A New Aquatic Nitrogen-Fixing Bacterium from Three Cambridgeshire Chalk Streams

SUMMARY: A motile rod-shaped bacterium which on nitrogen-free media fixed appreciable quantities of nitrogen gas was isolated in pure culture from three chalk streams near Cambridge. It was weakly Gram-positive and beaded in stained preparations. Flagellation was distinctive and unusual in that the flagella at the poles were coarser than those at the sides. Growth was promoted by sugars, and nitrate was rapidly reduced. Since the flagellation of the organism is unusual, its classification is difficult; but the organism does not appear to have been previously described.