School of Biosciences, University of Sheffield, Alfred Denny Building, Western Bank, Sheffield S10 2TN, United Kingdom.
John Innes Centre, Norwich Research Park, Colney Ln, Norwich NR4 7UH, United Kingdom.
FEMS Microbiol Ecol. 2023 Mar 23;99(4). doi: 10.1093/femsec/fiad027.
Plasmids drive bacterial evolutionary innovation by transferring ecologically important functions between lineages, but acquiring a plasmid often comes at a fitness cost to the host cell. Compensatory mutations, which ameliorate the cost of plasmid carriage, promote plasmid maintenance in simplified laboratory media across diverse plasmid-host associations. Whether such compensatory evolution can occur in more complex communities inhabiting natural environmental niches where evolutionary paths may be more constrained is, however, unclear. Here, we show a substantial fitness cost of carrying the large conjugative plasmid pQBR103 in Pseudomonas fluorescens SBW25 in the plant rhizosphere. This plasmid fitness cost could be ameliorated by compensatory mutations affecting the chromosomal global regulatory system gacA/gacS, which arose rapidly in plant rhizosphere communities and were exclusive to plasmid carriers. These findings expand our understanding of the importance of compensatory evolution in plasmid dynamics beyond simplified lab media. Compensatory mutations contribute to plasmid survival in bacterial populations living within complex microbial communities in their environmental niche.
质粒通过在谱系之间转移生态重要功能来驱动细菌的进化创新，但宿主细胞获得质粒往往会带来适应性成本。补偿突变可以减轻质粒携带的成本，促进质粒在不同质粒-宿主关联的简化实验室培养基中维持。然而，在更复杂的自然环境小生境中栖息的群落中，是否会发生这种补偿进化，这些进化路径可能受到更多限制，目前尚不清楚。在这里，我们表明，在植物根际中的荧光假单胞菌 SBW25 中携带大型可接合质粒 pQBR103 会带来很大的适应性成本。这种质粒适应性成本可以通过影响染色体全局调控系统 gacA/gacS 的补偿突变来减轻，该系统在植物根际群落中迅速出现，并且只存在于质粒载体中。这些发现扩展了我们对补偿进化在质粒动力学中的重要性的理解，超出了简化的实验室培养基。补偿突变有助于质粒在其生态位的复杂微生物群落中的细菌种群中存活。
