Microbial cooperation includes various behaviours, such as nutrient acquisition. However, little is known about the costs and benefits of cooperation in relation to microbial growth. A recent study by Sexton and Schuster investigated the effects of nutrient limitation on the production of the siderophore pyoverdine (PVD), one of the main models for bacterial cooperation in Pseudomonas aeruginosa. By using a genome-scale metabolic in silico model, the authors showed that the production of PVD has a fitness cost only when its metabolic building blocks — carbon and nitrogen — are limited, as under these conditions it competes with biomass synthesis. Moreover, by testing microbial growth in continuous culture chemostats, they showed that bacteria that do not produce PVD (cheaters) had a large fitness advantage over bacteria that do produce it (cooperators), and that they spread with high frequency when carbon sources (but not other nutrients, such as phosphorus) were limited.