Floc Formation Reduces the pH Stress Experienced by Microorganisms Living in Alkaline Environments
Floc Formation Reduces the pH Stress Experienced by Microorganisms Living in Alkaline Environments
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DOI：
10.1128/aem.02985-16
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发表时间：
2017-03-01
影响因子：
4.4
通讯作者：
Humphreys, P. N.
中科院分区：
文献类型：
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作者：
Charles, C. J.;Rout, S. P.;Humphreys, P. N.
在放射性废物胶凝地质处置设施中，微生物的生存在很大程度上取决于它们在胶凝材料溶解造成的以钙为主的高碱性条件下生存的能力。本研究结果表明，由细胞外聚合物质（EPS）的复杂混合物组成的絮凝体，对高达13.0的碱性pH值提供保护。絮凝体以Alishewanella和Dietzia属为主，产生富含甘露糖的碳水化合物，结合细胞外DNA，导致Ca2+封存。EPS在絮凝体中心的细胞周围形成了一层厚度约为10 μ m的膜层，在pH值为11.0和11.5的条件下，絮凝体能够生长，内部pH值分别保持在10.4和10.7。微生物在pH值为12.0时存活，其中观察到内部絮团pH值为11.6，相关生物量减少。我们观察到在pH为13.0时，絮凝体存活有限（< 2周）。该研究表明，在放射性废物胶凝地质处置设施内可能出现的高碱性条件下，絮凝体保持较低的内部ph值，并表明该设施内的絮凝体群落可以在ph值高达12.0的情况下存活。细胞外聚合物质（EPS）在高碱性条件下微生物存活中的作用尚不清楚。在这里，我们提出了一个基于eps的微生物絮团的分类、形态和化学特征，该絮团是由一个从人为高碱性位点分离出来的联合体形成的。在pH为13时观察到絮凝体的短期（< 2周）存活，在pH为12.0时观察到无限期存活。微pH电极（10 μ m直径的电极端）的测量结果表明，絮凝体在高碱性条件下（pH值为11.0、11.5和12.0）保持较低的内部pH值，这表明絮凝体的形成和EPS的产生是高碱性条件下的生存策略。结果表明微生物群落如何在高碱性环境中生存和繁殖，这种环境预计将在放射性废物的胶结地质处置设施中普遍存在；这些结果也与更广泛的极端微生物群落有关。
The survival of microorganisms within a cementitious geological disposal facility for radioactive wastes heavily depends on their ability to survive the calciumdominated, hyperalkaline conditions resulting from the dissolution of the cementitious materials. The results from this study show that the formation of flocs, composed of a complex mixture of extracellular polymeric substances (EPS), provides protection against alkaline pH values up to 13.0. The flocs were dominated by Alishewanella and Dietzia spp., producing a mannose-rich carbohydrate fraction incorporating extracellular DNA, resulting in Ca2+ sequestration. EPS provided a similar to 10-mu m thick layer around the cells within the center of the flocs, which were capable of growth at pH values of 11.0 and 11.5, maintaining internal pH values of 10.4 and 10.7, respectively. Microorganisms survived at a pH of 12.0, where an internal floc pH of 11.6 was observed, as was a reduced associated biomass. We observed limited floc survival (< 2 weeks) at a pH of 13.0. This study demonstrates that flocs maintain lower internal pHs in response to the hyperalkaline conditions expected to occur within a cementitious geological disposal facility for radioactive wastes and indicates that floc communities within such a facility can survive at pHs up to 12.0. IMPORTANCE The role of extracellular polymeric substances (EPS) in the survival of microorganisms in hyperalkaline conditions is poorly understood. Here, we present the taxonomy, morphology, and chemical characteristics of an EPS-based microbial floc, formed by a consortium isolated from an anthropogenic hyperalkaline site. Short-term (< 2 weeks) survival of the flocs at a pH of 13 was observed, with indefinite survival observed at a pH of 12.0. Measurements from micro-pH electrodes (10-mu m-diameter tip) demonstrated that flocs maintain lower internal pHs in response to hyperalkaline conditions (pH 11.0, 11.5, and 12.0), demonstrating that floc formation and EPS production are survival strategies under hyperalkaline conditions. The results indicate how microbial communities may survive and propagate within the hyperalkaline environment that is expected to prevail in a cementitious geological disposal facility for radioactive wastes; the results are also relevant to the wider extremophile community.