348 Marine Microbiology 



plained by a more rapid exhaustion of the nutritive substrate at 

 high Hght intensities. 



CONCLUSIONS 



Summing up the presented material, we come to the follow- 

 ing conclusions: 



1. The purple sulfur bacterium Chr. vinosum isolated from 

 Lake Beloye is a typical representative of the photosynthetic 

 microorganisms developing under light at the expense of carbon 

 dioxide as the sole carbon source. 



2. However, the bacteria may follow a photoheterotrophic 

 path of development making use of carbon contained in some 

 organic compounds (acetic acid, propionic acid, etc.) for build- 

 ing the organic material of their cells. 



3. The culture is capable of developing by photoassimilation 

 within the ranges of investigated intensities of physiological 

 radiation (from 1.4 X 10^ erg/cm^ sec. to 32 x 10^ erg/cm^ sec). 



4. When the intensity of the incident light is weak (under 

 3-5 X 10^ erg/cm^ sec), the bacteria develop and reproduce 

 very slowly. 



5. Light intensities of 5-6 X 10^ erg/crn^ sec. and higher are 

 sufficient for normal bacterial development; higher light in- 

 tensities cause strongly pronounced initial acceleration in the 

 development of cultures and higher yields than under compara- 

 tively weaker exposure; however, subsequently the cultures de- 

 veloped and grew equally well irrespective of the radiation rate. 



6. The highest dependence of the development of the cul- 

 ture on radiation intensity is obsen^ed in young cultures during 

 the first two to three days of growth. 



7. The obtained data are also of ecological interest as they 

 show the possibility for these bacteria to reproduce in natural 

 environments under various conditions of light exposure. 



REFERENCES 



1. Clayton, R.: Photosynthesis and respiration in Rhodospirillum riibrum. 



Arch, microbiologie, 22:18, 199, 1955. 



2. French, C. S.: The quantum yield of hydrogen and carbon dioxide 



assimilation in purple bacteria. /. Gen. Phijsiol., 20:711, 1937. 



