Different Scenarios for the Origin and the Subsequent Succession of a Hypothetical Microbial Community in the Cloud Layer of Venus.

The possible existence of a microbial community in the venusian clouds is one of the most intriguing hypotheses in modern astrobiology. Such a community must be characterized by a high survivability potential under severe environmental conditions, the most extreme of which are very low pH levels and water activity. Considering different scenarios for the origin of life and geological history of our planet, a few of these scenarios are discussed in the context of the origin of hypothetical microbial life within the venusian cloud layer. The existence of liquid water on the surface of ancient Venus is one of the key outstanding questions influencing this possibility. We link the inherent attributes of microbial life as we know it that favor the persistence of life in such an environment and review the possible scenarios of life's origin and its evolution under a strong greenhouse effect and loss of water on Venus. We also propose a roadmap and describe a novel methodological approach for astrobiological research in the framework of future missions to Venus with the intent to reveal whether life exists today on the planet.

Sequence Capture of Mitochondrial Genome with PCR-Generated Baits Provides New Insights into the Biogeography of the Genus Abies Mill.

Mitochondrial DNA (mtDNA), being maternally inherited in plants of the family Pinaceae, is an important source of phylogeographic information. However, its use is hindered by a low mutation rate and frequent structure rearrangements. In the present study, we tested the method of genomic libraries enrichment with mtDNA via the sequence capture method yielding mtDNA data which were further used to reconstruct the phylogenetic tree of the genus Abies. The baits for hybrid capture were obtained by long-range PCR using primers designed on the basis of the assembly of Abies sibirica Ledeb. mitochondrial genome. Mitochondrial genomes of Picea sitchensis (Bong.) Carr., Larix sibirica Ledeb., and Keteleeria davidiana (Bertrand) Beissn. were used as an outgroup. The resulting phylogenetic tree consists of two sister branches, including the Eurasian and American species, respectively, with some exceptions. The subclade of A. sachalinensis (F. Schmidt) Mast. and A. veitchii Lindl. (Japan and Sakhalin islands) occupies a basal position in the branch of American firs, probably due to the complex history of fir migrations from North America to Eurasia. The tree has high support for majority of clades. For species represented by more than one sample an intraspecific variability was found which is suitable to design mtDNA markers for phylogeographic and population studies.

Synthesis and Characterization of a Novel Biocompatible Alloy, Ti-Nb-Zr-Ta-Sn.

Many current-generation biomedical implants are fabricated from the Ti-6Al-4V alloy because it has many attractive properties, such as low density and biocompatibility. However, the elastic modulus of this alloy is much larger than that of the surrounding bone, leading to bone resorption and, eventually, implant failure. In the present study, we synthesized and performed a detailed analysis of a novel low elastic modulus Ti-based alloy (Ti-28Nb-5Zr-2Ta-2Sn (TNZTS alloy)) using a variety of methods, including scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and tensile test. Additionally, the in vitro biocompatibility of the TNZTS alloy was evaluated using SCP-1, SaOs-2, and THP-1 cell lines and primary human osteoblasts. Compared to Ti-6Al-4V, the elastic modulus of TNZTS alloy was significantly lower, while measures of its in vitro biocompatibility are comparable. O2 plasma treatment of the surface of the alloy significantly increased its hydrophilicity and, hence, its in vitro biocompatibility. TNZTS alloy specimens did not induce the release of cytokines by macrophages, indicating that such scaffolds would not trigger inflammatory responses. The present results suggest that the TNZTS alloy may have potential as an alternative to Ti-6Al-4V.

Water-Sulfuric Acid Foam as a Possible Habitat for Hypothetical Microbial Community in the Cloud Layer of Venus.

The data available at the moment suggest that ancient Venus was covered by extensive bodies of water which could harbor life. Later, however, the drastic overheating of the planet made the surface of Venus uninhabitable for Earth-type life forms. Nevertheless, hypothetical Venusian organisms could have gradually adapted to conditions within the cloud layer of Venus-the only niche containing liquid water where the Earth-type extremophiles could survive. Here we hypothesize that the unified internal volume of a microbial community habitat is represented by the heterophase liquid-gas foam structure of Venusian clouds. Such unity of internal space within foam water volume facilitates microbial cells movements and trophic interactions between microorganisms that creates favorable conditions for the effective development of a true microbial community. The stabilization of a foam heterophase structure can be provided by various surfactants including those synthesized by living cells and products released during cell lysis. Such a foam system could harbor a microbial community of different species of (poly)extremophilic microorganisms that are capable of photo- and chemosynthesis and may be closely integrated into aero-geochemical processes including the processes of high-temperature polymer synthesis on the planet's surface. Different complex nanostructures transferred to the cloud layers by convection flows could further contribute to the stabilization of heterophase liquid-gas foam structure and participate in chemical and photochemical reactions, thus supporting ecosystem stability.

