1. With the cultures of a strain of
Clostridium isolated from soil, the process of anaerobic fixation of molecular nitrogen as well as its inhibition by various substances was studied.
2. For the anaerobic N
2-fixation to be maintained in its active condition during sufficiently long culture periods, cares must be taken to keep the pH of the medium as constant as possible.
3. The level of anaerobic N
2-fixation thus achieved was usually as high as 90μg. N per ml. of the culture solution during the first 24 hours' incubation, a value almost comparable with those obtained by previous workers in aerobic fixation with
Azotobacter. 4. Carbon monoxide and nitrous oxide were found to inhibit the anaerobic N
2-fixation in a specific manner, in that they do not affect (N
2O) or do inhibit only in less pronounced extent (CO) the assimilation of ammonium-N by the bacterium.
5. Cyanide, azide, monoiodoacetate,
p-chloromercuribenzoate and
o-phenanthroline were also found to be powerful inhibitors of the anaerobic process, though their action on the fixation system seemed to be unspecific in nature.
6. Based on these findings, some discussions were made on the mechanism of the biological N
2-fications.
The writer wishes to express his sincere gratitude to Prof. T. Mori of this laboatory for his continuous encouragement and advices. Thanks are also due to Prof. H. Tamiya of the University of Tokyo and Dr. A. Takamiya of the Tokyo In-stitute of Technology for their valuable suggestions. The work was partly supported by the Grant in Aid for Scientific Research from the Ministry of Education.
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