Microbial activity is responsible for the transformation of at least one third of the elements in the periodic table. These transformations are the result of assimilatory, dissimilatory, or detoxification processes and form the cornerstones of many biogeochemical cycles. Arsenic and selenium are two elements whose roles in microbial ecology have only recently been recognized. Known as "essential toxins", they are required in trace amounts for growth and metabolism but are toxic at elevated concentrations. Arsenic is used as an osmolite in some marine organisms while selenium is required as selenocysteine (i.e. the twenty-first amino acid) or as a ligand to metal in some enzymes (e.g. FeNiSe hydrogenase). Arsenic resistance involves a small-molecular-weight arsenate reductase (ArsC). The use of arsenic and selenium oxyanions for energy is widespread in prokaryotes with representative organisms from the Crenarchaeota, thermophilic bacteria, low and high G+C gram-positive bacteria, and Proteobacteria. Recent studies have shown that both elements are actively cycled and play a significant role in carbon mineralization in certain environments. The occurrence of multiple mechanisms involving different enzymes for arsenic and selenium transformation indicates several different evolutionary pathways (e.g. convergence and lateral gene transfer) and underscores the environmental significance and selective impact in microbial evolution of these two elements.

中文翻译：

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元素的微生物转化：砷和硒。

微生物活动负责元素周期表中至少三分之一元素的转化。这些转化是同化，异化或解毒过程的结果，并形成了许多生物地球化学循环的基石。砷和硒是它们在微生物生态学中的作用直到最近才被认识到的两个元素。被称为“必需毒素”，它们是生长和代谢所需的微量元素，但在高浓度下有毒。砷在某些海洋生物中被用作渗透压剂，而硒则需要作为硒代半胱氨酸（即二十一种氨基酸）或某些酶（例如FeNiSe氢化酶）中金属的配体。砷抗性涉及一种小分子量的砷酸还原酶（ArsC）。在原核生物中普遍使用砷和硒氧阴离子作为能量，而原核生物具有来自Crenarchaeota，嗜热细菌，低和高G + C革兰氏阳性细菌以及变形杆菌的代表性生物。最近的研究表明，在某些环境中，这两种元素都是活跃循环的，并在碳矿化中起重要作用。涉及砷和硒转化的不同酶的多种机制的出现表明了几种不同的进化途径（例如会聚和横向基因转移），并强调了这两种元素的环境意义和对微生物进化的选择性影响。最近的研究表明，在某些环境中，这两种元素都是活跃循环的，并在碳矿化中起重要作用。涉及砷和硒转化的不同酶的多种机制的出现表明了几种不同的进化途径（例如会聚和横向基因转移），并强调了这两种元素的环境意义和对微生物进化的选择性影响。最近的研究表明，在某些环境中，这两种元素都是活跃循环的，并在碳矿化中起重要作用。涉及砷和硒转化的不同酶的多种机制的出现表明了几种不同的进化途径（例如会聚和横向基因转移），并强调了这两种元素的环境意义和对微生物进化的选择性影响。