PRODUCTS OF THE LOWER FUNGI 2!J7 



of butyrolactone and succinic acid with y-methyltetronic 

 acid and of butyrolactone and butyric acid with 

 y-carboxy-methyltetronic acid respecti v^el}^, as shown by 

 the formulae given in Table 19, (p. 287). 



It will be seen that they have stiTictures bearing a 

 close resemblance to that of ascorbic acid, vitamin G, 

 which is also said to be produced by some Aspergillus 

 and Penicillium species, although the evidence rests on 

 the demonstration of a substance reducing 2 : 6 dichloro- 

 phenolindophenol and not on isolation of ascorbic acid. 

 Terrestric and penicillic acids are also shown to be 

 derivatives of tetronic acid. 



Theories of Acid Production by Fungi.— There is still a 

 considerable amount of controversy as to the mechanism 

 of the production of acids by fungi, particularly as regards 

 the commercially important oxalic and citric acids. 

 Ehrlich, in 1911, suggested that citric acid was formed as 

 the result of the condensation of three molecules of 

 acetaldehyde followed by oxidation of a methyl group 

 and the aldehyde groups to give the carboxyl groups : — 

 CH2.CHO CH2.COOH 



--> CH.CH3 > C(OH).COOH (citric acid) 



^ + I I 



H.CHa.CHO CH2.CHO CH2.COOH 



This cannot be the correct mechanism, however, 

 since the maximum yield of citric acid from a hexose 

 would be 71 per cent., whereas in practice yields as high 

 as 95 per cent, can be obtained readily. 



The theory of Chrzaszcz and Tiukow, according to 

 whom acetic acid, derived by steps like those in alcoholic 

 fermentation, condenses via succinic, fumaric and malic 

 acids to give citric acid ; that of Bernhauer, according 

 to which acetic acid condenses with succinic acid to give 

 aconitic acid which in turn yields citric acid and that of 

 Emde which suggests that citric acid arises by oxidation 

 of (juinic acid are all su]>jeot to the same o])jecti()n that 

 they do not allow for yields of citric acid as high as those 



