Transients in Acid Production by Purple Sulfur 



Bacteria 



DANIEL D. HENDLEY, Department of Biochemistry {Pels Fund), University 



of Chicago, Chicago, Illinois 



A study of pH changes in suspensions of a photosynthetic bac- 

 terium, Chromatium, strain D, has revealed unexpected variations in 

 the rates of acid production and consumption (CO2 or other acid) 

 during alternate dark and light periods. 



The pH was measured in a static, single-phase liquid system with 

 glass and calomel electrodes, Beckman model R pH meter and re- 

 corder — a technique which has been used previously in this lab- 

 oratory (1-2). pH changes in suspensions of the bacteria in phosphate 

 or bicarbonate buffers were recorded with a lag of less than 0.8 

 second at 25° C. It is the low inertia of the method which is its chief 

 virtue. 



Some of the transient effects which may be observed are illustrated 

 in Fig. 1, which is a record of pH changes in an anaerobic suspension 

 of Chromatium in dilute bicarbonate buffer during a sequence of dark- 

 light-dark periods. In the region labeled "F" there is a steady rate of 

 acidification due to endogenous fermentation. At the arrow the sus- 

 pension was illuminated and an immediate "acid gush" occurred, 

 labeled ".4." (Disregard for the moment the dashed lines.) The 

 "acid gush" was quickly followed by an uptake of acid at "R'' 

 clearly distinct from steady-state photoreduction of CO2, "P." 



When the light was turned off, at the second arrow, a rapid "dark 

 gush" of acid occurred, indicated at "D." Following this there was a 

 secondary uptake of acid at "U" before a steady rate of endogenous 

 fermentation was reached. 



The dashed lines indicate characteristic pH changes which might 

 have taken place had the conditions been somewhat different. The 

 acid gush is dependent on a rather long preceding dark period; and, 

 had the dark period prior to the first illumination in Fig. 1 been shorter 

 than about V2 minute, the acid gush would probably have been re- 

 placed by a rapid "initial uptake" of acid, indicated at "/." Fre- 



450 



