Degradation of benz[a]anthracene by Mycobacterium vanbaalenii strain PYR-1

Abstract

Cultures of Mycobacterium vanbaalenii strain PYR-1 grown in mineral salts medium and nutrients in the presence of benz[a]anthracene metabolized 15% of the added benz[a]anthracene after 12 days of incubation. Neutral and acidic ethyl acetate extractable metabolites were isolated and characterized by high performance liquid chromatography (HPLC) and uv-visible absorption, gas chromatography/mass (GC/MS) and nuclear magnetic resonance (NMR) spectral analysis. Trimethylsilylation of the metabolites followed by GC/MS analysis facilitated identification of metabolites. The characterization of metabolites indicated that M. vanbaalenii initiated attack of benz[a]anthracene at the C-1,2-, C-5,6-, C-7,12- and C-10,11-positions to form dihydroxylated and methoxylated intermediates. The major site of enzymatic attack was in the C-10, C-11 positions. Subsequent ortho- and meta-cleavage of each of the aromatic rings led to the accumulation of novel ring-fission metabolites in the medium. The major metabolites identified were 3-hydrobenzo[f]isobenzofuran-1-one (3.2%), 6-hydrofuran[3,4-g]chromene-2,8-dione (1.3%), benzo[g]chromene-2-one (1.7%), naphtho[2,1-g]chromen-10-one (48.1%), 10-hydroxy-11-methoxybenz[a]anthracene (9.3%), and 10,11-dimethoxybenz[a]anthracene (36.4%). Enzymatic attack at the C-7 and C-12 positions resulted in the formation of benz[a]anthracene-7,12-dione, 1-(2-hydroxybenzoyl)-2-naphthoic acid, and 1-benzoyl-2-naphthoic acid. A phenyl-naphthyl metabolite, 3-(2-carboxylphenyl)-2-naphthoic acid, was formed when M. vanbaalenii was incubated with benz[a]anthracene cis-5,6-dihydrodiol, indicating ortho-cleavage of 5,6-dihydroxybenz[a]anthracene. A minor amount of 5,6-dimethoxybenz[a]anthracene was also formed. The data extend and propose novel pathways for the bacterial metabolism of benz[a]anthracene.