Since there was a lag in time of 1.5 hours be- 

 tween the time the zero hour bacterial counts 

 were plated and the time all of the bottles were 

 inoculated with NaHC-^Oj and placed in the water 

 bath, this should be taken into account in 

 following the bacterial populations. The 

 illuminance in the water bath was l^-OO i lUO 

 foot -candles. After 2, k, 8, l6, 2k, and 37-5 

 hour 6 of incubation at 25 ± 1°C, two bottles 

 were removed and the contents were plated in 

 duplicate for bacteria, and filtered to det- 

 ermine the C^ uptake by the organisms over the 

 particular time span tested. The results for 

 the bacteria/ml and the C-^ assimilation show- 

 ing the values for the replicates are tabulat- 

 ed for the light bottles (Table 10) and the 

 dark bottles (Table 11). The average C 1 up- 

 take was 171 counts/minute in the light during 

 the first two hours, with approximate doubling 

 after four hours and again after eight hours. 

 After eight hours, the C 1 ^ assimilation in- 

 creased by a factor of 1.5X during the next 

 eight hours and 1.3X during the last 20 hours 

 of the experiment. Meanwhile, the bacteria 

 were in the lag phase of growth for the first 

 four hours, after which they entered logarith- 

 mic growth, tapering off somewhat after l6 

 hours. It is interesting to note that the 

 development of the bacteria in the dark and 

 the light was very similar. 



lk 

 During the first four hours the C fixation 



was considerably suppressed in the dark compared 

 to the light. After two hours, 37 counts/minute 

 were recorded which increased to 51 counts/min- 

 ute after four hours. At this point, however, 

 the C uptake more than doubled during the 

 next two time intervals (up to l6 hours). 

 After this time, the C^ fixation proceeded at 

 about the same rate in the dark and in the 

 light . 



The replication of the bacterial counts and 

 Cl* fixation Was quite good with two excep- 

 tions. After 2k hours of C 1 ^ uptake in the light, 

 the duplicate bottles did not agree. The higher 

 figure is more consistent with the other results. 

 There was considerable disagreement in the dupli- 

 cation of the 37 .5-hour count /minute in the dark 

 but the average figure appears reasonable 

 (Table 11). 



DISCUSSION 



The necessity for maintaining dark-bottle 

 controls during productivity measurements 

 by the C^ method becomes evident upon exam- 

 ination of the data in Tables 10 and 11. 

 When employing radioactive C^ as an index of 

 assimilation of CO2 and productivity, dark- 

 bottle controls have not always been consider- 

 ed important as a correction factor (steemann 

 Nielsen, 1952) . In these experiments, dark- 

 bottle C fixation became very significant 

 after eight hours of incubation (half as 

 much C 1 **- fixation in the dark as in the 

 light after eight hours). As shown from 

 Tables 10 and 11, the error (dark bottle 

 fixation/light bottle fixation) which would 

 be incurred, if the dark bottles were not con- 

 sidered, would be 21.6°/ after two hours, 

 15.5% after four hours, 17.6% after 

 eight hours, 31.6% after 16 hours, W>.8% 

 after 2k hours, and 48.6% after 37-1/2 hours. 

 Thus, even during the customary incubation 

 period (up to eight hours), the error might 

 be expected to fall between 15 and 22°/, . 



The effect of bacteria on the total C 1 ^ fix- 

 ation i6 still somewhat uncertain. However, 

 the bacterial populations were very similar 

 in both the light and dark bottles and their 

 influence could be compensated for by using 

 dark-bottle controls. (The light source in 

 these experiments was artificial, not sun- 

 light, however.) This conclusion is support- 

 ed by the results of Vaccaro and Ryther (195 1 *-). 

 There was no indication in our studies of an 

 "antibiotic" effect wuch as that reported 

 by Steemann Nielsen (1955) for the fresh-water 

 green alga, Chlorella pyrenoidosa , and the 

 marine diatom, Thalassiosira nana. 



Some calculations are presented for estima- 

 tion of the magnitude of bacterial C uptake 

 by the Wood-Werkman reaction. If one assumes 

 that an average marine bacterium is a short 

 rod (l micron long by 0.5 micron in diameter), 

 the volume of one bacterium would be 2.0 x 

 10 -1 3 cc. At the end of 37.5 hours of in- 

 cubation, the volume of allrecorded bacteria 

 (6 x 109 cells/l) would be 1.2 x 10"3 cc/l. 

 If 80°/ o of this volume is considered as 



82 



