Motility of the mudflat diatom Cylindrotheca closterium (Bacillariophyceae): Behavior, physiology and ecology

Diatoms are the most ubiquitous group of microalgae in fine sediments of mudflats. Cylindrotheca closterium is a raphid diatom widely distributed in mudflat assemblages which has been attributed to its ability to move and position itself within the biofilm using gliding movements. Detailed study of C. closterium using video microscopy revealed several previously unknown movement modalities including corkscrew gliding and non-gliding movements such as: pirouette, pivot, rock and roll, rollover, and simultaneous pirouette and gliding. These cell movements may have important ecological implications in mudflat biofilm ecology.;Short-term responses to salinity change include dramatic alteration in movement modalities in hyposaline conditions, and cessation of motility in extreme hypersaline environments. Modality changes occurred within five seconds in response to hypersaline conditions and were reversible. Salinity changes resulted in progressive reduction in gliding movement and increased non-gliding modalities accompanied by changes in the HB (hot bicarbonate)- and EDTA (ethylenediaminetetraacetic acid)-soluble fractions of extracellular polymeric substances (EPS) as evidenced by a general increase in carbohydrate content, Con A-FITC (concanavalin A-fluorescein isothiocyanate) positive labeling, and change in monosaccharide composition. Sodium and chloride ions were essential for movement and substituting alternative sodium or chloride salts at osmolarity equivalent to normal seawater caused altered movements. This suggests that both osmotic and ionic aspects of salinity changes influence diatom osmoacclimation and movement. Exposure to known inhibitors of diatom gliding such as latrunculin A (actin-assembly inhibitor) and butanedione monoxime (myosin ATPase inhibitor) resulted in a reversible total inhibition of all movement modalities indicating that gliding and non-gliding movements may be driven by an actin-myosin system. The sodium ionophore, monensin, stopped gliding with concomitant increase in non-gliding movements, indicating that the latter modalities are not dependent on a sodium motive force. Electron transport uncouplers and inhibitors of polysaccharide and microtubule assembly decreased gliding and promoted non-gliding modalities suggesting that non-gliding modalities exhibited during unfavorable conditions are less dependent on these cellular processes.;The movement responses of C. closterium in response to environmental changes, accompanied by modifications in EPS, may form part of an adaptive strategy to survive in mudflats and could be useful as bioindicators of environmental changes.