The effects of silica, nitrogen, and phosphorus limitation on the amount of cellular lipid, fatty acid, glucan, protein and chlorophyll of Cyclotella meneghiniana Kutz. were investigated in batch and semi-continuous culture experiments. In batch cultures, cells were removed from nutrient-replete media and resuspended in nutrient-deficient media according to a 2('3) factorial design in fractional replication. Cells were analyzed 3 and 9 days after transfer to treatment media. Of the 3 nutrients, only silica had a significant effect on a biochemical variable. Silica deficiency caused a significant increase (300%) in the amount of cellular protein. Cellular protein was also significantly different between fractional replicates. In semi-continuous cultures, cells were grown in media with the nutrient under investigation at concentrations lower than necessary for maximum rates of growth. Daily dilution rates of 10, 25, and 50% produced 3 distinct rates of nutrient supply within each of the silica, nitrogen, and phosphorus-stressed experiments. Cellular lipid/glucan ratios significantly decreased (50%) with an increase in silica supply rate. The amount of cellular lipid, glucan, and protein significantly increased (300%) with an increase in nitrogen supply rate. The amounts of cellular lipid and glucan significantly increased (300 and 400%, respectively) with an increase in phosphorus supply rate;Fatty acids of lipid extracted from cells in semi-continuous cultures generally possessed carbon chain lengths of 14 to 24. However, carbon chain lengths of fatty acids from cells in silica-stressed cultures ranged from less than 14 to 18. No distinct differences in diatom fatty acid composition were observed among supply rates within silica-stressed and nitrogen-stessed cultures;The statistical significance of nutrient-limitation effects on cellular biochemical composition varied between batch and semi-continuous culture experiments. The semi-continuous cultures provided constant physiological and growth conditions while batch cultures did not. Therefore, results of semi-continuous cultures were more reliable than results of batch cultures. Discrepancies between results of this study and others were attributed to culture design, biochemical extraction techniques, the scaling factor used to express cellular biochemical composition, and the physiological characteristics of C. meneghiniana.
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