Studies On Characteristics Of Phenanthrene Degradation By Massilia Sp.WF1

Polycyclic aromatic hydrocarbons (PAHs) are a group of persistent organic pollutants which have detrimental biological effects, toxicity, mutagenecity and carcinogenicity to ecology and human beings by biological-chains accumultaion. Phenanthrene (PHE), a three-ring angular PAH with a similar "K-region" and "bay-region" to several carcinogenic PAHs, is often used as a model PAH for biodegradation. Furthermore, researchers indicated that microbial degradation is the principal way to removal PAHs from environment. Hence, study on PHE biodegradation can be valuable to provide knowledge for bioremediation of soil and other environment contaminated by PAHs.In the present study, a PHE-degrading strain WF1, isolated from an aged PAHs-contaminated soil, was chosed to investigate its optimum PHE biodegradation conditions, PHE degradation pathway, bioremediation potential in PHE contaminated soil, and its influence on soil bacterial community. The main results were as follows:(1) A bacterial strain WF1 was isolsted from PAHs-contaminated soil. WF1 was identified as Massilia sp. based on the analyses of morphology, physiology,16S rDNA and gyrB sequence.(2) With PHE as a sole carbon source, Massilia sp. WF1 could efficiently degrade PHE with a broad range of pH (5-8), temperature (20-35℃), and PHE concentration (25-400 mg L-1).96.78% of applied PHE (100 mg L-1) was degraded in 2 days by WF1 at the optimal conditions of 28℃, pH 6. Further analysis revealed that PHE biodegradation kinetics fitted well to Gompertz equation in the treatments with different carbon sources. Whereas, the added carbon sources had different effects on PHE degradation. PHE biodegradation was promoted by the additional carbon sources of glucose, citric acid, and succinic acid, but was inhibited by the addition of lactic acid. In addition, there were no obvious effects on PHE biodegradation by the addition of sucrose, fructose, lactose, salicylic acid and phthalic acid.(3) According to the identified degradation metabolites of PHE by GC-MS analyses, two intermediate metabolites of 1-hydroxy-2-naphthoic acid and phthalic acid were detected. But unlike the conventional pathways as reported previously, phthalic acid was not degraded by WF1.(4) In PHE bioremediation experiments, PHE was degraded effeciently in the bioaugmentation treatment of WF1 and the control treatment only containminated by PHE. In the bioaugmentation treatment of WFl, PHE-residual concentration in the test soil decreased from 84.41 mg kg-1 at 0 day to 16.41 mg kg-1 at 3 days. In the control treatment, the highest PHE degradation rates appeared from 5 days to 7 days whilst PHE-residual concentration declined from 56.00 mg kg-1 to 22.01 mg kg-1. However, PHE degradation rates became slow in both of these two treatments when PHE-residual concentration in the test soil decreased to about 5 mg kg-1, which might mainly caused by the lower bioavailability of PHE. Specifically, PHE-residual concentration maintained ranging from 47.79 mg kg-1 to 60.45 mg kg-1 in the microbe-inhibited treatment of NaN3.(5) Furthermore, soil micbial community structures of PHE bioremediation experiments were revealed by Illumina high-throughput sequencing technique.The abundance of indigenous microorganism, Mycobacterium, was coupled with PHE degradation and reached the highest abundance at 7 days in the control treatment. Except Bacillus sp. increased, most bacteria species changed slightly during the incubation periods in the microbe-inhibited treatment of NaN3. As in the bioaugmentation treatment of WF1, the abundance of Massilia reached the highest value in 3 days, and declined with the decreasing of PHE-residual concentration. Based on the microbial community structure analysis, it can be further concluded that soil indigenous microbial community did not changed obviously by WF1 at the end of 28-d incubation. Thus, Massilia sp. WF1 can be used as a promising bacterium for PAHs bioremediation.