Enhanced nitrogen fixation in a Rhizobium etli ntrC mutant that overproduces the Bradyrhizobium japonicum symbiotic terminal oxidase cbb{sub 3}

Journal Article · Sat May 01 04:00:00 EDT 1999 · Applied and Environmental Microbiology

OSTI ID:346830

Soberon, M; Lopez, O; Morera, C; Girard, M L; Tabche, M L; Miranda, J ^[1]

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1. Univ. Nacional Autonoma de Mexico, Cuernavaca (Mexico)

The ntrC gene codes for a transcriptional activator protein that modulates gene expression in response to nitrogen. The cytochrome production pattern of a Rhizobium etli ntrC mutant (CFN2012) was studied. CO difference spectral analysis of membranes showed that CFN2012 produced a terminal oxidase similar to the symbiotic terminal oxidase of bacteroids in free-living cells under aerobic conditions, with a characteristic trough at 553 nm. CFN2012 produced two c-type cytochromes with molecular masses of 27 and 32 kDa in contrast with the wild-type strain, which produced only a 32-kDa c-tye cytochrome. The expression levels of the R. etli fix/NOQP operon, which codes for terminal oxidase cbb{sub 3}, were not affected by the ntrC mutation. However, the production levels of the two c-type cytochromes (27 and 32 kDa) were enhanced at least eightfold when the Bradyrhizobium japonicum fixNOQP operon was expressed in CFN2012 from the nptII promoter (pMSfix{sup c}), suggesting that these proteins are subunits FixO (27 kDa) and FixP (32 kDa) of cbb{sub 3} and that CFN2012/pMSfix{sup c} overproduced this terminal oxidase. CFN2012/pMSfix{sup c} showed a significant increase in its symbiotic performance as judged by the determination of nitrogenase activities of plants inoculated with this strain, suggesting that the overproduction of cbb{sub 3} terminal oxidase correlates with an enhancement in symbiotic nitrogen fixation.

• OSTI ID: 346830
• Journal Information: Applied and Environmental Microbiology, Journal Name: Applied and Environmental Microbiology Journal Issue: 5 Vol. 65; ISSN AEMIDF; ISSN 0099-2240
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
56 BIOLOGY AND MEDICINE
APPLIED STUDIES
ENZYME ACTIVITY
GENE MUTATIONS
GENE REGULATION
GENES
NITROGEN FIXATION
OXIDOREDUCTASES
RHIZOBIUM
SOILS
SYMBIOSIS