Biodegradation of petroleum hydrocarbons and changes in microbial community structure in sediment under nitrate-, ferric-, sulfate-reducing and methanogenic conditions.

In the present study, the biodegradation behaviors of petroleum hydrocarbons under various reducing conditions were investigated. n-Alkanes and polycyclic aromatic hydrocarbons (PAHs) were degraded with NO, Fe, SO, or HCO as terminal electron acceptors (TEAs), which link to four typical reducing conditions (i.e., nitrate-reducing, ferric-reducing, sulfate-reducing and methanogenic conditions, respectively) in sediment. The fastest degradation rates were achieved under sulfate-reducing conditions with half-lives of 49.51 days for n-alkanes and 58.74 days for PAHs. For short-chain n-alkanes and low-molecular weight (LMW) PAHs, relatively higher removal efficiencies were achieved under nitrate- and ferric-reducing conditions. The degradation of long-chain n-alkanes and high-molecular weight (HMW) PAHs coupled to methanogenesis was the most favored as compared with other reducing conditions. Carboxylation was found to be the principle mechanism for regulating n-alkane degradation coupled to denitrification, while the activation of n-alkanes by the addition of fumarate was the principle mechanism for the n-alkane degradation under sulfate-reducing conditions. The anaerobic metabolism of n-alkanes may not proceed via fumarate addition or carboxylation under ferric-reducing and methanogenic conditions. Illumina HiSeq sequencing revealed dissimilar structures of the microbial communities under various reducing conditions. It is hypothesized that the utilization of different TEAs for n-alkane and PAH degradation resulted in distinct microbial community structures, which were highly correlated with the varied degradation behaviors of petroleum hydrocarbons in sediment. The current results may provide reference value on better understanding the biodegradation behaviors of n-alkanes and PAHs in association with the induced microbial communities in sedimentary environments under the four typical reducing conditions.