kluyver's contributions to microbiology and biochemistry 



'Amongst anaerobic metabolic processes it seemed that particularly 

 denitrification should fulfill the above-mentioned requirements' 



(P-3!9)- 



A beginning was therefore made with a study of the redox poten- 

 tials in cultures of denitrifying bacteria. The results clearly indicated 

 that the measured potentials were indeed dependent on the nature of 

 the metabolic process. During the first phase of the cultures, when 

 only nitrate was present, a potential of around — ioo mV was estab- 

 lished; when nitrite had accumulated the potential rose to a level of 

 — 40 mV; thereafter it gradually dropped again, eventually and quite 

 sharply to a new low level of about —260 mV, coinciding with the 

 disappearance of the nitrite. At this stage the addition of nitrate or 

 nitrite sufficed to restore the earlier established potentials. 



On account of the drastic changes in hydrogen ion concentration 

 during the development of cultures of denitrifying bacteria, and their 

 inevitable effect on the redox potential, the results obtained were not 

 interpretable in terms of absolute values; nevertheless, they showed 

 that the type of metabolic process was reflected in the measured 

 potentials. 



In passing it may here be mentioned that these studies had also 

 led Elema in Kluyver's laboratory to discover the reversible two-step 

 oxidation of reduced pyocyanine and chlororaphine, simultaneously 

 and independently found by Michaelis in the U.S.A. 



Spurred on by these promising results, the programme was soon ex- 

 panded by Kluyver and Hoogerheide [1934] to studies on the poten- 

 tials established in suspensions of micro-organisms provoking a char- 

 acteristic alcoholic fermentation. The organisms used included vari- 

 ous yeast species as well as the bacterium, Pseudomonas lindneri, which 

 Lindner had discovered as the causative agent of the alcoholic fer- 

 mentation of agave juice from which the Mexicans prepare the alco- 

 holic beverage known as 'pulque'. This bacterium had been thor- 

 oughly studied by Kluyver and Hoppenbrouwers [193 1] who had shown 

 that it can ferment sugar to equimolar amounts of carbon dioxide and 

 alcohol, accompanied by small quantities of lactic acid, and that, in 

 contradistinction to yeasts, it can ferment glucose and fructose, but 

 not mannose, so that it can be used for the quantitative determination 

 of mannose in sugar mixtures by means of the previously discussed 

 fermentation method. 



109 



