Probing the Adhesion of the Common Freshwater Diatom Nitzschia palea at Nanoscale

Abstract

Freshwater biofilms play an essential ecological role, but they also adversely affect human activities through undesirable biofouling of artificial submerged structures. They form complex aggregates of microorganisms that colonize any type of substratum. In phototrophic biofilms, diatoms dominate in biomass and produce copious amount of extracellular polymeric substances (EPSs), making them efficient early colonizers. Therefore, a better understanding of diatoms adhesive properties is essential to develop new anti-biofouling strategies. In this context, we used atomic force microscopy (AFM) to decipher the topography and adhesive mechanisms of the common freshwater diatom Nitzschia palea. Images taken in physiological conditions revealed typical ultrastructural features with a few nanometers resolution. Using single-cell force spectroscopy, we showed that N. palea strongly adheres to hydrophobic surfaces as compared to hydrophilic ones. Chemical force spectroscopy with hydrophobic tips further confirmed that the adhesion is governed by surface-associated hydrophobic EPS distributed in clusters at the frustule surface, and mostly composed of (glyco)-lipids as revealed by Raman spectroscopy. Collectively, our results demonstrate that AFM-based nanoscopy, combined with Raman spectroscopy, is a powerful tool to provide new insights into the adhesion mechanisms of diatoms.

“May the Force Be with You!” Force–Volume Mapping with Atomic Force Microscopy

“…The FVM mode can be used in combination with chemical force microscopy, an imaging strategy in which tips are functionalized to characterize chemically specific interactions with a sample. Multiple approaches have been developed for tip functionalization to design chemically specific tip–sample interactions, and representative examples of tip coatings that have been used with FVM are presented in Table …”

Physicochemical surface properties of Chlorella vulgaris: a multiscale assessment, from electrokinetic and proton uptake descriptors to intermolecular adhesion forces

“…Following the investigation of the electrostatic (and H-bonds) contributions of tip-to-cell adhesion, we proceed with the determination of the surface hydrophobicity of microalgae, described in literature as an important component of their interactions with their surrounding environment. 16,39,40 Accordingly, Fig. 6 reports CFM measurements performed on C. vulgaris surface using methyl-terminated thiol coated tips (tip-CH 3 )serving as hydrophobic probes 39,63,69 under similar pH and salt conditions as those prevailing in Fig.…”

“…Interestingly, variation of algae growth conditions 37 or environmental factors like pH 38 can change the nature of the dominant interactions in cell adhesion process. In that sense, recent studies have highlighted the crucial role played by algal surface hydrophobicity in cell/cell or cell/substrate interactions, 39 and in the adhesion of microalgae to air bubbles during harvesting flotation process. 28,40 Although both electrostatic and hydrophobic cell-wall properties can impact the stability of microalgae in aqueous media, very few techniques allow a proper quantitative assessment of their respective contributions depending on environmental conditions.…”

A methodological review on the characterization of microalgal biofilm and its extracellular polymeric substances

“…In addition to the techniques mentioned above, AFM is frequently integrated with Raman spectroscopy tools such as confocal resonance Raman microscopy (CRRM), tip‐enhanced Raman spectroscopy (TERS) and surface‐enhanced Raman spectroscopy (SERS) to provide valuable insights into the underlying cell and EPS adhesion mechanisms at different biofilm maturation phases (Keleştemur et al, 2018; Laviale et al, 2019; Lebedev et al, 2014; Schmid et al, 2008). Such combinations of topographical data, compositional data and microscopic data were worth‐mentioning to assist studies regarding quorum sensing, a chemical communication system or so‐called ‘molecular circuit’ in algal‐bacterial biofilm (Dow, 2021; Keleştemur et al, 2018).…”