Biodegradation of mixtures of polycyclic aromatic hydrocarbons under aerobic and nitrate-reducing conditions

Contaminated sites often contain complex mixtures of aromatic compounds. This complex mixture and the systemʹs redox condition may influence biodegradation patterns. In this study, the biodegradation of PAHs in varying mixture combinations by a pure culture of Pseudomonas putida strain KBM-1 under aerobic conditions showed that the presence of naphthalene (2-ringed PAH) stimulated phenanthrene (3-ringed PAH) degradation five-fold and pyrene (4-ringed PAH) degradation two-fold. However, the presence of phenanthrene inhibited pyrene degradation. Similar degradation patterns were observed under anaerobic, nitrate-reducing conditions; though the degradation rates were typically slower. For example, phenanthrene and pyrene degradation required 2–3 longer times to approach non-detectable levels under nitrate-reducing conditions. In contrast, the time to attain non-detectable levels using a different strain, Pseudomonas stutzeri SAG-R, was similar under both conditions. The results show the importance of improving our understanding of how to extrapolate single substrate biodegradation data obtained under aerobic conditions to multi-substrate situations in aerobic and anaerobic environments.