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At least 649 records · Page 36Linked to original sources
PubMed1975

Effect of pesticides on blue-green algae and nitrogen-fixation.

The effects of the pesticides, amitrol, a derivative of amitrol (viz. 3,5-diamino-1,2,4-triazole), diquat, paraquat, linuron, MCPA, malathion, and monuron, were studied on the nitrogen-fixing algae, Anabaena cylindrica, Aulosira sp., Calothrix elenkenii. Chlorogloeae frischii, Cylindrospermum muscicola, Nostoc sp. from Collema tenax, Nostoc muscorum Tolypothrix tenuis, and Westiellopsis sp. In general, two types of response were discernible; an initial period of depression succeeded by an increased activity and an initial period of depression followed by a distinct decrease on prolonged incubation. The results indicate that some pesticidal compounds can severely limit the nitrogen-fixing capacities of blue-green algae, thereby affecting the overall nitrogen economy of soils in general.

Culture Media↗
PubMed2001

[The different functions of glnB and glnZ from Azospirillum brasilense YU62 in the control of nitrogen fixation].

The glnB and glnZ genes of A. brasilense have 70% homology at nucleotide sequence. glnB is located in a 3.7 kb Eco RI+ PstI fragment and glnZ is located in a 3.7 kb SalI fragment. Both glnB and glnZ genes were mutagenized by Kmr cassette insertions and glnB- and glnZ- mutants were obtained. glnB- mutant did not have any nitrogenase activity, while glnZ- mutant still has nitrogenase activity. The coding regions of glnB and glnZ were cloned into pVK100 vectors and recombinant plasmids pVK-II and pVK-Z were obtained, respectively. The recombinant plasmids pVK-II and pVK-Z were introduced into glnB- and glnZ- to produce C-glnB and C-glnZ, respectively. C-glnB can restore nitrogenase activity and C-glnZ does not have effect on nitrogenase activity. When pVK-II and pVK-Z were introduced into A. brasilense Yu62 and draT-, respectively, the Yu62-II (containing pVK-II) and draT-II (containing pVK-II) have higher nitrogenase activity than that of wild type Yu62. In contrast, Yu62-Z (containing pVK-Z) and draT-Z (containing pVK-Z) has no effect on nitrogenase activity. The nifA(-)-II (containg pVK-II) and nifA(-)-Z (containing pVK-Z) still have no nitrogenase activity.

Azospirillum brasilense↗
PubMed1993

Characterisation of mutations in the Klebsiella pneumoniae nitrogen fixation regulatory gene nifL which impair oxygen regulation.

The nifL gene product of Klebsiella pneumoniae inhibits the activity of the positive activator protein NifA in response to increased levels either of fixed nitrogen or of oxygen in the medium. In order to demonstrate that the responses to these two effectors are discrete we have subjected nifL to hydroxylamine mutagenesis and isolated nifL mutants that are impaired in their ability to respond to oxygen but not to fixed nitrogen. Two such mutations were sequenced and shown to be single base pair changes located in different parts of nifL. The amino acid sequence of NifL shows limited homology to the histidine protein kinases which comprise the sensing component of bacterial two-component regulatory systems. In the light of the location of one of the oxygen-insensitive mutations (Leu294Phe) we have reassessed this homology and we suggest that the Gln273-Leu317 region of NifL may facilitate interactions between NifL and NifA.

Amino Acid Sequence↗
PubMed1986

Anaerobic regulation of nitrogen-fixation genes in Rhodopseudomonas capsulata.

A Rhodopseudomonas capsulata nifH::lacZ gene fusion was used to isolate constitutive mutants of R. capsulata, unable to repress nif gene transcription anaerobically with every fixed-nitrogen source tested. When these nifc strains were grown aerobically, nif gene transcription was repressed. These results indicate that the regulation of nif gene transcription by fixed nitrogen is different from the regulation by oxygen. Under anaerobic conditions, nif gene transcription in both R. capsulata and Klebsiella pneumoniae is specifically prevented by inhibitors of DNA gyrase [DNA topoisomerase type II (ATP-hydrolyzing), EC 5.99.1.3]. A recent study has shown that anaerobically grown Salmonella typhimurium have high DNA gyrase activity, whereas aerobically grown cells have high DNA topoisomerase type I (EC 5.99.1.2) activity and DNA that is more relaxed [Yamamoto, N. & Droffner, M. L. (1985) Proc. Natl. Acad. Sci. USA 82, 2077-2081]. In view of these results, we suggest that the control of nif gene transcription in response to oxygen is determined by the action of DNA gyrase and DNA topoisomerase I. Thus, although nitrogen control of nif gene expression requires the products of regulatory genes for which constitutive mutations can be isolated, oxygen appears instead to prevent the adoption of a DNA conformation necessary, directly or indirectly, for nif gene transcription.

Anaerobiosis↗