296 DOUGLAS C. PRATT, ALBERT W. FRENKEL, AND DONALD D. HICKMAN 



with air enriched with CO.,, and the rate of chlorophyll formation and 

 growth was varied by adjusting the flow of air through the spargers of the 

 culture tubes. With this method, however, it was difficult to obtain 

 reproducible results, except for the conditions when the cultures were 

 gassed rapidly* with air or with nitrogen. To obtain more reproducible 

 results we secured the following gas mixtures: 0-5, 1-55, and 7-3% 

 oxygen in nitrogen supplemented with 1% CO2 (the values for oxygen 

 indicated here were obtained by mass spectrometric analysis). All cultures 

 were gassed at sufficiently rapid rates* so that a further increase in gassing 



Fig. I. Effect of oxygen tension in the gassing mixtures on growth of R. 

 riibriwi in the dark (based on change in packed cell volume per ml. of culture 

 suspension) measured four days after inoculation. Initial concentration o-ii /nl. 

 of packed cells per ml. of culture suspension. Rate of gassing through spargers at 

 35 ml. of gas mixture per minute per 40 ml. of culture suspension in 100 ml. 

 culture tubes. Culture tubes incubated at 30". 



rates caused little if any effect on rates of growth and chlorophyll 

 production. 



Figure i shows the effect of oxygen tension in the gassing mixtures on 

 total growth per culture as measured after four days of incubation in the 

 dark. Growth was measured by measuring changes in cell mass or by 

 measuring changes in turbidity at 680 m/x calibrated against packed cell 

 volumes of aliquots of the culture suspensions which were centrifuged for 

 35 minutes at 2000 times gravity in Hopkins vaccine tubes. While growth 

 saturates at about 2",, oxygen (Fig. 1), chlorophyll concentration on a cell 

 volume basis decreases with increasing oxygen tensions and reaches 



* 35 40 ml. of gas per minute per 40 cm^ of liquid volume. 



