N2-fixing vibrios isolated from the gastrointestinal tract of sea urchins.

Facultatively anaerobic bacteria, capable of fixing N2 anaerobically or at low O2 concentrations, were isolated from the gastrointestinal tracts of temperate (Strongylocentrotus droebachiensis) and tropical (Tripneustes ventricosus) sea urchins. Morphological and biochemical characteristics, as well as the guanine plus cytosine content of their DNA (45.9 and 48.4 mol%), place these isolates in the genus Vibrio Pacini 1865 in the family Vibrionaceae. Members of this family have not previously been shown to fix N2. These isolates are not identical to any described species in the Vibrio genus and can be distinguished by a combination of biochemical and physiological traits.