CHAPTER XXIV 

 AUTOTROPHIC BACTERIA 



ROBERT L. STARKEY 

 New Jersey Agricultural Experiment Station, New Brunswick, N.J. 



Most of the lower forms of life, including the filamentous fungi, protozoa, and 

 most of the bacteria, derive the energy for their metabolic processes as well as the 

 carbon used for synthesizing their cells from complex organic compounds such as 

 carbohydrates, fats, proteins, degradation products of these, or other compounds of 

 the aliphatic and cyclic series. Such organisms are termed "heterotrophs." 



A typical reaction by which such organisms may obtain energy for their nutrition 

 may be represented as follows:' 



I. CeH^Oe (solid)+60. (i atm.)=6C0. (i atm.)+6H,0 (liquid) 



AF298= —689,800 calories^ 



From this reaction the complete oxidation of i gm. molecule or 180 gm. of glucose 

 liberates 689,800 calories which may be available to the organism bringing about such 

 a reaction. 



Organisms effecting the synthesis of their own organic compounds from inorganic 

 substances are termed "autotrophs." Of this group by far the most conspicuous forms 

 are the higher plants which contain chlorophyll. Among the microscopic forms of this 

 group would be included the smaller algae. Organic matter is produced within the 

 cells of such organisms by photosynthesis. In this reaction the sunlight furnishes the 

 necessary energy for the elaboration of organic compounds from carbon dioxide. 



There is another distinctive group of autotrophs which may live in the absence 

 of light. They are generally microscopic and are indistinguishable from other bacteria 

 in their morphological characteristics. These autotrophic bacteria are distinguished 

 from the heterotrophic forms in that they have the specific ability of obtaining energy 

 for their metabolism by the oxidation of certain inorganic substances. Autotrophic 

 bacteria differ from the autotrophic plants in that this energy, derived from the oxida- 

 tion of inorganic materials, is utilized by the bacteria for the reduction of carbon 

 dioxide to organic compounds. In the group of sulphur bacteria are found representa- 

 tives of forms which appear to be intermediate between the autotrophic bacteria and 

 the chlorophyllous plants. These are the purple bacteria which require both hydrogen 

 sulphide and light for their development. It would appear that their nutrition is 

 dependent upon both a photosynthetic reaction and an oxidation of an inorganic 

 substance. 



'Baas-Becking, L. G. M., and Parks, G. S.: Physiol. Rev., 7, 85-106. 1927. 



^ AF,58 refers to the free energy decrease or the maximum amount of useful work ol)tainable from 

 the process at 25° C. or 298° absolute temperature. The data reported in these pages on free energ>' 

 were all obtained from Baas-Becking and Parks {loc. cit.). 



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