Modified 3-oxoadipate pathway for the biodegradation of methylaromatics in Pseudomonas reinekei MT1.
Catechols are central intermediates in the metabolism of aromatic compounds. Degradation of 4-methylcatechol via intradiol cleavage usually leads to the formation of 4-methylmuconolactone (4-ML) as a dead-end metabolite. Only a few microorganisms are known to mineralize 4-ML. The mml gene cluster of Pseudomonas reinekei MT1, which encodes enzymes involved in the metabolism of 4-ML, is shown here to encode 10 genes found in a 9.4-kb chromosomal region. Reverse transcription assays revealed that these genes form a single operon, where their expression is controlled by two promoters. Promoter fusion assays identified 4-methyl-3-oxoadipate as an inducer. Mineralization of 4-ML is initiated by the 4-methylmuconolactone methylisomerase encoded by mmlI. This reaction produces 3-ML and is followed by a rearrangement of the double bond catalyzed by the methylmuconolactone isomerase encoded by mmlJ. Deletion of mmlL, encoding a protein of the metallo-beta-lactamase superfamily, resulted in a loss of the capability of the strain MT1 to open the lactone ring, suggesting its function as a 4-methyl-3-oxoadipate enol-lactone hydrolase. Further metabolism can be assumed to occur by analogy with reactions known from the 3-oxoadipate pathway. mmlF and mmlG probably encode a 4-methyl-3-oxoadipyl-coenzyme A (CoA) transferase, and the mmlC gene product functions as a thiolase, transforming 4-methyl-3-oxoadipyl-CoA into methylsuccinyl-CoA and acetyl-CoA, as indicated by the accumulation of 4-methyl-3-oxoadipate in the respective deletion mutant. Accumulation of methylsuccinate by an mmlK deletion mutant indicates that the encoded acetyl-CoA hydrolase/transferase is crucial for channeling methylsuccinate into the central metabolism.
Marín
Macarena
M
Department of Microbial Pathogenesis, Helmholtz Zentrum für Infektionsforschung, Braunschweig, Germany.
Pérez-Pantoja
Danilo
D
Donoso
Raul
R
Wray
Victor
V
González
Bernardo
B
Pieper
Dietmar H
DH
D000272:Adipates / Q000737:chemistry / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001673:Biodegradation, Environmental; D003470:Culture Media / Q000737:chemistry; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D006841:Hydrocarbons, Aromatic / Q000378:metabolism*; D007535:Isomerases / Q000235:genetics / Q000378:metabolism; D007783:Lactones / Q000737:chemistry / Q000378:metabolism*; D015394:Molecular Structure; D016366:Open Reading Frames; D011549:Pseudomonas / Q000378:metabolism*; D012459:Salicylates / Q000737:chemistry / Q000378:metabolism
D000272:Adipates; D001426:Bacterial Proteins; D003470:Culture Media; D006841:Hydrocarbons, Aromatic; D007783:Lactones; D012459:Salicylates; C027316:3-oxoadipic acid; D007535:Isomerases; C033069:methyl salicylate