The microbial impact on Fe & S cycling at oxic-anoxic interfaces: a single-cell view

At oxic-anoxic interfaces, competing biotic and abiotic reactions drive the rapid turnover of elements involved in biogeochemical cycles. As a result of the complexity of interactions between biological and chemical processes, the contribution of microorganisms to biogeochemical element cycling is still poorly constrained. Understanding the role of microorganisms at oxic-anoxic interfaces is important because they link the carbon cycle to other element cycles via carbon fixation and degradation using inorganic electron donors and acceptors, respectively. The aim of this thesis was to elucidate the microbial impact on the cycling of two of these elements a Fe and S a at oxic-anoxic interfaces. In combination with conventional analytical techniques in biogeochemistry, state-of-the-art single-cell instruments were used to investigate biogeochemical cycling on the level of single microbial cells, enabling novel insights into extremely rapid, even cryptic, microbial processes with transient intermediates. This approach was first applied to laboratory cultures to investigate sulfur metabolism in large, colorless sulfur bacteria under controlled laboratory conditions. Confocal Raman spectroscopy of living Beggiatoa sp. cells revealed that the chemical nature of stored zero valent sulfur reflects the physiological state of the bacteria. Zero-valent sulfur was present in the form of both cyclooctasulfur rings (S8) and inorganic polysulfide chains (Sx2-), the latter appearing to serve as intermediates during both the accumulation and the breakdown of sulfur storage globules. In the environment, the factors controlling the speciation of iron and sulfur were investigated in Lake Cadagno, a stratified lake in Switzerland. Despite low, 1-2 I molA l-1 iron concentrations, significant rates of microbially-driven iron turnover were measured within the chemocline. The oxidation of iron by anoxygenic phototrophic bacteria could potentially contribute to up to 10% of primary production in this anoxic zone. The coupling of iron oxidation to iron reduction by heterotrophic bacteria generated a closed, a cryptica iron cycle. These results suggest that rapid microbial redox cycling of iron may thus far have been overlooked in shallow, low-iron redoxclines which are globally widespread. Although sulfur cycling in Lake Cadagno has already been extensively studied, our high resolution time profiles combined with single-cell analyses revealed surprising insights into the metabolism of the sulfide oxidizing bacteria there. Anoxygenic phototrophic purple sulfur bacteria were actually highly active in the dark and respired sulfur aerobically under both light and dark conditions. To bridge spatially separated gradients of electron donors and acceptors, these bacteria utilized a novel mechanism of storage and transport that is not yet fully understood. Because we could not completely close the sulfur budget in the Lake Cadagno chemocline, the existence of yet-unknown sulfide oxidation mechanisms could not be excluded, presenting exciting possibilities for future research. In the course of these studies, the challenge of linking microbial identity with function using non-fluorescent-based, single-cell instruments led to the development of a new method (silver-DISH) for the targeted identification of environmental bacteria with nanometer secondary ion mass spectrometry (nanoSIMS), scanning electron microscopy energy-dispersive X-ray spectroscopy (SEM-EDS), and confocal Raman spectroscopy. This technique may be extremely useful for future environmental microbiology studies, especially for correlative imaging. Microorganisms evidently play an important role in biogeochemical cycling at oxic-anoxic interfaces in spite of competition with spontaneous chemical reactions. Overall, the results presented in this thesis may help to constrain and quantify the impact of microbes on carbon fixation and degradation processes in such environments

Selective Pressure of Temperature on Competition and Cross-Feeding within Denitrifying and Fermentative Microbial Communities

Hanke A, Berg J, Hargesheimer T, Tegetmeyer H, Sharp CE, Strous M. Selective Pressure of Temperature on Competition and Cross-Feeding within Denitrifying and Fermentative Microbial Communities. Front. Microbiol. 2016;6: 1461.In coastal marine sediments, denitrification and fermentation are important processes in the anaerobic decomposition of organic matter. Microbial communities performing these two processes were enriched from tidal marine sediments in replicated, long term chemostat incubations at 10 and 25°C. Whereas denitrification rates at 25°C were more or less stable over time, at 10°C denitrification activity was unstable and could only be sustained either by repeatedly increasing the amount of carbon substrates provided or by repeatedly decreasing the dilution rate. Metagenomic and transcriptomic sequencing was performed at different time points and provisional whole genome sequences (WGS) and gene activities of abundant populations were compared across incubations. These analyses suggested that a temperature of 10°C selected for populations related to Vibrionales/Photobacterium that contributed to both fermentation (via pyruvate/formate lyase) and nitrous oxide reduction. At 25°C, denitrifying populations affiliated with Rhodobacteraceae were more abundant. The latter performed complete denitrification, and may have used carbon substrates produced by fermentative populations (cross-feeding). Overall, our results suggest that a mixture of competition-for substrates between fermentative and denitrifying populations, and for electrons between both pathways active within a single population -, and cross feeding-between fermentative and denitrifying populations-controlled the overall rate of denitrification. Temperature was shown to have a strong selective effect, not only on the populations performing either process, but also on the nature of their ecological interactions. Future research will show whether these results can be extrapolated to the natural environment

