The Role of Extracellular DNA in Microbial Attachment to Oxidized Silicon Surfaces in the Presence of Ca2+ and Na.

Ana L Morales-García,Rachel Walton,Jamie T Blakeman,Stephen A Rolfe,Colin L Freeman,Steven A Banwart,Mark Geoghegan,John H Harding

doi:10.1021/acs.langmuir.1c01410

Ana L Morales-García, Rachel Walton + Show 6 more

Open Access

https://doi.org/10.1021/acs.langmuir.1c01410

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Abstract

Attachment assays of a Pseudomonas isolate to fused silica slides showed that treatment with DNaseI significantly inhibited cellular adsorption, which was restored upon DNA treatment. These assays confirmed the important role of extracellular DNA (eDNA) adsorption to a surface. To investigate the eDNA adsorption mechanism, single-molecule force spectroscopy (SMFS) was used to measure the adsorption of eDNA to silicon surfaces in the presence of different concentrations of sodium and calcium ions. SMFS reveals that the work of adhesion required to remove calcium-bound eDNA from the silicon oxide surface is substantially greater than that for sodium. Molecular dynamics simulations were also performed, and here, it was shown that the energy gain in eDNA adsorption to a silicon oxide surface in the presence of calcium ions is small and much less than that in the presence of sodium. The simulations show that the length scales involved in eDNA adsorption are less in the presence of sodium ions than those in the presence of calcium. In the presence of calcium, eDNA is pushed above the surface cations, whereas in the presence of sodium ions, short-range interactions with the surface dominate. Moreover, SMFS data show that increasing [Ca2+] from 1 to 10 mM increases the adsorption of the cations to the silicon oxide surface and consequently enhances the Stern layer, which in turn increases the length scale associated with eDNA adsorption.

Highlights

Biofilms are widespread in the natural environment with most microbial cells attached to a surface rather than existing in the planktonic form
■ RESULTS Cell Attachment to Fused Silica Surfaces Is Facilitated by Extracellular different charge ratio of the Si−O (DNA)
Initial experiments sought to characterize the properties of extracellular DNA (eDNA) produced by Pse[1] and determine the key properties of the eDNA required for cell attachment to fused silica

Summary

Introduction

Biofilms are widespread in the natural environment with most microbial cells attached to a surface rather than existing in the planktonic form. Many biopolymers can act as a “glue” including polysaccharides, proteins, phospholipids, and extracellular DNA (eDNA).[2] Extracellular DNA plays a key role in the structure of many biofilms.[3,4] In one study of freshwater bacteria, 25 out of 110 isolates produced large amounts of eDNA.[5] For example, Pseudomonas sp. Meshes of eDNA have been reported in Staphylococcus aureus.[6,7] In contrast, in Pseudomonas aeruginosa, eDNA is associated with specific biofilm structures such as the stalks within mushroom-shaped towers,[8] during trail formation in biofilm expansion,[9] and with type IV pili.[10] The roles played by eDNA in biofilms are varied and can depend on interactions with other EPS components

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