[The influence of acidic conditions on polar exopolysaccharides which bind Rhizobium japonicum to soybean root hairs].

The influence of acidic conditions on rhizobial exopolysaccharides (EPS) and their symbiotic association in host plants, were investigated. Light micrographs of soybean root hairs were taken with a Fahraeus' slide assembly after the inocubation of rhizobial bacteria; curled and swollen root hairs, and the typical shepherd's crook with an infection thread were observed. The colonizations of soybean root hairs by rhizobia were different under acidic and neutral conditions. For the Rhizobium japonicum strain USDA 136, and the indigenous acidic soil strain KR 23, morphologically distinct types of cells occurred in the acidic and neutral yeast-extract-mannitol broths. The surface structure of R. japonicum, as examined with the carbon replica and negative stain techniques, was rod shaped and polar flagellated only when the cells were incubated under neutral conditions. The materials which reacted with the ruthenium red positive reagent are in all likelihood an acidic EPS, and are believed to effect the adhesive properties of the cells. Bacterial polarity, which could be more readily observed under neutral conditions than under acidic conditions, was related to the distribution of EPS near one end of the bacteria. EPS was found to effect the initial step of polar attachment in the effective infection of host roots. By using DEAE-Sephacel ion exchange chromatography, the capsular polysaccharides from both strains of R. japonicum were also found to have different chemical components when observed in acidic and neutral cultures.