Exobiology of the Venusian Clouds: New Insights into Habitability through Terrestrial Models and Methods of Detection.

The search for life beyond Earth has focused on Mars and the icy moons Europa and Enceladus, all of which are considered a safe haven for life due to evidence of current or past water. The surface of Venus, on the other hand, has extreme conditions that make it a nonhabitable environment to life as we know it. This is in contrast, however, to its cloud layer, which, while still an extreme environment, may prove to be a safe haven for some extreme forms of life similar to extremophiles on Earth. We consider the venusian clouds a habitable environment based on the presence of (1) a solvent for biochemical reactions, (2) appropriate physicochemical conditions, (3) available energy, and (4) biologically relevant elements. The diversity of extreme microbial ecosystems on Earth has allowed us to identify terrestrial chemolithoautotrophic microorganisms that may be analogs to putative venusian organisms. Here, we hypothesize and describe biological processes that may be performed by such organisms in the venusian clouds. To detect putative venusian organisms, we describe potential biosignature detection methods, which include metal-microbial interactions and optical methods. Finally, we describe currently available technology that can potentially be used for modeling and simulation experiments.

Surface-Dependent Osteoblasts Response to TiO2 Nanotubes of Different Crystallinity.

One of the major challenges of implantology is to design nanoscale modifications of titanium implant surfaces inducing osseointegration. The aim of this study was to investigate the behavior of rat osteoblasts cultured on anodized TiO2 nanotubes of different crystallinity (amorphous and anatase phase) up to 24 days. TiO2 nanotubes were fabricated on VT1-0 titanium foil via a two-step anodization at 20 V using NH4F as an electrolyte. Anatase-phase samples were prepared by heat treatment at 500 °C for 1 h. VT1-0 samples with flat surfaces were used as controls. Primary rat osteoblasts were seeded over experimental surfaces for several incubation times. Scanning electron microscopy (SEM) was used to analyze tested surfaces and cell morphology. Cell adhesion and proliferation were investigated by cell counting. Osteogenic differentiation of cells was evaluated by qPCR of runt-related transcription factor 2 (RUNX2), osteopontin (OPN), integrin binding sialoprotein (IBSP), alkaline phosphatase (ALP) and osteocalcin (OCN). Cell adhesion and proliferation, cell morphology and the expression of osteogenic markers were affected by TiO2 nanotube layered substrates of amorphous and anatase crystallinity. In comparison with flat titanium, along with increased cell adhesion and cell growth a large portion of osteoblasts grown on the both nanostructured surfaces exhibited an osteocyte-like morphology as early as 48 h of culture. Moreover, the expression of all tested osteogenic markers in cells cultured on amorphous and anatase TiO2 nanotubes was upregulated at least at one of the analyzed time points. To summarize, we demonstrated that amorphous and anodized TiO2 layered substrates are highly biocompatible with rat osteoblasts and that the surface modification with about 1500 nm length nanotubes of 35 ± 4 (amorphous phase) and 41 ± 8 nm (anatase phase) in diameter is sufficient to induce their osteogenic differentiation. Such results are significant to the engineering of coating strategies for orthopedic implants aimed to establish a more efficient bone to implant contact and enhance bone repair.

From America to Eurasia: a multigenomes history of the genus Abies.

The origin of conifer genera, the main components of mountain temperate and boreal forests, was deemed to arise in the Mesozoic, although paleontological records and molecular data point to a recent diversification, presumably related to Neogene cooling. The geographical area(s) where the modern lines of conifers emerged remains uncertain, as is the sequence of events leading to their present distribution. To gain further insights into the biogeography of firs (Abies), we conducted phylogenetic analyses of chloroplast, mitochondrial and nuclear markers. The species tree, generated from ten single-copy nuclear genes, yielded probably the best phylogenetic hypothesis available for Abies. The tree obtained from five regions of chloroplast DNA largely corresponded to the nuclear species tree. Ancestral area reconstructions based on fossil calibrated chloroplast DNA and nuclear DNA trees pointed to repeated intercontinental migrations. The mitochondrial DNA haplotype tree, however, disagreed with nuclear and chloroplast DNA trees. It consisted of two clusters: one included mainly American haplotypes, while the other was composed of only Eurasian haplotypes. Presumably, this conflict is due to inter-continental migrations and introgressive hybridization, accompanied by the capture of the mitotypes from aboriginal species by the invading firs. Given that several species inhabiting Northeastern Asia carry American mitotypes and mutations typical for the American cluster, whereas no Asian mitotypes were detected within the American species, we hypothesize that Abies migrated from America to Eurasia, but not in the opposite direction. The direction and age of intercontinental migrations in firs are congruent with other conifers, such as spruces and pines of subsection Strobus, suggesting that these events had the same cause.