CHAPTER XIV 

 BACTERIAL OXIDATIONS AND REDUCTIONS 



JAMES WALTER McLEOD 

 University of Leeds, Leeds, England 



REDUCTIONS 



Clark^ has pointed out recently that the modern conceptions of reduction involve 

 more than the subtraction of oxygen or addition of hydrogen. Much the greater part of 

 the literature, however, dealing with bacterial reductions relates to observations of such 

 changes. A great deal of this work had already been done by the end of the last cen- 

 tury. The literature is considerable, and since a comprehensive summary of it would 

 require much space, only the more interesting points and those to which most work has 

 been devoted will be considered. Such are the reductions of compounds of nitrogen 

 and sulphur, of metallic salts such as those of selenium and tellurium, of a variety of 

 dyes, and of certain substances of biological importance, hemoglobin derivatives, 

 cystine or complexes containing it, and bacterial toxins. These various reactions have 

 been studied for a variety of ends, some on account of their economical importance, as 

 the reduction of nitrates and nitrites; others because of their possible value in bacteri- 

 ological technique, as the reduction of tellurium salts: others again because of their pos- 

 sible significance in explaining the pathogenic action of bacteria, as the reduction of 

 oxyhemoglobin; and almost all have been studied with a view to elucidating the in- 

 timate metabolism of the bacterial cell and particularly the mechanism of its respira- 

 tion. 



The reduction of nitrates and nitrites was fully studied by Maassen^ twenty-five 

 years ago. His chief conclusions were that the majority of the bacteria which are 

 capable of growing in simple media reduce nitrates to nitrites, that many but not all 

 of these destroy nitrites whereas some of the bacteria incapable of reducing nitrates 

 can yet destroy nitrites, that most bacteria destroy the nitrite by transforming it to 

 NH, which they utilize almost as rapidly as it is formed, but that one group — the true 

 denitrifying bacteria, B. fluorescens liquefaciens , and species allied to it — utilize the 

 oxygen of the nitrite and give off gaseous nitrogen. Braun and Cahn-Bronner-' refer 

 to this last quality in B. pyocyaneus as enabling it to show pseudo-anaerobic growth 

 in the presence of nitrate. Certain of the vibrios are among the group of bacteria 

 forming nitrite without reducing it further, and it is such of these as also produce indol 

 that give the cholera-red reaction. 



Not much of importance has been added to our knowledge of this subject since 

 Maassen's work, but some facts have been added with regard to some bacteria which 



'Clark, W. M.: Pub. Health Rep. (U.S. Public Health Service), 38, 443. 1923; cf. chap, xii, 

 this volume. 



^ Maassen, A.: Arbeilen a.d. kaiserliclien Gcsundheilsamte, 18, 21. 1902. 



^ Braun, H., and Cahn-Bronner, C. E.: Centralbl.f. Baklen'ol., Abt. I, Orig., 86, 380. 1902. 



