NITRATE AS A SOLE NITROGEN-SOURCE FOR METHANOCOCCUS-THERMOLITHOTROPHICUS AND ITS EFFECT ON GROWTH OF SEVERAL METHANOGENIC BACTERIA

Methanococcus (Mc.) thermolithotrophicus can use nitrate as the sole source of nitrogen, but four other species of methanogens cannot. The growth rate was similar on both nitrate and ammonium, but yields were 20-25% lower on nitrate. Mc. thermolithotrophicus, Methanobacterium thermoautotrophicum, and Methanobrevibacterium smithii were not inhibited by 20 m M nitrate, but Methanospirillum hungatei was inhibited 35%, and Methanosarcina barkeri was completely inhibited by 20 m M nitrate. When Mc. thermolithotrophicus was growing with nitrate as the sole source of nitrogen, growth was dependent on either molybdenum or tungsten, and the presence of both gave the best growth response; vanadium or chromium did not replace the requirement for these metals. Growth on ammonium could not be strictly demonstrated to require either of these metals, but both molybdenum and tungsten stimulated growth. © 1990 Springer-Verlag New York Inc.