Equipe Environnement et Microbiologie, UMR IPREM5254 Université de Pau et des Pays de l'Adour, Bâtiment IBEAS, BP1153, 64013, Pau Cedex, France.
Université de Bordeaux, EPOC, UMR CNRS 5805, 33120, Arcachon, France.
Environ Sci Pollut Res Int. 2017 Aug;24(23):19223-19233. doi: 10.1007/s11356-017-9597-x. Epub 2017 Jun 30.
Macrophyte floating roots are considered as hotspots for methylmercury (MeHg) production in aquatic ecosystems through microbial activity. Nevertheless, very little is known about periphyton bacterial communities and mercury (Hg) methylators in such ecological niches. The ability to methylate inorganic Hg is broadly distributed among prokaryotes; however, sulfate-reducers have been reported to be the most important MeHg producers in macrophyte floating roots. In the present work, the periphyton bacterial communities colonizing Ludwigia sp. floating roots were investigated through molecular methods. Among the 244 clones investigated, anaerobic microorganisms associated with the sulfur biogeochemical cycle were identified. Notably, members of the sulfur-oxidizing prokaryotes and the anoxygenic, purple non-sulfur bacteria (Rhodobacteraceae, Comamonadaceae, Rhodocyclaceae, Hyphomicrobiaceae) and the sulfate reducers (Desulfobacteraceae, Syntrophobacteraceae, and Desulfobulbaceae) were detected. In addition, 15 sulfate-reducing strains related to the Desulfovibrionaceae family were isolated and their Hg-methylation capacity was tested using a biosensor. The overall results confirmed that Hg methylation is a strain-specific process since the four strains identified as new Hg-methylators were closely related to non-methylating isolates. This study highlights the potential involvement of periphytic bacteria in Hg methylation when favorable environmental conditions are present in such ecological micro-niches.
水生生态系统中，大型植物漂浮根中的微生物活动被认为是甲基汞（MeHg）产生的热点。然而，对于这些生态位中的附生细菌群落和汞（Hg）甲基化菌知之甚少。能够将无机汞甲基化的能力在原核生物中广泛分布；然而，有报道称硫酸盐还原菌是大型植物漂浮根中最重要的 MeHg 生产者。在本研究中，通过分子方法研究了附着在水蕹菜漂浮根上的附生细菌群落。在所研究的 244 个克隆中，鉴定出与硫生物地球化学循环有关的厌氧微生物。值得注意的是，检测到硫氧化原核生物和非需氧、紫色非硫细菌（红杆菌科、贪噬菌科、红环菌科、生丝微菌科）以及硫酸盐还原菌（脱硫杆菌科、互营杆菌科和脱硫孤菌科）的成员。此外，还分离到 15 株与脱硫弧菌科相关的硫酸盐还原菌，并使用生物传感器测试了它们的 Hg 甲基化能力。总体结果证实，Hg 甲基化是一种菌株特异性的过程，因为鉴定为新的 Hg 甲基化菌的四个菌株与非甲基化分离株密切相关。本研究强调了当这些生态微生境中存在有利的环境条件时，附生细菌可能参与 Hg 甲基化过程。
