 |
Sulphate-reducing bacteria (SRB) are responsible for metal corrosion (reduction of Fe3+ to Fe2+ and siderite formation), can be used to purify some polluted areas or industrial effluents since they perform dehalogenation and are found in human large intestine, but here we focus on their importance in mercury methylation. Since SRB are accountable for more than 95 % of environmental mercury methylation and catalyse this process at variable rates depending on the species, an environmental investigation where methyl mercury (MeHg) and SRB populations are linked must be done. Water and sediment samples were taken weekly during the summer of 2002 at bay Saint-François (BSF), a wetland located in lake Saint-Pierre, where humid zones are protected by the RAMSAR conventions (UNESCO). Snow samples were collected at Kuujjuarapik (Hudson Bay) during the spring of 2002.
Total sample DNA was extracted to characterize SRB populations (most probable number and diversity) at different BSF sediments level and in water to demonstrate a relation with MeHg measured during the same periods by R. Goulet et al. (INRS-Eau). SRB diversity and abundance in Kuujjuarapik snows were investigated to determinate if these bacteria could be responsible for the fact that 60 % of total mercury is in MeHg form in snow during spring.
For both sites, a dsr (Dissimilatory Sulphite Reductase) gene amplification was done to construct gene banks to establish which SRB species were dominant and the competitive chain polymerase amplification (cPCR) was developed to study population densities at different sediment or snow levels. The product of this gene (dsr) is implicated in the 6 electron reduction of S6- to S2- and therefore is found in all SRB, bacteria that use sulphate ion as an oxidant for the degradation of organic material. Laboratory cultivation allowed us to demonstrate that cultivable SRB were 100 times more abundant in sediment than in water and that these bacteria were present in Kuujjuarapik snow.
|
