (30°C). In the model soil samples, the mixture of four degraders was the most effective at removing the A-fuel oil under mesophilic condition (>90%), suggesting that strains B and/or D might have factors that promote degradation. In contrast, A-fuel oil was efficiently removed (>80%) in the soil samples inoculated with A or C as well as that with mixture in cold temperature condition, suggesting that strains A and C were the major degraders under cold condition. Our results indicate that the four degraders could be applied to the bioaugmentation in cold areas.