The role of glutaminase in Rhizobium etli: studies with a new mutant

• Published in: Microbiology (Society for General Microbiology) 1995-11, Vol.141 (11), p.2883-2889
• Main Authors: DuraAn, Socorro, Du Pont, Gisela, Huerta-Zepeda, Alejandra, CalderoAn, Jorge
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Bacteriology; Biological and medical sciences; Economic plant physiology; Fabaceae - microbiology; Fundamental and applied biological sciences. Psychology; Glutamate-Ammonia Ligase - metabolism; Glutamic Acid - metabolism; Glutaminase - genetics; Glutaminase - metabolism; Glutamine - metabolism; Metabolism. Enzymes; Microbiology; Mutation; Nitrogen - metabolism; Phaseolus vulgaris; Phenotype; Plants, Medicinal; Rhizobium - genetics; Rhizobium - growth & development; Rhizobium - metabolism; Rhizobium etli; Symbiosis (nodules, symbiotic nitrogen fixation, mycorrhiza...); Symbiosis - genetics; Symbiosis - physiology
• ISSN: 1350-0872; 1465-2080
• DOI: 10.1099/13500872-141-11-2883

Departamento de Biotecnologia, Instituto de Investigaciones BiomíeAdicas, Universidad Nacional AutíoAnoma de MíeAxico, MíeAxico DF 04510 ABSTRACT Summary: In order to examine the role of glutaminase in Rhizobium etli, we isolated and characterized a R. etli glutaminase mutant (LM16). This mutant was selected for its impaired ability to grow on glutamine as nitrogen and carbon source while retaining the ability to grow on other nitrogen and carbon sources. The mutant showed very low levels of glutaminase activity under various growth conditions in comparison with the wild-type strain. With glutamine as the only nitrogen and carbon source, LM16 showed poor growth, with a very high content of glutamine, low glutamate content, and reduced ammonium excretion and 14 CO 2 evolution from [U- 14 C]glutamine compared to the wild-type strain. This indicates that the main role of R. etli glutaminase is in the use of glutamine as carbon source. R. etli glutaminase also plays a role in maintaining the balance between glutamate and glutamine, as shown by the accumulation of glutamine and the low glutamate content of the mutant under different growth conditions. These results also indicate that glutaminase participates in a glutamine cycle in which it degrades glutamine which is then resynthesized by glutamine synthetase. The higher glutamine and lower glutamate content found in bacteroids of LM16 in comparison with bacteroids of the wild-type strain indicate that glutamine degradation by glutaminase plays an important role during the symbiosis between R. etli and Phaseolus vulgaris . Author for correspondence: Jorge Calderón. Tel: + 52 6 22 38 80. Fax: [phone]. e-mail: JFCJ @ SERVIDOR.UNAM.MX Keywords: Rhizobium etli , mutant, glutaminase, catabolism, symbiosis