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Next Article 

Appl Environ Microbiol. 1988 June; 54(6): 1313-1317
Copyright © 1988, American Society for Microbiology. All Rights Reserved.

Enumeration of Free-Living Aerobic N2-Fixing H2-Oxidizing Bacteria by Using a Heterotrophic Semisolid Medium and Most-Probable-Number Technique

Wilfredo L. Barraquio, Ann Dumont and Roger Knowles*

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, C2H2 reduction and O2-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% C2H2, and thus, it was possible to test a single culture for both activities. Hydrogen uptake activity was detected for the first time in N2-fixing strains of Pseudomonas stutzeri. The method was then applied to the most-probable-number method of counting N2-fixing and H2-oxidizing bacteria in some natural systems. The numbers of H2-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 H2 transformation.

FOOTNOTES

* Corresponding author.

Appl Environ Microbiol. 1988 June; 54(6): 1313-1317
Copyright © 1988, American Society for Microbiology. All Rights Reserved.





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Copyright © 1988 by the American Society for Microbiology. All rights reserved.