Anaerobic degradation of benzene by a marine sulfate‐reducing enrichment culture, and cell hybridization of the dominant phylotype

Stable isotope probing (SIP) was used to identify the active members in a benzene-degrading sulfidogenic consortium. SIP-terminal restriction fragment length polymorphism analysis indicated that a 270-bp peak incorporated the majority of the 13C label and is a sequence closely related to that of clone SB-21 (GenBank accession no. AF029045). This target may be an important biomarker for anaerobic benzene degradation in the field.

supporting

confidence: 75%

mentioning

confidence: 99%

Identification of Critical Members in a Sulfidogenic Benzene-Degrading Consortium by DNA Stable Isotope Probing

Oka

Phelps²,

McGuinness

et al. 2008

“…Analysis of gene expression patterns indicated that benzene was first metabolized to benzoate (17), which was then metabolized via well-known pathways for anaerobic benzoate metabolism (18). The proposed carboxylation of benzene by F. placidus is consistent with evidence suggesting carboxylation in enrichment cultures (19)(20)(21)(22)(23). A gene encoding a putative benzene carboxylase in F. placidus was identified (17), but further analysis has been limited by a lack of a system for genetic manipulation of F. placidus.…”

mentioning

confidence: 54%

Anaerobic Benzene Oxidation via Phenol in Geobacter metallireducens

Zhang

Tremblay²,

Chaurasia³

et al. 2013

107

Anaerobic activation of benzene is expected to represent a novel biochemistry of environmental significance. Therefore, benzene metabolism was investigated in Geobacter metallireducens, the only genetically tractable organism known to anaerobically degrade benzene. Trace amounts (<0.5 M) of phenol accumulated in cultures of Geobacter metallireducens anaerobically oxidizing benzene to carbon dioxide with the reduction of Fe(III). Phenol was not detected in cell-free controls or in Fe(II)-and benzene-containing cultures of Geobacter sulfurreducens, a Geobacter species that cannot metabolize benzene. The phenol produced in G. metallireducens cultures was labeled with 18 O during growth in H 2 18 O, as expected for anaerobic conversion of benzene to phenol. Analysis of whole-genome gene expression patterns indicated that genes for phenol metabolism were upregulated during growth on benzene but that genes for benzoate or toluene metabolism were not, further suggesting that phenol was an intermediate in benzene metabolism. Deletion of the genes for PpsA or PpcB, subunits of two enzymes specifically required for the metabolism of phenol, removed the capacity for benzene metabolism. These results demonstrate that benzene hydroxylation to phenol is an alternative to carboxylation for anaerobic benzene activation and suggest that this may be an important metabolic route for benzene removal in petroleum-contaminated groundwaters, in which Geobacter species are considered to play an important role in anaerobic benzene degradation.

“…So far, only four anaerobic benzene-degrading bacteria have been described, two Dechloromonas strains (strains RCB and JJ) that degrade benzene in conjunction with (per)chlorate (only strain RCB), nitrate, or oxygen reduction (9) and two denitrifying Azoarcus strains (strains DN11 and AN9) (23). The optimal physiological conditions for anaerobic benzene-degrading bacteria and the biodegradation pathways are still largely unclear (6,8,17,26,33,48).…”

mentioning

confidence: 99%

Isolation and Characterization ofAlicycliphilus denitrificansStrain BC, Which Grows on Benzene with Chlorate as the Electron Acceptor

Weelink

Tan

Broeke

et al. 2008

104

A bacterium, strain BC, was isolated from a benzene-degrading chlorate-reducing enrichment culture. Strain BC degrades benzene in conjunction with chlorate reduction. Cells of strain BC are short rods that are 0.6 m wide and 1 to 2 m long, are motile, and stain gram negative. Strain BC grows on benzene and some other aromatic compounds with oxygen or in the absence of oxygen with chlorate as the electron acceptor. Strain BC is a denitrifying bacterium, but it is not able to grow on benzene with nitrate. The closest cultured relative is Alicycliphilus denitrificans type strain K601, a cyclohexanol-degrading nitrate-reducing betaproteobacterium. Chlorate reductase (0.4 U/mg protein) and chlorite dismutase (5.7 U/mg protein) activities in cell extracts of strain BC were determined. Gene sequences encoding a known chlorite dismutase (cld) were not detected in strain BC by using the PCR primers described in previous studies. As physiological and biochemical data indicated that there was oxygenation of benzene during growth with chlorate, a strategy was developed to detect genes encoding monooxygenase and dioxygenase enzymes potentially involved in benzene degradation in strain BC. Using primer sets designed to amplify members of distinct evolutionary branches in the catabolic families involved in benzene biodegradation, two oxygenase genes putatively encoding the enzymes performing the initial successive monooxygenations (BC-BMOa) and the cleavage of catechol (BC-C23O) were detected. Our findings suggest that oxygen formed by dismutation of chlorite can be used to attack organic molecules by means of oxygenases, as exemplified with benzene. Thus, aerobic pathways can be employed under conditions in which no external oxygen is supplied.