Xylene anaerobic degradation

Chakraborty R, SM O Connor, E Chan, JD Coates (2005) Anaerobic degradation of benzene, tolnene, ethylbenzene, and xylene componnds by Dechloromonas strain RCB. Appl Environ Microbiol 71 8649-8655. 

Edwards EA, LE Williams, M Reinhard, D Grbic-Galic (1992) Anaerobic degradation of toluene and xylene by aquifer microrganisms under sulfate-reducing conditions. Appl Environ Microbiol 58 ... 

It has become clear that benzoate occupies a central position in the anaerobic degradation of both phenols and alkylated arenes such as toluene and xylenes, and that carboxylation, hydroxylation, and reductive dehydroxylation are important reactions for phenols that are discussed in Part 4 of this chapter. The simplest examples include alkylated benzenes, products from the carboxylation of napthalene and phenanthrene (Zhang and Young 1997), the decarboxylation of o-, m-, and p-phthalate under denitrifying conditions (Nozawa and Maruyama 1988), and the metabolism of phenols and anilines by carboxylation. Further illustrative examples include the following ... 

Enrichment factors during the anaerobic degradation of o-xylene, m-xylene, m-cresol, and p-cresol by pure cultures of sulfate-reducing bacteria that use the fumarate pathway ranged from -1.5 to -3.9 ppm (Morasch et al. 2004). It was therefore proposed that this could be applied to evaluating in situ bioremediation of contaminants that use this pathway for biodegradation. 

A sulfate enrichment culture prepared from a contaminated site gave enrichment factors (e) of-1.1 for naphthalene and -0.9 for 2-methylnaphthalene (Griebler et al. 2004). These values combined with literature values from analogous laboratory experiments were used to quantify degradation of toluene, xylenes, and naphthalene at the site. Additional evidence for degradation of BTEX was derived from analyses of established metabolites produced by anaerobic degradation. 

Edwards, E. A. Grbic-Galic, D. (1994). Anaerobic degradation of toluene and o-xylene by a methanogenic consortium. Applied and Environmental Microbiology, 60(1), 313-22. 

Figure 12 Proposed pathways of anaerobic degradation of toluene, ethylbenzene, and o-xylene by the fumarate...

The vast amount of data from natural attenuation studies of petroleum hydrocarbon plumes generally supports anaerobic degradation, especially for benzene, toluene, ethylbenzene, xylenes (BTEX) under field conditions. The first-order degradation rates observed under unspecified anaerobic conditions (Suarez and Rifai, 1999) are typically one or two orders of magnitude lower than rates reported under aerobic conditions (Nielsen et al, 1996). 

It is worth noting that benzylsuccinates and benzylfumarates have been proved to be intermediates during the oxidation of methyl to carboxylate (Biegert et al. 1996 Beller and Spormann 1997), and that, as noted above, these compounds together with the analogous compounds that would be produced from xylenes have been used in support of the active in situ anaerobic degradation of toluene and xylenes (Beller et al. 1995). 

Simulation of Two-Column Experiments on Anaerobic Degradation of Toluene and Xylene... 

Numerical simulations with a reactive transport model were performed for two column experiments on the anaerobic degradation of o-xylene and toluene. The goal of the simulations was to test hypotheses on the interaction of toluene and o-xylene degradation processes. 

The fate of toluene and o-xylene in an aquifer contaminated with BTEX was examined by injecting toluene-dj and o-xylene-djo followed by quantification of the label in benzyl succinate and 2-methylbenzene succinate (Reusser et al. 2002) that are established metabolites on the anaerobic pathway for the degradation of toluene and o-xylene. 

Benzene is one of a group of related aromatic monocyclic hydrocarbons (BTEX—benzene, toluene, ethylbenzene, and xylene), and since these are water soluble, there has been concern for their dissipation and persistence in groundwater under both aerobic and anaerobic conditions. Although aerobic growth at the expense of benzene was established many years ago, the pathway for its degradation was established only much later. The aerobic degradation of benzene by bacteria is... 

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