Degradation of 2-methylbenzoic acid by Pseudomonas cepacia MB2.
We report the isolation of Pseudomonas cepacia MB2, believed to be the first microorganism to utilize 2-methylbenzoic acid as the sole carbon source. Its growth range included all mono- and dimethylbenzoates (with the exception of 2,5- and 2,6-dimethylbenzoates) and 3-chloro-2-methylbenzoate (but not 4- or 5-chloro-2-methylbenzoate) but not chlorobenzoates lacking a methyl group. 2-Chlorobenzoate, 3-chlorobenzoate, and 2,3-, 2,4-, and 3,4-dichlorobenzoates inhibited growth of MB2 on 2-methylbenzoate as a result of cometabolism to the corresponding chlorinated catechols which blocked the key enzyme catechol 2,3-dioxygenase. A metapyrocatechase-negative mutant, MB2-G5, showed accumulation of dimethylcatechols from 2,3- and 3,4-dimethylbenzoates, and phenols were detected in resting-cell transformation extracts bearing the same substitution pattern as the original substrate, presumably following thermal degradation of the intermediate dihydrodiol. 2-Methylphenol was also found in extracts of the mutant cells with 2-methylbenzoate. These observations suggested a major route of methylbenzoate metabolism to be dioxygenation to a carboxy-hydrodiol which then forms a catechol derivative. In addition, the methyl group of 2-methylbenzoate was oxidized to isobenzofuranone (by cells of MB2-G5) and to phthalate (by cells of a separate mutant that could not utilize phthalate, MB2-D2). This pathway also generated a chlorinated isobenzofuranone from 3-chloro-2-methylbenzoate.
Higson
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Department of Soil and Environmental Sciences, University of California, Riverside 92521.
Focht
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D001565:Benzoates / Q000737:chemistry / Q000378:metabolism*; D001673:Biodegradation, Environmental; D016956:Burkholderia cepacia / Q000254:growth & development / Q000378:metabolism*; D050548:Catechol 1,2-Dioxygenase; D050557:Catechol 2,3-Dioxygenase; D002723:Chlorobenzoates / Q000494:pharmacology; D049308:Dioxygenases; D013058:Mass Spectrometry; D015394:Molecular Structure; D010105:Oxygenases / Q000378:metabolism
D001565:Benzoates; D002723:Chlorobenzoates; C044605:methyl benzoate; D010105:Oxygenases; D049308:Dioxygenases; D050548:Catechol 1,2-Dioxygenase; D050557:Catechol 2,3-Dioxygenase