Denitrifying Conditions

Phenol is an important intermediate in the anaerobic degradation of many complex and simple aromatic compounds. Tschech and Fuchs proposed that the carboxylation of phenol to 4-hydroxybenzoate is the first step in the degradation of phenol under denitrifying conditions. However, 4-hydroxybenzoate is not detected in the cultures or cell extracts of the denitrifying Pseudomonas species in the presence of CO2 and phenol, but it is detected if phenol is replaced by phenolphosphate. In contrast, 4-hydroxybenzoate is readily detected as an intermediate of phenol degradation in the iron-reducing bacterium GS-15, and 4-hydroxybenzoate may prove to be a common intermediate in the anaerobic transformation. Thus, in anaerobic degradation of phenolic compounds, it has been postulated that carboxylation reactions may play important roles. 

Criddle CS, JT DeWitt, D Grbic-Galic, PL McCarty (1990) Transformation of carbon tetrachloride by Pseudomonas sp strain KC under denitrifying conditions. Appl Environ Microbiol 56 3240-3246. 

Thauera sp. strain DNT-1 is able to degrade toluene under aerobic conditions mediated by a dioxygenase, and under denitrifying conditions in the absence of oxygen by the anaerobic benzylsuccinate pathway (Shinoda et al. 2004). Whereas the tod genes were induced under aerobic conditions, the bss genes were induced under both aerobic and anaerobic conditions. 

These results may be viewed in the wider context of interactions between potential ligands of multifunctional xenobiotics and metal cations in aquatic environments and the subtle effects of the oxidation level of cations such as Fe. The Fe status of a bacterial culture has an important influence on synthesis of the redox systems of the cell since many of the electron transport proteins contain Fe. This is not generally evaluated systematically, although the degradation of tetrachloromethane by a strain of Pseudomonas sp. under denitrifying conditions clearly illustrated the adverse effect of Fe on the biotransformation of the substrate (Lewis and Crawford 1993 Tatara et al. 1993). This possibility should therefore be taken into account in the application of such organisms to bioremediation programs. 

The biodegradation of acenaphthene and naphthalene under denitrifying conditions was examined in soil-water slurries (Mihelcic and Luthy 1988), though in this case only analyses for the concentrations of the initial substrates were carried out. 

It has been shown that pure cultures of bacteria under anaerobic denitrifying conditions may produce benzylsuccinate as a metabolite of toluene (Evans et al. 1992 Migaud et al. 1996 Beller et al. 1996). Demonstration of this and the corresponding methylbenzyl succinates from xylenes has been used to demonstrate metabolism of toluene and xylene in an anaerobic aquifer (Beller et al. 1995, 2002). 

McNally DL, JR Mihelcic, DR Lucking (1998) Biodegradation of three- and four-ring polycyclic aromatic hydrocarbons under aerobic and denitrifying conditions. Environ Sci Technol 32 2633-2639. 

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 ... 

Under denitrifying conditions, 2-aminobenzoate is degraded by a Pseudomonas sp. to benzoate, which is then reduced to cyclohexene-l-carboxylate (Lochmeyer et al. 1992). 

The anaerobic metabolism of L-phenylalanine by Thauera aromatica under denitrifying conditions involves several steps that result in the formation of benzoyl-CoA (a) conversion to the CoA-ester by a ligase, (b) transamination to phenylacetyl-CoA, (c) a-oxidation to phenylglyoxalate, and (d) decarboxylation to benzoyl-CoA (Schneider et al. 1997). 

Degradation of 2-fluorobenzoate under denitrifying conditions has been reported without details several times during the past 25 years (Taylor et al. 1979 Schennen et al. 1985 Song et al. 2000a). 

Barbaro JR, JF Barker, LA Lemon, Cl Mayfield (1992) Biotransformation of BTEX nnder anaerobic, denitrifying conditions field and laboratory observations. J Contam Hydrol 11 245-272. 

Bradley, P.M., Chapelle F.H., and Landmeyer, J.E., Methyl /-butyl ether mineralization in surface-water sediment microcosms under denitrifying conditions, in Applied and Environmental Microbiology, US GS, pp. 1975-1978, April 2001. 

Bossert ID, Rivera MD, Young LY. 1986. p-Cresol biodegradation under denitrifying conditions Isolation of a bacterial coculture. Fed Eur Microbiol Soc Microbiol Ecol 38(5) 313-319. 

Indeed, these reactions play an important role in the Antarctic ozone hole and they have important implications for control strategies, particularly of the bromi-nated compounds. For example, Danilin et al. (1996) examined the effects of ClO -BrO coupling on the cumulative loss of O-, in the Antarctic ozone hole from August 1 until the time of maximum ozone depletion. Increased bromine increased the rate of ozone loss under the denitrified conditions assumed in the calculations by converting CIO to Cl, primarily via reactions (31b) and (31c) (followed by photolysis of BrCl). Danilin et al. (1996) estimate that the efficiency of ozone destruction per bromine atom (a) is 33-55 times that per chlorine atom (the bromine enhancement factor ) under these conditions in the center of the Antarctic polar vortex, a 60 calculated as a global average over all latitudes, seasons, and altitudes (WMO, 1999). 

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