Genes coding for a new pathway of aerobic benzoate metabolism in Azoarcus evansii.
A new pathway for aerobic benzoate oxidation has been postulated for Azoarcus evansii and for a Bacillus stearothermophilus-like strain. Benzoate is first transformed into benzoyl coenzyme A (benzoyl-CoA), which subsequently is oxidized to 3-hydroxyadipyl-CoA and then to 3-ketoadipyl-CoA; all intermediates are CoA thioesters. The genes coding for this benzoate-induced pathway were investigated in the beta-proteobacterium A. evansii. They were identified on the basis of N-terminal amino acid sequences of purified benzoate metabolic enzymes and of benzoate-induced proteins identified on two-dimensional gels. Fifteen genes probably coding for the benzoate pathway were found to be clustered on the chromosome. These genes code for the following functions: a putative ATP-dependent benzoate transport system, benzoate-CoA ligase, a putative benzoyl-CoA oxygenase, a putative isomerizing enzyme, a putative ring-opening enzyme, enzymes for beta-oxidation of CoA-activated intermediates, thioesterase, and lactone hydrolase, as well as completely unknown enzymes belonging to new protein families. An unusual putative regulator protein consists of a regulator protein and a shikimate kinase I-type domain. A deletion mutant with a deletion in one gene (boxA) was unable to grow with benzoate as the sole organic substrate, but it was able to grow with 3-hydroxybenzoate and adipate. The data support the proposed pathway, which postulates operation of a new type of ring-hydroxylating dioxygenase acting on benzoyl-CoA and nonoxygenolytic ring cleavage. A beta-oxidation-like metabolism of the ring cleavage product is thought to lead to 3-ketoadipyl-CoA, which finally is cleaved into succinyl-CoA and acetyl-CoA.
Gescher
Johannes
J
Mikrobiologie, Institut Biologie II, Universität Freiburg, Germany.
Zaar
Annette
A
Mohamed
Magdy
M
Schägger
Hermann
H
Fuchs
Georg
G
D000332:Aerobiosis; D000595:Amino Acid Sequence; D020627:Azoarcus / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D001565:Benzoates / Q000378:metabolism*; D001673:Biodegradation, Environmental; D003001:Cloning, Molecular; D015180:Electrophoresis, Gel, Two-Dimensional; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D005810:Multigene Family; D016366:Open Reading Frames / Q000235:genetics; D017422:Sequence Analysis, DNA
D001426:Bacterial Proteins; D001565:Benzoates