A novel evolutionary strategy revealed in the Phaeoviruses

Phaeoviruses infect the brown algae, which are major contributors to primary production of coastal waters and estuaries. They exploit a Persistent evolutionary strategy akin to a K- selected life strategy via genome integration and are the only known representatives to do so within the giant algal viruses that are typified by r- selected Acute lytic viruses. In screening the genomes of five species within the filamentous brown algal lineage, here we show an unprecedented diversity of viral gene sequence variants especially amongst the smaller phaeoviral genomes. Moreover, one variant shares features from both the two major sub-groups within the phaeoviruses. These phaeoviruses have exploited the reduction of their giant dsDNA genomes and accompanying loss of DNA proofreading capability, typical of an Acute life strategist, but uniquely retain a Persistent life strategy

Micrometeorites: Insights into the flux, sources and atmospheric entry of extraterrestrial dust at Earth

Micrometeorites (MMs) provide constraints on the flux and sources of extraterrestrial dust falling on Earth as well as recording the processes occurring during atmospheric entry. Collections of micrometeorites have been recovered from a wide variety of environments including Antarctic moraine, rock traps, ice and snow and on roof tops in urban areas. Studies of the mineralogy and composition of MMs suggest that most particles (>98%) >50 ​μm in diameter have asteroidal sources, whilst ~50% of particles smaller than 50 ​μm are likely to be derived from comets. The relative abundance of S(IV)-type asteroid materials, similar to ordinary chondrites increases with size, although C-type asteroidal materials, similar to carbonaceous chondrites dominate over all. Although MMs provide excellent evidence on the nature and abundance of extraterrestrial dust at the Earth’s orbit they are not without bias and uncertainty. Mineralogical and compositional change during atmospheric entry makes the exact nature of their precursors uncertain complicating evaluation of source beyond basic classes of material. This is particularly true at larger sizes when complete melting to form cosmic spherules occurs, however, unmelted MMs >50 ​μm in size are also often thermally altered. Mixing with atmospheric oxygen and mass fractionation by evaporation furthermore complicates the use of oxygen isotope compositions in identifying parent bodies. All MM collections are suggested to exhibit biases owing to: (1) collection method, (2) terrestrial weathering, (3) terrestrial contamination, and (4) erosion and deposition by terrestrial surface processes. Even in the least biased collections, those collected by dedicated melting of Antarctic snow, erosive loss of material is suggested here to make fluxes uncertain by factors of up to ~2. The abundance of asteroid-derived MMs observed in collections contradicts models of the orbital evolution of interplanetary dust to Earth, which suggests >70% should be provided by comets

Rapid heating rates define the volatile emission and regolith composition of (3200) Phaethon

Asteroid (3200) Phaethon experiences extreme solar radiant heating ( ~ 750 °C) during perihelion (0.14 au), leading to comet-like activity. The regolith composition and mechanism of volatile emission are unknown but key to understanding JAXA’s DESTINY+ mission data (fly-by in 2029) and the fate of near-Sun asteroids more generally. By subjecting CM chondrite fragments to fast, open system, cyclic heating (2-20 °C/min), simulating conditions on Phaethon we demonstrate that rapid heating rates combine with the low permeability, resulting in reactions between volatile gases and decomposing minerals. The retention of S-bearing gas limits the thermal decomposition of Fe-sulphides, allowing these minerals to survive repeated heating cycles. Slow escape of S-bearing gases provides a mechanism for repeated gas release from a thermally processed surface and, therefore the comet-like activity without requiring surface renewal to expose fresh material each perihelion cycle. We predict Phaethon regolith is composed of olivine, Fe-sulphides, Ca-sulphates and hematite

