Showing papers by "Tatiana A. Vishnivetskaya published in 2011"

Mercury and other heavy metals influence bacterial community structure in contaminated Tennessee streams

Abstract: High concentrations of uranium, inorganic mercury [Hg(II)], and methylmercury (MeHg) have been detected in streams located in the Department of Energy reservation in Oak Ridge, TN. To determine the potential effects of the surface water contamination on the microbial community composition, surface stream sediments were collected 7 times during the year, from 5 contaminated locations and 1 control stream. Fifty-nine samples were analyzed for bacterial community composition and geochemistry. Community characterization was based on GS 454 FLX pyrosequencing with 235 Mb of 16S rRNA gene sequence targeting the V4 region. Sorting and filtering of the raw reads resulted in 588,699 high-quality sequences with lengths of >200 bp. The bacterial community consisted of 23 phyla, including Proteobacteria (ranging from 22.9 to 58.5% per sample), Cyanobacteria (0.2 to 32.0%), Acidobacteria (1.6 to 30.6%), Verrucomicrobia (3.4 to 31.0%), and unclassified bacteria. Redundancy analysis indicated no significant differences in the bacterial community structure between midchannel and near-bank samples. Significant correlations were found between the bacterial community and seasonal as well as geochemical factors. Furthermore, several community members within the Proteobacteria group that includes sulfate-reducing bacteria and within the Verrucomicrobia group appeared to be associated positively with Hg and MeHg. This study is the first to indicate an influence of MeHg on the in situ microbial community and suggests possible roles of these bacteria in the Hg/MeHg cycle.

Mercury and other heavy metals influence bacterial community structure in low-order Tennessee streams

Abstract: High concentrations of the heavy metals U(VI) and Hg(II) as well as inorganic compounds including nitrate have contaminated streams located in the Department of Energy reservation in Oak Ridge, TN. Of particular concern is methylmercury (MeHg) as it is more neurotoxic than Hg0. Deltaproteobacteria including sulfate reducing bacteria (SRB) and iron reducing bacteria (IRB) have been generally identified as the primary methylators. In order to determine potential effects on microbial community composition by the contamination, surface stream sediments were collected 7 times during the year from 5 contaminated sites and 1 control site. Sixty samples were analyzed for bacterial community composition and geochemistry. Community characterization used GS 454 FLX pyrosequencing with 235 Mb of 16S rDNA sequence targeting the V4 region. Sorting and filtering of the raw reads resulted in 588,699 high quality sequences with lengths of >200 bp. The bacterial community was represented by 24 phyla and unclassified Bacteria including Proteobacteria (22.9-58.5%), Cyanobacteria (0.2-32.0%), Acidobacteria (1.6-30.6%), and Verrucomicrobia (3.4-31.0%). Redundancy analysis indicated there were no significant differences in the bacterial community structure between midchannel and near bank samples. However, significant correlations existed between the bacterial community and seasonal as well as geochemical variation. Further, several members of the communitymore » appear to be positively associated with MeHg including the Proteobacteria group that includes SRBs as well as Verrucomicrobia. This study is the first to indicate the influence of MeHg on an in-situ microbial community and suggests possible roles for each of these phyla in the Hg/MeHg cycle.« less

Microbial Carbon Cycling in Permafrost-Affected Soils

Abstract: The Arctic plays a key role in Earth s climate system as global warming is predicted to be most pronounced at high latitudes and because one third of the global carbon pool is stored in ecosystems of the northern latitudes. In order to improve our understanding of the present and future carbon dynamics in climate sensitive permafrost ecosystems, present studies concentrate on investigations of microbial controls of greenhouse gas fluxes, on the activity and structure of the involved microbial communities, and on their response to changing environmental conditions. Permafrost-affected soils can function as both a source and a sink for carbon dioxide and methane. Under anaerobic conditions, caused by flooding of the active layer and the effect of backwater above the permafrost table, the mineralization of organic matter can only be realized stepwise by specialized microorganisms. Important intermediates of the organic matter decomposition are hydrogen, carbon dioxide and acetate, which can be further reduced to methane by methanogenic archaea. Evolution of methane fluxes across the subsurface/atmosphere boundary will thereby strongly depend on the activity of anaerobic methanogenic archaea and obligately aerobic methane oxidizing proteobacteria, which are known to be abundant and to significantly reduce methane emissions in permafrost-affected soils. Thereforemore » current studies on methane-cycling microorganisms are the object of particular attention in permafrost studies, because of their key role in the Arctic methane cycle and consequently of their significance for the global methane budget.« less