The development of nitrogen-fixing nodules of the Rhizobium-legume symbiosis, especially the early stages of root hair deformation and curling, infection thread formation, and nodule initiation, has been well studied from a genetic standpoint. In contrast, the factors important for the colonization of surfaces by rhizobia, including roots-an important prerequisite for nodule formation-have not been as thoroughly investigated. We developed conditions for analyzing the ability of two fast-growing rhizobia, Sinorhizobium meliloti and Rhizobium leguminosarum bv. viciae, to produce biofilms on abiotic surfaces such as glass, plastic microtiter plates, sand and soil as a prelude to characterizing the genes important for aggregation and attachment. Factors involved in adherence to abiotic surfaces are likely to be used in rhizobial attachment to legume root cells. In this report, we show that S. meliloti exopolysaccharide-deficient mutants as well as exopolysaccharide overproducers exhibit reduced biofilm phenotypes that show parallels with their nodulation abilities. We also investigated two flagella-less S. meliloti mutants and found them to have reduced biofilming capabilities. To investigate whether there was a symbiotic phenotype, we tested one of the Fla- mutants on two different S. meliloti hosts, alfalfa and white sweetclover, and found that nodule formation was significantly delayed on the latter.

Biofilms are structured communities of bacterial cells enclosed in a self-produced polymeric matrix and adherent to an inert or living surface; they have clinical, industrial and environmental impacts. Biofilms that are established by bacteria on plants are found on the surfaces of roots, leaves, seeds and internal vascular tissues where the microbes live in commensal, mutualistic or parasitic/pathogenic associations with their host. The study of the structure of plant-associated biofilms has been considerably helped by the development of techniques using fluorescent markers coupled with confocal scanning laser microscopy as well as scanning electron microscopy. We review several of these techniques as well as some of the research that has dealt with plant-associated biofilms. Our investigations focus on biofilm formation in the early stages of the Rhizobium -legume symbiosis, in which Gram-negative rhizobia provide fixed nitrogen to a host legume, and in return, the legume provides carbon-containing molecules. Because root colonization is an important early step in the establishment of the nitrogen-fixing symbiosis, we looked at Sinorhizobium meliloti attachment and biofilm establishment on the roots of its legume hosts, Medicago sativa L. and Melilotus alba Desr. We also examined biofilm formation by Rhizobium leguminosarum bv. viciae on the roots of Arabidopsis thaliana (L.) Heynh., a non-legume and non-host. Our ultimate goal is to characterize the rhizobial genes involved in aggregation and attachment to roots because several of these appear to be shared in biofilm formation and rhizobial entry of legume root cells.

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This case shows the clinical course of a patient with an acute, massive dabigatran overdose with no significant clinical consequences. Currently, there is no ideal method to monitor anticoagulation levels; there is no pharmacologic reversal method, and hemodialysis is an undesirable treatment option.