108 



PHOTO- AND CHEMOSYNTHESIS OF BACTERIA 



CHAP. 5 



The following general equations can be derived for monobasic acids 



(5.11) 



and for dibasic acids: 



C„H2.+iC00H + ^^5^ CO2 + ^Vi H2O 



_^3«_+J- {CH2O} 



(5.12) C„H2,.(COOH)2 + ^^—^ CO2 + ^^-y^ H2O 



- ~ (12?i + 1) kcal 

 3n + 1 



(CH2O} 

 - ~ {ISn + 4) kcal 



The heats of the reactions (5.11) and (5.12) have been estimated by assuming 

 112 kcal for the heat of combustion of iCH20), (156ri + 55) kcal for that of monobasic 

 acids, and il50n + 60) kcal for that of dibasic acids. 



Equation (5.11) indicates consumption of carbon dioxide for n > 1 

 and liberation for n < 1, while equation (5.12) requires absorption of 

 carbon dioxide for n > 3 and its Hberation for n < 3. The theoretical 

 "photosynthetic quotients," ACO2/AFA (FA = fatty acid) are {n - l)/2 

 for monobasic and (n — 3)/2 for dibasic acids. 



On the whole, these deductions are confirmed by experiments, 

 although the agreement is only qualitative, and individual results scatter 

 considerably. Muller (1933) found that Thiorhodaceae liberate carbon 

 dioxide in the photoreduction of lactate and malate (as they should 

 according to stoichiometric equations, analogous to 5.11 and 5.12, which 

 can be set up for hydroxy acids), but consume it in that of butyrate (in 

 accordance with equation 5.11). Significantly, no butyrate assimilation 

 was observed unless bicarbonate was also provided. More detailed 

 results have been obtained by Gaffron (1933, 1935) with the Athio- 

 rhodaceae (Rhodovibrio) . He found the following values of the "photo- 

 synthetic quotient" Qp = ACO2/AFA. 



Table 5.V 

 Qp = ACO2/AFA FOR Rhodovibrio (Gaffron) and Spirillum rubrum (van Niel) 



