• CUBE - Computational Systems Biology

  • DOME - Microbial Ecology

  • TER - Terrestrial Ecosystem Research

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Latest publications

Flux Analysis of Free Amino Sugars and Amino Acids in Soils by Isotope Tracing with a Novel Liquid Chromatography/High Resolution Mass Spectrometry Platform

Soil fluxomics analysis can provide pivotal information for understanding soil biochemical pathways and their regulation, but direct measurement methods are rare. Here, we describe an approach to measure soil extracellular metabolite (amino sugar and amino acid) concentrations and fluxes based on a 15N isotope pool dilution technique via liquid chromatography and high-resolution mass spectrometry. We produced commercially unavailable 15N and 13C labeled amino sugars and amino acids by hydrolyzing peptidoglycan isolated from isotopically labeled bacterial biomass and used them as tracers (15N) and internal standards (13C). High-resolution (Orbitrap Exactive) MS with a resolution of 50 000 allowed us to separate different stable isotope labeled analogues across a large range of metabolites. The utilization of 13C internal standards greatly improved the accuracy and reliability of absolute quantification. We successfully applied this method to two types of soils and quantified the extracellular gross fluxes of 2 amino sugars, 18 amino acids, and 4 amino acid enantiomers. Compared to the influx and efflux rates of most amino acids, similar ones were found for glucosamine, indicating that this amino sugar is released through peptidoglycan and chitin decomposition and serves as an important nitrogen source for soil microorganisms. d-Alanine and d-glutamic acid derived from peptidoglycan decomposition exhibited similar turnover rates as their l-enantiomers. This novel approach offers new strategies to advance our understanding of the production and transformation pathways of soil organic N metabolites, including the unknown contributions of peptidoglycan and chitin decomposition to soil organic N cycling.

Hu Y, Zheng Q, Wanek W
2017 - analytical chemistry, 17: 9192-9200

Bottled aqua incognita: Microbiota assembly and dissolved organic matter diversity in natural mineral waters

Background: Non-carbonated natural mineral waters contain microorganisms that regularly grow after bottling despite low concentrations of dissolved organic matter (DOM). Yet, the compositions of bottled water microbiota and organic substrates that fuel microbial activity, and how both change after bottling, are still largely unknown.

Results: We performed a multifaceted analysis of microbiota and DOM diversity in twelve natural mineral waters from six European countries. 16S rRNA gene-based analyses showed that less than ten species-level operational taxonomic units (OTUs) dominated the bacterial communities in the water phase and associated with the bottle wall after a short phase of post-bottling growth. Members of the betaproteobacterial genera Curvibacter, Aquabacterium, and Polaromonas (Comamonadaceae) grew in most waters and represent ubiquitous, mesophilic, heterotrophic aerobes in bottled waters. Ultrahigh-resolution mass spectrometry of DOM in bottled waters and their corresponding source waters identified thousands of molecular formulae characteristic of mostly refractory, soil-derived DOM.

Conclusions. The bottle environment, including source water physicochemistry, selected for growth of a similar low-diversity microbiota across various bottled waters. Relative abundance changes of hundreds of multi-carbon molecules were related to growth of less than ten abundant OTUs. We thus speculate that individual bacteria cope with oligotrophic conditions by simultaneously consuming diverse DOM molecules.

Lesaulnier CC, Herbold CW, Pelikan C, Gérard C, Le Coz X, Gagnot S, Berry D, Niggemann J, Dittmar T, Singer GA, Loy A
2017 - Microbiome, In press

Depth distribution and assembly of sulfate-reducing microbial communities in marine sediments of Aarhus Bay

Most sulfate-reducing microorganisms (SRM) present in subsurface marine sediments belong to uncultured groups only distantly related to known SRM and it remains unclear how changing geochemical zones and sediment depth influence their community structure. We mapped the community composition and abundance of SRM by amplicon-sequencing and quantifying dsrB, which encodes dissimilatory sulfite reductase subunit beta, in sediment samples covering different vertical geochemical zones ranging from the surface sediment to the deep sulfate-depleted subsurface at four locations in Aarhus Bay, Denmark. SRM were present in all geochemical zones including sulfate-depleted methanogenic sediment. The biggest shift in SRM community composition and abundance occurring across the transition from bioturbated surface sediments into non-bioturbated sediments below, where redox fluctuations and input of fresh organic matter due to macrofaunal activity are absent. SRM abundance correlated with sulfate reduction rates determined for the same sediments. Sulfate availability showed weaker correlation with SRM abundances and no significant correlation with the composition of the SRM community. The overall SRM species diversity decreased with depth, yet we identified a subset of highly abundant community members that persists across all vertical geochemical zones of all stations. We conclude that subsurface SRM communities assemble by persistence of members of the surface community and that the transition from the bioturbated surface sediment to the unmixed sediment below is a main site of assembly of the subsurface SRM community.

Jochum LM, Chena X, Lever MA, Loy A, Jørgensen BB, Schramm A, Kjeldsen KU
2017 - Appl Environ Microbiol, In press