The Metabolism of Gallic Acid byPseudomonas convexaX.1

Unravelling the gallic acid degradation pathway in bacteria: the gal cluster from Pseudomonas putida

Gallic acid (3,4,5-trihydroxybenzoic acid, GA) is widely distributed in nature, being a major phenolic pollutant and a commonly used antioxidant and building-block for drug development. We have characterized the first complete cluster (gal genes) responsible for growth in GA in a derivative of the model bacterium Pseudomonas putida KT2440. GalT mediates specific GA uptake and chemotaxis, and highlights the critical role of GA transport in bacterial adaptation to GA consumption. The proposed GA degradation via the central intermediate 4-oxalomesaconic acid (OMA) was revisited and all enzymes involved have been identified. Thus, GalD is the prototype of a new subfamily of isomerases that catalyses a biochemical step that remained unknown, i.e. the tautomerization of the OMAketo generated by the GalA dioxygenase to OMAenol. GalB is the founding member of a new family of zinc-containing hydratases that converts OMAenol into 4-carboxy-4-hydroxy-2-oxoadipic acid (CHA). galC encodes the aldolase catalysing CHA cleavage to pyruvic and oxaloacetic acids. The presence of homologous gal clusters outside the Pseudomonas genus sheds light on the evolution and ecology of the gal genes in GA degraders. The gal genes were used for expanding the metabolic abilities of heterologous hosts towards GA degradation, and for engineering a GA cellular biosensor.

Metabolism of gallate in Penicillium simplicissimum

The pathway for the degradation of gallate (3,4,5-trihydroxybenzoate) by a new strain of Penicillium was examined by in vivo and in vitro cell-free systems. The organism was identified as P. simplicissimum (Oud) Thom. It grew optimally at pH 5.5 and 27 degrees C, with 11.75 mM (0.2%) gallate added to the basal salt media. Mycelia grown on gallate accumulated protocatechuate in the medium, and had inducible activity for protocatechuate 3,4-dioxygenase as determined by spectrophotometric and oxygen electrode studies. A NADPH-dependent reductase in the cell-free extract reduced gallate to dihydrogallate. Maleylacetate reductase was also detected in the gallate induced cell-free extract, while beta-ketoadipate was detected as the product produced. The possible steps in the degradation of gallate are discussed.