Cosmic dust fertilization of glacial prebiotic chemistry on early Earth

Earth’s surface is deficient in available forms of many elements considered limiting for prebiotic chemistry. In contrast, many extraterrestrial rocky objects are rich in these same elements. Limiting prebiotic ingredients may, therefore, have been delivered by exogenous material; however, the mechanisms by which exogeneous material may be reliably and non-destructively supplied to a planetary surface remains unclear. Today, the flux of extraterrestrial matter to Earth is dominated by fine-grained cosmic dust. Although this material is rarely discussed in a prebiotic context due to its delivery over a large surface area, concentrated cosmic dust deposits are known to form on Earth today due to the action of sedimentary processes. Here we combine empirical constraints on dust sedimentation with dynamical simulations of dust formation and planetary accretion to show that localized sedimentary deposits of cosmic dust could have accumulated in arid environments on early Earth, in particular glacial settings that today produce cryoconite sediments. Our results challenge the widely held assumption that cosmic dust is incapable of fertilizing prebiotic chemistry. Cosmic dust deposits may have plausibly formed on early Earth and acted to fertilize prebiotic chemistry

Varieties of living things: Life at the intersection of lineage and metabolism

publication-status: Publishedtypes: Articl

Viruses in extreme environments

The original publication is available at www.springerlink.comInternational audienceThe tolerance limits of extremophiles in term of temperature, pH, salinity, desiccation, hydrostatic pressure, radiation, anaerobiosis far exceed what can support non-extremophilic organisms. Like all other organisms, extremophiles serve as hosts for viral replication. Many lines of evidence suggest that viruses could no more be regarded as simple infectious ‘‘fragments of life'' but on the contrary as one of the major components of the biosphere. The exploration of niches with seemingly harsh life conditions as hypersaline and soda lakes, Sahara desert, polar environments or hot acid springs and deep sea hydrothermal vents, permitted to track successfully the presence of viruses. Substantial populations of double-stranded DNA virus that can reach 109 particles per milliliter were recorded. All these viral communities, with genome size ranging from 14 kb to 80 kb, seem to be genetically distinct, suggesting specific niche adaptation. Nevertheless, at this stage of the knowledge, very little is known of their origin, activity, or importance to the in situ microbial dynamics. The continuous attempts to isolate and to study viruses that thrive in extreme environments will be needed to address such questions. However, this topic appears to open a new window on an unexplored part of the viral world

Traces of the oxygen isotope composition of ancient air in fossilized cosmic dust

As a sub-type of micrometeorites, I-type cosmic spherules form by complete melting and oxidation of extraterrestrial Fe, Ni metal particles during their atmospheric entry. All oxygen in the resulting Fe, Ni oxides sources from the Earth’s atmosphere and hence makes them probes for the composition of atmospheric oxygen. When recovered from sedimentary rocks, they allow the reconstruction of the triple oxygen isotope composition of past atmospheric O2, providing quantitative constraints on past CO2 levels or global primary production. Here we establish using fossil I-type cosmic spherules as an archive of Earth’s atmospheric composition with the potential for a unique record of paleo-atmospheric conditions dating back billions of years. We present combined triple oxygen and iron isotope compositions of a collection of fossil I-type cosmic spherules recovered from Phanerozoic sediments. We reconstruct the triple oxygen isotope anomalies of past atmospheric O2 and quantify moderate ancient CO2 levels during the Miocene (~8.5 million years) and late Cretaceous (~87 million years). We also demonstrate this method’s competitive precision for paleo-CO2 determination, despite challenges in finding micrometer-sized unaltered fossil I-type cosmic spherules. Our work indicates that morphologically intact spherules can be isotopically altered by terrestrial processes, underscoring the need for rigorous sample screening

