A BRIEF SURVEY OF THE PHOTOSYNTHETIC 

 BACTERIA 



C. B. VANNIEL 



Hopkins Marine Station of Stanford University , 



Pacific Grove, Calif. 



INTRODUCTION 



The photosynthetic bacteria known at present comprise three major 

 groups. These are: 



(1) The green suKur bacteria, or Chlorobacteriaceae, represented by 

 the genera Chlorobium and Chloropseudomonas . 



(2) The purple sulfur bacteria, or Thiorhodaceae, among which the 

 best known are species of Chromatium and Thio spirillum. 



(3) The nonsulfur purple bacteria, or Athiorhodaceae, with the genera 

 Rhodopseudomonas , Rho do spirillum, and Rhodo microbium . 



Members of the first two groups are regularly found in nature in 

 environments that contain H2S and are exposed to light; here they often 

 develop in such profusion that they are readily visible to the naked 

 eye ("blooms"). Owing to their ability to use near infrared radiation 

 for photosynthesis, the green and purple sulfur bacteria can grow at 

 the expense of radiant energy that is not absorbed by the plant 

 chlorophylls. This accounts for the fact that so often mass develop- 

 ments of the colored sulfur bacteria can be observed underneath a 

 layer of algae and that for their cultivation in the laboratory incan- 

 descent bulbs are far more effective as a source of radiant energy 

 than fluorescent lights, which do not emit sufficient radiation in the 

 infrared region. 



The green bacteria have a greater tolerance for H2S than do the 

 purple sulfur bacteria. The former are therefore apt to occur closer 

 to the source of H2S, which is usually generated by biological activity 

 (sulfate reduction) in bottom sediments. Hence mass developments are 

 frequently stratified, with the purple above the green sulfur bacteria. 



Comparable blooms of nonsulfur purple bacteria have not been 

 reported so far; but these organisms are regularly found in stagnant 

 water, mud, and soil, from which they can be selectively cultivated in 

 the laboratory. 



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