An indigenous iron-reducing microbial community from MX80 bentonite - A study in the framework of nuclear waste disposal
An indigenous iron-reducing microbial community from MX80 bentonite - A study in the framework of nuclear waste disposal
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DOI：
10.1016/j.clay.2021.106039
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发表时间：
2021-03-06
影响因子：
5.6
通讯作者：
Gray, Neil
中科院分区：
文献类型：
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作者：
Gilmour, Katie A.;Davie, Colin T.;Gray, Neil
高度压实的MX80膨润土已被选择作为工程缓冲和回填材料，用于核废料的长期深层地质储存。铁还原细菌将铁（III）还原为铁（II），有些细菌适应高温和干燥的环境，以适应储存库中不适宜居住的条件。在一个潜在的英国储存库概念中，来自碳钢罐的铁可能有助于在粘土罐界面形成富铁环境。这可能会导致MX80膨润土的矿物学和铁含量因氧化还原状态和溶解度的变化而发生变化，从而改变粘土的地质力学性质。为了研究铁还原菌在这一过程中的潜在作用，我们用市售的MX80膨润土粉和压实的MX80膨润土进行富集，以确定粘土中存在本地铁相互作用群落。在这些富集过程中，测量了可溶性铁（II）、总铁（II）和pH，并对富集进行了16S rRNA群落分析。各富集组总Fe （II）浓度在第28天达到峰值；然而，当伴随细菌生长时，浓度总体较高。可溶铁（II）始终保持较低水平。16S rRNA基因测序显示存在几种假定的铁相互作用细菌，以及耐热和孢子形成物种。土著群落主要由厚壁菌组成，包括铁还原菌和形成孢子的细菌，如Desulfosporosinus。因此，MX80膨润土固有地携带一个可行的微生物群落，可能与存在于MX80膨润土或其他矿物成分（如碳钢废料罐）中的结构铁相互作用。各种研究表明，如果保持高压实，微生物活动不太可能在大块膨润土内进行。在粘土中发现了一个可行的、健壮的、功能多样的群落，强调了这种高压实的重要性，在局部膨胀压力可能没有充分发展的边缘地点和界面上，活动是可能的。
Highly compacted MX80 bentonite has been selected as the engineered buffer and backfill material in several proposed concepts for long-term deep geological storage of nuclear waste. Iron-reducing bacteria reduce Fe (III) to Fe (II) and some are adapted to high temperatures and desiccated environments, in keeping with periods of less habitable conditions within the repository. In one potential UK repository concept, iron from carbon steel canisters may contribute to an iron-rich environment at the clay-canister interface. This could lead to changes in the mineralogy and iron-content of MX80 bentonite due to variation of the redox state and solubility, which in turn could alter the geomechanical properties of the clay. To investigate the potential role of iron-reducing bacteria in this process enrichments were carried out with both commercially available MX80 bentonite powder and compacted MX80 bentonite to identify the presence of an indigenous iron-interacting community in the clay. Throughout these enrichments Fe (II) soluble, Fe (II) total, and pH were measured, and the enrichments were subjected to 16S rRNA community analysis. Concentrations of Fe (II) total peaked at day 28 in all enrichments; however, the concentration was overall higher when accompanied by bacterial growth. Fe (II) soluble remained low throughout. 16S rRNA gene sequencing revealed the presence of several putative iron-interacting bacteria, as well as thermotolerant and spore-forming species. The indigenous community was largely comprised of firmicutes, including iron-reducers and spore-forming bacteria such as Desulfosporosinus. Therefore, MX80 bentonite inherently carries a viable microbial community which could potentially interact with structural iron present within MX80 bentonite or other mineral components, such as a carbon steel waste canister. Various research has shown that microbial activity is unlikely within the bulk bentonite provided high compaction is maintained. The importance of this high compaction is highlighted by the finding here of a viable, robust and functionally diverse community within the clay and activity may be possible anyway at edge sites and interfaces where, locally, swelling pressures might not fully develop.