Accreted volatiles influence low-temperature rock equilibria on Europa

The subsurface ocean of Europa has been identified as a high-priority target in the search for habitable environments beyond Earth. Determining the chemical composition of Europa's ocean, a result of water-rock interaction in Europa's interior, is essential to understanding the moon's geological history and whether it can support life. In this study, we used a thermochemical computer modelling code (CHIM-XPT) to explore the range of potential ocean compositions that could result from water-rock interactions at the ocean-silicate interface immediately following the formation of the ocean. We modelled a range of plausible silicate starting materials (based on CV, L and LL chondritic material) and endmember accreted ice compositions (pure H2O vs. cometary) that could have contributed to the volatile inventory of Europa. These models assume a water/layer of its current size and do not incorporate compositional changes resulting from further processes (e.g., ice sheet formation) or additional sources of material (e.g., micrometeorite impacts). Our results show that the initial composition of volatiles had a stronger influence on the resulting ocean composition than the initial composition of the silicate, which produced variation in secondary mineral assemblages and differences in ocean chemistry that could be detectable by future missions. In particular, the absence of Fe-oxides in secondary mineral assemblages for cometary melt systems indicates limited Fe-oxidation, which could impact the generation of H2. We also show that, under all modelled scenarios, water-rock interactions would release redox elements into the ocean, albeit at varying concentrations, supporting proposals that Europa's ocean could be a habitable environment. Significantly, the ocean composition derived from water-rock reactions involving initial fluids with a cometary melt composition had relatively higher concentrations of Mg (by one to five orders of magnitude) and lower concentrations of Fe (by more than two orders of magnitude, except at W/Rs of 3–10) compared to those involving pure H2O initial fluids. This difference in Fe and Mg concentration found between the pure H2O and cometary melt systems could potentially be used as a diagnostic tool to identify the source material for Europa's volatile inventor

Water-rich C-type asteroids as early solar system carbonate factories

Micrometeorites represent a major potential source of volatiles for the early Earth, although often overlooked due to their small sizes and the effects of atmospheric entry. In this study we explore an unusual ~2000 μm, fine-grained unmelted micrometeorite TAM19B-7 derived from a water-rich C-type asteroid. Previous analysis revealed a unique O-isotope composition and intensely aqueously altered geological history. We investigated its carbon isotopic composition using the NanoSIMS and characterized the carbon-bearing carriers using Raman and Near-Infrared spectroscopy. We found that TAM19B-7 has a 13C enriched bulk composition (δ13C = +3 ± 8 ‰), including a domain with 13C depletion (δ13C = −27.1 ‰). Furthermore, a few micro-scale domains show 13C enrichments (δ13C from +12.9 ‰ to +32.7 ‰) suggesting much of the particle’s carbon content was reprocessed into fine-grained carbonates, likely calcite. The heavy bulk C-isotope composition of TAM19B-7 indicates either open system gas loss during aqueous alteration or carbonate formation from isotopically heavy soluble organics. Carbonates have been detected on small body surfaces, including across dwarf planet Ceres, and on the C-type asteroids Bennu and Ryugu. The preservation of both carbonates with 13C enrichments and organic carbon with 13C depletion in TAM19B-7, despite having been flash heated to high temperatures (<1000 °C), demonstrates the importance of cosmic dust as a volatile reservoir

Al‐Cu‐Fe alloys in the solar system: Going inside a Khatyrka‐like micrometeorite (KT01) from the Nubian desert, Sudan

A recently described micrometeorite from the Nubian desert (Sudan) contains an exotic Al‐Cu‐Fe assemblage closely resembling that observed in the Khatyrka chondrite (Suttle et al., 2019; Science Reports 9:12426). We here extend previous investigations of the geochemical, mineralogical, and petrographic characteristics of the Sudan spherule by measuring oxygen isotope ratios in the silicate components and by nano‐scale transmission electron microscopy study of a focused ion beam foil that samples the contact between Al‐Cu alloys and silicates. O‐isotope work indicates an affinity to either OC or CR chondrites, while ruling out a CO or CM precursor. When combined with petrographic evidence we conclude that a CR chondrite parentage is the most likely origin for this micrometeorite. SEM and TEM studies reveal that the Al‐Cu alloys mainly consist of Al metal, stolperite (CuAl), and khatyrkite (CuAl2) together with inclusions in stolperite of a new nanometric, still unknown Al‐Cu phase with a likely nominal Cu3Al2 stoichiometry. At the interface between the alloy assemblage and the surrounding silicate, there is a thin layer (200 nm) of almost pure MgAl2O4 spinel along with well‐defined and almost perfectly spherical metallic droplets, predominantly iron in composition. The study yields additional evidence that Al‐Cu alloys, the likely precursors to quasicrystals in Khatyrka, occur naturally. Moreover, it implies the existence of multiple pathways leading to the association in reduced form of these two elements, one highly lithophile and the other strongly chalcophile