ECOLOGICAL CONSIDERATIONS OF DIATOM CELL MOTILITY. I. CHARACTERIZATION OF MOTILITY AND ADHESION IN FOUR DIATOM SPECIES¹

Abstract

To better determine the ecological role of motility in pennate diatoms, we quantitatively characterized several motility and adhesion properties of four species of motile pennate diatoms (Craticula sp., Pinnularia sp., Nitzschia sp., and Stauroneis sp.) isolated from the same freshwater pond. Using computer‐assisted video microscopy, we measured speed, size/shape, functional adhesion, path curvature, and light sensitivity for these species, each of which shows a distinctive set of motile behaviors. The average speeds of Stauroneis, Pinnularia, Nitzschia, and Craticula cells are 4.6, 5.3, 10.4, and 10.0 μm · s−1, respectively. Craticula and Nitzschia cells move in a relatively straight path (<4 degrees rotation per 100 μm movement), Stauroneis exhibits minor rotation (about 7 degrees per 100 μm movement), and Pinnularia rotates considerably during movement (about 22 degrees per 100 μm moved). Functional adhesion (as measured by the release rate of attached cells from the underside of an inverted coverslip) shows a half time for cell release of approximately 50 min for Craticula, 192 min for Pinnularia, and >1 day for Nitzschia and Stauroneis. Direction reversal at light/dark boundaries, which appears to be the main contributor to diatom Phototaxis, is most responsive for Craticula, Pinnularia, and Nitzschia at wavelengths around 500 nm. Craticula and Nitzschia cells are the most sensitive in the photophobic response, with over 60% of these cells responding to a 30‐1x light/dark boundary at 500 nm, whereas Pinnularia cells are only moderately responsive at this irradiance, showing a maximal response of approximately 30% of cells at 450 nm. Stauroneis cells, in contrast, had a maximal photosensitive response at 700 nm, suggesting that this cell type may use a different response mechanism than the other three cell types. In addition, Craticula and Pinnularia show a net movement out of the light spot when illuminated at 650 nm, whereas Stauroneis shows a net movement out of the light spot when illuminated at 450 nm. Such quantitative characterizations of species‐specific responses to environmental stimuli should give us a firm foundation for future studies analyzing the behavior of interspecies diatom competition for limited light or nutrient resources.

High Energy Irradiation at the Leading Tip of Moving Diatoms Causes a Rapid Change of Cell Direction

“…The samples were washed several times with distilled H20 and then transferred to small polystyrene Petri dishes containing a defined Diatom Medium [DM: 300 pM Ca(NO&, 400 pM KH4P04, 100 pM MgS04, 0.01% v/v saturated Na2Si03 at pH 8.5, 1 pM FeSO4, 0.1 pM MnC12, 5% v/v soil extract, 1 pg mI-' niacinamide, lpg mI-' thiamine, 0.1 pg mI-' biotin, and 1 pg mL-' B12] at pH 6.7 (Cohn & Weitzell 1996). Cell cultures were incubated at 1Cb12"C on a 10:14 h LD cycle to simulate winter conditions when diatoms are most abundant in our source pond.…”

“…For motile pennate diatoms, these responses include the ability of cells to accumulate within areas of low to moderate intensity light, diurnal cycles of movement within the sediment, and avoidance of areas with high intensity light (Round & Palmer 1966, Harper 1977, Nultsch & Hader 1988, Hader & Hoiczyk 1992. These behaviours appear to be driven mainly by photophobic responses which change the direction of diatom movement, either as a step-down response (moving into the light) at low to moderate light levels or a step-up response (away from the light) at high light levels (Nultsch & Hader 1988, Cohn & Weitzell 1996.…”

“…The photo-induced movements are sensitive to both the wavelength and irradiance level of the light (Nultsch 1971, 1975, Wenderoth 1982a, b, 1983, 1984, and are species-specific (Cohn & Weitzell 1996), suggesting that differential light responses may be important in interspecific competition. For example, regulation of motile behaviours and light responses may be partially responsible for the immigration and stratification of diatom species during the development of benthic algal communities (Hudon & Bourget 1983, Stevenson & Peterson 1989, Stevenson et al 1991, Johnson et al 1996.…”

Effects of shallow and deep sediment disturbance on whole-stream metabolism in experimental sand-bed flumes

“…Pennate diatoms, the dominant algae in our experimental flumes (unpublished data), can actively move to the surface of sandy sediments (Stevenson, 1996). Gliding speeds in the range of 60-600 lm min -1 have been measured (Cohn & Weitzell, 1996, Gupta & Agrawal, 2007, Du et al, 2010. If one assumes an extreme scenario in which a cell moves upwards from 4 cm depth along a path defined by a sphere packing of idealized sand grains with a diameter of 200 lm, then a motile alga would need between 2 and 18 h (depending on gliding speed) to return to the surface.…”

Influence of light quality and gassing on the vertical migration of diatoms inhabiting the Wadden Sea

“…Wenderoth and IWF 1983). The threshold values which have to be exceeded or fallen below are species-specific (Nultsch 1956;Cohn and Weitzell 1996). Of major importance in diatoms (as photosynthesizing organisms) are light-regulated migratory reactions, i.e.…”