Liu Gui-Rong, Edwards Kelly, Eisenstark Abraham, Fu Ying-Mei, Liu Wei-Qiao, Sanderson Kenneth E, Johnston Randal N, Liu Shu-Lin
Department of Microbiology and Infectious Diseases, University of Calgary, Calgary, T2N 4N1 Alberta, Canada.
J Bacteriol. 2003 Apr;185(7):2131-42. doi: 10.1128/JB.185.7.2131-2142.2003.
To document genomic changes during long periods of storage, we analyzed Salmonella enterica serovar Typhimurium LT7, a mutator strain that was previously reported to have higher rates of mutations compared to other serovar Typhimurium strains such as LT2. Upon plating directly from sealed agar stabs that had been stocked at room temperature for up to four decades, many auxotrophic mutants derived from LT7 gave rise to colonies of different sizes. Restreaking from single colonies consistently yielded colonies of diverse sizes even when we repeated single-colony isolation nine times. Colonies from the first plating had diverse genomic changes among and even within individual vials, including translocations, inversions, duplications, and point mutations, which were detected by rare-cutting endonuclease analysis with pulsed-field gel electrophoresis. Interestingly, even though the colony size kept diversifying, all descendents of the same single colonies from the first plating had the same sets of detected genomic changes. We did not detect any colony size or genome structure diversification in serovar Typhimurium LT7 stocked at -70 degrees C or in serovar Typhimurium LT2 stocked either at -70 degrees C or at room temperature. These results suggest that, although colony size diversification occurred during rapid growth, all detected genomic changes took place during the storage at room temperature and were carried over to their descendents without further changes during rapid growth in rich medium. We constructed a genomic cleavage map on the LT7 strain that had been stocked at -70 degrees C and located all of the detected genomic changes on the map. We speculated on the significance of mutators for survival and evolution under environmentally stressed conditions.
为记录长时间储存过程中的基因组变化，我们分析了肠炎沙门氏菌鼠伤寒血清型LT7，这是一种突变菌株，先前报道其与其他鼠伤寒血清型菌株（如LT2）相比具有更高的突变率。从室温储存长达四十年的密封琼脂穿刺培养物中直接接种平板时，许多源自LT7的营养缺陷型突变体产生了大小不同的菌落。即使我们将单菌落分离重复九次，从单个菌落再次划线接种始终会产生大小各异的菌落。首次接种平板得到的菌落在各个小瓶之间甚至单个小瓶内部都有不同的基因组变化，包括易位、倒位、重复和点突变，这些变化通过脉冲场凝胶电泳的稀有切割内切酶分析得以检测。有趣的是，尽管菌落大小持续多样化，但首次接种平板中同一单个菌落的所有后代都有相同的一组检测到的基因组变化。我们在储存在-70℃的鼠伤寒血清型LT7或储存在-70℃或室温的鼠伤寒血清型LT2中未检测到任何菌落大小或基因组结构的多样化。这些结果表明，尽管菌落大小多样化发生在快速生长期间，但所有检测到的基因组变化都发生在室温储存期间，并在丰富培养基中快速生长期间传递给它们的后代，且没有进一步变化。我们构建了储存在-70℃的LT7菌株的基因组切割图谱，并在图谱上定位了所有检测到的基因组变化。我们推测了突变体在环境压力条件下生存和进化的意义。
