Diversity of Archaea in Brazilian savanna soils

Although the richness of Bacteria and Fungi in Cerrado’ soils has been reported, here we report, for the first time, the archaeal community in Cerrado’s soils. DNA extracted from soil of two distinct vegetation types, a dense subtype of sensu strict (cerrado denso) and riverbank forest (mata de galeria), was used to amplify Archaea-specific 16S rRNA gene. All of the fragments sequenced were classified as Archaea into the phylum Thaumarchaeota, predominantly affiliated to groups I.1b and I.1c. Sequences affiliated to the group I.1a were found only in the soil from riverbank forest. Soils from ‘cerrado denso’ had greater Archaea richness than those from ‘mata de galeria’ based on the richness indexes and on the rarefaction curve. β-Diversity analysis showed significant differences between the sequences from the two soil areas studied because of their different thaumarchaeal group composition. These results provide information about the third domain of life from Cerrado soils.     

Cryptophytes: An emerging algal group in the rapidly changing Antarctic Peninsula marine environments

The western Antarctic Peninsula (WAP) is a climatically sensitive region where foundational changes at the basis of the food web have been recorded; cryptophytes are gradually outgrowing diatoms together with a decreased size spectrum of the phytoplankton community. Based on a 11-year (2008–2018) in-situ dataset, we demonstrate a strong coupling between biomass accumulation of cryptophytes, summer upper ocean stability, and the mixed layer depth. Our results shed light on the environmental conditions favoring the cryptophyte success in coastal regions of the WAP, especially during situations of shallower mixed layers associated with lower diatom biomass, which evidences a clear competition or niche segregation between diatoms and cryptophytes. We also unravel the cryptophyte photo-physiological niche by exploring its capacity to thrive under high light stress normally found in confined stratified upper layers. Such conditions are becoming more frequent in the Antarctic coastal waters and will likely have significant future implications at various levels of the marine food web. The competitive advantage of cryptophytes in environments with significant light level fluctuations was supported by laboratory experiments that revealed a high flexibility of cryptophytes to grow in different light conditions driven by a fast photo-regulating response. All tested physiological parameters support the hypothesis that cryptophytes are highly flexible regarding their growing light conditions and extremely efficient in rapidly photo-regulating changes to environmental light levels. This plasticity would give them a competitive advantage in exploiting an ecological niche where light levels fluctuate quickly. These findings provide new insights on niche separation between diatoms and cryptophytes, which is vital for a thorough understanding of the WAP marine ecosystem.     

Damage to living trees contributes to almost half of the biomass losses in tropical forests

Accurate estimates of forest biomass stocks and fluxes are needed to quantify global carbon budgets and assess the response of forests to climate change. However, most forest inventories consider tree mortality as the only aboveground biomass (AGB) loss without accounting for losses via damage to living trees: branchfall, trunk breakage, and wood decay. Here, we use ~151,000 annual records of tree survival and structural completeness to compare AGB loss via damage to living trees to total AGB loss (mortality + damage) in seven tropical forests widely distributed across environmental conditions. We find that 42% (3.62 Mg ha⁻¹ year⁻¹; 95% confidence interval [CI] 2.36–5.25) of total AGB loss (8.72 Mg ha⁻¹ year⁻¹; CI 5.57–12.86) is due to damage to living trees. Total AGB loss was highly variable among forests, but these differences were mainly caused by site variability in damage-related AGB losses rather than by mortality-related AGB losses. We show that conventional forest inventories overestimate stand-level AGB stocks by 4% (1%–17% range across forests) because assume structurally complete trees, underestimate total AGB loss by 29% (6%–57% range across forests) due to overlooked damage-related AGB losses, and overestimate AGB loss via mortality by 22% (7%–80% range across forests) because of the assumption that trees are undamaged before dying. Our results indicate that forest carbon fluxes are higher than previously thought. Damage on living trees is an underappreciated component of the forest carbon cycle that is likely to become even more important as the frequency and severity of forest disturbances increase.     

Marine planktonic microbes survived climatic instabilities in the past

In the geological past, changes in climate and tectonic activity are thought to have spurred the tempo of evolutionary change among major taxonomic groups of plants and animals. However, the extent to which these historical contingencies increased the risk of extinction of microbial plankton species remains largely unknown. Here, I analyse fossil records of marine planktonic diatoms and calcareous nannoplankton over the past 65 million years from the world oceans and show that the probability of species' extinction is not correlated with secular changes in climatic instability. Further supporting these results, analyses of genera survivorship curves based on fossil data concurred with the predictions of a birth-death model that simulates the extinction of genera through time assuming stochastically constant rates of speciation and extinction. However, my results also show that these marine microbes responded to exceptional climatic contingencies in a manner that appears to have promoted net diversification. These results highlight the ability of marine planktonic microbes to survive climatic instabilities in the geological past, and point to different mechanisms underlying the processes of speciation and extinction in these micro-organisms.     

