Xylene is the "X" in the BTEX chemicals (Benzene, Toluene, Ethylbenzene, and Xylene) which are volatile organic compounds, common constituents of gasoline, and common groundwater contaminants. Nearly all para-xylene recovered from petroleum in the US is consumed in the manufacture of terephthalic acid (PTA), which is used in the production of polyester fiber, resin, and film. Some para-xylene is used as a solvent and in the manufacture of di-paraxylene and herbicides. United States industry consumed over 6 million pounds of para-xylene in 1995. The metabolic enzymes in this pathway have been shown to have similar specificty for toluene, para-xylene, and meta-xylene. [http://www.ncbi.nlm.nih.gov/pubmed/4850728|Davey and Gibson (1974)] report that para-xylene is degraded to 4-methylcatechol by the oxidation of a methyl substituent to an alcohol group and the addition of another alcohol group. [http://www.ncbi.nlm.nih.gov/pubmed/4342906|Murray and Duggleby (1972)] report that 4-methylcatechol is degraded by the meta (or alpha-ketoacid) pathway, in which the aromatic ring of 4-methylcatechol is cleaved in the meta-position. [http://www.ncbi.nlm.nih.gov/pubmed/7783002|Gunther and Schlosser (1994)] report that 4-methylcatechol is also degraded by ortho-cleavage to 4-methylmuconolactone. Ralstonia eutropha JMP134 degrades 4-methylcatechol via this route, converting 4-methylmuconolactone to 4-methyl-3-oxoadipate in several steps ([http://www.ncbi.nlm.nih.gov/pubmed/9461415|Erb et al., 1998]). Rhodococcus sp. strain YU6 is able to metabolize o-xylene via direct ring oxidation and meta-cleavage ([http://www.ncbi.nlm.nih.gov/pubmed/16145546|Jang et al., 2005]). The m-xylene and o-xylene pathways are also included in the EAWAG-BBD.