Observations on Phaeodactylum tricornutum

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Abstract
Phaeodactylum tricornutum Bohlin was isolated from a marine tank at Woods Hole, Mass. It appeared to be identical with the Plymouth strain of "Nitzschia closterium forma minutissima". Cells were of 2 characteristic types, oval and fusiform, each of which remained constant for many cell divisions in clonal culture. Triradiate cells arose rarely as atypical forms of the fusiform variety. Oval cells could arise as endospores within a fusiform cell. The transition from oval to fusiform was also studied, but details of the life cycle remain to be worked out. Electron micrographs showed the fusiform cells to be devoid of any organized siliceous structure, in agreement with previous observations. However, the oval cells were seen to possess a silica valve of a pennate diatom type, resembling those of the genus Cymbella. Only 1 valve was present on each cell, the remainder of the cell wall being unsilicified. The valve was 6.2[mu] long, was equipped with a raphe, and was perforated by pores arranged in 60 striae. Oval and fusiform cells both contained approximately the same amount of silica (0.4-0.5% dry weight). In each case, most of this silica could be recorded as a participate fraction resistant to digestion in hot nitric acid. The silica obtained from oval cells was in the form of diatom valves, whereas that from fusiform cells consisted of irregular particles clearly not derived from broken silica walls. Mucilaginous capsular material, soluble in hot water, represented 16% of the dry weight of oval cells; it was absent from fusiform cells. Acid hydrolysis and paper chromatography indicated xylose, mannose, fucose, and galactose as components of the capsule.

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