Influence of Soil Physical Properties on Plants of the Mussununga Ecosystem, Brazil

Distribution ranges of plant species are related to physical variables of ecosystems that limit plant growth. Therefore, each plant species response to physical factors builds up the functional diversity of an ecosystem. The higher the species richness of an ecosystem, the larger the probability of maintaining functions and the higher the potential number of plant functional groups (FGs). Thus, the richness potentially increases the number of functions of the highly diverse Atlantic Rainforest domain in Brazil. Severe plant growth limitations caused by stress, however, decrease species richness. In the Spodosols of the Mussununga, an associated ecosystem of Atlantic Rainforest, the percentage of fine sand is directly related to water retention. Moreover, the depth of the cementation layer in the Mussununga??s sandy soil is a physical factor that can affect the plants?? stress gradients. When a shallow cementation layer depth is combined with low water retention in soils and with low fine sand percentage, the double stresses of flooding in the rainy season and water scarcity in the dry season result. This study aimed to identify FGs among Mussununga plant species responding to water stress gradients of soil and to verify the effects of the gradients on plant species richness of the Mussununga. A canonical correspondence analysis (CCA) of species abundance and soil texture variables was performed on 18 plots in six physiognomies of the Mussununga. Species richness rarefactions were calculated for each vegetation form to compare diversity. The two main axes of the CCA showed two FGs responding to soil texture and cementation layer depth: stress tolerator species and mesic species. Physical variables affect plant diversity, with species richness rising as the fine sand proportion also rises in the Mussununga. The effect of the cementation layer is not significantly related to species richness variation.     

Stability of the Transthyretin Molecule as a Key Factor in the Interaction with A-Beta Peptide - Relevance in Alzheimer's Disease

Transthyretin (TTR) protects against A-Beta toxicity by binding the peptide thus inhibiting its aggregation. Previous work showed different TTR mutations interact differently with A-Beta, with increasing affinities correlating with decreasing amyloidogenecity of the TTR mutant; this did not impact on the levels of inhibition of A-Beta aggregation, as assessed by transmission electron microscopy. Our work aimed at probing differences in binding to A-Beta by WT, T119M and L55P TTR using quantitative assays, and at identifying factors affecting this interaction. We addressed the impact of such factors in TTR ability to degrade A-Beta. Using a dot blot approach with the anti-oligomeric antibody A11, we showed that A-Beta formed oligomers transiently, indicating aggregation and fibril formation, whereas in the presence of WT and T119M TTR the oligomers persisted longer, indicative that these variants avoided further aggregation into fibrils. In contrast, L55PTTR was not able to inhibit oligomerization or to prevent evolution to aggregates and fibrils. Furthermore, apoptosis assessment showed WT and T119M TTR were able to protect against A-Beta toxicity. Because the amyloidogenic potential of TTR is inversely correlated with its stability, the use of drugs able to stabilize TTR tetrameric fold could result in increased TTR/A-Beta binding. Here we showed that iododiflunisal, 3-dinitrophenol, resveratrol, [2-(3,5-dichlorophenyl)amino] (DCPA) and [4-(3,5-difluorophenyl)] (DFPB) were able to increase TTR binding to A-Beta; however only DCPA and DFPB improved TTR proteolytic activity. Thyroxine, a TTR ligand, did not influence TTR/A-Beta interaction and A-Beta degradation by TTR, whereas RBP, another TTR ligand, not only obstructed the interaction but also inhibited TTR proteolytic activity. Our results showed differences between WT and T119M TTR, and L55PTTR mutant regarding their interaction with A-Beta and prompt the stability of TTR as a key factor in this interaction, which may be relevant in AD pathogenesis and for the design of therapeutic TTR-based therapies.     

Biological role of endoreplication in the process of spermatogenesis inChara vulgaris L.

Summary During cell division in antheridial filaments ofChara vulgaris an increase in DNA content occurs in both shield cells and manubria within an antheridium, reaching 16C–64C and 8C–32C levels, respectively. Endoreplication ceases prior to the formation of spermatids and initiation of spermiogenesis, probably as a result of symplasmic isolation of the antheridium from the thallus. As the DNA content of the nuclei increases, the shield cells³H-leucine incorporation increases, and they grow intensively in the tangential plane. Translation decreases considerably after termination of shield cell growth. DNA content of mature manubria is half of that in shield cells, although their size is 10 times that of manubria. Translational activity of manubria also increases as DNA content rises and cells grow. However, during spermiogenesis, this activity remains at its maximum, which is associated with the secretory function of the manubria. Spermiogenesis is also accompanied by far-reaching ultrastructural changes within the manubrial cytoplasm.The level of endopolyploidy in both shield cells and manubria of antheridia formed in the spring is higher by one replication cycle, than in autumnal antheridia. AMO-1618, at a concentration of 10^–5M reduces the DNA content in the autumnal manubria. The higher the manubrial level of endopolyploidy in spermiogenesis, the greater their size, and the higher the translational activity and number of joined spermatids. The number of spermatozoids in the antheridium is also positively correlated with the internal volume of an antheridium, which is itself dependent on the endopolyploidy level of shield cells.The results obtained confirm the assumption that endoreplication favours the higher growth dynamics and potential translational activity, which occurs in the dynamic growth phase only in shield cells, while in manubria, i.e. cells producing substances necessary to spermatozoids development, it remains high until the end of spermiogenesis.