Antagonistic Interactions Among Yeasts

Abstract

In every biocenosis, competition for nutrients and space is one of the major factors that determines which organisms succeed and become established. The reasons for such ecological success vary. In many cases, the microbes often alter the environment with their metabolic products, securing their dominance in the habitat as they create conditions unfavourable for the survival of other microorganisms. Such interaction is known as antagonism. Some of these antimicrobial compounds are nonspecific. For example, the antibacterial activity of yeasts is commonly caused by pH changes in the medium as a result of organic acid production or by producing high concentrations of ethanol. This chapter will focus on much more specific interactions stemming from antifungal agent secretion by yeasts. By now two classes of such extracellular agents of yeasts are known: (glyco)proteins and glycolipids (Fig. 10.1). The proteinaceous compounds having fungicidal or fungistatic action are termed mycocins (zymocins, killer toxins) and they have been investigated for some 40 years, whereas the fungicidal activity of their extracellular glycolipids has only recently come to light.