Oxalic acid production and aluminum tolerance in Pseudomonas fluorescens

C-13 NMR studies on intact cells from Al-stressed Pseudomonas fluorescens i ncubated with citric acid or Al-citrate yielded peaks at 158 and 166 ppm th at were attributable to free and complexed oxalic acid, respectively. The p resence of oxalic acid was further confirmed with the aid of oxalate oxidas e. These peaks were not discernable in experiments performed with cells tak en from control cultures. Enzymatic analyses of cell fractions showed the h ighest production of oxalic acid in the inner membrane fraction of Al-stres sed cells incubated with glyoxylate. There was an eight-fold increase in th e synthesis of oxalic acid in the inner membrane fraction from the Al-stres sed cells compared to the control cells. Although oxalic acid production wa s observed when citrate, Al-citrate and isocitrate were utilized as substra tes, the inner membrane fraction did not mediate the formation of oxalic ac id from glycine/pyruvate, glycolic acid, oxaloacetate or ascorbate. These d ata suggest that the increased oxalic acid production in response to Al str ess is effected via the oxidation of glyoxylate. (C) 1999 Elsevier Science Inc. All rights reserved.