Dipartimento di Scienze Molecolari e Nanosistemi, Cà Foscari University of Venice, Dorsoduro 2137, 30123 Venice, Italy.
Environ Res. 2013 Aug;125:188-96. doi: 10.1016/j.envres.2012.11.008. Epub 2013 Feb 9.
A mechanism of mercury detoxification has been suggested by a previous study on Hg bioaccumulation in Manila clams (Ruditapes philippinarum) in the polluted Marano and Grado lagoons and in this study we demonstrate that this event could be partly related to the detoxifying activities of Hg-resistant bacteria (MRB) harbored in clam soft tissues. Therefore, natural clams were collected in six stations during two different periods (winter and spring) from Marano and Grado Lagoons. Siphons, gills and hepatopancreas from acclimatized clams were sterile dissected to isolate MRB. These anatomical parts were glass homogenized or used for whole, and they were lying on a solid medium containing 5mgl(-1) HgCl2 and incubated at 30°C. A total of fourteen bacterial strains were isolated and were identified by 16S rDNA sequencing and analysis, revealing that strains were representative of eight bacterial genera, four of which were Gram-positive (Enterococcus, Bacillus, Jeotgalicoccus and Staphylococcus) and other four were Gram-negative (Stenotrophomonas, Vibrio, Raoultella and Enterobacter). Plasmids and merA genes were found and their sequences determined. Fluorescence in situ hybridization (FISH) technique shows the presence of Firmicutes, Actinobacteria and Gammaproteobacteria by using different molecular probes in siphon and gills. Bacterial clumps inside clam flesh were observed and even a Gram-negative endosymbiont was disclosed by transmission electronic microscope inside clam cells. Bacteria harbored in cavities of soft tissue have mercury detoxifying activity. This feature was confirmed by the determination of mercuric reductase in glass-homogenized siphons and gills.
先前的一项研究表明，马尼拉蛤（Ruditapes philippinarum）在马拉诺和格拉多受污染的泻湖中汞的生物积累与汞解毒机制有关，本研究进一步证实，这种现象可能与蛤软组织中耐汞细菌（MRB）的解毒活性有关。因此，本研究在两个不同时期（冬季和春季）从马拉诺和格拉多泻湖采集了 6 个站位的天然蛤。从驯化蛤的虹吸管、鳃和肝胰腺无菌分离出 MRB。将这些解剖部位进行玻璃匀浆或整体化处理，铺在含有 5mg/L HgCl2的固体培养基上，在 30°C 下孵育。共分离出 14 株细菌，并通过 16S rDNA 测序和分析进行鉴定，结果表明这些菌株代表了 8 个细菌属，其中 4 个是革兰氏阳性菌（肠球菌、芽孢杆菌、约氏甲烷球菌和葡萄球菌），另外 4 个是革兰氏阴性菌（寡养单胞菌、弧菌、罗伊氏菌和肠杆菌）。发现了质粒和 merA 基因，并确定了它们的序列。荧光原位杂交（FISH）技术通过在虹吸管和鳃中使用不同的分子探针显示出厚壁菌门、放线菌门和γ-变形菌纲的存在。在虹吸管和鳃中观察到蛤肉内的细菌团块，甚至通过透射电子显微镜在蛤细胞内发现了革兰氏阴性内共生体。蛤软组织腔隙中存在具有汞解毒活性的细菌。这一特征通过测定玻璃匀浆虹吸管和鳃中的汞还原酶得到了证实。
