The type IV secretion system (T4SS) of the plant intracellular symbiont Sinorhizobium meliloti 1021 is required for conjugal transfer of DNA. However, it is not required for host invasion and persistence, unlike the T4SSs of closely related mammalian intracellular pathogens. A comparison of the requirement for a bacterial T4SS in plant versus animal host invasion suggests an important differenc...

In the symbiosis between rhizobia and legumes, host plants can form symbiotic root nodules with multiple rhizobial strains, potentially showing different symbiotic performances in nitrogen fixation. Here, we investigated the presence of mixed nodules, containing rhizobia with different degrees of mutualisms, and evaluate their relative fitness in the Sinorhizobium meliloti-Medicago sativa model...

It was found that S. meliloti strain SmA818, which is cured of pSymA, could not grow on defined medium containing only formate and bicarbonate as carbon sources. Growth experiments showed that Rm1021 was capable of formate/bicarbonate-dependent growth, suggesting that it was capable of autotrophic-type growth. The annotated genome of S. meliloti Rm1021 contains three formate dehydrogenase genes...

The long-term maintenance of specialized mutualisms remains an evolutionary puzzle. Recent focus has been on factors governing the stability of these mutualisms, including sanctions by the host, partner choice, and coevolutionary constraint, that is, the genetic correlation (r(G)) between fitness of both partners. So far these studies have been typically carried out in a single environment. Her...

During the course of the development of nitrogen-fixing root nodules induced by Sinorhizobium meliloti on the model plant Medicago truncatula, tubules called infection threads are cooperatively constructed to deliver the bacterial symbiont from the root surface to cells in the interior of the root and developing nodule. Three-dimensional reconstructions of infection threads inside M. truncatula...

Sinorhizobium meliloti requires exopolysaccharides in order to form a successful nitrogen-fixing symbiosis with Medicago species. Additionally, during early stages of symbiosis, S. meliloti is presented with an oxidative burst that must be overcome. Levels of production of the exopolysaccharides succinoglycan (EPS-I) and galactoglucan (EPS-II) were found to correlate positively with survival in...

Transgenic alfalfa (Medicago sativa L. cv Regen) roots carrying genes encoding soybean lectin or pea (Pisum sativum) seed lectin (PSL) were inoculated with Bradyrhizobium japonicum or Rhizobium leguminosarum bv viciae, respectively, and their responses were compared with those of comparably inoculated control plants. We found that nodule-like structures formed on alfalfa roots only when the rhi...