Publications

Publications in peer reviewed journals

5 Publications found
  • Historical factors associated with past environments influence the biogeography of thermophilic endospores in Arctic marine sediments

    Hanson CH, Müller AL, Loy A, Dona C, Appel R, Jørgensen BB, Hubert CRJ
    2019 - Front Microbiol, In press

    Abstract: 

    Selection by the local, contemporary environment plays a prominent role in shaping the biogeography of microbes. However, the importance of historical factors in microbial biogeography is more debatable. Historical factors include past ecological and evolutionary circumstances that may have influenced present-day microbial diversity, such as dispersal and past environmental conditions. Diverse thermophilic sulphate-reducing Desulfotomaculum are present as dormant endospores in marine sediments worldwide where temperatures are too low to support their growth. Therefore, they are dispersed to here from elsewhere, presumably a hot, anoxic habitat. While dispersal through ocean currents must influence their distribution in cold marine sediments, it is not clear whether even earlier historical factors, related to the source habitat where these organisms were once active, also have an effect. We investigated whether these historical factors may have influenced the diversity and distribution of thermophilic endospores by comparing their diversity in 10 Arctic fjord surface sediments. Although community composition varied spatially, clear biogeographic patterns were only evident at a high level of taxonomic resolution (>97% sequence similarity of the 16S rRNA gene) achieved with oligotyping. In particular, the diversity and distribution of oligotypes differed for the two most prominent OTUs (defined using a standard 97% similarity cutoff). One OTU was dominated by a single ubiquitous oligotype, while the other OTU consisted of ten more spatially localised oligotypes that decreased in compositional similarity with geographic distance. These patterns are consistent with differences in historical factors that occurred when and where the taxa were once active, prior to sporulation. Further, the influence of history on biogeographic patterns was only revealed by analysing microdiversity within OTUs, suggesting that populations within standard OTU-level groupings do not necessarily share a common ecological and evolutionary history.

  • Rapid transfer of plant photosynthates to soil bacteria via ectomycorrhizal hyphae and its interaction with nitrogen availability

    Gorka S, Dietrich M, Mayerhofer W, Gabriel R, Wiesenbauer J, Martin V, Zheng Q, Imai B, Prommer J, Weidinger M, Schweiger P, Eichorst SA, Wagner M, Richter A, Schintlmeister A, Woebken D, Kaiser C
    2019 - Frontiers in microbiology, in press

    Abstract: 

    Plant roots release recent photosynthates into the rhizosphere, accelerating decomposition of organic matter by saprotrophic soil microbes (’rhizosphere priming effect’) which consequently increases nutrient availability for plants. However, about 90% of all higher plant species are mycorrhizal, transferring a significant fraction of their photosynthates directly to their fungal partners. Whether mycorrhizal fungi pass on plant-derived carbon (C) to bacteria in root-distant soil areas, i.e. incite a ‘hyphosphere priming effect’, is not known. Experimental evidence for C transfer from mycorrhizal hyphae to soil bacteria is limited, especially for ectomycorrhizal systems. As ectomycorrhizal fungi possess enzymatic capabilities to degrade organic matter themselves, it remains unclear whether they cooperate with soil bacteria by providing photosynthates, or compete for available nutrients. To investigate a possible C transfer from ectomycorrhizal hyphae to soil bacteria, and its response to changing nutrient availability, we planted young beech trees (Fagus sylvatica) into ‘split-root’ boxes, dividing their root systems into two disconnected soil compartments. Each of these compartments was separated from a litter compartment by a mesh penetrable for fungal hyphae, but not for roots. Plants were exposed to a 13C-CO2–labeled atmosphere, while 15N-labeled ammonium and amino acids were added to one side of the split-root system. We found a rapid transfer of recent photosynthates via ectomycorrhizal hyphae to bacteria in root-distant soil areas. Fungal and bacterial phospholipid fatty acid (PLFA) biomarkers were significantly enriched in hyphae-exclusive compartments 24 h after 13C-CO2–labeling. Isotope imaging with nanometer-scale secondary ion mass spectrometry (NanoSIMS) allowed for the first time in situ visualization of plant-derived C and N taken up by extraradical fungal hyphae, and in microbial cells thriving on hyphal surfaces. When N was added to the litter compartments, bacterial biomass and the amount of incorporated 13C strongly declined. Interestingly, this effect was also observed in adjacent soil compartments where added N was only available for bacteria throughhyphal transport, indicating that ectomycorrhizal fungi were acting on soil bacteria. Together, our results demonstrate that (i) ectomycorrhizal hyphae rapidly transfer plant-derived C to bacterial communities in root-distant areas, and (ii) this transfer promptly responds to changing soil nutrient conditions.

