Isolation of soil bacteria species for degrading dibenzothiophene

Five bacterial strains, which are able to grow and to disintegrate dibenzothiophene (DBT) and dibenzothiophene sulfone (DBTO2) in fossil fuels, are isolated. Analysis of products of DBT metabolized by these strains shows that different bacteria strains oxidize DBT by different pathways. The isolated strains R-6, R-16, R-9 and R-8 can metabolize DBT to DBTO2 and 2-hydroxybiphenyl (HBP), which are identified as Bacillus brevis, Bacillus sphaericus, Nocardia globerula and Pseudomonas delafieldii respectively. Another strain R-12 identified as Pseudomonas sp. can degrade DBT completely but it cannot produce DBTO2 and HBP. The optimum temperature and initial pH for desulfurization by R-8 are 32degreesC and 7.02 respectively and pH of the broth decreases during biodegradation. The growth of strain R-8 with different sulfur-sources indicates that this strain in DBT medium has an induction period of 3 days, which is longer than those with dimethylsulfoxide and MgSO4 media, but the growth rate of the bacterial strain in DBT is higher after the induction. Higher growth and desulfurization rates are observed in the DBT-hexadecane system than in both DBT-ethanol and DBT-dimethylformamide systems. Both strains of R-8 and R-9 also show higher desulfurization activities toward other sulfur-substrates, indicating that they have greater desulfurization potential in application.