Bacterial biodegradation of aliphatic sulfides under aerobic carbon‐ or sulfur‐limited growth conditions

Aims:  To isolate bacteria capable of cleaving aliphatic carbon–sulfur bonds as potential biological upgrading catalysts for the reduction of molecular weight and viscosity in heavy crude oil. Methods and Results:  Thirty‐one bacterial strains isolated from enrichment cultures were able to biotransform model compounds representing the aliphatic sulfide bridges found in asphaltenes. Using gas chromatography and mass spectrometry, three types of attack were identified: alkyl chain degradation, allowing use as a carbon source; nonspecific sulfur oxidation; and sulfur‐specific oxidation and carbon–sulfur bond cleavage, allowing use as a sulfur source. Di‐ n ‐octyl sulfide degradation produced octylthio‐ and octylsulfonyl‐alkanoic acids, consistent with terminal oxidation followed by β ‐oxidation reactions. Utilization of dibenzyl sulfide or 1,4‐dithiane as a sulfur source was regulated by sulfate, indicating a sulfur‐specific activity rather than nonspecific oxidation. Finally, several isolates were also able to use dibenzothiophene as a sulfur source, and this was the preferred organic sulfur substrate for one isolate. Conclusions:  The use of commercially available alkyl sulfides in enrichment cultures gave isolates that followed a range of metabolic pathways, not just sulfur‐specific attack. Significance and Impact of the Study:  These results give new insight into biodegradation of organosulfur compounds from petroleum and for biotreatment of such compounds in chemical munitions.