Growth of Pure Cultures of Marine Phytoplankton in the Presence of Toxicants

The effects of 17 toxicants on the growth of five species of algae in pure culture were studied. The two species displaying the greatest sensitivity to the action of each of the compounds tested were Monochrysis lutheri and Phaeodactylum tricornutum , and the most resistant species was Protococcus . Of eight different classes of toxicants tested, substituted urea compounds and a mercuric compound were most effective in inhibiting growth of all algal species at the lowest concentrations.

AUXOTROPHY AND HETEROTROPHY IN MARINE LITTORAL DIATOMS

Forty-four pure cultures of marine littoral diatoms (43 pennate and 1 centric) have been studied to determine (a) whether any accessory organic factors (vitamins) are essential for growth in light, and (b) whether the cells can grow in darkness using glucose, acetate, or lactate as substrates.Six isolates were shown to require thiamine as sole growth factor; eleven require cobalamin only; and three require both thiamine and cobalamin. Sixteen are capable of heterotrophic growth using glucose but not acetate or lactate; eight can use glucose or lactate; one uses glucose or acetate; one uses glucose, acetate, or lactate; and two use only lactate.By the classical criteria of valve structure, the clones fall into about 25 different species, belonging to nine genera. However, it is evident that light microscopy is inadequate for the specific descriptions of many small diatoms. Electron micrographs of acid-cleaned frustules of each isolate served as an aid to specific identifications. Nutritional studies have demonstrated the existence of a range of distinct physiological races within the "species" Amphora coffaeiformis, Nitzschia closterium, and N. frustulum.

Silicon metabolism in diatoms. IV. Growth and frustule formation in Navicula pelliculosa

The cells of Navicula pelliculosa (Bréb.) Hilse, when grown in media which contained 3.5, 8.3, and 34.0 mg. Si per liter, reproduced with generation (doubling) times of 20.4, 13.7, and 13.1 hours respectively. The degree of silicification of the cells in each culture initially fell with increasing population. After exponential growth had ceased, this value varied between 0.8 × 10−9 and 2.2 × 10−9 mg. Si per cell, depending on the amount of silicon originally present in the medium and on the age of the culture. When placed in a fresh silicate solution, the cells took up additional silicate with increases in silicon content of 50%, 90%, and 15%, respectively. Silica (SiO2) may represent from 4% to 22% of the dry weight of the cells. The average thickness of the frustules has been calculated to range between 200 and 600 Å.