Simultaneous visualization of flow fields and oxygen concentrations to unravel transport and metabolic processes in biological systems

From individual cells to whole organisms, O2 transport unfolds across micrometer- tomillimeter-length scales and can change within milliseconds in response to fluid flows and organismal behavior. The spatiotemporal complexity of these processes makes the accurate assessment ofO2 dynamics via currently availablemethods difficult or unreliable. Here, we present ‘‘sensPIV,’’ a method to simultaneously measure O2 concentrations and flow fields. By tracking O2-sensitive microparticles in flow using imaging technologies that allow for instantaneous referencing,we measuredO2 transport within (1) microfluidic devices, (2) sinking model aggregates, and (3) complex colony-forming corals. Through the use of sensPIV, we find that corals use ciliary movement to link zones of photosynthetic O2 production to zones of O2 consumption. SensPIV can potentially be extendable to study flow-organism interactions across many life-science and engineering applications

Chromium Cycling in Redox‐Stratified Basins Challenges δ ⁵³ Cr Paleoredox Proxy Applications

Chromium stable isotope composition (δ53Cr) is a promising tracer for redox conditions throughout Earth's history; however, the geochemical controls of δ53Cr have not been assessed in modern redox-stratified basins. We present new chromium (Cr) concentration and δ53Cr data in dissolved, sinking particulate, and sediment samples from the redox-stratified Lake Cadagno (Switzerland), a modern Proterozoic ocean analog. These data demonstrate isotope fractionation during incomplete (non-quantitative) reduction and removal of Cr above the chemocline, driving isotopically light Cr accumulation in euxinic deep waters. Sediment authigenic Cr is isotopically distinct from overlying waters but comparable to average continental crust. New and published data from other redox-stratified basins show analogous patterns. This challenges assumptions from δ53Cr paleoredox applications that quantitative Cr reduction and removal limits isotope fractionation. Instead, fractionation from non-quantitative Cr removal leads to sedimentary records offset from overlying waters and not reflecting high δ53Cr from oxidative continental weathering.ISSN:0094-8276ISSN:1944-800

Carbohydrate compositional trends throughout Holocene sediments of an alpine lake (Lake Cadagno)

Carbohydrates are a ubiquitous constituent of organisms and contribute significantly to sedimentary organic carbon pools. Yet, the factors that control the degradation and long-term preservation of sedimentary carbohydrates are not well understood. Here, we investigate carbohydrate pool sizes and chemical compositions in high-altitude, meromictic Lake Cadagno (Switzerland) over a 13,500-year-old sedimentary succession that has recorded past changes from oxic to anoxic conditions and consists mostly of intercalations of lacustrine sediments and terrestrial-derived sediments. Analyses of the organic matter chemical composition by pyrolysis gas chromatography/mass spectrometry (Py-GC/MS) show that carbohydrates are selectively preserved over other organic matter constituents over time. The carbohydrate pyrolysis products levosugars (potentially cellulose-derived) and (alkyl)furans and furanones (potentially pectin-derived) dominate both lacustrine and terrestrially derived sediment layers, suggesting aquatic and terrestrial-derived sources of these compounds. Carbohydrate monomer analyses indicate galactose and glucose as dominant monomers and show no clear differences between aquatic and terrestrial organic matter. No clear impacts of past changes in redox conditions on carbohydrate compositions were observed. Our study shows that carbohydrates are a major contributor to sedimentary organic carbon burial in Lake Cadagno and indicates the effective preservation of both aquatic and terrestrial derived carbohydrates over millennia in lake sediments

Methanotrophy under Versatile Conditions in the Water Column of the Ferruginous Meromictic Lake La Cruz (Spain)

