Institute for Ecopreneurship, School of Life Sciences, University of Applied Sciences and Arts Northwestern Switzerland, Hofackerstrasse 30, 4132, Muttenz, Switzerland; Institute for Environmental Research, RWTH Aachen University, Worringerweg 1, 52074, Aachen, Germany.
Institute for Environmental Research, RWTH Aachen University, Worringerweg 1, 52074, Aachen, Germany.
Chemosphere. 2023 Dec;345:140548. doi: 10.1016/j.chemosphere.2023.140548. Epub 2023 Oct 25.
Selenium deficiency affects many million people worldwide and volatilization of biogenically methylated selenium species to the atmosphere may limit Se entering the food chain. However, there is very little systematic data on volatilization at nanomolar concentrations prevalent in pristine natural environments. Pseudomonas tolaasii cultures efficiently methylated Se at these concentrations. Nearly perfect linear correlations between the spiked Se concentrations and Dimethylselenide, Dimethyldiselenide, Dimethylselenylsulfide and 2-hydroxy-3-(methylselanyl)propanoic acid were observed up to 80 nM. The efficiency of methylation increased linearly with increasing initial Se concentration, arguing that the enzymes involved are not constitutive, but methylation proceeds promiscuously via pathways of S methylation. From the ratio of all methylated Se and S species, one can conclude that between 0.30% and 3.48% of atoms were Se promiscuously methylated at such low concentrations. At concentrations higher than 640 nM (∼50 μg/L) a steep increase in methylation and volatilization was observed, which suggested the induction of specific enzymes. Promiscuous methylation at low environmental concentrations calls into question that view that methylated Se in the atmosphere is a result of a purposeful Se metabolism serving detoxification. Rather, the concentrations of methylated Se in the atmosphere may be "coincidental" i.e., determined by the activity of S cycling microorganisms. Further, a steep increase in methylation efficiency when surpassing a certain threshold concentration (here ∼50 μg/L) calls into question that natural methylation can be estimated from high Se spikes in laboratory systems, yet highlights the possibility of using bacterial methylation as an effective remediation strategy for media higher concentrated in Se.
硒缺乏影响了全球数以百万计的人，生物甲基化硒物种向大气中的挥发可能限制了硒进入食物链。然而，在原始自然环境中普遍存在的纳摩尔浓度下，关于挥发的系统数据很少。恶臭假单胞菌在这些浓度下有效地将硒甲基化。在高达 80 nM 的浓度下，添加的硒浓度与二甲基硒、二甲基二硒、二甲基硒硫醚和 2-羟基-3-(甲基硒基)丙酸之间几乎存在完美的线性相关性。随着初始硒浓度的增加，甲基化效率呈线性增加，这表明所涉及的酶不是组成型的，而是通过 S 甲基化途径进行随机甲基化。从所有甲基化硒和 S 物种的比例可以得出结论，在如此低的浓度下，有 0.30%至 3.48%的原子被硒随机甲基化。在浓度高于 640 nM（约 50 μg/L）时，观察到甲基化和挥发的急剧增加，这表明诱导了特定的酶。在低环境浓度下的随机甲基化使得认为大气中的甲基化硒是一种有意的硒代谢解毒的观点受到质疑。相反，大气中甲基化硒的浓度可能是“偶然的”，即由 S 循环微生物的活性决定。进一步地，当超过一定的阈值浓度（这里约为 50 μg/L）时，甲基化效率的急剧增加质疑了从实验室系统中硒的高浓度冲击来估计自然甲基化的可能性，但突出了利用细菌甲基化为富含硒的介质进行有效修复的可能性。
