The Microbial Degradation of Aromatic Petroleum Products.
Annual rept. no. 3, 1 Jul 75-30 Jun 76,
TEXAS UNIV AT AUSTIN DEPT OF MICROBIOLOGY
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The biodegradation of ortho-xylene by a species of Nocardia is initiated by nuclear oxidation to form 3,4-dimethylcatechol. The latter compound is apparently formed from cis-3,4-dimethyl-3,5-cyclohexadien-1,2-diol cis-o-xylene dihydrodiol. Enzymatic fission of 3,4-dimethylcatechol produces an acid, 2-hydroxy-5-methyl-6-oxohepta-2,4-dienoic acid, that undergoes spectral changes at acid and alkaline pH. Further metabolism of the ring-fission product occurs by a hydrolytic reaction that forms acetic and 2-oxohex-4-enoic acids. Enzymatic hydration of the latter compound to give 4-hydroxy-2-oxohexanoate is followed by an aldolase reaction that produce pyruvate and propionaldehyde. The pathway proposed for the biodegradation of o-xylene is analogous to those reported for the degradation of a number of aromatic compounds. Commercial samples of 2-, 3- and 4-chlorobiphenyl contain impurities that cause lag periods in the growth of Beijerinckia on succinate. Purified preparations of these compounds also inhibited the initiation of growth of this organism but not to the same extent. Preliminary observations suggest that inhibition may be associated with the ease of oxidation of the monochlorinated biphenyl isomers.