Correia Raquel Rose Silva, Guimarães Jean Remy Davée
Laboratório de Traçadores Wolfgang C. Pfeiffer, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Bloco G/CCS/Ilha do Fundão, Rio de Janeiro, RJ, CEP: 21941-902, Brazil.
Chemosphere. 2017 Jan;167:438-443. doi: 10.1016/j.chemosphere.2016.09.153. Epub 2016 Oct 14.
Recent studies have shown Hg methylation in mangrove sediments, however, little is known about the different microorganism consortia involved. We investigated the participation of prokaryotes in general, iron-reducing bacteria-IRB, sulfate-reducing bacteria-SRB, methanogens and fungi in Hg methylation and sulfate reduction rates (SRR) in mangrove sediments using iron amendments for IRB and specific inhibitors for the other microorganisms. Sediment samples were collected from two mangrove zones, tidal flat and mangrove forest (named root sediments). Samples were incubated with Hg or SO and MeHg/Sulfur were measured by liquid scintillation. Methylmercury (MeHg) formation was significantly reduced when SRB (87.7%), prokaryotes (76%) and methanogens (36.5%) were inhibited in root sediments, but only SRB (51.6%) and prokaryotes (57.3%) in tidal flat. However, in the tidal flat, inhibition of methanogens doubled Hg methylation (104.5%). All inhibitors (except fungicide) significantly reduced SRR in both zones. In iron amended tidal flat samples, Hg methylation increased 56.5% at 100 μg g and decreased at 500 and 1000 μg g (57.8 and 82%). In the roots region, however, MeHg formation gradually decreased in response to Fe amendments from 100 μg g (37.7%) to 1000 μg g (93%). SRR decreased in all iron amendments. This first simultaneous evaluation of Hg methylation and sulfate-reduction and of the effect of iron and inhibitors on both processes suggest that SRB are important Hg methylators in mangrove sediments. However, it also suggests that SRB activity could not explain all MeHg formation. This implies the direct or indirect participation of other microorganisms such as IRB and methanogens and a complex relationship among these groups.
近期研究表明红树林沉积物中存在汞甲基化现象，然而，对于参与其中的不同微生物群落却知之甚少。我们使用针对铁还原细菌（IRB）的铁添加物以及针对其他微生物的特异性抑制剂，研究了原核生物、铁还原细菌、硫酸盐还原细菌（SRB）、产甲烷菌和真菌在红树林沉积物汞甲基化及硫酸盐还原率（SRR）中的作用。沉积物样本采自两个红树林区域，潮滩和红树林（称为根系沉积物）。样本与汞或硫酸根一起孵育，通过液体闪烁法测量甲基汞/硫。当根系沉积物中的SRB（87.7%）、原核生物（76%）和产甲烷菌（36.5%）受到抑制时，甲基汞（MeHg）的形成显著减少，但在潮滩中仅SRB（51.6%）和原核生物（57.3%）受到抑制时出现这种情况。然而，在潮滩中，抑制产甲烷菌会使汞甲基化增加一倍（104.5%）。所有抑制剂（除杀真菌剂外）均显著降低了两个区域的SRR。在添加铁的潮滩样本中，汞甲基化在100μg/g时增加了56. 在根系区域，然而，随着铁添加量从100μg/g（37.7%）增加到1000μg/g（93%），MeHg的形成逐渐减少。所有铁添加情况下SRR均降低。首次同时对汞甲基化和硫酸盐还原以及铁和抑制剂对这两个过程影响的评估表明，SRB是红树林沉积物中重要的汞甲基化剂。然而，这也表明SRB的活性无法解释所有MeHg的形成。这意味着其他微生物如IRB和产甲烷菌的直接或间接参与以及这些菌群之间存在复杂的关系。 5%，在500和1000μg/g时降低（57.8%和82%）。
