Characteristics of a nitrogen-fixing methanotroph,Methylocystis T-1

Abstract

A methane-oxidizing bacterium capable of nitrogen fixation was isolated from soil taken from an area which leaked methane gas. Strain T-1 was a catalase and oxidase-positive, gram-negative straight rod-shaped strictly aerobic bacterium which formed lipid cysts and type II intracytoplasmic membranes. The organism was a microaerophilic nitrogen-fixing methanotroph. Strain T-1 is considered to be classified intoMethylocystis. The organism evolved hydrogen gas when grown in the nitrogen-free medium of atmospheric oxygen concentrations of 1.5% or more. Below this level, however, hydrogen gas was not evolved. In addition to methanol, formaldehyde and formate, ethanol, acetate and hydrogen gas served as oxidizable substrates for the acetylene reduction test. H₂-stimulated nitrogenase activity was limited in a very narrow range of oxygen concentration and not detected at 2% O₂. With acetate as the substrate, however, about an 80% of the maximum acetylene reduction activity was detected at 2% O₂. These results suggest that strain T-1 is capable of recycling the hydrogen gas evolved during nitrogen fixation under low partial pressures of O₂.