82 Perspectives in Microbiology 



An example of energy-rich phosphate bond formation in 

 bacteria with a substrate molecule is the oxidation of 

 acetaldehyde or pyruvate to acetyl phosphate. Only a rela- 

 tively few reactions of this type, however, are known. Most 

 of the energy-rich phosphate required to drive biosyn- 

 thetic reactions in the oxidative metabolism of animals is 

 generated by the electron-transporting mechanisms. In 

 certain bacteria such mechanisms must have even greater 

 significance in the economy of the cell. The autotrophic 

 bacteria, in particular, obtain all their energy by the oxi- 

 dation of such compounds as hydrogen and sulfur; obvi- 

 ously they cannot generate energy-rich compounds by 

 substrate-linked reactions. They must be entirely depend- 

 ent upon their electron-transporting systems for this vital 

 function. As yet, however, virtually nothing is known 

 about energy-rich phosphate-bond formation by such sys- 

 tems in either autotrophic or heterotrophic bacteria. Here 

 then is an aspect of bacterial metabolism which obviously 

 needs to be explored, and which could yield information 

 of fundamental significance both to microbiology and to 

 biochemistry. 



Before leaving the topic of electron transport, I shall 

 refer briefly to recent developments in the knowledge of 

 bacterial cytochrome systems. The work of Smith and 

 Chance, of Vernon and Kamen, and others has shown 

 clearly that bacteria contain several types of cytochrome 

 and cytochrome oxidase that differ markedly from the 

 classical cytochrome components of heart muscle and 

 yeast. Another new and unexpected development has been 

 the discovery of relatively large amounts of cytochrome 

 components in some obligately anaerobic bacteria like the 

 sulfate-reducing bacteria (20) and some of the photosyn- 

 thetic bacteria. The role of cytochrome in the sulfate- 

 reducing bacteria is not yet known, though it presumably 

 acts as an electron carrier between the oxidizable substrate 

 and sulfate. Vernon and Kamen (26) have obtained evi- 



