CHAPTER XVI 



Energy Transformation in the Metabolism of Microorganisms 



Life and energy. Life involves the transformation of energy. A 

 perfectly resting organism changes a certain amount of potential 

 energy from a chemical form into heat energy; an active organism will, 

 in addition to that, also transform a certain amount of that potential 

 energy into kinetic energy; while a growing organism will also consume 

 energy for growth or for synthetic purposes and change it into another 

 form of potential energy. The amount of energy transformed by a 

 microorganism and the amount utilized by the same organism for 

 growth purposes depend on the nature of the organism, the source of 

 energy, the extent of the chemical transformation of this source of 

 energy and various environmental conditions. Respiration is the 

 process whereby energy is generated in the cell. Energy originates in 

 the cell, as a result of chemical changes in the compounds within the 

 cell. With each chemical reaction, a series of energy transformations 

 takes place, whereby the chemical energy is partly transformed into 

 chemical energy of a lower potential and partly into other forms of 

 energy The presence of free oxygen is not required for the release of 

 energy since the anaerobic bacteria derive their energy from the de- 

 composition of organic compounds rich in oxygen by a process of 

 oxidation-reduction, whereby one substance is oxidized and another 

 is reduced. 



The autotrophic groups of microorganisms obtain their energy either 

 chemosynthetically, by the oxidation of inorganic substances (including 

 simple compounds of carbon), or photosynthetically, as in the case of 

 the algae. The heterotrophic groups of microorganisms obtain both 

 the energy and carbon source from organic substances, such as carbohy- 

 drates, proteins and other complex carbon compounds, either by 

 oxidation or by intramolecular structural changes. 



Since the energy utilized by autotrophic and heterotrophic bacteria 

 is derived by two different processes, these will be considered separ- 

 ately. Some organisms which belong to the autotrophic group can 

 also grow readily under heterotrophic conditions, as the hydrogen bac- 



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