## Thieves among microorganisms

An example of the social behaviour of microorganisms can be observed in some types of yeast, which are often referred to as social cheaters. We are talking about liars who take advantage of the social community while contributing less than average to its functioning. There are types of baker's yeast, Saccharomyces cerevisiae, which cannot produce the invertase enzyme due to a mutation in the SUC2 gene. The latter breaks down the extracellular disaccharide sucrose into molecules of simple sugars, glucose and fructose, which are subsequently transported into the cells as a source of energy. This means that yeast with a mutation in the SUC2 gene cannot independently process such a disaccharide. However, if they are in a community with other yeasts that do not have the mutation, the wild type yeast will produce invertase, and shortly after breaking down sucrose, the mutant yeast "steal" glucose and fructose molecules from the environment and use them for their own metabolism (Figure 13.1). At the same time, they save energy that would otherwise have to be spent on enzyme production. Thus, social cheaters are favoured in the environment until the environment is full of yeast capable of producing invertase. The rogue behaviour of mutants resulting from the non-functionality of a single gene can change the default behaviour into an exploitative way of functioning in the social group of these yeasts.