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Periodic Report Summary 1 - WETLAND-ECOSYSBIOL (The hidden sulfur cycle in freshwater wetlands: an eco-systems biology approach to identify and characterize major microbial players)

Freshwater wetlands are a major source of the greenhouse gas methane but can also act as carbon sink, storing currently more than one third of the terrestrial organic carbon. Understanding their intertwined biogeochemistry and microbiology is therefore indispensable for foreseeing their influence on positive and negative climate feedback cycles. The aim of this project is to elucidate the identity and ecophysiology of sulfate reducing microorganisms (SRM) driving a highly active but hidden sulfur cycle in wetlands, which is not apparent from the low standing pools of sulfate and thus has been severely understudied. The objectives of this project are: (i) the identification of microorganisms involved in the hidden sulfur cycle with focus on SRM, (ii) elucidating their substrate preferences and preferred environmental conditions, (iii) identifying their interaction partners, and (iv) linking their function to their genome as well as their major transcripts and proteins. During the first reporting period, work was initiated and performed on a model peatland in the Fichtel Mountains, Germany, and a rice paddy in Vercelli, Italy, as representative habitats for natural and man-made wetlands. Both habitats were analyzed for the presence and activity of SRM using a combination of biogeochemical analyses (substrate, product, and sulfate monitoring) and molecular approaches including 16S-rRNA-gene high throughput amplicon sequencing, metagenomics coupled to metatranscriptomics or metaproteomics, and stable isotope probing. In addition, six single-cell genomes were obtained and sequenced from peatland samples. Results obtained during the first funding period were summarized in two manuscripts that were accepted for publication in the ISME Journal (Nature Publishing Group) and submitted to Environmental Microbiology Reports (the latter is currently under revision by expert referees). The first manuscript describes that in the studied model peatland small interaction networks of rare biosphere members exclusively drive sulfate. The majority of these species-level taxa increased their ribosome content but only weakly increased in abundance. Some taxa even maintained a constant low abundance throughout 50 days of incubation, highlighting a novel strategy of rare biosphere members to enter activity. Among those, a Desulfosporosinus sp. was central to all response networks by correlating best to net sulfate turnover among all responding SRM, including Desulfopila, Desulfomonile, and Desulfovibrio spp. These results highlight that networks of low-abundance microorganisms mediate key biogeochemical processes that control greenhouse gas production in peatlands. The second manuscript describes that gypsum as a typical sulfate-containing amendment to rice paddy soil decreased methane emissions by up to 99% from this habitat but had no major impact on the general phylogenetic composition of the bacterial community. It rather selectively stimulated or repressed a small number of microorganisms in the rhizosphere and bulk soil. Gypsum-stimulated OTUs were affiliated with several potential sulfate-reducing (Syntrophobacter, Desulfovibrio, unclassified Desulfobulbaceae, unclassified Desulfobacteraceae) and sulfur-oxidizing taxa (Thiobacillus, unclassified Rhodocyclaceae), while gypsum-repressed OTUs were dominated by aerobic methanotrophs (Methylococcaceae). Abundance correlation networks suggested that two abundant (>1%) OTUs (Desulfobulbaceae, Rhodocyclaceae) were central to the reductive and oxidative parts of the sulfur cycle. Parallel 13CO2 pulse labeling of rice plants indicated that sulfur bacteria did not directly utilize root exudates but rather cooperated syntrophically with primary degraders of plant-derived organic carbon. Final results to be expected from the second reporting period include (i) exploration of the genome of the rare peatland Desulfosporosinus and its transcriptional activity in situ using metatranscriptomics (results are already obtained and under analysis), (ii) exploration of further genomic bins obtained from the peatland that harbor unusual signature proteins for SRM (results are already obtained and under analysis), (iii) exploration of genomic SRM bins obtained from the studied rice paddy fields and analysis of expressed proteins by metaproteomics (results are already obtained and under analysis). The conducted research contributes to the establishment of eco-systems biology approaches to very complex microbial communities like the ones encountered in wetlands. This allows us to retrieve knowledge on the physiological potential of environmental microorganisms and how this is translated into actual ecological behavior. In addition, it contributes to our conceptual understanding of the vast and very diverse microbial rare biosphere. This directly contributes to a better understanding of the microbial ecology of wetlands as important ecosystems that buffer against climate change and that contribute to the sustainability of biodiversity, water quality, and flood protection.


Christina Leib, (Head of Financial Department)
Tél.: +49 7531 883605
Fax: +49 7531 883727


Life Sciences
Numéro d'enregistrement: 183918 / Dernière mise à jour le: 2016-06-10
Source d'information: SESAM