Positive linkage between bacterial social traits reveals that homogeneous rather than specialized behavioral repertoires prevail in natural Pseudomonas communities

Bacteria frequently cooperate by sharing secreted metabolites such as enzymes and siderophores. The expression of different public good traits can be interdependent, and studies on laboratory systems have shown that such trait linkage affects eco-evolutionary dynamics within bacterial communities. Here, we examine whether linkage among social traits occurs in natural Pseudomonas communities by examining investment levels and correlations between five public goods: biosurfactants, biofilm components, proteases, pyoverdines, and toxic compounds. Our phenotypic assays involving 315 isolates from soil and freshwater communities revealed that their social trait expression profiles varied dramatically, and that correlations between traits were frequent, exclusively positive, and sometimes habitat-specific. Our results indicate that Pseudomonas communities are dominated by isolates lying on a continuum between a social type producing multiple public goods, and an asocial type showing low investment into social traits. This segregation into different social types could reflect local adaptation to different microhabitats, or emerge from competition between different (social) strategies. Moreover, our results show that isolates with specialized trait repertoires are rare, suggesting limited scope for the mutual exchange of different public goods between isolates. Overall, our work indicates that complex interdependencies among social traits influence the evolution of microbial lifestyles in nature.