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SUMMARYThe 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 Aerobucter 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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. Thirty strains of V. anguillarum were tested for the production of inhibitory substances against closely‐related bacteria using the deferred antagonism test. Only one strain, Vibrio anguillarum VL4355, inhibited strains of V. ordalii and this effect was blocked by the addition of iron salts to the culture medium. Siderophore production was investigated for this strain. Results from bioassays suggested that strain VL4355 produced a siderophore related to anguibactin, the plasmid‐encoded phenolate siderophore produced by V. anguillarum strain 775. However, when plasmid DNA was compared for strains 775 and VL4355 the BamHI‐generated restriction profiles were different, although hybridization experiments indicated some homology. Using the chrome‐azurol sulphate assay to measure siderophore production, strain VL4355 yielded significantly higher values than other V. anguillarum strains. Amberlite XAD‐2 was used to produce concentrated siderophore preparations from strains VL4355 and 775. Both preparations were inhibitory to the growth of strains of V. ordalii, but not V. anguillarum, as were solutions of the iron chelator ethylenediamine‐di(o‐hydroxyphenylacetic acid). The difference in sensitivity to iron‐limiting conditions for V. ordalii and V. anguillarum, coupled with the inability of V. ordalii to utilize ferric‐anguibactin, could reflect different mechanisms of iron uptake for these two organisms.

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