Highly mineralized springs in the Scuol-Tarasp area of the Lower Engadin and in the Albula Valley near Alvaneu, Switzerland, display distinct differences with respect to the source and fate of their dissolved sulphur species. High sulphate concentrations and positive sulphur (δ(34)S) and oxygen (δ(18)O) isotopic compositions argue for the subsurface dissolution of Mesozoic evaporitic sulphate. In contrast, low sulphate concentrations and less positive or even negative δ(34)S and δ(18)O values indicate a substantial contribution of sulphate sulphur from the oxidation of sulphides in the crystalline basement rocks or the Jurassic sedimentary cover rocks. Furthermore, multiple sulphur (δ(34)S, Δ(33)S) isotopes support the identification of microbial sulphate reduction and sulphide oxidation in the subsurface, the latter is also evident through the presence of thick aggregates of sulphide-oxidizing Thiothrix bacteria.
The development of the phytoplankton in two years with very distinct weather situations was compared. In 1996, the ice on Jöri Lake III melted in mid June, summer stratification persisted during two months, and ice began to build up again in mid October. In 1997, the ice melted only at the end of July, which strongly influenced the development of the phytoplankton. Stratification persisted during two months and the lake froze up towards the end of October. The average chlorophyll-a concentrations were lower in 1996 than in 1997, which reflects the rather high temperatures and stable weather conditions in 1997 after the late melting of the ice. These observations lead us to suggest that the duration of the ice-free season is less decisive for biomass production than the weather conditions during this period. However, the date and duration of melting of the lake ice strongly influence the development of algal species that are typically observed in early season.
Hypersaline environments represent some of the most challenging settings for life on Earth. Extremely halophilic microorganisms have been selected to colonize and thrive in these extreme environments by virtue of a broad spectrum of adaptations to counter high salinity and osmotic stress. Although there is substantial data on microbial taxonomic diversity in these challenging ecosystems and their primary osmoadaptation mechanisms, less is known about how hypersaline environments shape the genomes of microbial inhabitants at the functional level. In this study, we analyzed the microbial communities in five ponds along the discontinuous salinity gradient from brackish to salt-saturated environments and sequenced the metagenome of the salt (halite) precipitation pond in the artisanal Cáhuil Solar Saltern system. We combined field measurements with spectrophotometric pigment analysis and flow cytometry to characterize the microbial ecology of the pond ecosystems, including primary producers and applied metagenomic sequencing for analysis of archaeal and bacterial taxonomic and functional diversity of the salt crystallizer harvest pond. Comparative metagenomic analysis of the Cáhuil salt crystallizer pond against microbial communities from other salt-saturated aquatic environments revealed a dominance of the archaeal genus Halorubrum and showed an unexpectedly low abundance of Haloquadratum in the Cáhuil system. Functional comparison of 26 hypersaline microbial metagenomes revealed a high proportion of sequences associated with nucleotide excision repair, helicases, replication and restriction-methylation systems in all of them. Moreover, we found distinctive functional signatures between the microbial communities from salt-saturated (>30% [w/v] total salinity) compared to sub-saturated hypersaline environments mainly due to a higher representation of sequences related to replication, recombination and DNA repair in the former. The current study expands our understanding of the diversity and distribution of halophilic microbial populations inhabiting salt-saturated habitats and the functional attributes that sustain them.
By adding sulfate in the form of solid gypsum, it was possible to transform in situ a predominantly methanogenic sediment ecosystem into a sulfate-reducing one. The concentrations of sulfate, sulfide, methane, acetate, propionate, soluble iron, and manganese were determined in the porewater before and after the transition. Although sulfate was no longer limiting, acetate and propionate continued to accumulate and reached much higher concentrations than under sulfate-limited conditions. Metabolic activities of fermenting bacteria and of sulfate reducers, which belong to the group that incompletely oxidizes organic material, might be responsible for the increased production of volatile fatty acids. The elevated concentrations of soluble Fe(II)2+ and Mn(II)2+ observed in the porewater stem from iron and manganese compounds which may be reduced chemically by hydrogen sulfide and other microbially produced reducing agents or directly through increased activities of the iron and manganese reducing bacteria. In the horizon with high sulfate-reducing activities the methane concentrations in the porewater were lower than in non-stimulated sediment regions. The shape of the concentration depth profile indicates methane consumption through sulfate reducing processes. The in situ experiment demonstrates the response of a natural microbial ecosystem to fluctuations in the environmental conditions.
An enriched mixed culture able to mineralize all three isomers of monochlorophenol (MCP) and a pure culture (Alcaligenes sp. A7-2) were used to inoculate a non-aerated fixed bed reactor filled with sintered glass beads. Oxygen was supplied in form of a 1% solution of H2O2. The 3 monochlorophenol isomers, added as a mixture (concentration of each compound 3.3 mgl−1), were eliminated to over 99%. When the MCP concentrations were lowered to 1 mgl−1 of each isomer, no addition of H2O2 was necessary since the oxygen concentration in the feed was sufficient for complete mineralization of the chlorophenols. Residual concentrations in the effluent of the reactor of below 0.2 μgl−1 for 2-MCP, 0.05 μgl−1 for 3-MCP and 4-MCP, respectively, were obtained. These values were also the detection limits for the three isomers. The low effluent levels were even obtained at hydraulic retention times of 0.7 h, which was reached stepwise. NO−3 did not serve as an alternative electron acceptor to O2.
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