ISOLATION OF A NITROGEN-FIXING VIBRIO SPECIES FROM THE ROOTS OF EELGRASS

ZOSTERA MARINA

Abstract

A facultative nitrogen-fixing bacterium was isolated from the roots of eelgrass (Zostera marina) growing in Aburatsubo Inlet, Kanagawa Prefecture, Japan. The isolate grew anaerobically using molecular nitrogen as the sole nitrogen source. However, NH₄Cl could also serve as a nitrogen source, under either aerobic or anaerobic conditions. The nitrogenase activity of the isolate was very weak under aerobic conditions, but was easily detected within a few hours under anaerobic conditions. It was enhanced by some sugars and was Na⁺-dependent. Morphological, physiological, and biochemical characteristics, as well as the guanine-plus- cytosine content of its DNA (45.4±0.3mol%) placed the isolate in the genus Vibrio of the family Vibrionaceae. The isolate was not identical to two previously described nitrogen-fixing species of the genus Vibrio, Vibrio
diazotrophicus and Vibrio natriegens.