PRODUCTS OF METABOLISM 1 73 



As a third group, B. coli may be mentioned which forms indol, but rio 

 ammonia from peptone, and whose proteolytic powers are very weak 

 as it does not even liquefy gelatin. 



Anaerobic decomposition of proteins is limited to very few species; 

 there is a great difference in the availability of proteins and of' carbo- 

 hydrates as a source of energy, protein being available only to a few 

 species, most of these preferring carbohydrates if they are present 

 together with protein. B. putrificus is the main representative, but 

 other forms exist. B. putrificus is strictly anaerobic, and a spore former, 

 very common in nature. Among the products are skatol, hydrogen 

 sulphide, ammonia and other very offensive compounds. 



Urea, uric acid, hippuric acid, are the end products of protein 

 metabolism of the higher animals. The decomposition of urea to 

 ammonium carbonate has been mentioned in several places, mainly 

 on page 146. It is a simple hydrolysis 



CO(NH2)2 + 2H2O = (NH4)2C03. 



This change can be brought about by only a few bacteria which are 

 commonly grouped together as "urea bacteria." These organisms 

 have hardly anything else in common, however, and the group is not a 

 well-defined one. There arfe rods and coccus forms, motile and non- 

 motile organisms, spore-formers and non-spore formers, and even molds 

 have recently been found to hydrolyze urea. All urea bacteria can 

 Uve without urea, feeding on organic matter like other bacteria, but 

 most of them require an alkaUne medium. 



Hippuric acid is spUt by certain bacteria to benzoic acid and 

 amino-acetic acid which can be oxidized completely. Uric acid can be 

 changed in several ways. In some of these changes, urea is found as 

 an intermediary product. 



Products from Mineral Compounds 



Minerals are used by microorganisms for cell construction almost 

 erclusively; consequently, they do not leave the living cell-hke fermen- 

 tation products. But a few organisms can actually decompose mineral 

 matter and when this takes place mineral products are secreted. Two 

 main processes can be distinguished, oxidation and reduction. 



Oxidations are the result of the organisms seeking a supply of 

 energy. Several oxidations of minerals have been indicated previously, 

 as the oxidation of ammonia to nitrites, of nitrites to nitrates, of hypo- 



