Birgit Sattler

Bacterial growth in supercooled cloud droplets

It is well known that the atmosphere is a conveyor of microorganisms, and that bacteria can act as ice or cloud condensation nuclei, but clouds have not been considered as a site where organisms can live and reproduce. Here we show that bacteria in cloud droplets collected at high altitudes are actively growing and reproducing at temperatures at or below 0°C. Since ∼60% of the earth surface is covered by clouds, cloud water should be considered as a microbial habitat.

Phylogenetic and functional heterogeneity of sediment biofilms along environmental gradients in a glacial stream.

ABSTRACT We used in situ hybridization with fluorescently labeled rRNA-targeted oligonucleotide probes concurrently with measurements of bacterial carbon production, biomass, and extracellular polymeric substances (EPS) to describe the bacterial community in sediments along a glacial stream. The abundance of sediment-associatedArchaea, as detected with the ARCH915 probe, decreased downstream of the glacier snout, and a major storm increased their relative abundance by a factor of 5.5 to 7.9. Bacteria of theCytophaga-Flavobacterium group were also sixfold to eightfold more abundant in the storm aftermath. Furthermore, elevated numbers of Archaea and members of theCytophaga-Flavobacterium group characterized the phylogenetic composition of the supraglacial ice community. We postulate that glacial meltwaters constitute a possible source of allochthonous bacteria to the stream biofilms. Although stream water temperature increased dramatically from the glacier snout along the stream (3.5 km), sediment chlorophyll a was the best predictor for bacterial carbon production and specific growth rates along the stream. Concomitant with an increase in sediment chlorophylla, the EPS carbohydrate-to-bacterial-cell ratio declined 11- to 15-fold along the stream prior to the storm, which is indicative of a larger biofilm matrix in upstream reaches. We assume that a larger biofilm matrix is required to assure prolonged transient storage and enzymatic processing of allochthonous macromolecules, which are likely the major substrate for microbial heterotrophs. Bacteria of theCytophaga-Flavobacterium cluster, which are well known to degrade complex macromolecules, were most abundant in these stream reaches. Downstream, higher algal biomass continuously supplies heterotrophs with easily available exudates, therefore making a larger matrix unnecessary. As a result, bacterial carbon production and specific growth rates were higher in downstream reaches.

Possible interactions between bacterial diversity, microbial activity and supraglacial hydrology of cryoconite holes in Svalbard

The diversity of highly active bacterial communities in cryoconite holes on three Arctic glaciers in Svalbard was investigated using terminal restriction fragment length polymorphism (T-RFLP) of the 16S rRNA locus. Construction and sequencing of clone libraries allowed several members of these communities to be identified, with Proteobacteria being the dominant one, followed by Cyanobacteria and Bacteroidetes. T-RFLP data revealed significantly different communities in holes on the (cold) valley glacier Austre Brøggerbreen relative to two adjacent (polythermal) valley glaciers, Midtre Lovénbreen and Vestre Brøggerbreen. These population compositions correlate with differences in organic matter content, temperature and the metabolic activity of microbial communities concerned. No within-glacier spatial patterns were observed in the communities identified over the 2-year period and with the 1 km-spaced sampling. We infer that surface hydrology is an important factor in the development of cryoconite bacterial communities.

Microorganisms in the atmosphere over Antarctica

Antarctic microbial biodiversity is the result of a balance between evolution, extinction and colonization, and so it is not possible to gain a full understanding of the microbial biodiversity of a location, its biogeography, stability or evolutionary relationships without some understanding of the input of new biodiversity from the aerial environment. In addition, it is important to know whether the microorganisms already present are transient or resident - this is particularly true for the Antarctic environment, as selective pressures for survival in the air are similar to those that make microorganisms suitable for Antarctic colonization. The source of potential airborne colonists is widespread, as they may originate from plant surfaces, animals, water surfaces or soils and even from bacteria replicating within the clouds. On a global scale, transport of air masses from the well-mixed boundary layer to high-altitude sites has frequently been observed, particularly in the warm season, and these air masses contain microorganisms. Indeed, it has become evident that much of the microbial life within remote environments is transported by air currents. In this review, we examine the behaviour of microorganisms in the Antarctic aerial environment and the extent to which these microorganisms might influence Antarctic microbial biodiversity.

Metabolic activity and diversity of cryoconites in the Taylor Valley, Antarctica

[1] Metabolic activity and biogeochemical diversity within cryoconites from the Canada, Commonwealth, Howard, and Hughes glaciers in the McMurdo Dry Valleys revealed the presence of a productive microbial refuge in this polar desert ecosystem. Fluorescent in situ hybridization showed a high percentage of Cytophaga-Flavobacteria cells in cryoconite sediments (87.2%), while b-Proteobacterial cells dominated the ice overlying the sediment layer (54.2%). The biomass of bacterial cells in the sediments was also greater (4.82 mgC ml � 1 ) than that in the overlying ice (0.18 mgC ml � 1 ) and was related to bacterial productivity (on the basis of thymidine incorporation), which ranged from 36 ng Cl � 1 d � 1 in the overlying ice to 3329 ng C l � 1 d � 1 in the sediment-containing layers. Bacteria within both the sediments and overlying ice were able to actively incorporate and respire radio-labeled glucose, as well as 17 other dissolved organic carbon compounds. The cryoconites in the Taylor Valley support an active, diverse assemblage of organisms despite the fact that they may remain sealed from the atmosphere for decades. Given the density of the cryoconites in the dry valleys (� 4–6% of ablation zone surfaces), flushing of the cryoconites during warm years could provide a vital nutrient and organic carbon source to the surrounding polar desert.

