Remarkably coherent population structure for a dominant Antarctic Chlorobium species

Background In Antarctica, summer sunlight enables phototrophic microorganisms to drive primary production, thereby “feeding” ecosystems to enable their persistence through the long, dark winter months. In Ace Lake, a stratified marine-derived system in the Vestfold Hills of East Antarctica, a Chlorobium species of green sulphur bacteria (GSB) is the dominant phototroph, although its seasonal abundance changes more than 100-fold. Here, we analysed 413 Gb of Antarctic metagenome data including 59 Chlorobium metagenome-assembled genomes (MAGs) from Ace Lake and nearby stratified marine basins to determine how genome variation and population structure across a 7-year period impacted ecosystem function. Results A single species, Candidatus Chlorobium antarcticum (most similar to Chlorobium phaeovibrioides DSM265) prevails in all three aquatic systems and harbours very little genomic variation (≥ 99% average nucleotide identity). A notable feature of variation that did exist related to the genomic capacity to biosynthesize cobalamin. The abundance of phylotypes with this capacity changed seasonally ~ 2-fold, consistent with the population balancing the value of a bolstered photosynthetic capacity in summer against an energetic cost in winter. The very high GSB concentration (> 108 cells ml−1 in Ace Lake) and seasonal cycle of cell lysis likely make Ca. Chlorobium antarcticum a major provider of cobalamin to the food web. Analysis of Ca. Chlorobium antarcticum viruses revealed the species to be infected by generalist (rather than specialist) viruses with a broad host range (e.g., infecting Gammaproteobacteria) that were present in diverse Antarctic lakes. The marked seasonal decrease in Ca. Chlorobium antarcticum abundance may restrict specialist viruses from establishing effective lifecycles, whereas generalist viruses may augment their proliferation using other hosts. Conclusion The factors shaping Antarctic microbial communities are gradually being defined. In addition to the cold, the annual variation in sunlight hours dictates which phototrophic species can grow and the extent to which they contribute to ecosystem processes. The Chlorobium population studied was inferred to provide cobalamin, in addition to carbon, nitrogen, hydrogen, and sulphur cycling, as critical ecosystem services. The specific Antarctic environmental factors and major ecosystem benefits afforded by this GSB likely explain why such a coherent population structure has developed in this Chlorobium species.

Happy 2 Smell (H2S)

A problem was initially identified: the emission of polluting gases into the atmosphere, namely hydrogen sulphide, H2S, by the tanneries close to our school district. After carrying out theoretical investigations in Biology and Chemistry, the students developed an idea for a project, which consisted of creating a biological filter, with a porous matrix that could be easily traversed by the H2S gas, using, for this purpose, the dry fruit of the plant Luffa aegyptiaca. This material possesses a high porosity and good physical and chemical resistance, serving as a support matrix for sulphur bacteria and, initially, also their culture medium. In collaboration with Alcanena's Wastwater Treatment Plant, sludge from different treatment stages containing sulphurous bacteria were collected. These bacteria manage to transform H2S into sulphur and water. Finally, in collaboration with CTIC (Technological Center for the Leather Industry), iodometric titrations were carried out, proving the effectiveness of the produced filter.

Comparison of bacterial communities associated withXestospongia testudinaria, sediment and seawater in a Singaporean coral reef ecosystem

Despite alterations caused by anthropogenic activities in Singaporean coral reefs, the sponge communities are quite diverse andXestospongia testudinariais one of the most common sponge species. In the present study, we used 16S rRNA gene barcoded pyrosequencing to characterize and compare bacterial communities from different biotopes (sponge, seawater and sediment) and to identify dominant bacterial symbionts ofX. testudinariain a Singaporean coral reef ecosystem. Our results showed that biotope appears to affect the richness, composition and abundance of bacterial communities. Proteobacteria was the most abundant phylum in sediment and seawater whilst Chloroflexi was more abundant inX. testudinaria.Members of the order Caldilineales (fermentation of organic substrates), Chromatiales (purple sulphur bacteria), Rhodospirillales (purple non-sulphur bacteria) and Syntrophobacterales (sulphate-reducing bacteria) were relatively more abundant inX. testudinariasamples.

Biological and chemical corrosion of cement materials modified with polymer

The article presents the effect of the addition of polymer to mortars with CEMI and its influence on durability under conditions of sulfuric acid or nitric and sulphur bacteria or nitrogen (nitrification and denitrification). Both acids corresponds to the products of metabolism of bacteriaAcidithiobacillus thiooxidansandThiobacillus denitrificans,Paracoccus denitrificansby the literature is about 0.15 mmol/dm3. The changes in tightness materials studied by determining moisture mass and absorption. Corrosion processes were identified by examination in a scanning microscope equipped with an X-ray microanalyzer and a mercury porosimeter. The research results presented showed that the solution has a significantly weaker effect on the composite cement and cement-polymer compared with the action of bacteria. The action of both environments caused two opposing processes: unsealing the structure and deposition of corrosion products.