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Glutathione Is Required by Rhizobium etli for Glutamine Utilization and Symbiotic Effectiveness

March 2012 , Volume 25 , Number  3
Pages  331 - 340

Rosarita Taté,1 Michele Cermola,1 Anna Riccio,1 Graciana Diez-Roux,2 and Eduardo J. Patriarca1

1Institute of Genetics and Biophysics, ‘A. Buzzati-Traverso’, CNR, Naples, 80131, Italy; 2Telethon Institute of Genetics and Medicine (TIGEM), Naples, 80131, Italy

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Accepted 7 October 2011.

Here, we provide genetic and biochemical evidence indicating that the ability of Rhizobium etli bacteria to efficiently catabolize glutamine depends on its ability to produce reduced glutathione (L-γ-glutamyl-L-cysteinylglycine [GSH]). We find that GSH-deficient strains, namely a gshB (GSH synthetase) and a gor (GSH reductase) mutant, can use different amino acids, including histidine, alanine, and asparagine but not glutamine, as sole source of carbon, energy, and nitrogen. Moreover, L-buthionine(S,R)-sulfoximine, a GSH synthesis inhibitor, or diamide that oxidizes GSH, induced the same phenotype in the wild-type strain. Among the steps required for its utilization, glutamine uptake, occurring through the two well-characterized carriers (Aap and Bra systems) but not glutamine degradation or respiration, was largely reduced in GSH-deficient strains. Furthermore, GSH-deficient mutants of R. etli showed a reduced symbiotic efficiency. Exogenous GSH was sufficient to rescue glutamine uptake or degradation ability, as well as the symbiotic effectiveness of GSH mutants. Our results suggest a previously unknown GSH–glutamine metabolic relationship in bacteria.

© 2012 The American Phytopathological Society