Ultrastructural and physico-chemical heterogeneities of yeast surfaces revealed by mapping lateral-friction and normal-adhesion forces using an atomic force microscope

Abstract

Scanning force microscopy has been used to probe the surface of the emerging pathogenic yeast Candida parapsilosis, in order to get insight into its surface structure and properties at submicrometer scales. AFM friction images eventually show patches with a very strong contrast, showing high lateral interaction with the tip. Adhesion force measurement also reveals a high normal interaction with the tip, and patches show extraordinarily high pull off values. The tip eventually sticks completely at the center of the patches. While an extraordinarily high interaction is measured by the tip at those zones, topographic images show extraordinarily flat topography over those zones, both of which characteristics are consistent with a liquid-like area. High resolution friction images show those zones to be surrounded by microfibrillar structures, concentrically oriented, of a mean width of about 25 nm, structures that become progressively less defined as we move away from the center of the patches. No structure can be appreciated inside the zones of maximum contrast. Also some helical or ribbon-like structure can be resolved from friction images. There is not only an ordered disposition of the microfibrillar structures, but also the adhesion force increases radially in the direction towards the center of the patches. These structures responsible for the high adhesion are thought to be incipient-emerging budding zones. Microfibrillar structures are thought to represent the first steps of chitin biosynthesis and cell wall digestion, with chitin polymers being biosynthesized, associated with other macromolecules of the yeast cell wall. They can be also beta glucan helical structures, made visible in the zone of yeast division due to the action of autolysins. The observed gradient in surface adhesion and elastic properties correlates well with that expected from a biochemical point of view. The higher adhesion force measured could be either due to the different macromolecular nature of the patches, or to a mechanical adhesion effect due to the different plasticity of that zone. This work reveals the importance of taking into account the dynamic nature of the cell wall physico-chemical properties. Processes related to the normal cell-cycle, as division, can strongly alter the surface morphology and physico-chemical properties and cause important heterogeneities that might have a profound impact on the adhesion behavior of a single cell, which could not be detected by more macroscopic methods.

Oral bacterial adhesion forces to biomaterial surfaces constituting the bracket–adhesive–enamel junction in orthodontic treatment

“…3. It is unknown whether the non‐parametric distribution of the adhesion forces is caused by an inherent heterogeneity on the surface of a single cell (30), or whether it represents population heterogeneity. Adhesion forces of bacteria on material surfaces without a salivary conditioning film were almost 10‐fold higher than in the presence of a conditioning film ( P < 0.01), except for S. mutans NS and L. acidophilus JP on enamel.…”

Application of atomic force microscopy in bacterial research

“…One of the first approaches used to achieve strong attachment of microorganisms on a specific substrate required drying the sample, therefore limiting cell viability (Mendez-Vilas et al 2006a).…”

The impact of nanoscale chemical features on micron-scale adhesion: Crossover from heterogeneity-dominated to mean-field behavior

“…Long before the advent of chemical force spectroscopy to quantify chemical heterogeneities in systems including minerals [4][5][6][7], polymers [8][9][10], and biological cells [11][12][13][14], chemical heterogeneity was known to influence and even dominate colloidal forces and adhesion. For instance impurities on mineral surfaces often dictate aggregation [15][16][17][18], while small chemical features on polymer surfaces control contact angle and wetting [19][20][21], produce membrane fouling [22,23], enhance engineering adhesion [8,24,25], and determine biomaterial effectiveness [26][27][28][29][30].…”