The metabolism of benzoate and methylbenzoates via the meta-cleavage pathway by Pseudomonas arvilla mt-2.

Abstract

Pseudomonas arvilla mt‐2 grows at the expense of benzoate, m‐toluate (3‐methylbenzoate) and p‐toluate (4‐methylbenzoate), but not o‐toluate (2‐methylbenzoate). Under various conditions compounds with spectra characteristic of muconic semialdehydes can be made to accumulate in the media. These spectra indicate that benzoate is metabolised through catechol and 2‐hydroxymuconic semialdehyde (2‐hydroxy‐6‐oxohexa‐2,4‐dienoate), m‐toluate through 3‐methylcatechol and 2‐hydroxy‐6‐oxohepta‐2,4‐dienoate and p‐toluate through 4‐methylcatechol and 2‐hydroxy‐5‐methylmuconic semialdehyde (2‐hydroxy‐5‐methyl‐6‐oxohexa‐2,4‐dienoate). Freshly harvested cells grown on all three substrates only consume oxygen at a significant rate when presented with the growth substrates themselves and catechol and the methylcatechols, but not with salicylate, protocatechuate or phenol or the cresols. Extracts of cells grown on these substrates contain high induced levels of the suite of meta cleavage enzymes, including both the hydrolytic branch and the 4‐oxalocrotonate branch. The substrate specificity of the early enzymes of the pathway suggests that only one non specific enzyme expresses each activity in cell‐free extracts and that it is nonspecifically induced during growth on all three carbon sources. It is suggested that the metabolic role of the hydrolytic branch of the pathway is the assimilation of 3‐methylcatechol and its precursor, and that of the 4‐oxalocrotonate branch is to assimilate catechol and 4‐methylcatechol and their precursors. o‐Toluate is not metabolised because it is neither a substrate for the benzoate oxidase system nor an inducer of any of the meta pathway enzymes. It appears that benzoate and m‐and p‐‐toluates are the substrate inducers of the meta pathway enzymes in this organism. The ortho pathway is induced on incubating cells with catechol and the first inducer appears to be cis,cis‐muconate or possibly catechol itself.