Biology of Trichoderma sp. isolated from polluted sediment and its potential in degradation of phenanthrene (PAHs)

Polycyclic Aromatic hydrocarbons (PAHs) as contaminants are one of the most recalcitrant, persistent organic compounds and this has made their fate in the environment of significant interest. PAHs have become a great concern as they are highly ecotoxic with potential of being human carcinogens, making their rapid elimination and detoxification from the environment of necessary importance. This study aimed to isolate and screen indigenous soil and sediment fungi for possible application in the remediation of these contaminants. It also aimed to investigate how two important factors, temperature and pH influence the PAHs degradative capability of the potent fungus using phenanthrene as a model substrate. The study also involves evaluating the suitability of this isolate in qualitative phenanthrene degradation through the detection of metabolites. Soil and sediment samples were collected for fungal isolation. Forty-four isolates were obtained and screened to select the best isolate with the potential to degrade phenanthrene as a substrate. Trichoderma sp., a filamentous Sordariomycetes isolated from Bagan Lalang sediment showed the best phenanthrene tolerance with a high growth percentage of 76.9% at 72 hrs and a percentage phenanthrene degradation of 60.4% after 10days of incubation in liquid mineral medium. Evaluation of the effects of environmental factors on phenanthrene degradation showed that both parameters (temperature and pH) had a significant effect on the fungus ability to degrade phenanthrene. Laboratory studies using Mineral Salt Broth (MSB) showed that phenanthrene degradation efficiency was influenced by temperature with the highest degradation of 69.5% occurring at 35°C. This temperature also supported a good biomass accumulation of 62mg dry weight. Less phenanthrene degradation was observed at lower and higher temperatures. Influence of pH on substrate degradation showed thatthe optimum pH for phenanthrene degradation by the fungus was at a neutral pH 7. This pH point facilitated both effective phenanthrene degradation of 76.8% and biomass growth of 48mg dry weight thus, making it evident that higher rates of degradation was somewhat related to a high biomass growth. Qualitative analyses by GC-MS of extracts after incubation showed that Trichoderma sp. could degrade phenanthrene; yielding metabolites such as 9,10-dihydro-9,10- dihydroxyphenanthrene, 9,10-dihydrophenanthrene, 9-Phenanthrol, 1,2,3,4- tetrahydrophenanthrene and phthalic acid. Based on the detected metabolites, the mechanism of phenanthrene degradation by this fungus, suggests the activities of both ligninolytic and non-ligninolytic type of enzymes with major attack on the Kregion (C-9 and C-10) of phenanthrene. The metabolite 1,2,3,4- tetrahydrophenanthrene detected in culture extracts suggests that another pathway utilized by the fungus may exist in substrate degradation. Thus, this Trichoderma isolate could serve as a potential innoculum that can be utilized in microbial PAHs degradation and environmental factors such as pH and temperature does have an influence on the strains ability to act on phenanthrene.

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