Bacterial Fermentations

Abstract

Large areas in the soil, in rivers, lakes, and oceans are devoid of oxygen. Nevertheless, numerous microorganisms live in these anaerobic environments. We have already discussed the dissimilatory reduction of nitrate, which takes place under anaerobic conditions. Besides this process, two other microbiological processes account to a large extent for the biological activities in environments devoid of oxygen: bacterial fermentations and bacterial photosynthesis. The term fermentation was first defined by Pasteur, to whom we owe the pioneering work in this field; he described fermentations as life in the absence of oxygen. Today fermentations can be defined as those biological processes that occur in the dark and that do not involve respiratory chains with oxygen or nitrate as electron acceptors. In many fermentations ATP is formed only by substrate-level phosphorylation. However, in a number of fermentations electron transport phosphorylation is also involved in ATP synthesis.