Table 1. Definition of terms used in this paper.

Cooperative trait	A trait that confers benefits to a recipient individual. The cooperative trait can be costly to the actor (altruistic trait) or beneficial to the actor (mutualism) (West et al, 2006)
Cooperator	An individual or a strain carrying the cooperative trait, also called the ‘actor’
Defector	An individual or a strain lacking a cooperative trait but capable of exploiting the cooperation of others
Metabolic prudence	A mechanism of gene expression regulation that allows wild-type Pseudomonas aeruginosa to produce biosurfactants at no cost to its fitness (Xavier et al, 2011)
Selfishness	A defector strategy where individuals lack a costly cooperative trait but exploit the cooperation of others