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Mechanism of Nitrification by Arthrobacter sp

^a Laboratory of Soil Microbiology, Department of Agronomy, Cornell University, Ithaca, New York 14850

ABSTRACT

Resting cells of Arthrobacter sp. excrete as much as 60 µg of hydroxylamine-nitrogen per ml when supplied with ammonium. An organic carbon source in abundant supply is necessary for the oxidation. Resting cells oxidize hydroxylamine to nitrite and 1-nitrosoethanol, the former accumulating only when an exogenous carbon source is available. Cell-free extracts contain an enzyme catalyzing the formation of hydroxylamine from acetohydroxamic acid, a hydroxylamine-nitrite oxido-reductase, and an enzyme producing nitrite and nitrate from various primary nitro compounds. Nitrite is not produced from hydroxylamine by the extracts, but 1-nitrosoethanol is formed from hydroxylamine in the presence of acetate. 1-Nitrosoethanol is also produced from acetohydroxamic acid by these preparations. Nitrite was formed from hydroxylamine, however, by extracellular enzymes excreted by the bacterium.

¹ Present address: Department of Microbiology, Faculty of Agricultural Sciences, University of Ghent, Ghent, Belgium.