Degradation Of Petroleum Pollutants By Rhodococcus Sp.Strain P52

Petroleum as an energy source is increasingly used in modern technologies. During exploitation, transportation, storage and usage, leakage of petroleum into soil and water bodies is inevitable, and causes serious pollution. Petroleum hydrocarbons have high biological toxicity, having entered the environment, they tend to persist with potentially devastating consequences to ecosystems. The remediation challenge is largely met by microbes, which biodegrade petroleum pollutants through diverse metabolic processes. As effective, low-cost natural degraders, microbes play a significant role in environmental depuration.This study focuses on investigating the ability of Rhodococcus sp. strain p52, a dibenzofuran degrader, to degrade alkanes of variable chain length and to degrade aromatic hydrocarbons. Strain p52can use linear alkanes (tetradecane, tetracosane, and dotriacontane), branched alkane (pristane), and aromatic hydrocarbons (naphthalene and phenanthrene) as sole carbon and energy sources. Specifically, the strain removes85.7%of tetradecane within48h at a degradation rate of3.8mg h-1g-1dry cells, and79.4%of tetracosane,66.4%of dotriacontane, and63.9%of pristane within9-11days at degradation rates of20.5,14.7and20.3mg day-1g-1dry cells, respectively. Moreover, strain p52consumes almost100%naphthalene and55.3%phenanthrene within9-11days at respective degradation rates of16and12.9mg d-1g-1dry cells. Based on the identified metabolites and reference pathways, tetradecane was deduced to be initially degraded via monoterminal, diterminal, and sub-terminal oxidation, while pristane was oxidized through a sub-terminal pathway only. Additionally, naphthalene was initially monooxygenated, while phenanthrene was both monooxygenated and dioxygenated. Genes encoding alkane-hydroxylating enzymes, including cytochrome P450(CYP450) enzyme (CYP185) and two alkane-1-monooxygenases, were amplified and sequenced, which shared high identity with the corresponding sequences of other reported gram-positive bacteria. The amino acid sequences of two alkane-1-monooxygenases shared only62% identity. The transcriptional activities of these genes in the presence of petroleum hydrocarbons were detected by reverse transcription-polymerase chain reaction. In addition, the plasmids, pDF01and pDF02, which related to the degradation of aromatic compounds, could conjugatively transfer among the congeneric and intergeneric bacteria. Through continuous subculture, the plasmids exhibited relatively high inheritance stability. The results revealed strong application potential of strain p52to bioremediate petroleum hydrocarbons.