DONLAC

Degradation and transformation of organic nitrogen compounds in the water column and sediments

The SNF funded project is a joint venture between the Biogeochemistry and Microbial Ecology group.
Whereas there exist several studies on organic matter decomposition in marine systems, we aim to investigate the fate of organic nitrogen compounds in lakes.
The study sites are two Swiss lakes distinguishing themselves by their trophic and redox conditions: The ultraoligotrophic and fully oxic Lake Brienz and eutrophic Lake Zug, which exhibits an anoxic water body.
Methods of organic and isotope geochemistry are applied to track degradation and transformation patterns of single amino acids and single amino sugars (AS) from the sites of their production in the water column to the sediments where recalcitrant material is deposited. Molecular ecology techniques such as quantitative PCR and pyrosequencing should decipher the sites of microbial degradation and microbial species involved as they are known to be the main drivers of organic matter decomposition.
From bacterial cell counts and concentrations of the AS muramic acid, the contribution of bacterial carbon to the total organic carbon pool was derived. Changes in AS ratios along the water columns disclosed a replacement of the AS signature indicative for chitin-rich organic matter (phyto- and zooplankton) by an AS signature indicative for heterotrophic microorganisms.
By comparing the two lakes organic matter degradation/transformation was found to be more enhanced in the fully oxic water column of Lake Brienz. Concluding the abundance of the functional gene chiA responsible for the hydrolysis of the AS polymer chitin, this recalcitrant compound seems to be a more significant carbon and nitrogen source in ultraoligotrophic Lake Brienz compared to eutrophic Lake Zug.
From these first results we are confident to advance the understanding of how and by whom organic nitrogen compounds are transformed during sedimentation in lacustrine systems.

Funding

• Swiss National Science Foundation, grant K-23K1-118111 / 1

Publications and Presentations

• Bacterial chitin hydrolysis in two lakes of contrasting trophic status (in press). Köllner K.E., Carstens D., Vazquez F., Schubert C.J., Bürgmann H. Applied and Environmental Microbiology
  
• Amino sugars dynamics in two lacustrine ecosystems (in revision). Carstens D., Köllner K.E., Bürgmann H., Wehrli B., and Schubert C.J.

• Sites of bacterial chitin hydrolysis in two Swiss lakes of different trophic status. Köllner K.E., Carstens D., Vazquez F., Schubert C.J., Bürgmann H., Poster: 4TH Congress of European Microbiologists (FEMS), Geneva, Switzerland, June 26-30, 2011
• Hot-spots of bacterial chitin hydrolyzation in two Swiss lakes of different trophic status. Köllner K.E., Carstens D., Schubert C.J., Bürgmann H. Poster: 4th Swiss Microbial Ecology (SME) Meeting, Engelberg, Switzerland, February 2-4, 2011