Privatisation rescues function following loss of cooperation.

A single cheating mutant can lead to the invasion and eventual eradication of cooperation from a population. Consequently, cheat invasion is often considered equal to extinction in empirical and theoretical studies of cooperator-cheat dynamics. But does cheat invasion necessarily equate extinction in nature? By following the social dynamics of iron metabolism in Pseudomonas aeruginosa during cystic fibrosis lung infection, we observed that individuals evolved to replace cooperation with a 'private' behaviour. Phenotypic assays showed that cooperative iron acquisition frequently was upregulated early in infection, which, however, increased the risk of cheat invasion. With whole-genome sequencing we showed that if, and only if, cooperative iron acquisition is lost from the population, a private system was upregulated. The benefit of upregulation depended on iron availability. These findings highlight the importance of social dynamics of natural populations and emphasizes the potential impact of past social interaction on the evolution of private traits.

Gene and library synthesis without amplification: polymerase step reaction (PSR).

Current gene synthesis methods often incorporate a PCR amplification step in order to yield final material sufficient for resolution from multiple off-products. These amplification steps can cause stochastic sampling effects that propagate errors in gene synthesis or decrease variability when applied to the construction of randomized libraries. We have developed a simple DNA polymerase-based gene synthesis reaction, polymerase step reaction (PSR), that assembles DNA oligonucleotides in a unidirectional fashion without the need for amplification. We demonstrate that PSR is efficient, with little off-product production, no detectable error propagation, and maximized variability in the synthesis of a phage display library.