Oxygen Effects on Biodegradation of Fuels in a Corroding Environment

Experiments were designed to evaluate biodegradation of plantand petroleum-based fuels and blends exposed to seawater under anaerobic conditions. The experimental set-up included natural aerobic seawater, fuel and unprotected carbon steel coupons, simulating a potential fuel storage situation. Corrosion was due to microbiologically produced sulfides reacting with carbon steel. There were few differences between electrochemically measured corrosion rates between plant-based, petroleum fuels or their mixtures. Transient oxygen influenced both metabolic degradation pathways and resulting metabolites. Detection of catechols suggested that initial exposure to oxygen resulted in their formation. Transient exposure to oxygen resulted in higher proportions of Firmicutes, Deltaproteobacteria (primarily sulfatereducing bacteria), Chloroflexi, and Lentisphaerae in seawaters exposed to fuels than the original seawater. Relative proportions of sequences affiliated with these bacterial groups varied with fuel. Methanogen sequences similar to those of Methanolobus species were found in multiple incubations. Despite the dominance of characteristically anaerobic taxa, sequences coding for an aerobic hydrocarbon-degrading enzyme (alkane monooxygenase) were obtained following PCR amplification. The alkane monooxygenase and 16S rRNA clone libraries from seawater contained sequences with high similarity to marine hydrocarbon-degrading genera, mainly Gammaproteobacteria, suggesting that seawater was the source of these organisms and that they survived the anaerobic incubations.