Abstract

Five isolates able to use dibenzothiophene (DBT) as a sole sulfur source with high rates were selected to investigate their potentialities as biocatalysts of biodesulfurization reactions. The desulfurizing activities of selected strains were investigated in growing and resting cell state. The biodegradation yields were considerably higher in resting cell reaction especially for two strains tentatively named S1 (98.8%) and S27 (97.5%). These results insinuated that biodegradation activity was mainly related to secondary metabolism on these strains. Their biotransformation potentialities were also evaluated under various conditions in order to evaluate their stability in both aqueous and organic media; and their sensitivity to the presence of squalene, used in this study as a representative of hydrocarbons in petroleum. The results showed that the 5 selected strains were still active in the presence of 95% of squalene but no transformation observed at 99% of squalene. The sulfur substrate selectivity was studied in presence of other organosulfur compounds such us dimethylsulfoxide DMSO and benzothiazole BTH. The presence of these substrates inhibited the DBT uptake by the bacteria and consequently decreased its degradation rate. Moreover, conventional analysis of 16S ribosomal DNA sequencing showed that the strain-with highest bioconversion rates-belonged to Serratia marcescens species. To far of our knowledge, Serratia sp. was rarely reported as DBT degrder strain. Thus, the rate and the extent of the biodesulfurization reaction, exhibited by the strain Serratia marcescens S27, suggested that it could be used in practical scale.

Keywords: Dibenzothiophene; Biodesulfurization; Organosulfur compounds; Xenobiotics; Biodegradation; Serratia sp