Biotransformation of the high‐molecular weight polycyclic aromatic hydrocarbon (<scp>PAH</scp>) benzo[<i>k</i>]fluoranthene by <scp><i>S</i></scp><i>phingobium</i> sp. strain <scp>KK</scp>22 and identification of new products of non‐alternant <scp>PAH</scp> biodegradation by liquid chromatography electrospray ionization tandem mass spectrometry

<jats:title>Summary</jats:title><jats:p>A pathway for the biotransformation of the environmental pollutant and high‐molecular weight polycyclic aromatic hydrocarbon (<jats:styled-content style="fixed-case">PAH</jats:styled-content>) benzo[<jats:italic>k</jats:italic>]fluoranthene by a soil bacterium was constructed through analyses of results from liquid chromatography negative electrospray ionization tandem mass spectrometry (<jats:styled-content style="fixed-case">LC</jats:styled-content>/<jats:styled-content style="fixed-case">ESI</jats:styled-content>(–)‐<jats:styled-content style="fixed-case">MS</jats:styled-content>/<jats:styled-content style="fixed-case">MS</jats:styled-content>). Exposure of <jats:styled-content style="fixed-case"><jats:italic>Sphingobium</jats:italic></jats:styled-content> sp. strain <jats:styled-content style="fixed-case">KK</jats:styled-content>22 to benzo[<jats:italic>k</jats:italic>]fluoranthene resulted in transformation to four‐, three‐ and two‐aromatic ring products. The structurally similar four‐ and three‐ring non‐alternant <jats:styled-content style="fixed-case">PAHs</jats:styled-content> fluoranthene and acenaphthylene were also biotransformed by strain <jats:styled-content style="fixed-case">KK</jats:styled-content>22, and <jats:styled-content style="fixed-case">LC</jats:styled-content>/<jats:styled-content style="fixed-case">ESI</jats:styled-content>(–)‐<jats:styled-content style="fixed-case">MS</jats:styled-content>/<jats:styled-content style="fixed-case">MS</jats:styled-content> analyses of these products confirmed the lower biotransformation pathway proposed for benzo[<jats:italic>k</jats:italic>]fluoranthene. In all, seven products from benzo[<jats:italic>k</jats:italic>]fluoranthene and seven products from fluoranthene were revealed and included previously unreported products from both <jats:styled-content style="fixed-case">PAHs</jats:styled-content>. Benzo[<jats:italic>k</jats:italic>]fluoranthene biotransformation proceeded through <jats:styled-content style="fixed-case"><jats:italic>ortho</jats:italic></jats:styled-content>‐cleavage of 8,9‐dihydroxy‐benzo[<jats:italic>k</jats:italic>]fluoranthene to 8‐carboxyfluoranthenyl‐9‐propenic acid and 9‐hydroxy‐fluoranthene‐8‐carboxylic acid, and was followed by <jats:styled-content style="fixed-case"><jats:italic>meta</jats:italic></jats:styled-content>‐cleavage to produce 3‐(2‐formylacenaphthylen‐1‐yl)‐2‐hydroxy‐prop‐2‐enoic acid. The fluoranthene pathway converged with the benzo[<jats:italic>k</jats:italic>]fluoranthene pathway through detection of the three‐ring product, 2‐formylacenaphthylene‐1‐carboxylic acid. Production of key downstream metabolites, 1,8‐naphthalic anhydride and 1‐naphthoic acid from benzo[<jats:italic>k</jats:italic>]fluoranthene, fluoranthene and acenaphthylene biotransformations provided evidence for a common pathway by strain <jats:styled-content style="fixed-case">KK</jats:styled-content>22 for all three <jats:styled-content style="fixed-case">PAHs</jats:styled-content> through acenaphthoquinone. Quantitative analysis of benzo[<jats:italic>k</jats:italic>]fluoranthene biotransformation by strain <jats:styled-content style="fixed-case">KK</jats:styled-content>22 confirmed biodegradation. This is the first pathway proposed for the biotransformation of benzo[<jats:italic>k</jats:italic>]fluoranthene by a bacterium.</jats:p>