Lin Chu-Ching, Jay Jennifer A
Department of Civil and Environmental Engineering, University of California, Los Angeles, 5732H Boelter Hall, Los Angeles, California 90095, USA.
Environ Sci Technol. 2007 Oct 1;41(19):6691-7. doi: 10.1021/es062304c.
While biofilms are now known to be the predominant form of microbial growth in nature, very little is yet known about their role in environmental mercury (Hg) methylation. Findings of Hg methylation in periphyton communities have indicated the importance of investigating how environmental biofilms affect Hg methylation, as periphyton can be the base of the food webs in aquatic ecosystems. Chemical speciation influences the microbial uptake and methylation of inorganic Hg by planktonic cultures of sulfate-reducing bacteria; however, the effect of speciation on Hg methylation by biofilm cultures of these organisms has previously not been studied. In the present study, Hg methylation rates in biofilm and planktonic cultures of two isolates of Desulfovibrio desulfuricans from a coastal wetland were compared. Notably, the specific Hg methylation rate found was approximately an order of magnitude higher (0.0018 vs. 0.0002 attomol cell(-1) day(-1)) in biofilm cells than in planktonic cells, suggesting an important role for environmental biofilms in Hg methylation. To investigate the role of chemical speciation of Hg, experiments were conducted at two levels of sulfide. Both biofilm and planktonic cultures produced methylmercury at roughly twice the rate at low sulfide, when HgS(0)(aq), rather than HgHS2-, was the dominant Hg species. This indicates that the presence of a biofilm does not alter the relative availability of the dominant Hg species in sulfidic medium, in accordance with our previous studies of Hg uptake by Escherichia coli along a chloride gradient.
虽然现在已知生物膜是自然界中微生物生长的主要形式，但关于它们在环境汞（Hg）甲基化中的作用却知之甚少。在周丛生物群落中汞甲基化的研究结果表明，研究环境生物膜如何影响汞甲基化非常重要，因为周丛生物可以是水生生态系统食物网的基础。化学形态会影响硫酸盐还原菌浮游培养物对无机汞的微生物吸收和甲基化；然而，此前尚未研究形态对这些生物的生物膜培养物汞甲基化的影响。在本研究中，比较了来自沿海湿地的两株脱硫脱硫弧菌生物膜和浮游培养物中的汞甲基化率。值得注意的是，生物膜细胞中的特定汞甲基化率比浮游细胞中的高出约一个数量级（分别为0.0018和0.0002阿托摩尔细胞⁻¹天⁻¹），这表明环境生物膜在汞甲基化中起重要作用。为了研究汞的化学形态的作用，在两个硫化物水平上进行了实验。当HgS(0)(aq)而非HgHS₂⁻是主要汞形态时，生物膜和浮游培养物在低硫化物条件下产生甲基汞的速率大致都是高硫化物条件下的两倍。这表明生物膜的存在不会改变硫化介质中主要汞形态的相对可利用性，这与我们之前关于大肠杆菌沿氯离子梯度吸收汞的研究结果一致。
