Charged and hydrophobic groups are localised in the short and long tuft fibrils on Streptococcus sanguis strains

Colloidal gold is both negatively charged and hydrophobic and these properties were used to probe for positive charges and hydrophobic groups on two strains of Streptococcus sanguis (CR 311 and PSH lb), carrying lateral tufts of long and short fibrils. Large numbers of colloidal gold particles were attached to the short fibrils at pH 3–7, but at pH 5–4 and above gold did not attach to the short fibrils. Therefore the association between gold and the short fibrils is pH dependent. Between pH 3–7 and pH 9–0, gold particles attached to the ends of the long fibrils in a pH independent interaction, but not to the sides of the long fibrils. Cationised ferritin at pH 6–5 only attached to the ends of the short fibrils. Protease treatment reduced cell surface hydrophobicity of both strains, damaged the short fibrils of PSH lb and completely removed them from CR 311, and almost abolished gold binding to the short fibrils. However protease treatment did not alter gold binding to the ends of the long fibrils, indicating that protein was probably not present on the ends of these. The hypothesis is proposed that the ends of the long fibrils are hydrophobic and that the shqrt fibrils contain protein components that carry both positive and negative charges.

Key words:

• Cationised ferritin
• colloidal gold
• charge
• fibrillar tufts
• hydrophobicity
• Streptococcus sanguis

Notes

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