2012年4月
NAD(P)(+)-Malic Enzyme Mutants of Sinorhizobium sp Strain NGR234, but Not Azorhizobium caulinodans ORS571, Maintain Symbiotic N-2 Fixation Capabilities
APPLIED AND ENVIRONMENTAL MICROBIOLOGY
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- 巻
- 78
- 号
- 8
- 開始ページ
- 2803
- 終了ページ
- 2812
- 記述言語
- 英語
- 掲載種別
- 研究論文(学術雑誌)
- DOI
- 10.1128/AEM.06412-11
- 出版者・発行元
- AMER SOC MICROBIOLOGY
C-4-dicarboxylic acids appear to be metabolized via the tricarboxylic acid (TCA) cycle in N-2-fixing bacteria (bacteroids) within legume nodules. In Sinorhizobium meliloti bacteroids from alfalfa, NAD(+)-malic enzyme (DME) is required for N-2 fixation, and this activity is thought to be required for the anaplerotic synthesis of pyruvate. In contrast, in the pea symbiont Rhizobium leguminosarum, pyruvate synthesis occurs via either DME or a pathway catalyzed by phosphoenolpyruvate carboxykinase (PCK) and pyruvate kinase (PYK). Here we report that dme mutants of the broad-host-range Sinorhizobium sp. strain NGR234 formed nodules whose level of N-2 fixation varied from 27 to 83% (plant dry weight) of the wild-type level, depending on the host plant inoculated. NGR234 bacteroids had significant PCK activity, and while single pckA and single dme mutants fixed N-2 at reduced rates, a pckA dme double mutant had no N-2-fixing activity (Fix(-)). Thus, NGR234 bacteroids appear to synthesize pyruvate from TCA cycle intermediates via DME or PCK pathways. These NGR234 data, together with other reports, suggested that the completely Fix(-) phenotype of S. meliloti dme mutants may be specific to the alfalfa-S. meliloti symbiosis. We therefore examined the ME-like genes azc3656 and azc0119 from Azorhizobium caulinodans, as azc3656 mutants were previously shown to form Fix(-) nodules on the tropical legume Sesbania rostrata. We found that purified AZC3656 protein is an NAD(P)(+)-malic enzyme whose activity is inhibited by acetyl-coenzyme A (acetyl-CoA) and stimulated by succinate and fumarate. Thus, whereas DME is required for symbiotic N-2 fixation in A. caulinodans and S. meliloti, in other rhizobia this activity can be bypassed via another pathway(s).
- リンク情報
- ID情報
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- DOI : 10.1128/AEM.06412-11
- ISSN : 0099-2240
- eISSN : 1098-5336
- Web of Science ID : WOS:000302147300035