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SUMMARY: The screening of several hundred isolates from tussock-grassland soils for nitrogen-fixing ability resulted in the isolation of Clostridium butyricum and five facultatively anaerobic nitrogen-fixing species. These latter have been identified as Bacillus circulans (tentative identification), B. polymyxa, Enterobacter aerogenes (formerly Aerobacter aerogenes), Klebsiella pneumoniae and Escherichia intermedia. Estimates of numbers of these species indicate that they will be responsible for only very low rates of nitrogen fixation in the soils tested.
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Line et al. (1971) studied this question.
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