Enzymatic degradation and metabolic pathway of phenanthrene by manglicolous filamentous fungus Trichoderma sp. CNSC-2

Manglicolous filamentous fungi release extracellular lignolytic enzymes that can readily degrade polycyclic aromatic hydrocarbons (PAHs). The present study emphasizes the role of the extracellular enzyme in phenanthrene degradation by the manglicolous fungus Trichoderma sp. CNSC-2 isolated from the Indian Sundarban mangrove ecosystem. The removal efficiency reached 64.05 ± 0.75 % in 50 mg l^-1 phenanthrene-amended mineral salt medium at pH 5.6 after 10 days of incubation. Phenanthrene removal was optimized at different pH, nutrient sources, and Cu²⁺ concentrations. The degradation significantly increased to 67.75 ± 4.32 % at pH 6 (P < 0.0001). The addition of Cu²⁺ (30 mg l^-1) increased the degradation to 78.15 ± 0.36 % (P < 0.0001). The validation experiment confirmed the increase in phenanthrene degradation up to 79.9 ± 1.67 % under optimized conditions. The Lac1 and CytP₄₅₀ genes encoding for extracellular and intracellular enzymes, respectively, were identified. The GC-MS derived phenanthrene degradation metabolites, i.e., phthalic acid, isobutyl 2-pentyl ester derivative, 1, 2 benzene dicarboxylic acid, butyl 2-methyl propyl ester derivative, TMS derivative of benzoic acid and 3,5 dihydroxy benzoic acid determined two possible metabolic pathways. The laccase enzyme activity was higher in the presence of Phe+Cu²⁺ (P < 0.0001), indicating the enzyme induction potential of PAH and Cu²⁺ ions. Purified laccase had a molecular weight of 45 kDa and was highly stable at pH 4-6 and temperature 20-50 °C. The enzyme retained 47 %, 87 %, and 63 % of enzyme activity at 30 mg l^-1 concentration of Pb²⁺, Cd^2+, and Hg²⁺. However, laccase activity was induced by 1.37 folds in the presence of 30 mg l^-1 Cu²⁺ concentration. Thus, the study suggests the potential role of Trichoderma sp. CNSC-2 in phenanthrene degradation.