摘要

胶囊允许细菌定居新环境，承受多种压力，并抵抗抗生素。然而，即使在这种情况下与其他细胞的遗传交换应该是适应性的，已经提出胶囊降低了同源重组和水平基因转移的速率。我们分析了超过100个泛基因组和数千个细菌基因组，以证明遗传交换（或其缺乏）与胶囊系统存在之间的关联。我们发现编码胶囊的细菌具有更大的泛基因组，更高的水平基因转移率，以及核心基因组中更高的同源重组率。因此，编码胶囊的基因组具有更多的质粒，接合元件，转座酶，前噬菌体和整合子。此外，荚膜位点在质粒中很常见，并且可以在预先发现。这些结果对细菌有效，与它们自然转化的能力无关。由于我们之前已经表明胶囊通常存在于医院病原体中，我们分析了它们与抗生素抗性基因的共存。编码胶囊的基因组具有更多抗生素抗性基因，尤其是那些编码外排泵的基因，它们构成了最令人担忧的医院内细菌的大多数。我们得出结论，具有胶囊系统的细菌具有更多的遗传多样性，并且具有快速进化的基因库，这可能进一步有助于他们在抗生素治疗下定殖新的小生境如人类。

Capsules allow bacteria to colonize novel environments, to withstand numerous stresses, and to resist antibiotics. Yet, even though genetic exchanges with other cells should be adaptive under such circumstances, it has been suggested that capsules lower the rates of homologous recombination and horizontal gene transfer. We analysed over one hundred pan-genomes and thousands of bacterial genomes for the evidence of an association between genetic exchanges (or lack thereof) and the presence of a capsule system. We found that bacteria encoding capsules have larger pan-genomes, higher rates of horizontal gene transfer, and higher rates of homologous recombination in their core genomes. Accordingly, genomes encoding capsules have more plasmids, conjugative elements, transposases, prophages, and integrons. Furthermore, capsular loci are frequent in plasmids, and can be found in prophages. These results are valid for Bacteria, independently of their ability to be naturally transformable. Since we have shown previously that capsules are commonly present in nosocomial pathogens, we analysed their co-occurrence with antibiotic resistance genes. Genomes encoding capsules have more antibiotic resistance genes, especially those encoding efflux pumps, and they constitute the majority of the most worrisome nosocomial bacteria. We conclude that bacteria with capsule systems are more genetically diverse and have fast-evolving gene repertoires, which may further contribute to their success in colonizing novel niches such as humans under antibiotic therapy.

https://www.ncbi.nlm.nih.gov/pubmed/30576310