Requirement of glutathione for acid tolerance response in Rhizobium tropici CIAT899

RICCILLO, P. M.; MUGLIA, C. I.; DE BRUJIN, F. J.; AGUILAR, O. M.

Foz do Iguazú, Brasil

Congreso; 12th International Congress on Nitrogen Fixation; 1999

We generated a collection of R. tropici CIAT899 mutants by using transposon Tn5-luxAB and isolated a mutant strain (CIAT899-13T2) which fails to grow under acid conditions. This mutant carries a single transposon insertion in a gene with a high degree of similarity to the gene gshB, which encodes the enzyme glutathione synthetase (GS). This mutant is also sensitive in response to oxidative and osmotic stress and its growth is inhibited by methylglyoxal. Under acidic conditions, the intracellular pH and the level of potassium were lower in the mutant. Supplementation with exogenous glutathione restored the wild type phenotype. Our results seem to indicate that in R. tropici glutathione is required for potassium movement through a mechanism similar to E. coli which involves the glutathione-dependent channels KefB and KefC and that pH homeostasis leads to rise the intracellular potassium. Coinoculation of beans with wild type strain and the mutant strain in a 1:1 ratio had shown that mutant strain is outcompeted by the wild type in nodule occupancy.