PRELIMINARY STUDIES OF BACTERIAL GROWTH IN RELATION TO DARK AND LIGHT 

 FIXATION OF CO- DURING PRODUCTIVITY DETERMINATIONS 



G. E. Jones, W. H. Thomas, and F. T. Haxo 



The technique of studying, productivity hy use 

 of radioactive carbon (C ) has been widely 

 employed in recent years (Steemann Nielsen, 

 1951, 1952, 195 1 *-; Ryther and Vaccaro, 195k; 

 Ryther, 1956b). Steemann Nielsen (1952), us- 

 ing the green alga, Scenedesmus quadricauda , 

 showed that C^ assimilation in the dark was 

 very small (about l*/» of maximal fixation in 

 the light). When this method is used in a 

 natural ecosystem, such as in the pelagic 

 waters of the open ocean, a complex of factors 

 and organisms must be considered. Both phytop- 

 lankton and zooplankton assimilate carbon 

 dioxide in the dark. Chemosynthetic bacteria 

 fix carbon dioxide as their sole source of 

 carbon and even heterotrophic bacteria fix 

 some of their carbon as carbon dioxide via 

 the Wood-Werkman reaction (Wood and Werkman, 

 1938, 19IK); Wood et al., 19^1; and Utter and 

 Wood, 1951). Consequently, mixed populations 

 collected from nature might be expected to fix 

 a greater percentage of CO2 in the dark than 

 the 1% reported by Steemann Nielsen (1952). 

 The complicating effects of the presence of 

 bacteria have been recognized, although as yet 

 unsatisfactorily assessed, in productivity 

 measurements. 



One of the first methods of estimating product- 

 ivity was the "light and dark bottle" experiments 

 of Gaarder and Gran (1927). When this technique 

 is used, water samples from various depths are 

 dispensed in bottles and lowered to different 

 depths for time intervals of a day or more. 

 Oxygen production in dark (wrapped with masking 

 tape to prevent the entrance of light) and 

 light bottles is determined by measuring the 

 quantities of oxygen before and after the in- 

 cubation period. A modification of this method 

 was used in the productivity measurements of 

 Riley (1938, 1939, 19^1a, 191+lb). Riley's 

 rather large estimates for productivity in the 

 Sargasso Sea were criticized by Steemann Nielsen 

 on the grounds that the bactericidal effect of 

 sunlight inhibited the bacteria in the light 

 bottles, causing a considerable difference in 

 oxygen content between the light and dark 

 bottles (Steemann Nielsen, 1952). It was 



correctly pointed out by Steemann Nielsen 

 that the added surface of the containers 

 would promote bacterial growth to a far greater 

 degree than in pelagic sea water under natural 

 conditions in both light and dark bottles 

 (ZoBell and Anderson, 193^) . However, while 

 the bacterial activities in the bottles are 

 increased, most of the wave-lengths shorter 

 than 3500 A which are most inhibitory toward 

 bacteria are absorbed by glass bottles (Vaccaro 

 and Ryther, 195^). Also, those solar radia- 

 tions transmitted at a depth of 10 inches did 

 not affect the growth of marine bacteria as com- 

 pared with bacterial development in the dark. 

 Ten inches is the depth employed by Riley in 

 his experiments. Steemann Nielsen later (1955) 

 presented experiments suggesting that anti- 

 biotics produced by the plankton algae in 

 the light decreased the bacterial activity. 

 An antibiotic from Chlorella , chlorellin, 

 has been reported (Pratt et al., 19^4). 



It was the purpose of the following experiments 

 to assess the numbers of bacteria developing 

 in light and dark bottles containing sea- 

 water samples from the tropical Pacific Ocean 

 over different periods of time ranging up 

 to 1+0 hours and estimate their influence on 

 the carbon dioxide fixed by the total popula- 

 tion. Any influence of the planktonic pop- 

 ulation on the marine bacteria was also noted. 



METHODS 



The 250-ml. glass -stoppered reagent bottles 

 used in these experiments were cleaned as 

 follows : thoroughly washed with a detergent 

 ("Tide"), rinsed three or four times with 

 sea water, filled with 10°/« HC1 for at least 

 5 to 10 minutes and rinsed five or six times 

 with sea water. The surface sea-water samples 

 were collected in a plastic bucket (cleaned 

 as above) and dispensed into the reagent 

 bottles. The bottles were always rinsed 

 with the sea-water sample before filling. 

 Radioactive NaHC ll+ Oo (0.9uc) was added 

 to each bottle. The dark bottles 



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