Degradation Of Dibenzothiophene By Some Newly Isolated Bacterial Strains

Dibenzothiophene (DBT) is a major heterocyclic organic sulfide in petroleum. It is very difficult to be degraded by traditional desulfurization method. Therefore, DBT is always considered as model compound for biodesulfurization research. In this article, a strain 6-1 which is capable of desulfurizing DBT as sulfur source was isolated from the waste water polluted by petroleum.The strain 6-1 was identified by analyzing 16S rDNA gene sequence. The searches were conducted with BLAST program in the GenBank (NCBI), which exhibited high levels of 99% similarity with Cronobacter turicensis strain.The growth curve of this strain indicated that the strain 6-1 stepped into logarithmic phase after 12 hours which lasted for about 50 hours. Then, the growth of strain 6-1 entered stationary phase which lasted for 40 hours. During stationary phase, cell concentration of the strain remained nearly invariable. The degrading curve of this strain indicated that DBT was degraded with the growth of the culture. From 36h to 48h, more than 80% DBT was degraded.Five single-factor experiments have been carried out to optimize the culture conditions for strain 6-1. Results showed the optimal culture conditions: 2g/L glycerol as carbon source; 2g/L ammonium chloride as nitrogen source; 0.2mM DBT as sulfur source; the most appropriate initial pH of culture media was 7.0 while the optimal temperature for growth was 30℃。The metabolites of DBT were identified by GC-MS analyses of dichloromethane extracts of the culture supernatants. The result indicates that the DBT ring is cleaved and DBT is mineralized completely to CO₂ , H₂O and SO₄^2- by the culture.