The weathering of rocks is a process important for the understanding of soil formation as well as a general understanding of the interaction between litho- and hydrosphere. Phyllosilicates in general are of special importance for the understanding of weathering processes due to their abundance in rocks and soils. A common phyllosilicate in soils is chlorite, which has a structure composed of a combination of two distinct layers, the tetrahedral-octahedral-tetrahedral (TOT) and the interlayer (i.e., the octahedral layer between TOT layers). In this study, the morphology and dissolution of chlorite in pure water has been visualized using atomic force microscopy. Upon cleavage, the TOT layer shows atomically flat terraces and steps, while the interlayer presents strips and voids. In pure water, dissolution channels and equilateral, mono-oriented triangular etch pits form in the interlayer and lead to progressively increased solubilization. Dissolution channels are proposed to originate from structural defects, while a conceptual model is discussed to explain the presence of triangular etch pits. In this model, their formation is driven by the different reactivity of the two octahedral configurations along the etch pits. It is not currently known which of these is the most stable configuration, however we propose arguments that point toward a specific orientation. The conceptual model is supported by experimental data and is potentially applicable to all mineral structures constituted by continuous octahedral layers.

13 Chlorite has a structure composed of a combination of two distinct layers, the tetrahedral14 octahedral-tetrahedral (TOT) and the interlayer (i.e. the octahedral layer between TOT layers). 15 In this study, the morphology and dissolution of chlorite in pure water has been visualized 16 using Atomic Force Microscopy. Upon cleavage, the TOT layer shows atomically flat 17 terraces and steps, while the interlayer presents strips and voids. In pure water, dissolution 18

In this highlight, we discuss the multifaceted biology of mucins, where molecular architecture meets function, and especially the collective properties of mucin networks and gels that select adherent bacteria and restrict penetration.

The roots of many trees in temperate and boreal forests are sheathed with ectomycorrhizal fungi (EMF) that extend into the soil, forming intimate contact with soil minerals, from which they absorb nutrient elements required by the plants and, in return, are supported by the organic carbon photosynthesized by the trees. While EMF are strongly implicated in mineral weathering, their effects on mineral surfaces at the nanoscale are less documented. In the present study, we investigated the effects of symbiotic EMF on the topography of a chlorite mineral using atomic force microscopy. A cleaning protocol was successfully applied to remove fungal hyphae without altering the underlying mineral structure and topography. Examination of the exposed chlorite surface showed the presence of primary channels, of the order of a micron in width and up to 50 nm in depth, the morphology of which strongly indicates a fungal‐induced origin. Smaller secondary channels were observed extending from the primary channels and would appear to be involved in their enlargement. The presence of channels is the first nanoscale demonstration of the effects of fungal interaction, fuelled by plant photosynthate, on the topography of a chlorite mineral, and it provides clear evidence of the ability of EMF to enhance mineral dissolution.

The interaction between mycorrhizal fungi and minerals is of fundamental importance in affecting the geochemical carbon cycle and CO2 concentration in the atmosphere, alongside roles in soil creation and the release of nutrients. The symbiosis between the fungi and the plant, supported by photosynthesis in the host plant, has as one of its key features the interfacial zone where mineral and fungi come into contact. At this interface, the organism exudes a complex mixture of organic acids, chelating molecules, protons, and extracellular polysaccharide. In this review, examples will be given of recent Atomic Force Microscopy experiments to monitor the colonization of phyllosilicate minerals in sterile controlled microcosm environments containing only tree seedlings, mineral chips and mycorrhizal fungi. The surface activity of the colonizing fungal hyphae is extensive and complex. In complementary experiments involving exposure of minerals surfaces to single organic acids, it has been possible to monitor dissolution at the unit cell level and to extract activation energies for specific dissolution processes, for example 49 kJ mol(-1) for 100 mM oxalic acid acting upon a biotite sample. The link between these simpler model experiments and the whole microcosm studies is illustrated partly by observations of fungal-colonized mineral surfaces from microcosms after careful removal of the organism and biolayer. These mineral surfaces give clear indications of basal plane modification and fungal weathering.

This study explores the mechanical unfolding of elastic protein analogues as a function of temperature, in both H 2 O and D 2 O, using atomic force microscopy (AFM) force spectroscopy in a specially constructed AFM liquid cell. This represents the first time that the effect of D 2 O on protein flexibility has been investigated at the single molecule level by this technique. Model elastic peptides, R6, were encoded from synthetic genes expressed in Escherichia coli . The peptides possess short N‐ and C‐terminal domains with central repetitive domains containing 13 repeats of the motif PGQGQQ‐plus‐GYYPTSLQQ. These sequences mimic those in native high molecular weight subunit glutenin proteins which confer elasticity to bread dough. Fitting single molecule stretching events to the worm‐like chain model, allows determination of the molecular persistence length under various experimental conditions. The effect of increasing the temperature is to increase the persistence length of the peptide in both H 2 O and D 2 O, consistent with the expected “thermal softening” effect. However, the effect is significantly enhanced in D 2 O, in which the persistence length at 45°C is ∼25% greater than the value measured in H 2 O at the same temperature. Stronger intrapeptide H‐bonding due to isotopic substitution of hydrogen for deuterium is the most likely cause of the enhanced backbone rigidity. Microsc. Res. Tech. 74:170–176, 2011. © 2010 Wiley‐Liss, Inc.

