Horizontal gene transfer via plasmids could favour cooperation in bacteria, because transfer of a cooperative gene turns non-cooperative cheats into cooperators. This hypothesis has received support from theoretical, genomic and experimental analyses. By contrast, we show here, with a comparative analysis across 51 diverse species, that genes for extracellular proteins, which are likely to act as cooperative ‘public goods’, were not more likely to be carried on either: (1) plasmids compared to chromosomes; or (2) plasmids that transfer at higher rates. Our results were supported by theoretical modelling which showed that, while horizontal gene transfer can help cooperative genes initially invade a population, it has less influence on the longer-term maintenance of cooperation. Instead, we found that genes for extracellular proteins were more likely to be on plasmids when they coded for pathogenic virulence traits, in pathogenic bacteria with a broad host-range.

通过质粒的水平基因转移可能有利于细菌的合作，因为合作基因的转移会将不合作的骗子变成合作者。这一假设得到了理论、基因组和实验分析的支持。相比之下，我们在此通过对 51 个不同物种的比较分析表明，可能作为合作“公共产品”的细胞外蛋白基因不太可能在任何一种上携带：（1）与质粒相比染色体；或 (2) 以更高速率转移的质粒。我们的结果得到了理论模型的支持，该模型表明，虽然水平基因转移可以帮助合作基因最初侵入种群，但对长期维持合作的影响较小。反而，