Dibenzothiophene desulfurization capability and evolutionary divergence of newly isolated bacteria

Nasrin Akhtar, Muhammad A. Ghauri, Kalsoom Akhtar

Metabolically microorganisms are diverse, and they are capable of transforming almost every known group of chemical compounds present in coal and oil in various forms. In this milieu, one of the important microbial metabolic processes is the biodesulfurization [cleavage of carbon-sulfur (C-S) bond] of thiophenic compounds, such as dibenzothiophene (DBT), which is the most abundant form of organic sulfur present in fossil fuels. In the current study, ten newly isolated bacterial isolates, designated as species of genera Gordonia, Amycolatopsis, Microbacterium and Mycobacterium, were enriched from different samples in the presence of DBT as a sole source of organic sulfur. The HPLC analysis of the DBT grown cultures indicated the consumption of DBT and accumulation of 2-hydroxybiphenyl (2-HBP). Detection of 2-HBP, a marker metabolite of 4S (sulfoxide-sulfone-sulfinate-sulfate) pathway, suggested that the newly isolated strains harbored metabolic activity for DBT desulfurization through the cleavage of C-S bond. The maximum 2-HBP formation rate was 3.5 µmol/g dry cell weight (DCW)/h. The phylogenetic analysis of the new isolates showed that they had diverse distribution within the phylogenetic tree and formed distinct clusters, suggesting that they might represent strains of already reported species or they were altogether new species. Estimates of evolutionary divergence showed high level of nucleotide divergence between the isolates within the same genus. The new isolates were able to use a range of heterocyclic sulfur compounds, thus making them suitable candidates for a robust biodesulfurization system for fossil fuels.