Surface physicochemistry and ionic strength affects eDNA's role in bacterial adhesion to abiotic surfaces

Extracellular DNA (eDNA) is an important structural component of biofilms formed by many bacteria, but few reports have focused on its role in initial cell adhesion. The aim of this study was to investigate the role of eDNA in bacterial adhesion to abiotic surfaces, and determine to which extent eDNA-mediated adhesion depends on the physicochemical properties of the surface and surrounding liquid. We investigated eDNA alteration of cell surface hydrophobicity and zeta potential, and subsequently quantified the effect of eDNA on the adhesion of Staphylococcus xylosus to glass surfaces functionalised with different chemistries resulting in variable hydrophobicity and charge. Cell adhesion experiments were carried out at three different ionic strengths. Removal of eDNA from S. xylosus cells by DNase treatment did not alter the zeta potential, but rendered the cells more hydrophilic. DNase treatment impaired adhesion of cells to glass surfaces, but the adhesive properties of S. xylosus were regained within 30 minutes if DNase was not continuously present, implying a continuous release of eDNA in the culture. Removal of eDNA lowered the adhesion of S. xylosus to all surfaces chemistries tested, but not at all ionic strengths. No effect was seen on glass surfaces and carboxyl-functionalised surfaces at high ionic strength, and a reverse effect occurred on amine-functionalised surfaces at low ionic strength. However, eDNA promoted adhesion of cells to hydrophobic surfaces irrespective of the ionic strength. The adhesive properties of eDNA in mediating initial adhesion of S. xylosus is thus highly versatile, but also dependent on the physicochemical properties of the surface and ionic strength of the surrounding medium.Peer reviewe

Effect of DNase on the adhesion of <i>S. xylosus</i> to glass surface in flow cell.

<p>Black bars indicate untreated cells. Crossed bars indicate cells treated with DNase (50 µg/ml), washed and resuspended in PBS. White bars indicate cells resuspended in PBS containing DNase (50 µg/ml). Asterisk indicates statistically significant differences between samples with and without eDNA (t-test, *p<0.05, **p<0.01).</p

Effect of ionic strength and surface chemistries on eDNA mediated adhesion of <i>S. xylosus</i>.

<p>Black bars indicate untreated cells. White bars indicate cells treated with DNase. Experiments were carried out at low (I = 0.015 M), medium (I = 0.19 M) and high (I = 0.70 M) ionic strength. Values are average of 3 replicates (error bars  =  S.D.) Asterisk indicates statistically significant differences between samples with and without eDNA (t-test, *p<0.05, **p<0.01).</p

Cell surface properties with and without eDNA.

<p>Water contact angle and zeta potential measurements of <i>S. xylosus</i> cells with and without eDNA.</p><p>*indicates statistically significant difference (t-test, p<0.05).</p