Lakes represent a considerable natural source of methane to the atmosphere compared to their small global surface area. Methanotrophs in sediments and in the water column largely control methane fluxes from these systems, yet the diversity, electron accepting capacity, and nutrient requirements of these microorganisms have only been partially identified. Here, we investigated the role of electron acceptors alternative to oxygen and sulfate in microbial methane oxidation at the oxycline and in anoxic waters of the ferruginous meromictic Lake La Cruz, Spain. Active methane turnover in a zone extending well below the oxycline was evidenced by stable carbon isotope-based rate measurements. We observed a strong methane oxidation potential throughout the anoxic water column, which did not vary substantially from that at the oxic/anoxic interface. Both in the redox-transition and anoxic zones, only aerobic methane-oxidizing bacteria (MOB) were detected by fluorescence in situ hybridization and sequencing techniques, suggesting a close coupling of cryptic photosynthetic oxygen production and aerobic methane turnover. Additions of nitrate, nitrite and to a lesser degree iron and manganese oxides also stimulated bacterial methane consumption. We could not confirm a direct link between the reduction of these compounds and methane oxidation and we cannot exclude the contribution of unknown anaerobic methanotrophs. Nevertheless, our findings from Lake La Cruz support recent laboratory evidence that aerobic methanotrophs may be able to utilize alternative terminal electron acceptors under oxygen limitation

Dark aerobic sulfide oxidation by anoxygenic phototrophs in anoxic waters

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 O2·h−1. Single‐cell analyses of lake water incubated with 13CO2 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

Impact of errors in recorded compressed breast thickness measurements on volumetric density classification using volpara v1.5.0 software

Purpose: Mammographic density has been demonstrated to predict breast cancer risk. It has been proposed that it could be used for stratifying screening pathways and recommending additional imaging. Volumetric density tools use the recorded compressed breast thickness (CBT) of the breast measured at the x-ray unit in their calculation, however the accuracy of the recorded thickness can vary. The aim of this study was to investigate whether inaccuracies in recorded CBT impact upon volumetric density classification and to examine whether the current quality control (QC) standard is sufficient for assessing mammographic density. Methods: Raw data from 52 digital screening mammograms were included in the study. For each image, the clinically recorded CBT was artificially increased and decreased to simulate measurement error. Increments of 1mm were used up to ±15% error of recorded CBT was achieved. New images were created for each 1mm step in thickness resulting in a total of 974 images which then had Volpara Density Grade (VDG) and volumetric density percentage assigned. Results: A change in VDG was recorded in 38.5% (n= 20) of mammograms when applying ±15% error to the recorded CBT and 11.5 % (n= 6) were within the QC standard prescribed error of ±5mm. Conclusion: The current QC standard of ±5mm error in recorded CBT creates the potential for error in mammographic density measurement. This may lead to inaccurate classification of mammographic density. The current QC standard for assessing mammographic density should be reconsidered

Social comparisons on social media: THE impact of Facebook on young women's body image concerns and mood

© 2014 Elsevier Ltd. The present study experimentally investigated the effect of Facebook usage on women's mood and body image, whether these effects differ from an online fashion magazine, and whether appearance comparison tendency moderates any of these effects. Female participants (. N=. 112) were randomly assigned to spend 10. min browsing their Facebook account, a magazine website, or an appearance-neutral control website before completing state measures of mood, body dissatisfaction, and appearance discrepancies (weight-related, and face, hair, and skin-related). Participants also completed a trait measure of appearance comparison tendency. Participants who spent time on Facebook reported being in a more negative mood than those who spent time on the control website. Furthermore, women high in appearance comparison tendency reported more facial, hair, and skin-related discrepancies after Facebook exposure than exposure to the control website. Given its popularity, more research is needed to better understand the impact that Facebook has on appearance concerns

Perceived ethnic discrimination and persecutory paranoia in individuals at ultra-high risk for psychosis

Despite a consensus that psychosocial adversity plays a role in the onset of psychosis, the nature of this role in relation to persecutory paranoia remains unclear. This study examined the complex relationship between perceived ethnic discrimination and paranoid ideation in individuals at Ultra High Risk (UHR) for psychosis using a virtual reality paradigm to objectively measure paranoia. Data from 64 UHR participants and 43 healthy volunteers were analysed to investigate the relationship between perceived ethnic discrimination and persecutory ideation in a virtual reality environment. Perceived ethnic discrimination was higher in young adults at UHR in comparison to healthy controls. A positive correlation was observed between perceived ethnic discrimination and paranoid persecutory ideation in the whole sample. Perceived ethnic discrimination was not a significant predictor of paranoid persecutory ideation in the VR environment. Elevated levels of perceived ethnic discrimination are present in individuals at UHR and are consistent with current biopsychosocial models in which psychosocial adversity plays a key role in the development of psychosis and attenuated symptomatology