Iron is an important nutrient for the bacterium Pseudomonas aeruginosa, however, iron is not easily accessible in the environment. To overcome this problem, P. aeruginosa produces siderophores to bind and transport iron. But the bacterium that produced the siderophores does not necessarily receive the direct benefit of iron intake. Rather all members of the cellular population are equally likely to access the iron-siderophore complexes. The production of siderophores also requires the bacterium to expend energy. Thus, siderophore production can be looked at as an altruistic trait because it is beneficial for the local group but costly for the individual. This altruistic dynamic requires every member of the cellular population to equally contribute to siderophore production. But at times mutations can occur that result in some bacteria producing lower amounts of siderophore. These mutations give an evolutionary advantage because the bacterium can benefit from siderophore production without suffering the energy cost. Thus, more energy can be allocated to growth. Members of the cellular population that can efficiently produce these siderophores are commonly referred to as cooperators; members that produce little to no siderophores are often referred to as cheaters. Research has shown when cooperators and cheaters are grown together, cooperators have a decrease in fitness while cheaters have an increase in fitness. It is observed that the magnitude of change in fitness increases with increasing iron-limitation. With an increase in fitness, the cheaters can outcompete the cooperators; this leads to an overall decrease in fitness of the group, due to lack of sufficient siderophore production.