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Nanomechanical properties of glucans and associated cell-surface adhesion of Streptococcus mutans probed by atomic force microscopy under in situ conditions

Sarah E. Cross^1,3,

Jens Kreth^4,

¹ UCLA Department of Chemistry and Biochemistry, Los Angeles, CA 90095, USA
² UCLA California NanoSystems Institute, Los Angeles, CA 90025, USA
³ UCLA Institute for Cell Mimetic Space Exploration, Los Angeles, CA 90095, USA
⁴ UCLA School of Dentistry, Los Angeles, CA 90095, USA
⁵ UCLA Molecular Biology Institute, Los Angeles, CA 90095, USA
⁶ Colgate-Palmolive, Piscataway, NJ 08855, USA

Correspondence
James K. Gimzewski
gim{at}chem.ucla.edu

This study used atomic force microscopy (AFM) to probe the local cell-surface interactions associated with the glucan polymers of Streptococcus mutans, the macromolecules most commonly attributed to the virulence of this microbe. In situ force spectroscopy was used to quantitatively probe and correlate cell-surface adhesion and dynamics with S. mutans UA140 wild-type and five glucosyltransferase mutants. Adhesion between the tooth surface and S. mutans is largely mediated by glucan production from sucrose via three glucosyltransferases (Gtfs; GtfB, GtfC and GtfD). To monitor the contribution of these particular Gtfs, isogenic mutants of S. mutans were constructed by specific gene inactivation and compared to the wild-type under sucrose and non-sucrose conditions. We report direct measurement of the mechanical properties associated with glucan macromolecules demonstrating that the local adhesion strength increases in a time-dependent process, with a decrease in the average number of rupture events. This finding suggests that S. mutans attaches mainly through glucans to surfaces in the presence of sucrose. In addition, a possible role of the Gtf proteins in sucrose-independent attachment is supported by the decreased adhesion properties of the GtfBCD mutant compared to the wild-type.

These authors contributed equally to this paper.