Fission of Oxygenated Rings

After formation of the 1,2-dihydroxy compounds, ring fission is mediated by 1 2 (intradiol fission) or 2 3 (extradiol and distal fission) dioxygenases. There are, however, important variations in the pathways used by various groups of microorganisms  

In the degradation of 3-hydroxybenzoate, divergent pathways are used by different groups of pseudomonads  

FIGURE 8.30 Biodegradation of 3,4-dihydroxybenzoate mediated by (a) 4,5-dioxygenase in Pseudomonas testosteroni and (b) 2,3-dioxygenase in Bacillus macerans. 

The enzymes of alternative pathways may be induced in a given strain by growth with different substrates for example, growth of Pseudomonas putida R1 with salicylate induces enzymes of the extradiol fission pathway, whereas growth with benzoate induces those of the intradiol pathway (Chakrabarty 1972). As a broad generalization, the extradiol fission is preferred for the degradation of more complex compounds such as toluene, naphthalene, and biphenyl (Furukawa et al. 1983). 

Strains of Bacillus megaterium and Streptomyces sp. strain 179 transformed vanillate to guaiacol by decarboxylation (Crawford and Olson 1978), and the gene cluster encoding decarboxylation in Streptomyces sp. strain m D7 has been characterized (Chow et al. 1999). 

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