| Résumé | Growth of the planktonic, euryhaline diatom (Bacillariophyceae) Thalassiosira fluviatilis, both in nature and in culture, is accompanied by the production of a large amount of extracellular "mucilage". This mucilagenous condition is due to the formation of long, narrow fibers, composed of a number of microfibrils, which originate from the marginal and central pores in the silica valves. These fibers, previously referred to as mucilage or slime threads, were found upon hydrolysis to be composed entirely of glucosamine residues. Evidence will be presented in a subsequent paper (20) to show that these fibers consist entirely of pure, crystalline poly-N-acetyl-D-glucosamine linked by β-(1→4) bonds. This polymer has been given the systematic name chitan to distinguish it from chitin as isolated from other sources. This is the first report of the occurrence of this glycan in diatoms, and in a pure crystalline state in nature. The chitan was localized in the extracellular fibers, and was not found as part of the protoplasmic constituents. Approximately 18% of the nitrogen added to the culture medium was incorporated into the chitan fibers, which, in turn, comprised 31–38% of the cellular material (including the silica) of this diatom. Methods of production and isolation of the fibers are described, together with a discussion of the nature of the fibers as derived from light and electron microscopic observations. The presence of chitin in other algae also is discussed. |
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