Biodegradation of phloroglucinol and gallic acid by the soil fungus Penicillium simplicissimum

Hameed, Nuzhat S. (1987) Biodegradation of phloroglucinol and gallic acid by the soil fungus Penicillium simplicissimum. Masters thesis, Memorial University of Newfoundland.

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Abstract

Studies were undertaken to define the biodegradative pathway of aromatic compounds namely phloroglucinol and gallic acid by the soil fungus Penicillium simplicissimum. Optimal growth conditions were determined for the utilization of phloroglucinol and gallic acid as sole sources of carbon P. simplicissimum grew best at pH 5.5 and the optimal temperature was about 27-29°C. The optimal concentration of substrate was 1.5 % (w/v) in the case of phloroglucinol and 0.2 % (w/v) for gallic acid. -- The metabolic pathways of these aromatic compounds were studied in crude extracts from mycelia grown on the respective substrates. P. simplicissimum mycelia used for enzymatic studies were 24 hours and 30 hours old. The biodegradation of phloroglucinol was initiated by phloroglucinol reductase (PG-R), an NADPH+H⁺ dependent enzyme, forming dihydrophloroglucinol as the first intermediate. The second intermediate detected and isolated in crude extract was resorcinol and the third one, possibly a ring cleavage substrate, was 1,2,4-benzenetriol. This intermediate was detected and isolated from the culture medium containing phloroglucinol as a substrate. The enzymes responsible for ring cleavage, catechol 1,2 oxygenase and catechol 2,3 oxygenase, were found to be present in the crude extract. -- The utilization of gallic acid followed a different metabolic pathway. The initial step was catalyzed by gallic acid reductase (GA-R) in the presence of NADPH+H⁺. The ring fission enzymes, catechol 1,2 oxygenase and catechol 2,3 oxygenase, were again found to be present in the crude extract. Catechol 1,2 oxygenase was more active and stable than catechol 2,3 oxygenase. The possible substrate for the oxygenases was 1,2,4-benzenetriol which was detected and isolated from the culture medium. The product of ring cleavage was shown to be maleylacetate by the enzymatic breakdown with maleylacetate reductase in the presence of reduced NADPH⁺. The end product of enzymatic reduction of maleylacetate was β-ketoadipate, which was detected and isolated from the reaction mixture containing maleylacetate, NADPH+H⁺ and maleylacetate reductase.

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