A glacier respires: Quantifying the distribution and respiration CO2 flux of cryoconite across an entire Arctic supraglacial ecosystem

Hodson, A., Anesio, A. M., Ng, F., Watson, R., Quirk, J., Irvine-fynn, T., Dye, A., Clark, C., McCloy, P., Kohler, J., Sattler, B. (2007). A glacier respires: Quantifying the distribution and respiration Co2 flux of cryoconite across an entire Arctic supraglacial ecosystem. Journal of Geophysical Research, 112 (G4).

Coupled cryoconite ecosystem structure–function relationships are revealed by comparing bacterial communities in alpine and Arctic glaciers

Cryoconite holes are known as foci of microbial diversity and activity on polar glacier surfaces, but are virtually unexplored microbial habitats in alpine regions. In addition, whether cryoconite community structure reflects ecosystem functionality is poorly understood. Terminal restriction fragment length polymorphism and Fourier transform infrared metabolite fingerprinting of cryoconite from glaciers in Austria, Greenland and Svalbard demonstrated cryoconite bacterial communities are closely correlated with cognate metabolite fingerprints. The influence of bacterial-associated fatty acids and polysaccharides was inferred, underlining the importance of bacterial community structure in the properties of cryoconite. Thus, combined application of T-RFLP and FT-IR metabolite fingerprinting promises high throughput, and hence, rapid assessment of community structure-function relationships. Pyrosequencing revealed Proteobacteria were particularly abundant, with Cyanobacteria likely acting as ecosystem engineers in both alpine and Arctic cryoconite communities. However, despite these generalities, significant differences in bacterial community structures, compositions and metabolomes are found between alpine and Arctic cryoconite habitats, reflecting the impact of local and regional conditions on the challenges of thriving in glacial ecosystems.

Carbon fluxes through bacterial communities on glacier surfaces

Abstract There is very little information about the activity of microbial communities on the surface of glaciers, though there is an increasing body of evidence to show that they strongly influence the biogeochemistry of these habitats. We measured bacterial abundance and production in cryoconite holes on Arctic, Antarctic and Alpine glaciers in order to estimate the role of heterotrophic bacteria within the carbon budget of glacial ecosystems. Our results demonstrate an active bacterial community on the surface of glaciers with doubling times that vary from a few hours to hundreds of days depending on the glacier and position (water or sediments) within the cryoconite hole. However, bacterial production is only ∼2–3% of the published literature values of community respiration from similar habitats, indicating that other types of microbes (e.g. eukaryotic organisms) may also play a role in the C cycle of glaciers. We estimate that only up to 7% of the organic C in cryoconite sediments is utilized by the heterotrophic bacterial community annually, suggesting that the surface of glaciers can accumulate organic carbon, and that this C may be important for biogeochemical activity downstream to adjacent ecosystems.

The dynamic bacterial communities of a melting High Arctic glacier snowpack

Snow environments can occupy over a third of land surface area, but little is known about the dynamics of snowpack bacteria. The effect of snow melt on bacterial community structure and diversity of surface environments of a Svalbard glacier was examined using analyses of 16S rRNA genes via T-RFLP, qPCR and 454 pyrosequencing. Distinct community structures were found in different habitat types, with changes over 1 week apparent, in particular for the dominant bacterial class present, Betaproteobacteria. The differences observed were consistent with influences from depositional mode (snowfall vs aeolian dusts), contrasting snow with dust-rich snow layers and near-surface ice. Contrary to that, slush as the decompositional product of snow harboured distinct lineages of bacteria, further implying post-depositional changes in community structure. Taxa affiliated to the betaproteobacterial genus Polaromonas were particularly dynamic, and evidence for the presence of betaproteobacterial ammonia-oxidizing bacteria was uncovered, inviting the prospect that the dynamic bacterial communities associated with snowpacks may be active in supraglacial nitrogen cycling and capable of rapid responses to changes induced by snowmelt. Furthermore the potential of supraglacial snowpack ecosystems to respond to transient yet spatially extensive melting episodes such as that observed across most of Greenland’s ice sheet in 2012 merits further investigation.

A metagenomic snapshot of taxonomic and functional diversity in an alpine glacier cryoconite ecosystem

Cryoconite is a microbe‐mineral aggregate which darkens the ice surface of glaciers. Microbial process and marker gene PCR-dependent measurements reveal active and diverse cryoconite microbial communities on polar glaciers. Here, we provide the first report of a cryoconite metagenome and culture-independent study of alpine cryoconite microbial diversity. We assembled 1.2 Gbp of metagenomic DNA sequenced using an Illumina HiScanSQ from cryoconite holes across the ablation zone of Rotmoosferner in the Austrian Alps. The metagenome revealed a bacterially-dominated community, with Proteobacteria (62% of bacterialassigned contigs) and Bacteroidetes (14%) considerably more abundant than Cyanobacteria (2.5%). Streptophyte DNA dominated the eukaryotic metagenome. Functional genes linked to N, Fe, S and P cycling illustrated an acquisitive trend and a nitrogen cycle based upon efficient ammonia recycling. A comparison of 32 metagenome datasets revealed a similarity in functional profiles between the cryoconite and metagenomes characterized from other cold microbe‐mineral aggregates. Overall, the metagenomic snapshot reveals the cryoconite ecosystem of this alpine glacier as dependent on scavenging carbon and nutrients from allochthonous sources, in particular mosses transported by wind from ice-marginal habitats, consistent with net heterotrophy indicated by productivity measurements. A transition from singular snapshots of cryoconite metagenomes to comparative analyses is advocated.