Data from: Mridha S and Kümmerli R (2022) Enforced specialization fosters mutual cheating and not division of labour in the bacterium Pseudomonas aeruginosa

A common way for bacteria to cooperate is via the secretion of beneficial
public goods (proteases, siderophores, biosurfactants) that can be shared
among individuals in a group. Bacteria often simultaneously deploy
multiple public goods with complementary functions. This raises
the question whether natural selection could favour division of labour
where subpopulations or species specialise in the production of a single
public good, whilst sharing the complementary goods at the group level.
Here we use an experimental system, where we mix engineered specialists of
the bacterium Pseudomonas aeruginosa that can each only
produce one of the two siderophores, pyochelin or pyoverdine, and explore
the conditions under which specialization can lead to division of labour.
When growing pyochelin and pyoverdine specialists at different mixing
ratios under different levels of iron limitation, we found that
specialists could only successfully complement each other in environments
with moderate iron limitation and grow as good as the generalist wildtype
but not better. Under more stringent iron limitation, the dynamics in
specialist communities was characterized by mutual cheating and
with higher proportions of pyochelin producers greatly compromising group
productivity. Nonetheless, specialist communities remained stable through
negative frequency-dependent selection. Our work shows that specialization
in a bacterial community can be spurred by cheating and does not
necessarily result in beneficial division of labour. We propose that
natural selection might favour fine-tuned regulatory mechanisms in
generalists over division of labour because the former enables generalists
to remain flexible and adequately adjust public good investments in
fluctuating environments.