Synthetic and Systems Biology Unit, Institute of Biochemistry, Biological Research Centre of the Eötvös Lóránd Research Network, Szeged, Hungary.
Faculty of Science and Informatics, Doctoral School in Biology, University of Szeged, Szeged, Hungary.
PLoS One. 2021 Mar 8;16(3):e0243517. doi: 10.1371/journal.pone.0243517. eCollection 2021.
Deuterium (D), the second most abundant isotope of hydrogen is present in natural waters at an approximate concentration of 145-155 ppm (ca. 1.5E-4 atom/atom). D is known to influence various biological processes due to its physical and chemical properties, which significantly differ from those of hydrogen. For example, increasing D-concentration to >1000-fold above its natural abundance has been shown to increase the frequency of genetic mutations in several species. An interesting deterministic hypothesis, formulated with the intent of explaining the mechanism of D-mutagenicity is based on the calculation that the theoretical probability of base pairs to comprise two adjacent D-bridges instead of H-bridges is 2.3E-8, which is equal to the mutation rate of certain species. To experimentally challenge this hypothesis, and to infer the mutagenicity of D present at natural concentrations, we investigated the effect of a nearly 100-fold reduction of D concentration on the bacterial mutation rate. Using fluctuation tests, we measured the mutation rate of three Escherichia coli genes (cycA, ackA and galK) in media containing D at either <2 ppm or 150 ppm concentrations. Out of 15 pair-wise fluctuation analyses, nine indicated a significant decrease, while three marked the significant increase of the mutation/culture value upon D-depletion. Overall, growth in D-depleted minimal medium led to a geometric mean of 0.663-fold (95% confidence interval: 0.483-0.911) change in the mutation rate. This falls nowhere near the expected 10,000-fold reduction, indicating that in our bacterial systems, the effect of D abundance on the formation of point mutations is not deterministic. In addition, the combined results did not display a statistically significant change in the mutation/culture value, the mutation rate or the mutant frequency upon D-depletion. The potential mutagenic effect of D present at natural concentrations on E. coli is therefore below the limit of detection using the indicated methods.
氘（D）是氢的第二丰富同位素，在天然水中的浓度约为 145-155ppm（约为 1.5E-4 原子/原子）。由于其物理和化学性质与氢有很大的不同，D 已知会影响各种生物过程。例如，将 D 浓度增加到其自然丰度的 1000 倍以上，已被证明会增加几个物种的基因突变频率。一个有趣的确定性假设，是为了解释 D 的诱变机制而提出的，其依据是计算出碱基对由两个相邻的 D 桥而不是 H 桥组成的理论概率为 2.3E-8，这与某些物种的突变率相等。为了实验性地挑战这一假设，并推断出天然浓度下 D 的诱变作用，我们研究了将 D 浓度降低近 1000 倍对细菌突变率的影响。使用波动试验，我们测量了三种大肠杆菌基因（cycA、ackA 和 galK）在含有 D 的培养基中的突变率，D 的浓度分别为<2ppm 或 150ppm。在 15 次成对波动分析中，有 9 次表明突变/培养值显著降低，而有 3 次表明 D 耗尽后突变/培养值显著增加。总的来说，在 D 耗尽的最小培养基中生长导致突变率发生了 0.663 倍（95%置信区间：0.483-0.911）的几何平均变化。这远低于预期的 10000 倍降低，表明在我们的细菌系统中，D 丰度对点突变形成的影响不是确定性的。此外，D 耗尽后，突变/培养值、突变率或突变频率的综合结果没有显示出统计学上的显著变化。因此，使用所指示的方法，在天然浓度下的 D 对大肠杆菌的潜在诱变作用低于检测限。
