Biodegradation of high molecular weight hydrocarbons under saline condition by halotolerant Bacillus subtilis and its mixed cultures with Pseudomonas species

Biodegradation of high-molecular-weight petroleum hydrocarbons in saline conditions appears to be complicated and requires further investigation. This study used heavy crude oil to enrich petroleum-degrading bacteria from oil-contaminated saline soils. Strain HG 01, with 100% sequence similarity to Bacillus subtilis, grew at a wide range of salinities and degraded 55.5 and 77.2% of 500 mg/l pyrene and 500 mg/l tetracosane, respectively, at 5% w/v NaCl. Additionally, a mixed-culture of HG 01 with Pseudomonas putida and Pseudomonas aeruginosa, named TMC, increased the yield of pyrene, and tetracosane degradation by about 20%. Replacing minimal medium with treated seawater (C/N/P adjusted to 100/10/1) enabled TMC to degrade more than 99% of pyrene and tetracosane, but TMC had lesser degradation in untreated seawater than in minimal medium. Also, the degradation kinetics of pyrene and tetracosane were fitted to a first-order model. Compared to B. subtilis, TMC increased pyrene and tetracosane's removal rate constant (K(1)) from 0.063 and 0.110 per day to 0.123 and 0.246 per day. TMC also increased the maximum specific growth rate of B. subtilis, P. putida, and P. aeruginosa, respectively, 45% higher in pyrene, 24.5% in tetracosane, and 123.4% and 95.4% higher in pyrene and tetracosane.