Maintenance of cooperation in a yeast population in a public-good driven system.

The phenomenon of cooperation is prevalent at all levels of life. In microbial communities, some groups of cells exhibit cooperative behaviour by producing costly extracellular resources that are freely available to others. These resources are referred to as public goods. Saccharomyces cerevisiae secretes invertase (public good) in the periplasm to hydrolyse sucrose into glucose and fructose, which are further imported by the cells. After hydrolysis of sucrose, the cells retain only 1% of the monosaccharides, while 99% diffuse into the environment and can be utilised by all neighbouring cells. The non-producers of invertase (cheaters) exploit the invertase-producing cells (cooperators) by utilising the monosaccharides and paying nothing for the latter. In this work, we investigate the evolutionary dynamics of this cheater-cooperator system. If cheaters are selected for their higher fitness, the population will collapse. For cooperators to survive cheating and thrive in nature, they should have evolved some survival strategies. To understand the adaptation of cooperators in sucrose, we performed a coevolution experiment in sucrose. Our results show that cooperators increase in fitness as the experiment progresses. This phenomenon was not observed in environments which involved a non-public good system. Genome sequencing reveals the molecular basis for the cooperator adaptating is because of increased privatization of the public-good released carbon resource.