SYNOPSIS. The development of three 8-liter and four 12-liter cultures of the photosynthetic dinoflagdate Gonyadax monilata was followed for 4 months. Weekly estimates were made of population levels of this chain-forming flagellate, along with incidence of cells in chains and toxicity to fish. Guppies (Lebistes reticulatus) were used to assay toxicity. Populations reached a peak when cultures were 3-5 weeks old, declined during weeks 6-10, and tended to stabilize thereafter thru the 17th (final week).

1. Nitrate reduction and assimilation have been studied in Chlorella pyrenoidosa under growth conditions by observing effects on the CO2/O2 gas exchange quotient. 2. During assimilation of glucose in the dark, nitrate reduction is noted as an increase in the R.Q. to about 1.6 caused by an increased rate of carbon dioxide production. 3. During photosynthesis at low light intensity nitrate reduction is evidenced by a reduction in the CO2O2 quotient to about 0.7 caused by a decreased rate of carbon dioxide uptake. 4. Chlorella will assimilate nitrogen from either nitrate or ammonia. When both sources are supplied, only ammonia is utilized and no nitrate reduction occurs. It is inferred that under the usual conditions of growth nitrate is reduced only at a rate required for subsequent cellular syntheses. The effect of nitrate reduction on the CO2O2 quotient therefore provides a measure of the relative rate of nitrogen assimilation. 5. Over-all photosynthetic metabolism may be described from elementary analysis of the cells since excretory products are negligible. The gas exchange predicted in this way is in good agreement with the observed CO2/O2 quotients.

No abstract

The variability of metabolism observed quite generally in microorg~nl.qms has never been systematically studied in the green algae. The frequent use of forms such as ChloreUa pyrenoidosa in the study of photosynthesis has led to common use of purposely standardized culture conditions. This practice has been pushed toward its limit in the development of a continuous culture apparatus (Myers and Clark, 1944) which provides uniform experimental material day after clay. At the same time the continuous culture method also a~ords a basis for the study of variability in metabolism imposed by various conditions.The quotient of gas exchange has long been recognized as a practical tool in metabolic studies. Its usefulness in Chlordla has been extended by the work of the preceding paper (Cramer and Myers, 1948 b) which showed that the effect of nitrate reduction on the gas exchange quotient provides an index of the rate of nitrogenous synthesis. This finding is now applied to cells subjected to such conditions as might be expected to affect their metabolic activities. The present study began in an attempt to explain the effect of light intensity on the CO~/O2 quotient noted in the preceding paper. It has been extended to include consideration of the changes in over-all metabolism induced by starvation, high light intensity, and nitrogen deficiency in comparison with the metabolism of growing cells. The general experimental methods and the overall carbon and nitrogen metabolism in growing cells have been described in the preceding paper. It should be emphasized that the term growing cells, ~s used herein, specifically describes a standard preparation; i.e., cells cultured photosynthetically under an illumination light-limiting for both growth and photosynthesis. The merit of this particular choice of reference will be justified in the subsequent discussion. StarvationGrowing cells may be starved aerobically by shaking a suspension in the dark. Starvation results in a gradual decrease in capacity for photosynthesis, a disappearance of starch, and a marked decrease in endogenous respiration which approaches a constant rate with an R.Q. of 1.0 (Cramer and Myers, 1948 a). Table I describes the time course of the ~.Q. after addition of glucose to growing and starved cells.