<i>nif</i>genes in alien backgrounds

Postgate, J. R.; Dixon, Ray; Hill, Susan; Kent, Helen M.

doi:10.1098/rstb.1987.0059

Cited by 7 publications

(2 citation statements)

References 75 publications

(84 reference statements)

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“…These two his mutants were chosen because the K. pneumoniae Nif+ plasmid pRD1 or pMF100 could be retained by his prototrophy, and in such transconjugants, good levels of N2 fixation or nitrogenase activity have previously been found (30). The transductants were shown to have received the cydAB deletion because, unlike cydA+B+ strains, they failed to grow on NAAZ medium (see Materials and Methods).…”

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Roles for enteric d-type cytochrome oxidase in N2 fixation and microaerobiosis

et al. 1990

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Escherichia coli strains that lacked the d-type cytochrome oxidase, the terminal oxidase with a high affinity for 02, grew anaerobically as well as the wild type did and were not impaired in the ability to evolve H2 from either glucose or formate. The anaerobic synthesis and activity of nitrogenase in transconjugants of these strains carrying Klebsiella pneumoniae nif genes were also normal. However, the behavior towards 02 of anaerobically grown bacteria lacking the d-type oxidase differed from that of the wild type in the following ways: the potential 02 uptake was lower, H2 evolution and nitrogenase activity supported by fermentation were more strongly inhibited by 02, and microaerobic 02-dependent nitrogenase activity in the absence of a fermentable carbon source did not occur. These results show that the d-type oxidase serves two functions in enteric bacteria-to conserve energy under microaerobic conditions and to protect anaerobic processes from inhibition by 02A branched respiratory chain terminating in oxidases of differing affinities for 02 is common among procaryotes (1,28). In Escherichia coli, the low-affinity o-type oxidase (or cytochrome bo) is the principal oxidase under aerobic conditions and the high-affinity d-type oxidase (or cytochrome bd) (encoded by cyd genes) predominates under microaerobic or anaerobic conditions (1, 9, 34). Mutants of E. coli that lack either oxidase have no growth defects under the various laboratory conditions tested (3, 11), implying a possible redundancy of terminal oxidases (see reference 9). In strictly aerobic diazotrophs, a high-affinity terminal oxidase has been implicated in N2 fixation as a means of supporting ATP production at low 02 concentration so that the O2-sensitive nitrogenes can function. However, in none of them has this requirement been unequivocally established, although three types of evidence supporting this hypothesis have been published. First, the biochemical and physiological analyses of microaerophilic N2 fixation, such as that occurring in the legume symbiosis, show that the 02 concentration surrounding the bacteroids is very low (2, 4, 5). Second, the inferior growth yield of an ascorbate-tetramethyl-p-phenylenediamine-oxidase-negative mutant of Azotobacter vinelandii during O2-limited N2-dependent growth suggests that the higher-affinity cytochrome a1o branch of the respiratory chain is needed for energy conservation at low dissolved 02 concentration (DOC) (25). Third, the correction Of 02-sensitive mutants of Azotobacter chroococcum to aerotolerance by the provision of tricarboxylic acid cycle intermediates suggests that a high electron pressure to maintain an adequate 02 uptake at low DOC is required for nitrogen fixation in air (31-33).In E. coli J62-1 and UNF3501 were transduced with the chloramphenicol-resistant bacteriophage P1 grown on E. coli G0103, which carries a kanamycin (Km) resistance cassette close to the partially deleted cydAB locus (R.

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Roles for enteric d-type cytochrome oxidase in N2 fixation and microaerobiosis

et al. 1990

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“…One can imagine a second organelle, a nitroplast, also derived from a cyanobacterium, that fixes N2 and, like the chloroplast, is stably inherited. 46,47 Modifying a free-living N2-fixing cyanobacterium so that it might function as an organelle poses formidable obstacles. Can it survive in the plant cell cytoplasm?…”

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Engineering of crop plants to facilitate bottom-up innovation: A possible role for broad host-range nitroplasts and neoplasts

Elhai¹

2023

Preprint

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The astonishing gains in agricultural output since the 1960's has come at an environmental cost. It has also failed to bring much benefit to sub-Saharan Africa, the region of the world that is predicted to have the greatest population increase in the coming decades and greatest agricultural need. The increase in productivity required to feed the billions that will soon be added to the world's population is more likely to succeed if creative direction lies in the hands of those most intimately acquainted with local agricultural concerns. Nitrogen has been a major limitation, particularly in sub-Saharan agriculture, and I look here at the prospect for extending biological nitrogen fixation to the crops and practices of local interest. A source of optimism in this historically intractable problem is the discovery in certain algae of natural organelles – nitroplasts – derived from unicellular cyanobacteria that fix N2. Transferring nitroplasts to land plants seems possible only if the organelles rely little on their hosts. A survey of the metabolic capabilities of three of them indicate different degrees of independence. The nitroplast from the diatom Rhopalodia gibberula may need nothing from its host except a source of carbon (the nature of which is explored). The nitroplast from another diatom, Epithema turgida, is somewhat less independent, while the nitroplast from Braarudosphaera bigelowii (called UCYN-A) requires a great deal from its host, including imported protein. The evolutionary route to acquire proteins may have been greatly simplified if nitroplasts share proteins with chloroplasts, a co-resident cyanobacteria-derived organelle. The genomes of the diatom nitroplasts suggest the presence of a few enzymes that are rare in cyanobacteria but seemingly well suited to the special needs of a nitrogen-fixing organelle. I describe how the host-range of nitroplasts might be explored and how a stripped down version, called a neoplast, might simplify strain modification to such a degree that the process becomes accessible to academic researchers with limited resources, even to individual farmers.

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Trends and Perspectives in Nitrogen Fixation Research

Postgate

1990

Advances in Microbial Physiology

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nifgenes in alien backgrounds

Cited by 7 publications

References 75 publications

Roles for enteric d-type cytochrome oxidase in N2 fixation and microaerobiosis

Roles for enteric d-type cytochrome oxidase in N2 fixation and microaerobiosis

Engineering of crop plants to facilitate bottom-up innovation: A possible role for broad host-range nitroplasts and neoplasts

Trends and Perspectives in Nitrogen Fixation Research

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