  • Long-term transcriptional activity at zero growth by a cosmopolitan rare biosphere member

    Hausmann B, Pelikan C, Rattei T, Loy A, Pester M
    2019 - mBio, 10: e02189-18

    Abstract: 

    Microbial diversity in the environment is mainly concealed within the rare biosphere (all species with <0.1% relative abundance). While dormancy explains a low-abundance state very well, the mechanisms leading to rare but active microorganisms remain elusive. We used environmental systems biology to genomically and transcriptionally characterise Candidatus Desulfosporosinus infrequens, a low-abundance sulfate-reducing microorganism cosmopolitan to freshwater wetlands, where it contributes to cryptic sulfur cycling. We obtained its near-complete genome by metagenomics of acidic peat soil. In addition, we analyzed anoxic peat soil incubated under in situ-like conditions for 50 days by Desulfosporosinus-targeted qPCR and metatranscriptomics. The Desulfosporosinus population stayed at a constant low abundance under all incubation conditions, averaging 1.2 × 10⁶ 16S rRNA gene copies per cm³ soil. In contrast, transcriptional activity of Ca.D. infrequens increased at day 36 by 56- to 188-fold when minor amendments of acetate, propionate, lactate, or butyrate were provided with sulfate, as compared to the no-substrate-control. Overall transcriptional activity was driven by expression of genes encoding ribosomal proteins, energy metabolism and stress response but not by expression of genes encoding cell growth-associated processes. Since our results did not support growth of these highly active microorganisms in terms of biomass increase or cell division, they had to invest their sole energy for maintenance, most likely counterbalancing acidic pH conditions. This finding explains how a rare biosphere member can contribute to a biogeochemically relevant process while remaining in a zero growth state over a period of 50 days.

  • Dark aerobic sulfide oxidation by anoxygenic phototrophs in anoxic waters.

    Berg JS, Pjevac P, Sommer T, Buckner CRT, Philippi M, Hach PF, Liebeke M, Holtappels M, Danza F, Tonolla M, Sengupta A, Schubert CJ, Milucka J, Kuypers MMM
    2019 - Environ. Microbiol., in press

    Abstract: 

    Anoxygenic phototrophic sulfide oxidation by green and purple sulfur bacteria (PSB) plays a key role in sulfide removal from anoxic shallow sediments and stratified waters. Although some PSB can also oxidize sulfide with nitrate and oxygen, little is known about the prevalence of this chemolithotrophic lifestyle in the environment. In this study, we investigated the role of these phototrophs in light-independent sulfide removal in the chemocline of Lake Cadagno. Our temporally resolved, high-resolution chemical profiles indicated that dark sulfide oxidation was coupled to high oxygen consumption rates of ~9 μM O ·h . Single-cell analyses of lake water incubated with CO in the dark revealed that Chromatium okenii was to a large extent responsible for aerobic sulfide oxidation and it accounted for up to 40 % of total dark carbon fixation. The genome of Chr. okenii reconstructed from the Lake Cadagno metagenome confirms its capacity for microaerophilic growth and provides further insights into its metabolic capabilities. Moreover, our genomic and single-cell data indicated that other PSB grow microaerobically in these apparently anoxic waters. Altogether, our observations suggest that aerobic respiration may not only play an underappreciated role in anoxic environments, but also that organisms typically considered strict anaerobes may be involved. This article is protected by copyright. All rights reserved.

  • Surface-enhanced Raman spectroscopy of microorganisms: limitations and applicability on the single-cell level.

    Weiss R, Palatinszky M, Wagner M, Niessner R, Elsner M, Seidel M, Ivleva NP
    2019 - Analyst, 3: 943-953
    Raman single cell isotope imaging

    Abstract: 

    Detection and characterization of microorganisms is essential for both clinical diagnostics and environmental studies. An emerging technique to analyse microbes at single-cell resolution is surface-enhanced Raman spectroscopy (surface-enhanced Raman scattering: SERS). Optimised SERS procedures enable fast analytical read-outs with specific molecular information, providing insight into the chemical composition of microbiological samples. Knowledge about the origin of microbial SERS signals and parameter(s) affecting their occurrence, intensity and/or reproducibility is crucial for reliable SERS-based analyses. In this work, we explore the feasibility and limitations of the SERS approach for characterizing microbial cells and investigate the applicability of SERS for single-cell sorting as well as for three-dimensional visualization of microbial communities. Analyses of six different microbial species (an archaeon, two Gram-positive bacteria, three Gram-negative bacteria) showed that for several of these organisms distinct features in their SERS spectra were lacking. As additional confounding factor, the physiological conditions of the cells (as influenced by e.g., storage conditions or deuterium-labelling) were systematically addressed, for which we conclude that the respective SERS signal at the single-cell level is strongly influenced by the metabolic activity of the analysed cells. While this finding complicates the interpretation of SERS data, it may on the other hand enable probing of the metabolic state of individual cells within microbial populations of interest.

Book chapters and other publications

2 Publications found
  • Mikrobiome – Wissensstand und Perspektiven

    2019 - 17-29. in Die unbekannte 
Welt der Mikrobiome; Rundgespräche Forum Ökologie Bd. 47. (Bauer J & von Mutius E). Bayerische Akademie der Wissenschaften; Verlag Dr. Friedrich Pfeil
  • Up-close-and-personal with the human microbiome

    2019 - Environ Microbiol Rep, 1: 17-19