Growth Factors in Bacterial Nutrition 



ESMOND E. SXELL 



THE term "growth factor" has been used in a variety of wavs. In 

 the discussion to follow we shall use it to mean those organic factors, 

 exclusive of the compound or compounds utilized as an energs' source, 

 which are required lor growth of an organism in a given environment. 

 This definition excludes, on purely arbitrary grounds, consideration of 

 the inorganic nutrition of bacteria or of the variety of compounds which 

 these microscopic plants may use to supply their requirements for 



energy. 



Bacteria vary widely in their requirements tor growth factors. Thus 

 certain of the photosynthetic autotrophs — for example, members of 

 the Thiorhodaceae — are similar to the higher plants in that they grow 

 well in appropriate mineral media with light as their energy* source and 

 carbon dioxide as their sole source of carbon. Such organisms require 

 no growth factors in the sense defined above. The chemosynthetic 

 autotrophs, such as Thiobadlliis thiooxxdans, and the simpler hetero- 

 trophs, such as Escherichia coli, hkewise require no growth factors in this 

 sense of the term, althouijh thev oxidize either inorganic or orcranic 

 materials to supply energy for synthetic purposes. A great many bacteria 

 do, however, require organic materials other than an energy* source for 

 growth, and many organisms which do not require a specific growth 

 factor mav be greatlv stimulated bv it. 



\\'e may now examine the nature of the compounds which have been 

 found to be essential growth factors for one or more species of bacteria. 

 It will be seen from Table i that these represent almost all of the known 

 water-soluble vitamins, most of the common amino acids, and a variety 

 ot miscellaneous biologically important compounds. The striking thing 

 about this hst is that with one or two exceptions to be considered later, 



