Yunda Elena, Gutensohn Mareike, Ramstedt Madeleine, Björn Erik
Department of Chemistry, Umeå University, Umeå, Sweden.
Front Microbiol. 2023 Jan 13;14:1079000. doi: 10.3389/fmicb.2023.1079000. eCollection 2023.
Mercury (Hg) is a major environmental pollutant that accumulates in biota predominantly in the form of methylmercury (MeHg). Surface-associated microbial communities (biofilms) represent an important source of MeHg in natural aquatic systems. In this work, we report MeHg formation in biofilms of the iron-reducing bacterium .
Biofilms were prepared in media with varied nutrient load for 3, 5, or 7 days, and their structural properties were characterized using confocal laser scanning microscopy, cryo-scanning electron microscopy and Fourier-transform infrared spectroscopy.
Biofilms cultivated for 3 days with vitamins in the medium had the highest surface coverage, and they also contained abundant extracellular matrix. Using 3 and 7-days-old biofilms, we demonstrate that biofilms prepared in media with various nutrient load produce MeHg, of which a significant portion is released to the surrounding medium. The Hg methylation rate constant determined in 6-h assays in a low-nutrient assay medium with 3-days-old biofilms was 3.9 ± 2.0 ∙ 10 L ∙ cell ∙ h, which is three to five times lower than the rates found in assays with planktonic cultures of in this and previous studies. The fraction of MeHg of total Hg within the biofilms was, however, remarkably high (close to 50%), and medium/biofilm partitioning of inorganic Hg (Hg(II)) indicated low accumulation of Hg(II) in biofilms.
These findings suggest a high Hg(II) methylation capacity of biofilms and that Hg(II) transfer to the biofilm is the rate-limiting step for MeHg formation in this systems.
汞（Hg）是一种主要的环境污染物，在生物群中主要以甲基汞（MeHg）的形式积累。与表面相关的微生物群落（生物膜）是天然水生系统中甲基汞的重要来源。在这项工作中，我们报告了铁还原细菌生物膜中甲基汞的形成。
在营养负荷不同的培养基中制备生物膜3天、5天或7天，并使用共聚焦激光扫描显微镜、冷冻扫描电子显微镜和傅里叶变换红外光谱对其结构特性进行表征。
在培养基中添加维生素培养3天的生物膜具有最高的表面覆盖率，并且还含有丰富的细胞外基质。使用3天和7天龄的生物膜，我们证明在营养负荷不同的培养基中制备的生物膜会产生甲基汞，其中很大一部分会释放到周围培养基中。在含有3天龄生物膜的低营养测定培养基中进行的6小时测定中确定的汞甲基化速率常数为3.9±2.0∙10 L∙细胞∙小时，这比本研究和先前研究中浮游培养物测定的速率低三到五倍。然而，生物膜中甲基汞占总汞的比例非常高（接近50%），无机汞（Hg(II)）在培养基/生物膜之间的分配表明Hg(II)在生物膜中的积累较低。
这些发现表明生物膜具有很高的Hg(II)甲基化能力，并且Hg(II)向生物膜的转移是该系统中甲基汞形成的限速步骤。
