Microbial Biotechnology Laboratory, Faculty of Sciences and Techniques, Sidi Mohamed Ben Abdellah University, Route Immouzer, 2202, Fez, Morocco.
Rev Environ Contam Toxicol. 2015;233:45-69. doi: 10.1007/978-3-319-10479-9_2.
Chromium has been and is extensively used worldwide in multiple industrial processes and is routinely discharged to the environment from such processes. Therefore, this heavy metal is a potential threat to the environment and to public health, primarily because it is non-biodegradable and environmentally persistent. Chromium exists in several oxidation states, the most stable of which are trivalent Cr(Ill) and hexavalent Cr(VI) species. Each species possesses its own individual chemical characteristics and produces its own biological effects. For example, Cr (Ill) is an essential oligoelement for humans, whereas Cr(VI) is carcinogenic and mutagenic. Several chemical methods are used to remove Cr(VI) from contaminated sites. Each of these methods has advantages and disadvantages. Currently, bioremediation is often the preferred method to deal with Cr contaminated sites, because it is eco-friendly, cost-effective and is a "natural" technology. Many yeast, bacterial and fungal species have been assessed for their suitability to reduce or remove Cr(VI) contamination. The mechanisms by which these microorganisms resist and reduce Cr(VI) are variable and are species dependent. There are several Cr-resistance mechanisms that are displayed by microorganisms. These include active efflux of Cr compounds, metabolic reduction of Cr(VI) to Cr (ill), and either intercellular or extracellular prec1p1tation. Microbial Cr (VI) removal typically involves three stages: binding of chromium to the cell surface, translocation of chromium into the cell, and reduction of Cr(VI) to Cr (ill). Cr(VI) reduction by microorganisms may proceed on the cell surface, outside the cell, or intracellularly, either directly via chromate reductase enzymes, or indirectly via metabolite reduction of Cr(VI). The uptake of chromium ions is a biphasic process. The primary step is known as biosorption, a metabolic energyindependent process. Thereafter, bioaccumulation occurs, but is much slower, and is dependent on cell metabolic activity. Choosing an appropriate bioremediation strategy for Cr is extremely important and must involve investigating and understanding the key mechanisms that are involved in microbial resistance to and removal of Cr(VI).
铬在世界范围内被广泛应用于多个工业过程中，并经常从这些过程中排放到环境中。因此，这种重金属对环境和公众健康构成了潜在威胁，主要是因为它不可生物降解且在环境中持久存在。铬存在于几种氧化态中，最稳定的是三价 Cr(III) 和六价 Cr(VI) 物种。每种物质都具有其独特的化学特性，并产生其自身的生物效应。例如，Cr(III) 是人体必需的微量元素，而 Cr(VI) 则具有致癌性和致突变性。有几种化学方法可用于从污染场地中去除 Cr(VI)。这些方法各有优缺点。目前，生物修复通常是处理 Cr 污染场地的首选方法，因为它环保、经济实惠，是一种“自然”技术。许多酵母、细菌和真菌已被评估其适用于还原或去除 Cr(VI) 污染的能力。这些微生物抵抗和还原 Cr(VI)的机制因物种而异。微生物表现出几种 Cr 抗性机制。这些机制包括 Cr 化合物的主动外排、Cr(VI)的代谢还原为 Cr(III)，以及细胞内或细胞外沉淀。微生物 Cr(VI)去除通常涉及三个阶段：铬与细胞表面的结合、铬向细胞内的转运以及 Cr(VI)的还原为 Cr(III)。微生物 Cr(VI)还原可以在细胞表面、细胞外或细胞内进行，直接通过铬酸盐还原酶，或间接通过 Cr(VI)的代谢还原进行。铬离子的摄取是一个两相过程。第一步称为生物吸附，是一种不需要代谢能量的过程。此后，会发生生物积累，但速度较慢，并且依赖于细胞代谢活性。选择合适的 Cr 生物修复策略非常重要，必须研究和了解微生物对 Cr(VI)的抗性和去除所涉及的关键机制。
