The Pure Culture Isolation of Ammonia-oxidizing Bacteria

Abstract

The autotrophic nature and agricultural importance of the ammonia-oxidizing bacteria has long stimulated the interest of bacteriologists. Studies of these organisms have been neglected, however, because of the difficulties in obtaining pure cultures. Such cultures were first described by Winogradsky (1890) and have since been obtained by several other investigators (Bonazzi, 1919; Heubtilt, 1928; Rubentschik, 1929; Nelson, 1931; Boltjes, 1935). Nevertheless, generally useful isolation methods have not been developed, as illustrated by the fact that no pure cul-tures were available to the writers in 1933. Since that time, Boltjes (1935) has reported an admirable study of the nitrifying bacteria and has isolated pure cultures of Nitrosomonasl and Nitrobacter. Inasmuch as the pertinent literature on the isolation of nitrifying bacteria has been reviewed recently by Winogradsky and Winogradsky (1933) and by Boltjes, it is necessary to point out only that Nelson's method of picking single cells is impractical, that Winogradsky (1935) in his recent work has neither sought nor possessed pure cultures and that Boltjes employed a micro-manipulator for picking his colonies. It was the purpose of the present investigation to develop a method of isolation which would require no special apparatus and in which the colonies could be picked by hand, so that the isola-tion could be made in bacteriological laboratories in general. The I One of these cultures was obtained through the kindness of Dr. H. Humfeld of the Bureau of Chemistry and Soils, United States Department of Agriculture. This strain nitrified actively and did not grow in broth. 653