68 Perspecfives in Microbiology 



requirements have been examined carefully. A great many 

 bacteria, however, have not been studied adequately from 

 the nutritional point of view. The general requirements of 

 these organisms undoubtedly will be similar to those al- 

 ready known. But from past experience, it can be antici- 

 pated that at least a few of these bacteria will ultimately be 

 found to require new types of giowth factors. Within re- 

 cent years several such substances have been discovered 

 through the study of microbial nutrition. One is lipoic 

 acid, which has been shown to play an essential role in the 

 oxidation of a-keto acids. Another is ferrichrome, an iron- 

 containing polypeptide derivative isolated by Neilands (18) 

 from a smut fungus, Ustilago sphaerogena, and found to 

 stimulate the growth of a soil bacterium. A third is a di- 

 saccharide of galactose and N-acetyl-glucosamine, recently 

 shown by Zilliken and others (30) to have growth-promot- 

 ing activity for Lactobacillus hifidus. Undoubtedly many 

 more new compounds of biological importance will be 

 found by further systematic investigation of bacterial nu- 

 trition. 



Respiration and Fermenfafion 



Next are the problems of the oxidation and fermentation 

 of the major substrates. Much is known about the com- 

 pounds utilized and the major excretory products. A good 

 beginning has been made in determining the chemical steps 

 by which these energy-yielding reactions proceed. Yet here 

 also much remains to be done. Only recently, for example, 

 have we begun to discover some of the pathways by which 

 bacteria convert glucose to three carbon compounds (6, 29). 



GLUCOSE DECOMPOSITION 



Until a few years ago, it was commonly accepted that 

 sugar decomposition in bacteria occurs by the glycolytic 

 mechanism. As late as 1952, Elsden (3), in a review of exist- 



