Intracellular accumulation of glycine betaine has been shown to confer an enhanced level of osmotic stress tolerance in Rhizobium meliloti. In this study, we used a physiological approach to investigate the mechanism by which glycine betaine is accumulated in osmotically stressed R. meliloti. Results from growth experiments, 14C labeling of intermediates, and enzyme activity assays are presente...

Rhizobia are a group of bacteria that form nodules on the roots of legume host plants. The sequenced genomes of the rhizobia are characterized by the presence of many putative insertion sequences (IS) elements. However, it is unknown whether these IS elements are functional and it is therefore relevant to assess their transposition activity. In this work, several functional insertion sequences ...

Cosmids containing hydrogen uptake genes have previously been isolated in this laboratory. Four new cosmids that contain additional hup gene(s) have now been identified by conjugal transfer of a Rhizobium japonicum 122DES gene bank into a Tn5-generated Hup(-) mutant and screening for the acquisition of Hup activity. The newly isolated cosmids, pHU50-pHU53, contain part of the previously isolate...

Using transposon Tn5-mediated mutagenesis, an essential Rhizobium meliloti nitrogen fixation (nif) gene was identified and located directly downstream of the regulatory gene nifA. Maxicell and DNA sequence analysis demonstrated that the new gene is transcribed in the same direction as nifA and codes for a 54-kilodalton protein. In Klebsiella pneumoniae, the nifBQ operon is located directly down...

Production of complex extracellular polysaccharides (EPSs) by the nitrogen-fixing soil bacterium Sinorhizobium meliloti is required for efficient invasion of root nodules on the host plant alfalfa. Any one of three S. meliloti polysaccharides, succinoglycan, EPS II, or K antigen, can mediate infection thread initiation and extension (root nodule invasion) on alfalfa. Of these three polysacchari...

Most species in the Leguminosae (legume family) can fix atmospheric nitrogen (N₂) via symbiotic bacteria (rhizobia) in root nodules. Here, the literature on legume-rhizobia symbioses in field soils was reviewed and genotypically characterised rhizobia related to the taxonomy of the legumes from which they were isolated. The Leguminosae was divided into three sub-families, the Caesalpinioideae, ...

In the Rhizobium-legume symbiosis, compatible bacteria and host plants interact through an exchange of signals: Host compounds promote the expression of bacterial biosynthetic nod (nodulation) genes leading to the production of a lipochito-oligosaccharide signal, the Nod factor (NF). The particular array of nod genes carried by a given species of Rhizobium determines the NF structure synthesize...