moisture content (Porter, I9I+6) then 2.1+ x 

 10" cc/l would be the dry volume or, multi- 

 plying by the average specific gravity, - 

 1.1 (Ruffilli, 1933), the dry weight of the 

 bacterial cells would equal 2. 61+ x 10"^ g/l. 

 If 50% of the dry weight of the bacterial 

 cells is considered as carbon (Porter, I9I+6) , 

 then 1.32 x 10"^ g/l is the calculated weight 

 of total carbon. Since it has been estimated 

 that about 5°/ of cell carbon of heterotrophic 

 bacteria may be fixed by the Wood-Werkman re- 

 action, approximately 6.6 x 10"° g/l of C^ 

 could have been fixed by the heterotrophic 

 bacteria at the end of the 37.5-hour period in 

 this experiment. 



The total C0 2 /C fixed in any of the sets of 

 bottles may be calculated as follows : 

 Total C0 2 /C fixed/L = 

 Total COg/C present in mg/l x 

 count s/min/250 ml recovered x 1+ 4- 

 Count/min added x 1+ 



In this experiment 5,222,500 counts/minute (as 

 measured with our apparatus) of NaHC-^Oo were 

 added to each 250-ml. reagent bottle. The 

 total carbon dioxide carbon in the, surface sea- 

 water sample was approximately 25 mg/l. 

 Calculating the total carbon dioxide fixed in 

 each set of bottles in this manner and compar- 

 ing these values with the estimates of the 

 amount of C^ fixed by heterotrophic bacteria 

 for each period, an estimation of the percent- 

 age of COg/C fixed by the bacteria can be 

 obtained, as shown in Table 12 for each test 

 period in the dark. 



Steemann Nielsen (1952) has estimated that 

 the amount of organically bound C^ is not a 

 completely accurate measure of the gross produc- 

 tion by photosynthesis since C-^02 is actually 

 assimilated at a rate 6°/ slower than C-^Og. 

 In addition, Steemann Nielsen (1952) applies a 

 correction of 1+°/° of the photo synthetic in- 

 tensity at optimum light intensity in a four- 

 hour experiment for the loss of C through 

 the respiration of substances produced during 

 the experimental period. Thus, a 10°/o correc- 

 tion is applied. Steemann Nielsen neglects the 



1^ 



negative correction due to C assimilation 



in the dark which he estimates at l°/o, as 

 mentioned previously. However, in these 

 experiments the dark fixation of C^ was 15 

 to 20 times the dark fixation reported by 

 Steemann Nielsen (1952). The correction for 

 isotopic fractionation and respiration were 

 not applied in these calculations . 



Various considerations which may affect the 

 calculations presented in Table 12 should be 

 mentioned. For example, the size of marine 

 bacteria is variable (ZoBell and Upham, I9I+I+) . 

 An increase in the length of the rod- shaped 

 cells from one micron to two micra would 

 double the importance of the bacteria in the 

 foregoing calculations. However, since marine 

 bacteria are generally veiy small, the values 

 used are considered reasonable. In addition, 

 the error in the pour-plate technique may be 

 considerable. It has been estimated that 

 only 1 to 10°/ o of the bacteria present in a 

 sample are recorded by this method (ZoBell, 

 19^), which would increase their importance 

 in these calculations by at least a factor of 

 10. Little is known of the abundance or impor- 

 tance of chemosynthetic bacteria in the marine 

 environment which utilize carbon dioxide as 

 their sole source of carbon. 



The various influences of bacteria, phytoplank- 

 ton, zooplankton and other components in the 

 marine ecosystem on Cl^ assimilation may 

 perhaps be elucidated by studies on pure 

 cultures and simple mixed populations. The 

 uptake of C^ by various members of the marine 

 population in pure cultures and in natural 

 mixtures should provide much additional 

 information on the actual uptake of C^ by 

 these organisms as well as offer more defini- 

 tive results concerning the effect of their 

 mutual interrelationships. These experiments 

 have been planned. 



84 - 



