Chemical and genomic analyses of polycyclic aromatic hydrocarbon biodegradation in Sphingobium barthaii KK22 reveals divergent pathways in soil sphingomonads

Biodegradation of phenanthrene at high concentrations by Acidovoraxsp. JG5 and its functional genomic analysis

“…18 The steps involved in the aerobic degradation of PHE by most bacteria are: (i) oxidation of C3 (or C1) and C4 (or C2) sites with dioxygenase to produce cis-3,4-phenodihydrodiol (or cis-1,-2-phenodihydrodiol), (ii) reaction of cis-3,4-phenodihydrodiol (or cis-1,2-phenodihydrodiol) with dehydrogenase to form 3,4-dihydroxyphenanthrene (or 1,2-dihydroxyphenanthrene), (iii) cleavage of the benzene ring to produce 2-hydroxy-1-naphthoic acid (or 1-hydroxy-2-naphthoic acid), and finally, (iv) mineralization of 2-hydroxy-1-naphthoic acid (or 1-hydroxy-2-naphthoic acid) via the phthalic acid or salicylic acid pathways. 13,18,21,42,43 As shown in Supporting information, Figs S2 and S3, 2-hydroxy-1-naphthoic acid was detected in these studies, suggesting that Acidovorax sp. JG5 can degrade PHE through the above-mentioned pathways.…”

“…In pathway A, the C-9 and C-10 positions of PHE are hydroxylated under the action of dioxygenase (possibly produced by gene 1666: i.e., nahAa) to form 9,10-phenanthrenediol via ring cleavage, generating 9,10-phenanthraquinone, and finally producing 2,2 0 -diphenic acid. In pathway B, the C-1 and C-2 positions on PHE are carboxylated by dioxygenase (gene 1666: i.e., nahAa) to produce 1,2-dihydroxyphenanthrene, which is subsequently acted upon by multiple dehydrogenation processes to yield 2-hydroxy-1-naphthoic acid, 18,21 and then degraded to 1,2-dihydroxynaphthalene by hydroxylase (catalyzed by gene 0923 and gene 2501).…”

“…Metabolites of PHE degradation include dihydroxyphenanthrene, hydroxy-naphthoic acid, phthalic acid, and salicylic acid. 20,21 Many studies have identified the pathways of PHE degradation by bacteria, but it is still necessary to identify pathways for every new strain.…”

Complete Genome Sequence of Sphingobium barthaii KK22, a High-Molecular-Weight Polycyclic Aromatic Hydrocarbon-Degrading Soil Bacterium

“…The Gram-negative alphaproteobacterium Sphingobium barthaii KK22 T has been investigated (i) for its capabilities to biotransform high-molecular-weight (HMW) polycyclic aromatic hydrocarbons (PAHs), (ii) for its major role in a hydrocarbon-degrading bacterial consortium, and (iii) as a model organism in DNA damage studies ( 1 – 7 ). It was isolated from a diesel fuel-grown bacterial consortium that originated from cattle pasture soil from the Gulf region of Texas ( 1 , 8 , 9 ).…”

“…Notably, it was found that all seven sets of aromatic ring-hydroxylating dioxygenase (ARHD) genes encoded in the S. barthaii genome ( 2 ) were located on the megaplasmid, with six sets being tightly clustered. This ARHD gene cluster is shared among some aromatic hydrocarbon-degrading sphingomonads and is considered to be responsible for biotransformation of various xenobiotic aromatic hydrocarbons ( 14 , 15 ).…”