Nanostructure and nanomechanics of live Phaeodactylum tricornutum morphotypes

Abstract

The ultrastructure and mechanical properties of the fusiform, triradiate and ovoid morphotypes of Phaeodactylum tricornutum were investigated using atomic force microscopy. Using topographic imaging, we showed that the surface of the ovoid form is rougher than those of the two other specimens, and coated with an outer layer of extracellular polymers. Using spatially resolved force-indentation curves, we found that the valve of the ovoid form is about five times stiffer (Young modulus of approximately 500 kPa) than those of the other forms (approximately 100 kPa), a finding fully consistent with the fact that only the ovoid form has a silica valve, whereas the valves in the other two consist mostly of organic material. Notably, the girdle region of both fusiform and ovoid forms was five times softer than the valve, suggesting that this region is poor in silica and enriched in organic material. For the triradiate form, we showed the arms to be softer than the core region, presumably as a result of organelle localization. Last, we observed mucilaginous footprints of moderate stiffness (approximately 100 kPa) in the vicinity of ovoid diatoms, which we believe are secreted extracellular polymers.

Differential antibacterial activities of fusiform and oval morphotypes of Phaeodactylum tricornutum (Bacillariophyceae)

“…These are known to have strong antibacterial activity against our test bacterium, Staphylococcus aureus, as well as various marine bacteria (Desbois et al, 2008(Desbois et al, , 2009. Greater quantities of antibacterial free fatty acids in the extracts from fusiform cells may be due to fusiform cells containing more lipid as a proportion of cell composition than the oval cells or alternatively, the fusiform cells may be more fragile due to their shape and cell wall structure compared with the oval cell, which is more siliceous and rigid (Lewin et al, 1958;Borowitzka & Volcani, 1978;Francius et al, 2008).…”

“…It is well documented that the oval morphotype tends to occur on surfaces (Lewin et al, 1958;Hayward, 1968;Gutenbrunner et al, 1994;Tesson et al, 2009) and seems to dominate under conditions of stress or sub-optimal growth conditions (De Martino et al, 2007). The oval cells are motile, have siliceous valves and can produce exopolysaccharides; features that may help protect them when conditions are hostile (Lewin et al, 1958;Iwasa & Shimizu, 1972;Borowitzka & Volcani, 1978;Marsot & Houle, 1989;Hamm et al, 2003;Reynolds, 2007;Francius et al, 2008). By contrast, the fusiform morphs have an elongated spindle shape and possess intracellular vacuoles that provide buoyancy (Lewin et al, 1958;Borowitzka & Volcani, 1978).…”

“…By contrast, the fusiform morphs have an elongated spindle shape and possess intracellular vacuoles that provide buoyancy (Lewin et al, 1958;Borowitzka & Volcani, 1978). They are non-motile, lack siliceous valves and do not produce exopolysaccharides (Lewin et al, 1958;Borowitzka & Volcani, 1978;Marsot & Houle, 1989;Francius et al, 2008). Fusiform cells favour planktonic growth conditions and so often dominate over ovals in suspension cultures (Lewin et al, 1958;Hayward, 1968;Marsot & Houle, 1989;Gutenbrunner et al, 1994).…”

Structure and mechanical properties of selected protective systems in marine organisms

“…As there is an immense number of different profiles [122], it has been theorized that diatom species have evolved to defend against specific local predators [121]. The strength of the frustule itself varies by up to an order of magnitude along the diatom surface with the maximum strength approaching that of pure silica [123][124][125]. This variation has been associated with different regions of the exoskeleton's growth, with the highest strength region running along the center of the body, effectively creating a load-bearing beam of harder material (Fig.…”

Urea and nickel utilization in marine cyanobacteria as evaluated by incubation, proteomic, and uptake techniques

“…morphotype from this P.t. strain may explain this result on account of its distinguishing silica demand [22]. Ovoid cells of this P.t.…”