2.4- dichlorobenzoate, degradation

Another example that illustrates the plasticity of genes in the environment is the construction of a 3-chlorobenzoate, 4-chlorobenzoate and 3,5-dichlorobenzoate degrading Pseudomonas species from two distinct Pseudomonas strains (Reineke Knackmuss, 1980). Pseudomonas sp. B13 is able to grow on 3-chlorobenzoate, but cannot grow on 4-chlorobenzoate and 3,5-dichlorobenzoate. P.putida mt-2, however... 

An additional variant that involves both hydrolytic and reductive reactions has been found in the degradation of 2,4-dichlorobenzoate by Alcaligenes denitrificans strain NTB-1 (van den Tweel et al. 1987) (Figure 9.16), and via the CoA ester by Corynebacterium sepedonicum (Romanov and Hausinger 1996). 

Subsequent degradation of the 3-chlorobenzoate does not proceed until most of the 3,5-dichlorobenzoate is transformed. The explanation for this finding is that the dichloro aromatic substrate competes with the monochloro compound for the same enzyme active site. As a result, 3,5-dichlorobenzoate acts as a competitive inhibitor of the biochemical removal of 3-chlorobenzoate. Once nearly all the dichloro... 

Plants. Degradation rate varies greatly with species. In wheat, the major metabolite is 5-hydroxy-2-methoxy-3,6-dichlorobenzoic acid, while 3,6-dichlorosalicylic acid is also a metabolite... 

When both C02and a substituent such as halogen are eliminated, no dehydrogenation is required to produce the catechol. This is also the case in the degradation of 3,4-dichlorobenzoate where spontaneous loss of HCI from the initially produced 4,5-rfs-diol formed 3-chloro-4,5-dihydroxybenzoate without intervention of a dehydrogenase that is necessary for 3-chlorobenzoate (Nakatsu et al. 1997). These examples stand in contrast to the situation for aromatic hydrocarbons in which a dehydrogenase is necessary. 

In view of current interest in the persistence of recalcitrant organochlorine compounds, it is appropriate to note the degradation of 2,7-dichlorobenzo-1,4-dioxin by Phanerochaete chrysosporium (Valli et al. 1992a). Degradation involves dechlorination and ring scission as the initial reactions (Figure 6.61) ... 

Unhindered aryl nitriles are rapidly hydrolyzed via the amide to the carboxylic acid, but the hindered aryl nitriles are only transformed slowly into amides that are even more stable. Whereas 8 (Hal = Br) and 9 (Hal = 1) form in soil, by hydrolysis and dehalogenation, less toxic substances such as 4-hydroxybenzoic acid [29], 10 undergoes degradation to the stable 2,6-dichlorobenzamide, which is slowly further hydrolyzed into the 2,6-dichlorobenzoic acid [30]. 

Chlorinated benzoic acids have been shown to be intermediates in the biodegradation of several chlorinated aromatic compounds, for example, 4-chlorobenzoic acid is formed in the biodegradation of both polychlorinated biphenyls [103]. Mixed microbial cultures, which have been studied by a number of groups under aerobic conditions, can degrade a wide range of chlorinated benzoic acids, including 2-, 3- and 4-chlorobenzoic acid as well as 3,4-dichloro- and 2,4-dichlorobenzoic acid [104]. By contrast, under anaerobic conditions, only reductive dechlorination of meta-substituted benzoic acids has been observed [49,105,106]. Cometabolism of chlorobenzoic acids in the presence of unsubstituted benzoic adds leads to the formation of the corresponding... 

Valli, K., H. Wariishi, and M. H. Gold. 1992. Degradation of 2,7-dichlorobenzo-p-dioxin by the lignindegrading basidiomycete Phanerochaete chrysosporium. J. Bacteriol. 174 2131-2137. 

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