Effect of Nitrogen Source on Biodegradation of Crude Oil by a Defined Bacterial Consortium Incubated under Cold, Marine Conditions

Abstract

Studies have been carried out using a defined bacterial consortium which degrades crude oil under cold, marine conditions. The type of nitrogen supplement (i.e. ammonium versus nitrate) in the artificial sea water medium used in the experiments affected the degree of oil biodegradation observed, and was correlated with spent culture medium pH. Supplementation with ammonium led to progressive acidification of cultures, whereas nitrate amendment resulted in a neutral culture medium. The presence of ammonium in cultures incubated with the full consortium of strains was correlated with decreased aromatic fraction biodegradation, suggesting that aromatic degradation is sensitive to pH and possibly to by-products of saturate fraction biodegradation. The pH effect was shown to be caused primarily by one or more of the three saturate-degrading bacterial strains in the inoculum, when incubated in the presence of ammonium, while the aromatic-degrading strains did not acidify culture medium to the same degree. Acidification was not linked solely to oil biodegradation, as the inoculum also caused acidification of medium containing glucose and ammonium. The pH effect could be lessened with increased concentrations of phosphate buffer in the medium to maintain a culture pH near neutrality. It was observed that the greatest overall biodegradation occurred with a nitrate supplement and adequate buffering with phosphate.