Cometabolic benzo[a]pyrene biotransformation by Sphingobium barthaii KK22 proceeds through the kata-annelated ring and 1-pyrenecarboxylic acid to downstream products.

Abstract

Benzo[a]pyrene is a hazardous environmental pollutant that is resistant to bacterial biodegradation and biotransformation pathway development has not been advanced. Considering this, cometabolic benzo[a]pyrene biotransformation by a member of the genus Sphingobium was investigated by cell growth on phenanthrene as a carbon and energy source in conjunction with comparative analyses of culture extracts by gas chromatography (GC) and liquid chromatography electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS). Under these culture conditions, approximately 20% of 100 mg/L benzo[a]pyrene (apparent solubility) was biodegraded in 14 days and benzo[a]pyrene biotransformation products were detected and identified to be extradiol and intradiol ring-cleavage products of the benzo[a]pyrene kata-annelated ring. The o‑hydroxy-tetraaromatic acids, 2-hydroxypyrene-1-carboxylic acid, and 1-hydroxypyrene-2-carboxylic acid were identified in addition to 7,8- and 9,10-dihydroxy-benzo[a]pyrenes, carboxyvinylpyrene-carboxylic acids, hydroxypyrene-oxobutenoic acids, pyrene-1,2-dicarboxylic acid, 1,2-dihydroxypyrene and different oxophenalene compounds. 1-Pyrenecarboxylic acid and other ring-opened oxidized compounds were identified as novel benzo[a]pyrene biodegradation products. In separate assays, 2-hydroxypyrene-1-carboxylic acid was found to be produced from 1-pyrenecarboxylic acid and these results reshaped our understanding of bacterial benzo[a]pyrene biotransformation pathways. Overall, the identities of thirteen products were proposed and new benzo[a]pyrene biodegradation pathways were constructed from experimental chemical evidence. This work extends our understanding of benzo[a]pyrene biotransformation by gram-negative bacteria.