SUMMARY: Very numerous small transparent colonies appeared on plates of nitrogen-poor agar inoculated with soils from various places in Rhodesia. Eighty-three cultures of bacteria were isolated from these colonies, all but two of them small Gram-negative rods. Two cultures contained Gram-positive cocci. Thirty-nine of the isolates fixed nitrogen, ten of them fixing as much as or more than a Beijerinckia culture grown under the same conditions. The Gram-negative isolates are not all alike; their identity is uncertain, but some might be Pseudomonas species, some Achromobacter (or Acinetobacter), and one good fixer might be a Flavobacterium. There are also a few isolates which attack glucose fermentatively. Nitrogen-fixers of these types—aerobic bacteria with very small colonies—appear to be numerous and widely distributed in Rhodesian soils.


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