Role of extracellular DNA in initial bacterial adhesion and surface aggregation

Abstract

Extracellular DNA (eDNA) is an important component of the biofilm matrix. We show that removal of eDNA from Gram-positive bacteria reduces initial adhesion to and aggregation of bacteria on surfaces. Thermodynamic analyses indicated that eDNA introduces favorable acid-base interactions, explaining the effect of eDNA on aggregation and adhesion to the surface.

FIG. 1.

Example of the adhesion kinetics of S. mutans LT11 on a hydrophilic surface for 60 min in the presence (closed symbols) or absence (open symbols) of naturally occurring eDNA. The error bars denote the standard deviations over three experiments with separately grown bacteria. The lines indicate the initial deposition rates (j₀) calculated by linear least-square fitting.

FIG. 2.

Percentages of adhering bacteria involved in large aggregates 60 min after deposition onto a hydrophilic (panel A) or a hydrophobic DDS-coated (panel B) glass surface in the presence (white) or absence (striped) of naturally occurring eDNA. For the hydrophilic surface, control experiments were conducted with heat-inactivated DNase I (black), with results similar to those obtained with untreated samples. The error bars denote the standard deviations over three experiments with separately grown bacteria. Asterisks indicate statistically significant difference between data obtained in the presence or absence of eDNA (P < 0.05).

FIG. 3.

Lifshitz-Van der Waals (LW) and acid-base (AB) interactions involved in staphylococcal adhesion and surface aggregation to a hydrophobic and hydrophilic surface in the presence or absence of eDNA. The thickness of the arrows referring to the different interactions indicates their relative importance.