EVIDENCE OF 2 PATHWAYS FOR THE METABOLISM OF PHENOL BY ASPERGILLUS-FUMIGATUS

Aspergillus fumigatus (ATCC 28282), a thermotolerant fungus, has been shown to be capable of growth on phenol as the sole carbon and energy source. During growth of the organism on phenol, catechol and hydroquinone accumulated transiently in the medium; cells grown on phenol oxidised these compounds without a lag period. Two different routes operating simultaneously, leading to different ring-fission substrates, are proposed for the metabolism of phenol. In one route, phenol undergoes oi-tho-hydroxylation to give catechol, which is then cleaved by an intradiol mechanism leading to 3-oxoadipate. In the other route, phenol is hydroxylated in the pal-a-position to produce hydroquinone, which is then converted into 1,2,4-trihydroxybenzene for ring fission by ol tho-cleavage to give maleylacetate. Cell-free extracts of phenol-grown mycelia were found to contain enzymic activities for the proposed steps. Two ring-fission dioxygenases, one active towards 1,2,4-trihydroxybenzene, but not catechol, and one active towards both ring-fission substrates, were separated by FPLC. Succinate-grown mycelia did not oxidise any of the intermediates until a clear lag period had elapsed and did not contain any of the enzymic activities for phenol metabolism.