New Metabolites in Dibenzofuran Cometabolic Degradation by a Biphenyl-Cultivated Pseudomonas putida Strain B6-2

Abstract

A biphenyl (BP)-utilizing bacterium, designated B6-2, was isolated from soil and identified as Pseudomonas putida. BP-grown B6-2 cells were capable of transforming dibenzofuran (DBF) via a lateral dioxygenation and meta-cleavage pathway. The ring cleavage product 2-hydroxy-4-(3'-oxo-3'H-benzofuran-2'-yliden)but-2-enoic acid (HOBB) was detected as a major metabolite. B6-2 growing cells could also cometabolically degrade DBF using BP as a primary substrate. A recombinant Escherichia coli strain DH10B (pUC118bphABC) expressing BP dioxygenase, BP-dihydrodiol dehydrogenase, and dihydroxybiphenyl dioxygenase was shown to be capable of transforming DBF to HOBB. Using purified HOBB that was produced by the recombinant as the substrate for B6-2, we newly identified a series of benzofuran derivatives as metabolites. The structures of these metabolites indicate that an unreported HOBB degradation pathway is employed by strain B6-2. In this pathway, HOBB is proposed to be transformed to 2-oxo-4-(3'-oxobenzofuran-2'-yl)butanoic acid and 2-hydroxy-4-(3'-oxobenzofuran-2'-yl)butanoic acid (D4) through two sequential double-bond hydrogenation steps. D4 is suggested to undergo reactions including decarboxylation and oxidation to produce 3-(3'-oxobenzofuran-2'-yl)propanoic acid (D6). 3-Hydroxy-3-(3'-oxobenzofuran-2'-yl)propanoic acid (D7) and 2-(3'-oxobenzofuran-2'-yl)acetic acid (D8) would represent metabolites involved in the processes of beta- and alpha-oxidation of D6, respectively. D7 and D8 are suggested to be transformed to their respective products 3-hydroxy-2,3-dihydrobenzofuran-2-carboxylic acid (D10) and 2-(3'-hydroxy-2',3'-dihydrobenzofuran-2'-yl)acetic acid. D10 is proposed to be transformed to salicylic acid (D14) via 2,3-dihydro-2,3-dihydroxybenzofuran, 2-oxo-2-(2'-hydroxyphenyl)acetic acid and 2-hydroxy-2-(2'-hydroxyphenyl)acetic acid. Further experimental results revealed that B6-2 was capable of growing with D14 as the sole carbon source. Because benzofuran derivatives may have biological, pharmacological, and toxic properties, the elucidation of this new pathway should be significant from both biotechnological and environmental views.

Characterization of a novel cometabolic degradation carbazole pathway by a phenol-cultivated Arthrobacter sp. W1

“…The Andrews model analyses indicated that the q max and K i of strain W1 grown on phenol were larger than that of grown on phenol + CA, which confirmed that the presence of CA or its metabolites could inhibit the growth of strain W1 and phenol degradation. Similar findings were reported for the cometabolic degradation of dibenzofuran (Li et al, 2009).…”

“…Several bacteria that utilize CA as the sole carbon and energy source have been isolated, and most of these bacteria have been shown to degrade CA via the angular dioxygenation and meta-cleavage pathway (Gieg et al, 1996;Schneider et al, 2000;Gai et al, 2007). Because polycyclic aromatic compounds (PACs) including CA are widespread and usually coexist in the polluted environments, cometabolic degradation of these heterocyclic compounds by bacteria growing with some others PACs should be common (Li et al, 2009).…”

Genome Sequence of Pseudomonas putida Strain B6-2, a Superdegrader of Polycyclic Aromatic Hydrocarbons and Dioxin-Like Compounds

“…Microbial remediation is one of the most effective ways to reduce these pollutants/toxicants from the environment (2,3,7,9,14). The versatile metabolic capacity of pseudomonads enables graceful degradation of these compounds (4,6,11).…”

“…Pseudomonas putida strain B6-2 was isolated and characterized (6). With its unique tolerance to organic solvents, this superstrain can efficiently and cometabolically degrade PAHs and dioxin-like compounds, such as (polychlorinated) biphenyls, (polychlorinated) dibenzofurans, (polychlorinated) dibenzo-p-dioxins, (polybrominated) diphenyl ethers, (methylated) carbazoles, (methylated) dibenzothiophenes, and (methylated) benzothiphenes (unpublished data).…”

“…With its unique tolerance to organic solvents, this superstrain can efficiently and cometabolically degrade PAHs and dioxin-like compounds, such as (polychlorinated) biphenyls, (polychlorinated) dibenzofurans, (polychlorinated) dibenzo-p-dioxins, (polybrominated) diphenyl ethers, (methylated) carbazoles, (methylated) dibenzothiophenes, and (methylated) benzothiphenes (unpublished data). Biphenyl-grown B6-2 cells can transform dibenzofuran via a new 2-hydroxy-4-(3Ј-oxo-3ЈH-benzofuran-2Ј-yliden)but-2-enoic acid degradation pathway, which produces a series of benzofuran derivatives as metabolites (6). The excellent characteristics of strain B6-2 may play important roles in bioremediation of seriously polluted habitats.…”