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Preface
Anyone who has peered into a microscope and observed the movement of diatoms knows they have witnessed an intriguing example of cellular biology. Unlike most other of their sister algae, this movement involves neither swimming through solution (like Euglena or Chlamydomonas) or amoeboid crawling of membrane and cytoplasm (like Synchroma). Surrounded by a hardened silicified cell wall, motile diatoms are still able to glide gracefully along surfaces while the cell protoplast remains contained within these ornate cell walls. As such, the mysteries involving this curious form of movement have been of interest for well over a hundred years, and models of many sorts have been proposed to explain it (see [1.20]).
Our hope is that this volume will help to not only convey our excitement about research in diatoms, but also demonstrate a variety of techniques and approaches currently used to understand some of the aspects of diatom movement. We have included chapters centering on a number of areas: detailed observation of movements [1.23] [1.43], cellular aspects of motility [1.5] [1.8], ecology and environmental interactions [1.13] [1.40] [1.44], more passive and epiphitic movements [1.18] [1.42], new and novel methodologies [1.2] [1.51] and potential models of motility [1.7] [1.20] [1.47].
Our goal is not to vigorously promote and defend any one particular model, but rather to present the reader with the variety of experimental approaches that are currently being used to address the problem. In this way readers will be able to assess for themselves the areas of diatom motility that require further exploration, and the predictions of various models that still need to be tested. For example, the exact mechanism of force production for diatom motility is still unresolved. While models of force generation arising from motor proteins interacting with the cytoskeleton and coupled to secreted mucilage strands are favored by some, others currently favor models generating motile force generated by the explosive release and hydration of mucilage regulated by the localization of the secretory site directed by the underlying cytoskeleton.
There are certainly areas of diatom motility that were unfortunately not able to be included in this volume, and we encourage readers to explore these areas if they wish to be more fully aware of important work in the field. In particular, the editors want to note a number of areas of diatom motility that are not fully addressed in the current volume or are open areas and questions needing more research:
Chemotaxis: Understanding the chemical triggers that can stimulate and help regulate diatom movement, especially during cell pairing during reproduction, is crucial to a full understanding of the process. Important work on diatom chemoattractants and pheromones has been done in recent years (e.g., diatom pheromones [1.19] [1.39]), although the mechanisms by which these chemical stimulants interact with and help to regulate the motility generating process are still poorly understood.
Tube-dwelling diatoms: A number of species have the ability to specialize their extracellular secretions to provide their own surfaces for movement [1.27] [1.48], generating types of stalks and tubes through which the diatoms can move, but providing three-dimensional structures important for attachment and ecology of other organisms [1.17] [1.28].
Centric diatoms: While centric diatoms have little or no direct substratum motility as seen with many of the pennate diatoms, they can modify their position in the water column [1.36] and there has been some great recent work demonstrating there is direct regulation of diatom buoyancy [1.16] [1.34]. We encourage readers to explore this topic as well if they wish to be further engaged in current approaches regarding functional regulation of centric movement.
Composition of diatom mucilage: Understanding the chemical and physical
