Figure 1.38 Number of free diatoms (blue) and the number of diatoms bound in colonies (red) over 24 days. A yellow bar indicates the phases of bright light.
Figure 1.39 Total number of diatoms (red) with exponential fitting (blue).
Figure 1.40 Number of diatoms in motion over the last 10 observation days.
Errors in this analysis mainly occur when diatoms do not continually move during the analyzed period (for example, by connecting to a colony) or when they cross the boundaries of the region of interest. Figure 1.40 shows the number of moving diatoms over the last 10 days of the observation time. Apparently, the movement activity drops off quickly after the beginning of the light phase. One can observe Cymbella species, which show high movement activity during the whole light phase. It can be assumed that there is a strong dependence on the light intensity.
Colonies in Petri dishes are growing on a flat surface. On leaf surfaces or stones with unevenness which is smaller than the size of the diatoms, similar conditions could exist. In three-dimensional fibrous nettings, heaps or spherical colonies would be more likely to form. Diatoms escaping from dense populations must then move along thin filaments. Such netting was found in a sample from a pond where nutrient solution was added. A migration from and to colonies over the fibers could be observed. In this topology, a much lower fluctuation and less exchange between colonies are to be expected, as the colonies only offer possibilities for moving in and out at a few points.
1.7 Conclusion
The present study consolidates observations on motile pennate diatoms in different environments. With respect to the movement on a smooth solid substrate, it is demonstrated that the inclusion of the orientation of the apical axis as a degree of freedom is useful in the analysis of trajectories, as it provides information about the point of the valve where the diatom touches the substrate. This point is subject to statistical fluctuations and is at different positions in Navicula sp. and Craticula cuspidata. Methodically independent observations confirm these results and allow investigating the question of the processes of motion reversal.
In and on biofilms, pennate diatoms move with significantly different motion patterns and speeds. Adhesion to the surface of the viscoelastic film is sufficient to enable movement similar to that on a solid substrate. When the activity of the raphe branches is opposite, distortions of a biofilm marked with particles can be observed. Diatoms inside the biofilm without contact to the substrate rotate around changing axes.
At the water-air interface, Pinnularia gentilis can perform active movements without coupling to a substrate, which is interpreted as the interaction between raphe activity and the surrounding water. Significantly different phenomena occur in Nitzschia sigmoidea. Hydrophobia of unknown origin at the apices gives this species buoyancy and leads to the formation of connected dynamic patterns. A deeper understanding of hydrophobia and dynamic pattern formation requires further investigation.
The formation of colonies in Cymbella lanceolata can be described on the basis of elementary processes and their light dependence. They enable the exchange of diatoms between colonies, whose frequency depends on the topology of the environment.
References
[1.1] Aumeier, C. and Menzel, D., Secretion in the Diatoms, in Secretions and Exudates, in: Biological Systems, J.M. Vivanco and F. Baluška (Eds.), pp. 221–250, Springer, Berlin Heidelberg, 2012.
[1.2] Bertrand, J., Mouvements des diatomées. II - Synthèse des mouvements. Cryptogam. Algol., 13, 49–71, 1992.
[1.3] Bertrand, J., Les Diatomées et la tension superficielle: un outil de recherche et de démonstration [movie], in: Association des Diatomistes de Langue Francaise, du 12 au 17 Septembre 1999, 18eme Collogue, Nice, France, 1999.
[1.4] Bertrand, J., Mouvements des diatomées VIII: synthèse et hypothèse. Diatom Res., 23, 1, 19–29, 2008.
[1.5] Bondoc, K.G., Heuschele, J., Gillard, J., Vyverman, W., Pohnert, G., Selective silica-directed motility in diatoms. Nat. Commun., 1–6, 2016.
[1.6] Bondoc, K.G., Lembke, C., Vyverman, W., Pohnert, G., Searching for a Mate: Pheromone-Directed Movement of the Benthic Diatom Seminavis robusta. Microb. Ecol., 72, 287–294, 2016.
[1.7] Cohn, S.A., Photo-stimulated effects on diatom motility, in: Photomovement, D.P. Häder and M. Lebert (Eds.), pp. 375–401, Elsevier, Amsterdam, 2001.
[1.8] Consalvey, M., Paterson, D.M., Underwood, G.J.C., The ups and downs of life in a benthic biofilm: Migration of benthic diatoms. Diatom Res., 19, 2, 181–202, 2004.
[1.9] Donlan, R.M., Biofilms: microbial life on surfaces. Emerging Infect. Dis., 8, 9, 881–890, 2002.
[1.10] Edgar, L.A., Diatom locomotion, computer assisted analysis of cine film. Br. Phycol. J., 14, 83–101, 1979.
[1.11] Edgar, L., Diatom locomotion: a consideration of movement in a highly viscous situation. Br. Phycol., 17, 243–251, 1983.
[1.12] Edgar, L.A. and Pickett-Heaps, J.D., The mechanism of diatom locomotion. I. An ultrastructural study of the motility apparatus. Proc. R. Soc. B, 218, 331–343, 1983.
[1.13] Fabbri, S. and Stoodley, P., Mechanical properties of biofilms, in: The perfect slime, H.-C. Flemming, T. Neu, J. Wingender (Eds.), pp. 153–177, IWA Publ., London, 2016.
[1.14] Fauvel, P. and Bohn, G., Le rythme des marées chez les diatomée littorales. C. R. Séances Soc. Biol., 62, 121–123, 1907.
[1.15] Frenkel, J., Vyverman, W., Pohnert, G., Pheromone signaling during sexual reproduction in algae. Plant J.: Cell Mol. Biol., 79, 632–644, 2014.
[1.16] Gutiérrez-Medina, B., Guerra, A.J., Maldonado, A.I.P., Rubio, Y.C., Meza, J.V.G., Circular random motion in diatom gliding under isotropic conditions. Phys. Biol., 1–10, 2014.
[1.17] Häder, D.-P. and Hoiczyk, E., Gliding motility, in: Algal cell motility, M. Melkonian (Ed.), pp. 1–38, Chapman and Hall, New York, 1992.
[1.18] Harper, M.A. and Harper, J.T., Measurements of diatom adhesion and their relationship with movement. Br. Phycol. Bull., 3, 195–207, 1967.
[1.19] Harper, M.A., Movement and migrations of diatoms on sand grains. Br. Phycol. J., 4, 97–103, 1969.
[1.20] Harper, M.A., Movements, in: The Biology of Diatoms, D. Werner (Ed.), pp. 224–249, Blackwell, Oxford, 1977.
[1.21] Lauterborn, R., Untersuchungen über Bau, Kernteilung und Bewegung