We have used a direct imaging technique, in situ atomic force microscopy (AFM), to observe the dissolution of the basal biotite surface by oxalic acid over a range of temperatures close to ambient conditions, using a specially designed AFM liquid cell and non-invasive intermittent contact mode of operation. From the 3-dimensional nanometre-resolution data sets, we observe a process characterised by the slow formation of shallow etch pits in the (001) surface and fast growth of etch pits from the resulting steps, which represent proxies for the {hk0} surface. Measurements of dissolution rates as a function of temperature allow a determination of an apparent activation energy (Ea,app) for the process, via mass-loss calculations from image analysis. We obtain a value of Ea,app=49±2kJmol−1, which is consistent with separate calculations based on planar area etch pit growth, and measurements of etch pit perimeters, indicating that this value of Ea,app is representative of {hk0} surface dissolution. The measurement of etch pit perimeters also enables an estimation of apparent activation energy as a function of step density indicating substantially higher apparent activation energy, up to Ea,app=140kJmol−1, on extrapolation towards a pristine surface with no defects. We suggest that this higher value of Ea,app represents the slow formation of etch pits into the (001) surface.

Microcosms with Pinus sylvestris seedlings in symbiosis with the fungus mycorrhizal Paxillus involutus were established, and atomic force microscopy (AFM) was used to characterise plant photosynthate-driven fungal interactions with mineral surfaces. Comparison of images of the same area of the minerals before and after mycorrhizal fungal colonization showed extensive growth of hyphae on three different mineral surfaces – hornblende, biotite and chlorite. A layer of biological exudate, or biolayer, covered the entire mineral surface and was composed of globular features of diameter 10–80 nm, and the morphology of the biolayer differed among mineral types. Similar-sized components were found on the fungal hyphae, but with a more elongated profile. Biolayer and hyphae surfaces both appeared to be hydrophobic with the hyphal surfaces yielding higher maximal adhesive interactions and a wider range of values: the mean (± SE) adhesive forces were 2.63 ± 0.03 and 3.46 ± 0.18 nN for biolayer and hypha, respectively. The highest adhesion forces are preferentially localized at the hyphal surface above the Spitzenkörper region and close to the tip, with a mean interaction force in this locality of 5.24 ± 0.49 nN. Biolayer thickness was between 10 and 40 nm. The underlying mineral was easily broken up by the tip, in contrast to the native mineral. These observations of mineral surfaces colonised by mycorrhizal fungus demonstrate how fungal hyphae are able to form a layer of organic exudates, or biolayer, and its role in hyphal attachment and potential weathering of ferromagnesian silicates, which may supply nutrients to the plant.

Atomic force microscopy has been used to follow in real time the adsorption from solution of two of the gliadin group of wheat seed storage proteins onto hydrophilic (mica) and hydrophobic (graphite) surfaces. The liquid cell of the microscope was used initially to acquire images of the substrate under a small quantity of pure solvent (1% acetic acid). Continuous imaging as an injection of gliadin solution entered the liquid cell enabled the adsorption process to be followed in situ from zero time. For omega-gliadin, a monolayer was formed on the mica substrate during a period of approximately 2000 s, with the protein molecules oriented in parallel to the mica surface. In contrast, the omega-gliadin had a relatively low affinity for the graphite substrate, as demonstrated by slow and weak adsorption to the surface. With gamma-gliadin, random deposition onto the mica surface was observed forming monodispersed structures, whereas on the graphite surface, monolayer islands of protein were formed with the protein molecules in a perpendicular orientation. Sequential adsorption experiments indicated strong interactions between the two proteins that, under certain circumstances, caused alterations to the surface morphologies of preadsorbed species. The results are relevant to our understanding of the interactions of proteins within the hydrated protein bodies of wheat grain and how these determine the processing properties of wheat gluten and dough.

We have used Atomic Force Microscopy (AFM) to map the spatial distribution of epitopes in the peptide core of mucin glycoconjugates, and also their glycosylation. Using AFM in a physiological environment, and tips functionalised with antibodies against MUC-gene specific epitopes in the peptide core, and also with lectins which recognise terminal sugars, we mapped both single molecules and complex macromolecular structures. From the simultaneous topographic and force-spectroscopy data, the force-volume maps, we directly quantified the localization, number, and rupture force of recognition bonds on different epitopes of mucin molecules (Figure 1). The specificity of the interactions was confirmed using antibody-blocking peptides, and blocking sugars, and as expected, we observed a loading rate dependence of the unbinding strength. We have extended these single molecule measurements to more complex physiological gel systems, such as the soft gel layer of the tear film. Binding experiments confirmed the relative abundance of two sugars, previously established by chemical analysis of purified mucins. This comprehensive approach to single molecules and their macromolecular assembly provides an insight into extracellular configuration and packaging of mucins in a gel, and points towards new applications of AFM force mapping.

We have used Atomic Force Microscopy (AFM) in a force-measuring mode to map the specific locations of physiologically important channel proteins on the primary cilia of kidney epithelial cells. Primary cilia protrude from the apical membrane into the nephron cavity, function as a mechanochemical sensor, and are decorated with a rich variety of protein molecules. The distribution and role of channel proteins such as Polycystin-1 (PC-1) and Polycystin-2 (PC-2) are the subject of ongoing debate, related to Polycystic Kidney Disease (PKD) amongst others. Therefore we have adopted a multi-factorial microscopy approach to investigate the biophysical properties of the primary cilium. A combined AFM/confocal microscope has been used to compare the cilia (MDCK cell lines) AFM images, to those using immunofluorescence. Using imaging force spectroscopy we have correlated specific antibody-antigen recognition events with cilial topography, and observed the punctuate distribution of PC-1, PC-2 and β-Integrin, to nanometre resolution, an order of magnitude improvement on conventional immunofluorescence. We have also correlated AFM maps with elasticity and cilia persistence length. Finally we will demonstrate electrophysiological techniques to probe cilial mechanochemical sensor behaviour, correlated with AFM.