Effect of nitrogens source on biodegradation of crude oil by a defined bacterial consortium incubated under cold, marine conditions

Studies have been carried out using a defined bacterial consortium which de grades crude oil under cold, marine conditions. The type of nitrogen supple ment (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 re sulted in a neutral culture medium. The presence of ammonium in cultures in cubated with the full consortium of strains was correlated with decreased a romatic fraction biodegradation, suggesting that aromatic degradation is se nsitive to pH and possibly to by-products of saturate fraction biodegradati on. The pH effect was shown to be caused primarily by one or more of the th ree saturate-degrading bacterial strains in the inoculum, when incubated in the presence of ammonium, while the aromatic-degrading strains did not aci dify 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 incr eased concentrations of phosphate buffer in the medium to maintain a cultur e pH near neutrality. It was observed that the greatest overall biodegradat ion occurred with a nitrate supplement and adequate buffering with phosphat e.