Microbial metabolism of alkylbenzene sulphonates. Fungal metabolism of 1-phenylundecane-p-sulphonate and 1-phenyldodecane-p-sulphonate.

Abstract

A study was made of the biodegradation of 1-phenylundecane-p-sulphonate and 1-phenyldodecane-p-sulphonate byCladosporium resinae (CMI 88968) which was capable of growth on a number of such alkylbenzene sulphonate homologues as the sole source of carbon and sulphur. The results from both whole-cell and cell-free systems indicated that the alkyl, aryl and sulphonate moieties of detergent homologues were metabolised by the fungus. The alkyl side-chain, after a presumed initial oxidation of the terminal methyl group, was subsequently oxidised by a β-oxidation pathway. Three enzymes of the β-oxidation pathway, i.e. acyl-CoA synthetase, acyl-CoA dehydrogenase and β-hydroxyacyl-CoA dehydrogenase were identified in detergent-grown cell-free extracts of the fungus. The sulphonate moiety was released as sulphate by a desulphonating enzyme. The combined results of continuous sampling programmes monitored by both TLC and sulphate appearance in the growth medium indicated that desulphonation of the aromatic moiety was an early event in the overall biodegradation of synthetic detergent homologues. The presence of 1-phenylvalerate, 1-phenylpropionate, benzoate,p-hydroxybenzoate and 3,4-dihydroxybenzoate in cells after growth on 1-phenylundecane-p-sulphonate was indicated by GLC analysis. Cells grown on 1-phenyldodecane-p-sulphonate were shown to contain 1-phenylhexanoate, 1-phenylbutyrate, phenylacetate,p-hydroxyphenylacetate and 3,4-dihydroxyphenylacetate. The aromatic nuclei remaining after alkyl side-chain biodegradation were further metabolised by an oxidation sequence involving an “ortho-cleavage” pathway. An overall metabolic pathway for the biodegradation of alkylbenzene sulphonates byCladosporium resinae is proposed.