Rhizobium strain N 31 , isolated from the arctic legume Astragalus alpinus, nodulates sainfoin (Onobrychis viciifolia) as efficiently as strain SM-2, isolated from sainfoin. Nodule shape and tissue arrangement of 70-day-old plants infected by these two strains were examined. Sainfoin nodules formed by either strain N 31 or SM-2 were cylindrical, with indeterminate growth, and similar to those found on arctic legumes. However, in the active symbiotic zone of sainfoin nodules, bacteroids of strain N 31 were pleiomorphic or spherical and found individually or in groups of three, surrounded by the membrane envelope, whereas the bacteroids of strain SM-2 were elongated and enclosed in clusters of 3 to 12 by each membrane envelope. Thus, arctic strain N 31 affects the internal structure of sainfoin nodules. Nodules of arctic legumes A. alpinus, Oxytropis maydelliana, and Oxytropis arctobia, infected with either strain N 31 or SM-2, contained lipid droplets, while sainfoin nodules did not show such characteristics. This phenomenon seems specific to arctic legumes and it is not influenced by the origin of the nodulating strain.
A glutamyl-tRNA synthetase has been purified to homogeneity from Rhizobium meliloti, using reversed-phase chromatography as the last step. Amino acid sequencing of the amino-terminal region of the enzyme indicates that it contains a single polypeptide, whose molecular weight is about 54 000, as judged by SDS–gel electrophoresis. The primary structures of the amino-terminus region and of an internal peptide obtained by cleavage of the enzyme with CNBr have similarities of 58 and 48% with regions of the glutamyl-tRNA sythetase of Escherichia coli; these are thought to be involved in the binding of ATP and tRNA, respectively. The small amount of glutamyl-tRNA synthetase present in R. meliloti is consistent with the metabolic regulation of the biosynthesis of many aminoacyl-tRNA synthetases.Key words: glutamyl-tRNA synthetase, Rhizobium meliloti, purification, reverse-phase chromatography, amino acid sequence.
A correlation was established between peroxidase activity of soil and its capacity to transform 3,4-dichloroaniline, a breakdown product of several herbicides, to 3,3′,4,4′-tetrachloroazobenzene. Supplementation of soil by carbon and nitrogen sources for microbial growth stimulated both activities, and pointed to the microbial origin of soil peroxidases. Several peroxidase-producing bacteria, actinomycetes, and fungi were isolated from soil and were characterized. On the basis of its rapid growth and high peroxidase activity, a Geotrichum candidum strain was selected for further study. The culture filtrate of this organism exhibited both peroxidase and aniline oxidase activity. The highest per milligram dry weight activity of these enzymes was observed after cultivation on a mineral salts medium supplemented with soil extract and yeast extract.
Specific activities of the assimilatory and "regulatory" types of nitrate reductase were studied in 41 strains of Rhizobium meliloti having different symbiotic nitrogen fixation activities. Both nitrate reductase enzymes were present in very effective and ineffective strains and no significant correlation was found between the specific activities of the two enzymes and the dry matter yields of alfalfa obtained with the 41 strains. Measurements of the specific activities of the two nitrate reductase enzymes in the vegetative bacteria cannot be used as a rapid physiological test for the selection of very effective strains of R. meliloti.
