Binding of 18F by cell membranes and cell walls of Streptococcus mutans

Area of Science:

• Microbiology
• Biochemistry
• Radiochemistry

Background:

• Oral bacteria, such as Streptococcus mutans, are key players in dental caries.
• Understanding bacterial cell envelope interactions with ions is crucial for developing targeted therapies.
• Fluoride, particularly the radioisotope Fluorine-18 (18F), has applications in diagnostics and potentially therapeutics.

Purpose of the Study:

• To investigate the binding characteristics of Fluorine-18 (18F) to isolated cell membranes and cell walls of oral bacteria.
• To determine factors influencing 18F binding, including pH, calcium ions, and enzymatic treatments.
• To quantify the binding capacity of bacterial cell envelopes for 18F.

Main Methods:

• Assaying 18F binding to isolated cell envelopes (membranes and walls) of Streptococcus mutans GS-5 and other oral bacteria.
• Investigating the effects of calcium ions (Ca2+), pH, and varying 18F concentrations on binding.
• Evaluating the impact of enzymatic pretreatments (RNase, DNase, trypsin) and sodium dodecyl sulfate (SDS) on 18F binding.
• Quantifying 18F binding using saturated assay systems and comparing binding capacities of cell membranes versus cell walls.

Main Results:

• 18F binding to bacterial cell envelopes was a slow process, reaching equilibrium within 60 minutes.
• Calcium ions (1 mM) significantly stimulated 18F binding.
• Binding was dependent on pH, 18F concentration, and binder dose.
• Enzymatic pretreatments with RNase, DNase, or trypsin did not affect 18F binding, but SDS significantly reduced it in cell membranes.
• Cell membranes of S. mutans GS-5 exhibited higher 18F binding capacity (10^15–10^16 atoms/mg dry weight) compared to cell walls (10^12–10^13 atoms/mg dry weight).

Conclusions:

• This study provides the first evidence of 18F binding to both cell membranes and cell walls of oral bacteria.
• Bacterial cell membranes demonstrate a significantly higher capacity for 18F binding than cell walls.
• The findings suggest potential mechanisms for fluoride interaction with oral microflora, relevant for understanding cariogenic processes and developing new diagnostic or therapeutic strategies.