Biodegradation of high molecular weight polycyclic aromatic hydrocarbon by isolated fungi

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are recalcitrant pollutants with two or more fused benzene rings. Almost 90% of PAHs emission to the environment is anthropogenic, causing carcinogenic and mutagenic effects in humans. These PAHs are subject to removal by biological treatment. However, because of the physiochemical characteristics of PAHs and especially high molecular weight (HMWPAHs), the biodegradation by microorganisms is difficult. Fungi were collected from contaminated soil and rain forest in Malaysia, isolated based on their ability to decolorize RB5 and RBBR due to the similarity in chemical structure and ease in its measurement on agar medium. The best-performing fungi were identified based on the DNA sequence and phylogenetic tree. Three fungi were identified in the lab as Candida sp. S1, Meyerzoma sp. S7 and Rhizoctonia zeae SOL3. The biodegradation of PAHs by these fungi have been studied in 7, 15, 21, 30 days of incubation in liquid medium. Among the screened and collected fungi, R.zeae SOL3 showed the highest degradation of pyrene in 15 days (42%). Parameters such as temperature, glucose concentration, NaCl, pyrene concentration, agitation and pH were investigated to show their effect on the biodegradation by Candida sp. S1 and R.zeae SOL3. The results showed that these fungi are mesophilic and halophilic. The degradation of pyrene by Candida sp. S1 and R.zeae SOL3 have been optimized based on the response surface method (RSM), the predicted values from the model were very close to the actual data from the experiments. This indicated the suitability of the model in prediction of the experiment. The metabolites of pyrene biodegradation by R.zeae SOL3 were identified by GC-MS as 4-hydroxy benzoic acid, benzoic acid and butanedioic acid. These fungi showed a good ability to remove HMW-PAHs from the liquid medium in extreme saline and acidic conditions, producing metabolites less dangerous than the parent compound, which can be used in the removal of PAHs in industrial wastewater.