Formic acid fermentation
The formic acid fermentations are the ways of degradation of sugars for energy under anoxic conditions which in some facultative anaerobic bacteria occur, especially at the enterobacteria . The breakdown of sugars takes place in different ways and a number of end products are formed. A characteristic end product or intermediate product is always formate (anion of formic acid ). Formate is completely or partially excreted or split into molecular , elemental hydrogen (H 2 ) and carbon dioxide (CO 2 ).
There are two types of formic acid fermentation:
- 2,3-Butanediol fermentation in which the characteristic end product is 2,3-butanediol and acids are only formed in small quantities. The pH of the culture medium therefore only drops slightly. Acetoin, formed as a precursor of 2,3-butanediol, can be detected as a characteristic intermediate product with the Voges-Proskauer reaction .
- Mixed acid fermentation in which a number of acids ( lactic acid , acetic acid , succinic acid ) are formed in large quantities, but no 2,3-butanediol and no acetoin. The pH of the culture medium therefore drops significantly, the test for acetoin with the Voges-Proskauer reaction turns out negative.
The presence of one of these two fermentations is an important distinguishing feature when identifying the enterobacteria.
literature
- Georg Fuchs (Ed.): General Microbiology (started by Hans G. Schlegel). 8th edition. Georg Thieme Verlag, Stuttgart, New York 2007, ISBN 978-3-13-444608-1 .