Aggregation-deficient Mutants ofStreptococcus gordoniiChannon Altered in Production of Cell-surface Polysaccharide and Proteins

Abstract

Three spontaneous mutants of Streptococcus gordonii strain Channon were isolated that were deficient in cell-cell aggregation. The mutants had reduced cell-surface hydrophobicity, were impaired in saliva-mediated cell aggregation, and had greatly reduced amounts of ruthenium red stained material at their cell surfaces as visualised by electron microscopy. Alkali treatment of intact cells removed the ruthenium red-stained material together with a subset of polypeptides. One of these, a surface protein of molecular mass approximately 150 kDa, was present in the wild-type strain but not in the mutants. Parent and mutant strains secreted similar amounts of SSP-5 salivary agglutinin receptor, glucosyltransferase, and proteinase. The results implicate the ruthenium red-stained material and a 150-kDa polypeptide in hydrophobicity and aggregation properties of S. gordonii . Keywords: Oral streptococci; Streptococcus gordonii ; Aggregation; Saliva; Ruthenium red layer; Cell-surface proteins.