The first to describe anaerobic fermentative metabolism
was Louis Pasteur, who described fermentation as ‘la vie
sans l’air’. Today, three physiological groups of anaerobic
microorganisms can be distinguished: (i) the anaerobic
phototrophs, (ii) the anaerobic respirers such as denitri-
fiers, sulfate reducers, methanogens and homoacetogens,
which use nitrate, sulfate and carbon dioxide, respectively,
as electron acceptors in the absence of oxygen, and (iii) the
fermentative organisms.