ON THE CYTOLOGY AND SYNTHETIC CAPACITIES OF NATURAL AND ARTIFICIALLY PRODUCED BACTEROIDS OF RHIZOBIUM LEGUMINOSARUM

Abstract

Bacteroids of Rhizobium leguminosarum were formed rapidly in media containing 0.35% yeast extract, but not in media containing 0.1% yeast extract. Bacteroid production in the former media could be prevented by increasing the oxygen tension, suggesting that the limited oxygen supply within root nodules may be the principal factor initiating the natural formation of bacteroids. The artificially produced bacteroids were shorter and possessed a more irregular external morphology than bacteroids extracted from red root nodules of field pea, although the internal organization of both types of bacteroids was similar.During the development of bacteroids in laboratory media there was a rapid decrease in viable count and a concurrent increase in nephelos, although this increase was at a reduced rate compared to that exhibited by the normal small rod forms of rhizobia. These data indicate an inhibition of cellular division and a continued synthesis of at least certain protoplasmic constituents. In this connection the capacity to synthesize nucleic acids was similar in both artificially produced bacteroids and the small, rod types of the test organism, although some minor differences were found with bacteroids in situ within the nodules when nodule age varied.All types of bacteroids, whether they were within the nodule, had been extracted from the nodule, or were produced in laboratory media, suffered an impairment in the synthesis of protein and cell wall. Therefore, in several important respects, artificially produced and naturally produced bacteroids are physiologically similar. The alteration in wall-synthesizing capacity and the possible formation of limited amounts of abnormal wall material incapable of employing certain ions, such as Mg2+, for maintenance of rigidity is a likely cause of both the inhibition of cellular division and of the abnormal external morphology of these rather unusual cells.