1 88 AIDS TO BACTEBIOLOGY 



CHAPTER XVIII 



FERMENTATION ENZYMES SULPHUR AND 

 IRON BACTERIA 



Fermentation. 



FERMENTATION by yeasts, see p. 162 et seq. Fermentation 

 by moulds, see p. 170. Bacterial fermentation may 

 involve oxidation, hydration, reduction, or simple de- 

 composition processes^ 



Acetic Acid Bacteria. Mycoderma aceti, the oxidising 

 agent used in the manufacture of vinegar, consists of two 

 species of bacteria B. aceti (Hanseri) and B. Pastorianum 

 (Hansen). 



B. aceti (Kutzing} Hansen forms a gelatinous film on 

 ' double ' beer when grown at 34 C. for twenty-four hours. 

 The film consists of chains of hour-glass-shaped indi- 

 viduals. The mucilage surrounding the organisms is not 

 stained by iodine. On wort-gelatin at 25 C. grey, waxy, 

 well-defined colonies are formed in four days, but no chains 

 are produced. 



B. Pastorianum (Hansen} forms a dry, wrinkled film 

 on ' double ' beer in twenty-four hours at 34 C. The 

 mucilage is stained blue by iodine. The growth on wort- 

 gelatin consists chiefly of chains. 



B. Kiltzingianum (Hansen} on ' double ' beer at 34 C. 

 in twenty-four hours forms a dry film, which,"* unlike 

 B. Pastorianum, grows high above the level of ^the^liquid, 

 along the sides of the flask. The mucilage stains blue 

 with iodine, and long chains are seldom found in the 

 colonies on wort-gelatin. 



The term ' acetic acid bacteria ' is confined to those 

 that give off acetic acid as a main product. Their number 

 is small, though many bacteria produce minute quantities 

 of this acid. 



Micrococcus urese produces an enzyme (urease) that 

 hydrolyses urea to ammonium carbonate. The cocci 

 vary from 08^ to l'0/u, in diameter, occur as pairs, tetrads, 

 or chains, and sometimes assume a bacillary form. 



B. acidi lactici is aerobic, non-motile, and non-sporing. 



