Characterization of exopolysaccharide isolated from Prevotella nigrescens

Abstract

Previous studies have shown that exopolysaccharide (EPS) from Prevotella intermedia is related to the invasiveness of bacteria. In this study, we attempted to purify EPS derived from Prevotella nigrescens strains 22 and 23, and compared these EPSs with that from P. intermedia. We also isolated an EPS^- strain (designated as strain 328) from the EPS^+ strain (strain 22) by treatment with ethidium bromide, and examined the geno- and phenotypic characteristics of these strains. Purified EPSs were primarily neutral sugar consisting of mannose as a major component. Both EPSs contained glucose, galactose, arabinose and xylose. Fructose (15.8μg/mg) was detected in EPS from strain 22, but not in that from strain 23. The ratio of mannose to glucose was greater in the EPSs from P. nigrescens strains 22 (20:1) and 23 (25:1) than in that from the P. intermedia strain 17 (5:1). The plasmid bands and enzymatic activities were the same for both strains 22 and 328, suggeesting that the gene controlling the production of EPS was not on these plasmids. We were unable to detect phage particles after irradiation with ultraviolet light. We also failed to detect differences in the restriction fragment length when we performed polymorphism analysis of the chromosomal DNA of both strains using Not I and Bgl I. Therefore, we examined the phenotypic characteristics and did SDS-PAGE analysis. Scanning electron microscopy revealed net-like structures around the cells of strain 22, but not around those of strain 328.This supports the results of Nakatani et al. The hemagglutinating activity of strain 328 was greater, indicating that EPS tends to interfere with hemagglutination rather than mediate it. Although other characteristics of the two strains, such as carbohydrate fermentation, enzyme production and hemolysis, were quite similar, the SDS-PAGE patterns revealed that strain 328 lacks the 52kDa protein. These results coloectively suggest that this 52kDa protein may control the production of EPS.