Figure 5.

Proposed benzene catabolic pathways in C. metallidurans CH34. Main pathway for benzene degradation in strain CH34 is indicated with continuous arrows, whereas the oxidation pathway that was not preferred is indicated with dashed arrows. Intermediate metabolites with experimental data are underlined. (A) Upper pathway for benzene degradation via consecutive monooxygenation. The substrates and products are as follows: 1, benzene; 2, phenol; 3, catechol. The enzymes involved are as follows: T2MO (toluene 2-monooxygenase), TMO (toluene monooxygenase), PH (phenol hydroxylase). (B) Lower pathway for catechol via meta-cleavage. The substrates and products are as follows: 4, 2-hydroxymuconic semialdehyde; 5, 2-hydroxymuconate; 6, 4-oxalocrotonate; 7, 2-oxopenta-4-enoate; 8, 4-hydroxy-2-oxopentanoate; 9, pyruvate; 10, acetaldehyde; 11, acetyl-CoA. The enzymes involved are as follows: TomB (catechol 2,3-dioxygenase), TomC (semialdehyde-2-hydroxymuconate dehydrogenase), TomI (4-oxalocrotonate tautomerase), TomH (4-oxalocrotonate decarboxylase), TomD (semialdehyde-2-hydroxymuconate hydrolase), TomE (2-hydroxypent-2,4-dienoate hydratase), TomG (4-hydroxy-2-ketovalerate aldolase), TomF (acetaldehyde-CoA dehydrogenase). (C) Lower pathway for catechol via ortho-cleavage. The substrates and products are as follows: 12, cis-cis muconate; 13, muconolactone; 14, 3-oxoadipate-enol-lactone; 15, 3-oxoadipate; 16, 3-oxoadipyl-CoA; 17, succinyl-CoA. The enzymes involved are as follows: CatA (catechol 1,2-dioxygenase), CatB (muconate cycloisomerase), CatC (muconolactone delta-isomerase), CatD/PcaD (3-oxoadipate enol-lactonase), PcaIJ (3-oxoadipate CoA-transferase), PcaF (3-oxoadipyl-CoA thiolase).