Occurrence of nitrogen fixation among Vibrio spp.

Virtually all Vibrio spp. known and available in culture collections and several newly isolated Vibrio sp. were tested for their ability to fix molecular nitrogen, using the acetylene reduction technique, the fixation of the heavy isotope ¹⁵N, and by growth on media devoid of combined nitrogen. Among the 27 species tested, four, including V. diazotrophicus, proved to be nitrogenase-positive. The potential of nitrogen fixation was now also discovered in V. natriegens, V. pelagius and V. cincinnatiensis. Among the 9 newly isolated strains, 4 were nitrogenase-positive. These strains were classified as V. diazotrophicus on the basis of DNA homology studies. Nitrogenase was only induced during growth under anaerobic conditions. Dissolved oxygen as low as 1 M inhibited nitrogenase completely. This inhibition at low oxygen concentration, however, was reversible. 50–100 M dissolved oxygen inhibited nitrogenase irreversibly.This work was carried out at Geomicrobiology Division, the University of Oldenburg, FRG