376 METABOLISM OF MICROORGANISMS 



Formulas with (+H0O) mean that their peculiar structure is present 

 only in water. These compounds crystallize as anhydrides. y-Methyl 

 tetronic acid may be regarded as the parent substance, and the others, 

 as substitution products. Carolinic acid has a succinyl group in place 

 of the hydrogen on the a-carbon. Carolic acid has a carbinol group 

 instead of a carboxyl group in the side chain. In carlosic acid the end 

 group in the R' side chain is methyl. These three compounds clearly 

 represent different degrees of oxidation. In carlosic acid and carlic acid 

 there are also carboxyl groups replacing the hydrogen at R in the formula. 

 All of these compounds are produced in only small amounts, in the order 

 of 1 to 2 per cent of the sugar fermented. It is of special interest that 

 five of the compounds are produced by the same mold. These must be 

 interrelated in the metabolism of P. charlesii. 



Many other such series of compounds have been described by Raistrick 

 as characteristic of mold metabolism, e.g., a citric, an anthraquinone, 

 and a tropolone series. Over 200 mold products have been isolated in 

 more than a quarter century of research work by Raistrick and co-workers. 

 From this wealth of material many interesting features of mold metabolism 

 have been discovered. For more information see his review paper listed 

 in the references at the end of this chapter. 



Another noteworthy aspect of mold metabolism is the formation of 

 organic chlorine compounds. Examples of such compounds are erdin 

 (C16H10O7CI2), and geodin (C17H12O7CI2). These two compounds are 

 produced by the same mold, Aspergillus terreus, and are closely related 

 in structure. 



Spoilage of such commercial products as wood, paper, leather, hay, 

 grain, bread, etc., constitutes a debit side of mold activities. An 

 inhibitor of mold growth, propionic acid, is widely used in the bread 

 industry. For use on nonfood materials, there are a number of mold 

 inhibitors, e.g., pentachlorphenol, CeClsOH. 



ANAEROBIC METABOLISM OF CARBOHYDRATES 



By bacteria 



The anerobic metabolism of bacteria is probably more diversified than 

 the aerobic and probably results in a larger number of products. (See 

 Table 14-1.) The principal types of anaerobic fermentations can be 

 classified by their major end products, as follows: 



1. The homolactic type of fermentation {e.g., by S. lactis) accounts for 

 more than 90 per cent of the glucose as lactic acid. Thus 



CgHioOe -^ 2CH3 • CHOH • COOH 



