Enumeration of Free-Living Aerobic N 2 -Fixing H 2 -Oxidizing Bacteria by Using a Heterotrophic Semisolid Medium and Most-Probable-Number Technique

Author:

Barraquio Wilfredo L.1,Dumont Ann1,Knowles Roger1

Affiliation:

1. Department of Microbiology, Macdonald College of McGill University, 21111 Lakeshore Road, Ste. Anne de Bellevue, Québec, Canada H9X 1C0

Abstract

A heterotrophic semisolid medium was used with two sensitive assay methods, C 2 H 2 reduction and O 2 -dependent tritium uptake, to determine nitrogenase and hydrogenase activities, respectively. Organisms known to be positive for both activities showed hydrogenase activity in both the presence and absence of 1% C 2 H 2 , and thus, it was possible to test a single culture for both activities. Hydrogen uptake activity was detected for the first time in N 2 -fixing strains of Pseudomonas stutzeri. The method was then applied to the most-probable-number method of counting N 2 -fixing and H 2 -oxidizing bacteria in some natural systems. The numbers of H 2 -oxidizing diazotrophs were considerably higher in soil surrounding nodules of white beans than they were in the other systems tested. This observation is consistent with reports that the rhizosphere may be an important ecological niche for H 2 transformation.

Publisher

American Society for Microbiology

Subject

Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology

Reference36 articles.

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2. Isolation and identification of N2-fixing Pseudomonas associated with wetland rice;Barraquio W. L.;Can. J. Microbiol.,1983

3. Berndt H. and D. Wolfle. 1978. Hydrogenase: its role as electron generating enzyme in the nitrogen-fixing hydrogen bacterium Xanthobacter autotrophicus p. 327-351. In H. G. Schlegel and K. Schneider (ed.) Hydrogenases: their catalytic activity structure and function. Goltze Verlag Gottingen Federal Republic of Germany.

4. Physiology and biochemistry of aerobic hydrogen-oxidizing bacteria. Annu;Bowien B.;Rev. Microbiol.,1981

5. Hydrogen metabolism of Azospirillium brasilense in nitrogen-free medium;Chan Y.;Can. J. Microbiol.,1980

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