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    Bacterial symbionts of amoebae

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Dome News

Latest publications

On the evolution and physiology of cable bacteria

Cable bacteria of the family Desulfobulbaceae form centimeter- long filaments comprising thousands of cells. They occur world-wide in the surface of aquatic sediments, where they connect sulfide oxidation with oxygen or nitrate reduction via long-distance electron transport. In the absence of pure cultures, we used single-filament genomics and metagenomics to retrieve draft genomes of 3 marine Candidatus Electrothrix and 1 freshwater Ca. Electronema species. These genomes contain >50% unknown genes but still share their core genomic makeup with sulfate- reducing and sulfur-disproportionating Desulfobulbaceae, with few core genes lost and 212 unique genes (from 197 gene families) conserved among cable bacteria. Last common ancestor analysis indicates gene divergence and lateral gene transfer as equally important origins of these unique genes. With support from meta-proteomics of a Ca. Electronema enrichment, the genomes suggest that cable bacteria oxidize sulfide by reversing the canonical sulfate reduction pathway and fix CO2 using the Wood–Ljungdahl pathway. Cable bacteria show limited organotrophic potential, may assimilate smaller organic acids and alcohols, fix N2, and synthesize polyphosphates and polyglucose as storage compounds; several of these traits were confirmed by cell-level experimental analyses. We propose a model for electron flow from sulfide to oxygen that involves periplasmic cytochromes, yet-unidentified conductive periplasmic fibers, and periplasmic oxygen reduction. This model proposes that an active cable bacterium gains energy in the anodic, sulfide-oxidizing cells, whereas cells in the oxic zone flare off electrons through intense cathodic oxygen respiration without energy conservation; this peculiar form of multicellularity seems unparalleled in the microbial world.

Kjeldsen KU, Schreiber L, Thorup CA, Boesen T, Bjerg JT, Yang T, Dueholm MS, Larsen S, Risgaard-Petersen N, Nierychlof M, Schmid M, Bøggildd A, van de Vossenbergh J, Geelhoedi JS, Meysman FJR, Wagner M, Nielsen PH, Nielsen LP, Schramm A
2019 - Proc Natl Acad Sci U S A, PNAS Latest Articles

Antioxidative activity and health benefits of anthocyanin-rich fruit juice in healthy volunteers.

Oxidative cell damage has been linked to the pathogenesis of numerous diseases such as atherosclerosis, type 2 diabetes, and cancer. The consumption of foods rich in polyphenols (e.g. anthocyanins) has been shown to exert preventive effects against such diseases. We investigated the biological effects of anthocyanin-rich fruit juice in a 9-week, placebo-controlled intervention study with 57 healthy male volunteers. The study design encompassed an initial 1 week of wash-out, followed by 8 weeks of intervention period with anthocyanin-rich fruit juice or placebo. The anthocyanin-rich fruit juice demonstrated DNA-protective and antioxidant effects; however, the placebo beverage, rich in vitamin C, showed similar effects based on the tested biomarkers. A significant reduction in background and total DNA strand breaks was observed in both groups within 24 h as well as after 8 weeks of intervention. Only anthocyanin-rich fruit juice consumption provided a significant reduction in body fat and an increase in fat-free mass. The activity of superoxide dismutase (SOD) was significantly elevated after consumption of anthocyanin-rich fruit juice. Both groups showed decreased levels of LDL and total cholesterol (TC) within the first week of the intervention. Similar results in both groups could be explained by the relatively high vitamin C contents of both beverages (>500 mg/L), which may have masked the effects of anthocyanins and other antioxidants in the studied juice. Taken together, anthocyanin-rich fruit juice as well as the placebo drink, both of which had high vitamin C content, can improve DNA integrity and might influence lipid metabolism in humans.

Bakuradze T, Tausend A, Galan J, Maria Groh IA, Berry D, Tur JA, Marko D, Richling E
2019 - Free Radic. Res., 1-11

The membrane lipid composition of the moderately thermophilic ammonia-oxidizing archaeon Ca. Nitrosotenuis uzonensis at different growth temperatures

Ca. Nitrosotenuis uzonensis is the only cultured moderately thermophilic member of the thaumarchaeotal order Nitrosopumilales (NP) that contains many mesophilic marine strains. We examined its membrane lipid composition at different growth temperatures (37, 46 and 50 °C). Its lipids were all membrane-spanning glycerol dialkyl glycerol tetraethers (GDGTs), with 0 to 4 cyclopentane moieties. Crenarchaeol (cren), the characteristic thaumarchaeotal GDGT, and its isomer (crenʹ) were present in high abundance (30-70 %). The GDGT polar headgroups were mono-, di- and trihexoses and hexose/phosphohexose. The ratio of glycolipid to phospholipid GDGTs was highest in the cultures grown at 50 °C. With increasing growth temperature, the relative contribution of cren and crenʹ increased, while GDGT-0 to GDGT-4 (including isomers) decreased. TEX86 (tetraether index of tetraethers consisting of 86 carbons)-derived temperatures were much lower than the actual growth temperatures, further demonstrating that TEX86 does not accurately reflect the membrane lipid adaptation of thermophilic Thaumarchaeota. As temperature increased, specific GDGTs changed relative to their isomers, possibly representing temperature adaption-induced changes in cyclopentane ring stereochemistry. Comparison of a wide range of thaumarcheotal core lipid compositions revealed the Ca. N. uzonensis cultures clustered separately fromother members of the NP order and the Nitrososphaerales (NS) order. While phylogeny generally seems to have a strong influence on GDGT distribution, our analysis of Ca. Nitrosotenuis uzonensis demonstrates that its terrestrial, higher temperature niche has led to a lipid composition that clearly differentiates it from other NP members and that this difference is mostly driven by its high crenʹ content.

Bale NJ, Palatinszky M, Rijpstra WIC, Herbold CW, Wagner M, Damste JSS
2019 - Appl Environ Microbiol, in press

Lecture series

Advanced Chemical Microscopy for Life Science and Precision Medicine

Ji-Xin Cheng
Boston University, USA
12:00 h
Lecture Hall HS2, UZA 1, Althanstrasse 14, 1090 Wien

Exploring and Exploiting the Chemistry of Microbial Interactions

Thomas Böttcher
Department of Chemistry, University of Konstanz, Germany
12:00 h
Lecture Hall HS2, UZA1, Althanstrasse 14, 1090 Wien

Metals and microbial respiration: the molecular basis of bioelectricity production and greenhouse gas destruction

David Richardson
University of East Anglia, Norwich Research Park, Norwich, UK
12:00 h
Lecture Hall HS2, UZA1, Althanstrasse 14, 1090 Wien