Biodegradation of High Molecular Weight Polycyclic Aromatic Hydrocarbons in Soils by Defined Bacterial and Fungal Cocultures

Author: Christopher William Minto Lease

Lease, Christopher William Minto, 2006 Biodegradation of High Molecular Weight Polycyclic Aromatic Hydrocarbons in Soils by Defined Bacterial and Fungal Cocultures, Flinders University, School of Biological Sciences

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Abstract

Despite microbial degradation being the primary route of degradation of PAHs in soils, high molecular weight polycyclic aromatic hydrocarbons (such as benzo[a]pyrene) have consistently proven to e resistant to microbial attack. However, recent research has demonstrated the potential for bacterial-fungal co-cultures to achieve biodegradation of high molecular weight PAHs. The aim of this research was to determine the efficacy of co-culture bioaugmentation for the remediation of high molecular weight PAHcontaminated soils. PAH degrading bacteria were enriched on multiple PAHs and isolated on pyrene from both contaminated (soil from a former manufactured gas plant) and uncontaminated (agricultural soil, termite mound matrix and kangaroo faeces) sources. The bacterial isolates were identified using 16SrRNA analysis as Mycobacterium sp. Strain BS5, Mycobacterium sp. Strain KA5 and Mycobacterium sp. Strain KF4 or fatty acid methyl ester (FAME) analysis as Ralstonia pickettii and Stenotrophomonas maltophilia. The initial phase of assessment of PAH degradation by fungal and bacterial coculture components was undertaken using liquid media. Two fungal isolates from a previous investigation into the coculture process (Penicillium janthinellum) and the American Type Culture Collection (Phanerochaete chrysosporium) were assessed for their ability to degrade benzo[a]pyrene in minimal media and MYPD. The fungal isolates were found to be able to degrade benzo[a]pyrene cometabolically in MYPD. The bacterial isolates and two others from previous investigations were assessed for their ability to degrade single PAHs (fluorene, phenanthrene, fluoranthene, pyrene and benzo[a]pyrene) in liquid culture. This process was used as an initial screen to select the best bacterial isolates for further investigation of PAH degradation by axenic cultures and cocultures with the fungal isolates using a PAH mixture. Based on the results of these experiments four bacterial isolates (VUN 10,010, Mycobacterium 1B, Mycobacterium sp. Strain BS5 and Mycobacterium sp. Strain KA5) and the two fungal isolates were selected to investigate further using a PAH mixture composed of the previously mentioned PAHs. It was found that the use of a fungal bacterial coculture increased the degradation of the PAH mixture beyond that of axenic bacterial cultures. Based on these experiments, the coculture composed of P. janthinellum and VUN 10,010 was selected for assessment of its ability to degrade the same PAH mixture in spiked soil microcosm experiments. Natural attenuation, axenic P. janthinellum, axenic VUN 10,010 and a coculture of these two organisms were assessed for PAH degradation in soil microcosms over a 100 day period. Inoculation of microcosms with the coculture resulted in the removal of benzo[a]pyrene by 11 mg/kg (± 1.21 mg/kg) (30%) over the 100 day incubation period. Substantial PAH degradation was also observed in the microcosms assesing natural attenuation. Using an alternative sequential inoculation method, initially inoculating with P. janthinellum then 50 days later with VUN 10,010 significantly enhanced the removal of benzo[a]pyrene. After 100 days incubation, benzo[a]pyrene was degraded below detection limits in two of three microcosms, compared to a 4.95 mg/kg (± 4.64 mg/kg) (14.7 %) reduction in soil microcosms inoculated using an alternative inoculation process of VUN 10,010 followed by P. janthinellum. Attempts were made to optimise the process using sequential inoculation and soil amendments intended to enhance the performance of the fungal component using distilled water and 1% glucose. The addition of distilled water was not observed to substantially influence the ability of the coculture to degrade PAHs, whereas the addition of 1% glucose was found to inhibit PAH degradation.

Keywords: Coculture,bacterial,fungal,degradation,polycyclic,hydrocarbons,soil
Subject: Biological sciences thesis

Thesis type: Doctor of Philosophy
Completed: 2006
School: School of Biological Sciences
Supervisor: Dr Richard Bentham