Characterization of a gene cluster encoding the maleylacetate reductase from Ralstonia eutropha 335T, an enzyme recruited for growth with 4-fluorobenzoate

A gene cluster containing a gene for maleylacetate reductase (EC 1.3.1.32) was cloned from Ralstonia eutropha 335(T) (DSM 531(T)), which is able to utilize 4-fluorobenzoate as sole carbon source. Sequencing of this gene cluster showed that the R. eutropha 335 T maleylacetate reductase gene, macA, is part of a novel gene cluster, which is not related to the known maleylacetate-reductase-encoding gene clusters. It otherwise comprises a gene for a hypothetical membrane transport protein, macB, possibly co-transcribed with macA, and a presumed regulatory gene, macR, which is divergently transcribed from macBA. MacA was found to be most closely related to TftE, the maleylacetate reductase from Burkholderia cepacia AC1100 (62 % identical positions) and to a presumed maleylacetate reductase from a dinitrotoluene catabolic gene cluster from B. cepacia R34 (61 % identical positions). By expressing macA in Escherichia coli, it was confirmed that macA encodes a functional maleylacetate reductase. Purification of maleylacetate reductase from 4-fluorobenzoate-grown R. eutropha 335(T) cells allowed determination of the N-terminal sequence of the purified protein, which was shown to be identical to that predicted from the cloned macA gene, thus proving that the gene is, in fact, recruited for growth of R. eutropha 335(T) with this substrate.