The Stability of Cultures of Rhizobium

Abstract

The data to be presented here bear primarily on the relationships of six types of cultures, derived from clover or pea nodules, or stock cultures of Rhizobium trifolii or R. leguminosarum. These six types, while they were derived from sources which might lead one to suspect their identity with the clover and pea nodule organisms, nevertheless possessed cultural characteristics markedly different from those of the rhizobia. A number were chromogenic, and some produced only negligible amounts of gum. These facts were considered worthy of further investigation, for they pointed to the possibility of radical changes in the root-nodule organisms which, if properly understood, might help to explain the sudden losses in infective power which are known to occur and the fluctuations in nitrogen-fixing ability when in association with leguminous plants. The transformations, one to another, of the six abnormal types of organisms and of the normal type as treated in this paper, coupled with the presence of filterable forms, are suggestive of dissociation phenomena as described by those who have worked with other organisms. Previous citations of cultural variation however among the species of Rhizobium have been few. With minor modifications, only one type of colony for each crossinoculation group has been recognized. Deviations from these types have usually been looked upon by other workers as contaminations. The only unquestioned description of a rough form is that of Israilsky and Starygin (1930). No intermediates are mentioned. Our cultures do not conform to their description of a rough race.

Biochemical and Symbiotic Properties of the Rhizobia 1

“…Especially is this true, since a complex life cycle was once believed a basic explanation for the occurrence of diverse cell types. Only two outstanding contributions (27,228), as judged by precision in experimentation, have appeared in the last two decades.…”

“…Six divergent colony types obtained from nodules, filtered phage lysates, Berkefeld filtrates of rhizobial cultures and from single cell cultures grown in media vitiated by the protracted growth of the same and other cultures are described by Almon and Baldwin (27). Cultural aberrance was manifested by the lack of 19501 24ETHEL K. ALLEN AND 0.…”

“…Only occasional mention has been made of pigmented aberrant rhizobia resulting from lytic action (27,337).…”

“…The stability of their antigenic pattern is shown by an unaltered specificity subsequent to passage through plants other than their original hosts (127, 177). Serodiagnostic methods seemingly offer the only hope of proving the identity of dissociants which have lost their nodulating ability (27,150).…”

Variation within Strains of Clover Nodule Bacteria in Size of Nodule Produced and in “Effectivity” of Symbiosis

“…The dissociant type was morphologically indistinguishable from the normal type. Israilsky and Starygin (1930) have described what are probably similar rough variants, and Almon and Baldwin (1933) have also described variants in pigmentation and gumminess, but no studies of the effectivity of these variants were made.…”