Anaerobic Transformation

Novel aromatic carboxylation reactions have been observed in the anaerobic transformation of phenols to ben2oates (82). A mixed anaerobic microbial consortium apparentiy transforms phenol (33) through an intermediate to ben2oic acid (34) via dehydroxylation. This reaction has not yet been widely exploited for its obvious synthetic value. 

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. 

Important reductions are involved in the anaerobic transformations of steroid and flavanoids ... 

Evans PJ, W Ling, B Goldschmidt, ER Ritter, LY Young (1992) Metabolites formed during anaerobic transformation of toluene and o-xylene and their proposed relationship to the initial steps of toluene mineralization. Appl Environ Microbiol 58 496-501. 

The procedure is particularly suited to the study of anaerobic transformations since there are no problems resulting from problems with oxygen limitation. A good example is provided by the application of C NMR to the intricate relations of fumarate, succinate, propionate, and acetate in a syntrophic organism both in the presence (Houwen et al. 1991), and in the absence of methanogens (Plugge et al. 1993 Stams et al. 1993). 

So CM, CD Phelps, LY Young (2003) Anaerobic transformation of alkanes to fatty acids by a sulfate-reducing bacterium strain Hxd3. Appl Environ Microbiol 69 3892-3900. 

Considerable effort has been devoted to the anaerobic transformation of polychlorinated Cj alkanes and C2 alkenes in view of their extensive use as industrial solvents and their identification as widely distributed groundwater contaminants. Early experiments, which showed that tetrachloroethene was transformed into chloroethene (Vogel and McCarty 1985) (Figure 7.67), aroused concern though it has now been shown that complete dechlorination can be accomplished by some organisms. 

Ruppe S, A Neumann, E Braekevalt, GT Tomy, GA Stern, KA Maruya, W Vetter (2004) Anaerobic transformation of compounds of technical toxaphene. 2. Fate of compounds lacking geminal chlorine atoms. Environ Toxicol Chem 23 591-598. 

FIGURE 9.37 Anaerobic transformation of 6-fluoro-3-methylphenol. (From Neilson, A.H. and Allard, A.-S., The Handbook of Environmental Chemistry, Vol. 3R, Springer Verlag, 2002, pp. 1-74. With permission.)... 

Genther BRS, GT Townsend, PJ Chapman (1990) Effect of fluorinated analogues of phenol and hydroxyben-zoates on the anaerobic transformation of phenol to benzoate. Biodegradation 1 65-74. 

Preuss A, J Fimpel, G Diekert (1993) Anaerobic transformation of 2,4,6-trinitrotoluene (TNT). Arch Microbiol 159 345-353. 

Odoriferous polyphenol compounds may be present initially in manure or result from the anaerobic transformation of animal waste. Recently, HRP C and minced... 

Percentage expresses HPLC recovery of 2-bromo-4,6-dinitroaniline (BDNA). Additional thin layer chromatography measurements indicate anaerobic transformation BDNA... 

Tanaka, N. and T. Hvitved-Jacobsen (1999), Anaerobic transformations of wastewater organic matter under sewer conditions. In I.B. Joliffe and J.E. Ball (eds.), Proceedings of the 8th International Conference on Urban Storm Drainage, Sydney, Australia, August 30-September 3, 1999, pp. 288-296. 

The difference between aerobic and anaerobic transformations of wastewater organic matter is crucial. From a basic point of view, however, still related to the sewer systems, aerobic and anaerobic microbial processes have been dealt with in Chapter 3. The aerobic transformations and a corresponding conceptual model were the main subjects of Chapter 5. 

These anaerobic processes have been investigated under sewer conditions (Tanaka and Hvitved-Jacobsen, 1998, 1999, 2000 Hvitved-Jacobsen et al., 1999 Tanaka et al., 2000a, 2000b). The results from experiments in the laboratory, in a pilot sewer and under full-scale sewer conditions combined with theoretical considerations have provided knowledge on the anaerobic transformations of carbon that can be expressed conceptually (Figure 6.8). 

FIGURE 6.8. A simplified concept for anaerobic transformations of organic matter in wastewater and biofilm of a sewer system. 

The two concepts for aerobic and anaerobic transformations of organic matter shown in Figure 5.5 and Figure 6.8, respectively, can be integrated. Although the active biomass is different for aerobic and anaerobic processes, the same fractions of organic substrates—readily biodegradable and hydrolyzable — are relevant in both cases. The fractions of substrate and their formation and utilization form a natural link between the aerobic and anaerobic heterotrophic processes. 

Procedures 1 to 3 described in the previous three subsections have typically been performed on wastewater samples at an upstream point of a sewer. The objective of these procedures has been to characterize the incoming wastewater to the sewer system in terms of COD fractions and process-relevant parameters. Contrary to this, the present procedure number 4 is performed with the overall objective of determining sewer process-related characteristics including the biofilm and reaeration. The characteristics of the water phase considered in procedures 1 to 3 are hereby extended to include all major processes relevant for the microbial transformations in gravity sewers, especially when dealing with aerobic processes. Further detailed characterization that is needed when including the anaerobic transformations will be dealt with in Section 7.2.5. 

The first three methods can be considered more or less explicit methods for the determination of process components and parameters. The four groups of methods for investigation of anaerobic transformations will be outlined in the following. 

Preservation and formation of readily biodegradable organic substrate, Ss, is a major characteristic that is observed under anaerobic conditions in wastewater. An experimental procedure that can be applied for this purpose is crucial for the prediction of the anaerobic transformation of the organic matter and particularly as a basis for estimation of the anaerobic hydrolysis rate (cf. Figure 6.10). 

Griebler C, Adrian L, Meekenstock RV, Richnow HH (2004) Stable carbon isotope fractionation during aerobic and anaerobic transformation of trichlorbenzene. Micro Ecol 48 313-321... 

Chen et al. (1999) studied the anaerobic transformation of 1,1,1-trichloroethane, 1,1-dichloroethane, and choroethane in a lab-scale, municipal wastewater sludge digester. 1,1,1-Trichloroethane degraded via reductive dechlorination to give 1,1-dichloroethane, chloroethane, and then ethane. When cell-free extracts were used, 1,1,1-trichloroethane degraded to acetic acid (90% yield) and 1,1-dichloroethylene, the latter degrading to ethylene. 

Hageman, K. J. Istok, J. D. Eield, J. A. Buscheck, T. E. Semprini, L. In Situ Anaerobic Transformation of Trichlorofluoroethene in Trichloroethene-Contaminated Groundwater. Environ. Sci. Technol. 2001,35, 1729-1735. 

Schneider, H., Schwiertz, A., Collins, M.D., and Blaut, M., Anaerobic transformation of querce-tin-3-glucoside by bacteria from the human intestinal tract, Arch. Microbiol, 171, 81, 1999. 

Stamper, D. M., S. J. Traina, and O. H. Tuovinen, Anaerobic transformation of alachlor, propachlor, and metalachlor with sulfide , J. Environ. Qual., 26,488-494 (1997). 

Figure 3.1. Proposed pathways for the initial anaerobic transformation of toluene. Dashed lines indicate pathways for which identification of the intermediate is based on indirect evidence.

This work is dedicated to the memory of Dunja Grbif-Galif. Her initial work in this area was critical in demonstrating that the anaerobic transformation of BTEX compounds can occur. Subsequent studies done in her lab, as illustrated in this review, has provided a basis for our general interpretation of the fate of BTEX compounds in the environment. 

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