Arcondéguy T, Huez I, Fourment J, Kahn D
Laboratoire de Bíologie Moléculaire des Relations Plantes-Microorganismes, UMR 215 INRAICNRS, Chemin de Borde Rouge, Castanet-Tolosan, France.
FEMS Microbiol Lett. 1996 Nov 15;145(1):33-40. doi: 10.1111/j.1574-6968.1996.tb08553.x.
Symbiotic nitrogen fixation is accompanied by a shift of Rhizobium nitrogen metabolism from ammonium assimilation to ammonium export, which probably involves genetic or metabolic regulation of glutamine synthetase activity. In free-living Rhizobium meliloti glutamine synthetase I (GSI) is regulated post-translationally by reversible adenylylation in response to ammonium addition. Moreover, full expression of the GSI gene glnA requires the transcriptional activator, NtrC. A glnA1 mutant synthesizing a non-adenylylatable GSI produces normal nitrogen-fixing nodules on alfalfa: GSI adenylylation is dispensable for symbiotic nitrogen fixation. This is rationalized by the observation that less GS protein is present in R. meliloti bacteroids than in free-living bacterial cells.
共生固氮伴随着根瘤菌氮代谢从铵同化向铵输出的转变，这可能涉及谷氨酰胺合成酶活性的遗传或代谢调控。在自由生活的苜蓿根瘤菌中，谷氨酰胺合成酶I（GSI）在添加铵后通过可逆的腺苷酸化进行翻译后调控。此外，GSI基因glnA的完全表达需要转录激活因子NtrC。合成不可腺苷酸化的GSI的glnA1突变体在苜蓿上产生正常的固氮根瘤：GSI腺苷酸化对于共生固氮是可有可无的。苜蓿根瘤菌类菌体中存在的GS蛋白比自由生活的细菌细胞中少，这一观察结果解释了这一现象。
