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Consequences of Cryopreservation in Diverse Natural Isolates of Saccharomyces cerevisiae.
Genome Biology and Evolution ( IF 3.3 ) Pub Date : 2020-07-01 , DOI: 10.1093/gbe/evaa121
Kieslana M Wing 1 , Mark A Phillips 1 , Andrew R Baker 1 , Molly K Burke 1
Affiliation  

Experimental evolution allows the observation of change over time as laboratory populations evolve in response to novel, controlled environments. Microbial evolution experiments take advantage of cryopreservation to archive experimental populations in glycerol media, creating a frozen, living “fossil” record. Prior research with Escherichia coli has shown that cryopreservation conditions can affect cell viability and that allele frequencies across the genome can change in response to a freeze-thaw event. We expand on these observations by characterizing fitness and genomic consequences of multiple freeze-thaw cycles in diploid yeast populations. Our study system is a highly recombinant Saccharomyces cerevisiae population (SGRP-4X) which harbors standing genetic variation that cryopreservation may threaten. We also investigate the four parental isogenic strains crossed to create the SGRP-4X. We measure cell viability over 5 consecutive freeze-thaw cycles; while we find that viability increases over time in the evolved recombinant populations, we observe no such viability improvements in the parental strains. We also collect genome-wide sequence data from experimental populations initially, after one freeze-thaw, and after five freeze-thaw cycles. In the recombinant evolved populations, we find a region of significant allele frequency change on chromosome 15 containing the ALR1 gene. In the parental strains, we find little evidence for new mutations. We conclude that cryopreserving yeast populations with standing genetic variation may have both phenotypic and genomic consequences, though these same cryopreservation practices may have only small impacts on populations with little or no initial variation.

中文翻译:

酿酒酵母的多种天然分离物中冷冻保存的后果。

随着实验室人口对新的受控环境的发展而不断发展,实验的演变可以观察随着时间的变化。微生物进化实验利用冷冻保存的优势将实验种群归档在甘油培养基中,从而形成了冷冻的,活着的“化石”记录。先前对大肠杆菌的研究表明,低温保存条件会影响细胞活力,而基因组中的等位基因频率会因冻融事件而改变。我们通过表征二倍体酵母种群中多次冻融循环的适应性和基因组后果来扩展这些观察结果。我们的研究系统是高度重组的酿酒酵母具有低温保存可能威胁的常设遗传变异的种群(SGRP-4X)。我们还研究了创建SGRP-4X的四个亲本同基因菌株。我们在连续5次冻融循环中测量细胞活力;尽管我们发现进化后的重组群体中的活力随着时间的推移而增加,但我们在亲本菌株中却没有看到这种活力的提高。我们还从最初的实验种群,一次冻融后和五个冻融循环后收集实验人群的全基因组序列数据。在重组的进化种群中,我们在含有ALR1基因的15号染色体上发现了一个重要的等位基因频率变化区域。在亲本菌株中,我们几乎找不到新突变的证据。
更新日期:2020-07-01
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