Utnes Ane L G, Sørum Vidar, Hülter Nils, Primicerio Raul, Hegstad Joachim, Kloos Julia, Nielsen Kaare M, Johnsen Pål J
Department of Pharmacy, Faculty of Health Sciences, UiT The Arctic University of Norway, Tromsø, Norway.
Department of Microbiology and Infection Control, University Hospital of North Norway, Tromsø, Norway.
ISME J. 2015 Oct;9(10):2221-31. doi: 10.1038/ismej.2015.35. Epub 2015 Apr 7.
Natural transformation in bacteria facilitates the uptake and genomic integration of exogenous DNA. This allows horizontal exchange of adaptive traits not easily achieved by point mutations, and has a major role in the acquisition of adaptive traits exemplified by antibiotic resistance determinants and vaccination escape. Mechanisms of DNA uptake and genomic integration are well described for several naturally transformable bacterial species; however, the selective forces responsible for its evolution and maintenance are still controversial. In this study we evolved transformation-proficient and -deficient Acinetobacter baylyi for 175 days in serial transfer cultures where stress was included. We found that natural transformation-proficient populations adapted better to active growth and early stationary phase. This advantage was offset by the reduced performance in the late stationary/death phase. We demonstrate fitness trade-offs between adaptation to active growth and survival in stationary/death phase caused by antagonistic pleiotropy. The presented data suggest that the widely held assumption that recombination speeds up adaptation by rapid accumulation of multiple adaptive mutations in the same genetic background is not sufficient to fully account for the maintenance of natural transformation in bacteria.
细菌中的自然转化促进了外源DNA的摄取和基因组整合。这使得适应性性状能够进行水平交换，而这是点突变难以轻易实现的，并且在获得以抗生素抗性决定因素和疫苗逃逸为代表的适应性性状方面发挥着重要作用。对于几种自然可转化的细菌物种，DNA摄取和基因组整合的机制已有详尽描述；然而，导致其进化和维持的选择压力仍存在争议。在本研究中，我们在包含压力的连续传代培养中，使具备转化能力和缺乏转化能力的拜氏不动杆菌进化了175天。我们发现，具备自然转化能力的群体能更好地适应活跃生长和早期稳定期。但这一优势在稳定期末期/死亡期的表现下降中被抵消。我们证明了由拮抗性多效性导致的在适应活跃生长与在稳定期/死亡期存活之间的适合度权衡。所呈现的数据表明，那种认为重组通过在相同遗传背景中快速积累多个适应性突变来加速适应的普遍假设，不足以充分解释细菌中自然转化的维持。
