Hülter Nils, Sørum Vidar, Borch-Pedersen Kristina, Liljegren Mikkel M, Utnes Ane L G, Primicerio Raul, Harms Klaus, Johnsen Pål J
Genomic Microbiology, Institute of Microbiology, Christian-Albrechts-University Kiel, Am Botanischen Garten 11, 24118, Kiel, Germany.
Department of Pharmacy, Faculty of Health Sciences, UiT The Arctic University of Norway, P.O. Box 6050 Langnes, Tromsø, Norway.
BMC Microbiol. 2017 Feb 15;17(1):34. doi: 10.1186/s12866-017-0953-2.
Natural transformation enables acquisition of adaptive traits and drives genome evolution in prokaryotes. Yet, the selective forces responsible for the evolution and maintenance of natural transformation remain elusive since taken-up DNA has also been hypothesized to provide benefits such as nutrients or templates for DNA repair to individual cells.
We investigated the immediate effects of DNA uptake and recombination on the naturally competent bacterium Acinetobacter baylyi in both benign and genotoxic conditions. In head-to-head competition experiments between DNA uptake-proficient and -deficient strains, we observed a fitness benefit of DNA uptake independent of UV stress. This benefit was found with both homologous and heterologous DNA and was independent of recombination. Recombination with taken-up DNA reduced survival of transformed cells with increasing levels of UV-stress through interference with nucleotide excision repair, suggesting that DNA strand breaks occur during recombination attempts with taken-up DNA. Consistent with this, we show that absence of RecBCD and RecFOR recombinational DNA repair pathways strongly decrease natural transformation.
Our data show a physiological benefit of DNA uptake unrelated to recombination. In contrast, recombination during transformation is a strand break inducing process that represents a previously unrecognized cost of natural transformation.
自然转化能够使原核生物获得适应性性状并推动基因组进化。然而，由于摄取的DNA也被假定可为单个细胞提供诸如营养或DNA修复模板等益处，因此负责自然转化进化和维持的选择压力仍然难以捉摸。
我们研究了在良性和基因毒性条件下，DNA摄取和重组对天然感受态细菌拜氏不动杆菌的直接影响。在DNA摄取能力强和弱的菌株之间的直接竞争实验中，我们观察到DNA摄取具有适应性优势，且与紫外线胁迫无关。这种优势在同源和异源DNA中均有发现，且与重组无关。随着紫外线胁迫水平的增加，与摄取的DNA进行重组会通过干扰核苷酸切除修复降低转化细胞的存活率，这表明在与摄取的DNA进行重组尝试期间会发生DNA链断裂。与此一致地，我们表明RecBCD和RecFOR重组DNA修复途径的缺失会强烈降低自然转化。
我们的数据表明DNA摄取具有与重组无关的生理优势。相反，转化过程中的重组是一个诱导链断裂的过程，这代表了自然转化之前未被认识到的代价。
