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The spectacular outbursts of energy associated with supernovae (SNe) have long motivated research into their potentially hazardous effects on Earth and analogous environments. Much of this research has focused primarily on the atmospheric damage associated with the prompt arrival of ionizing photons within days or months of the initial outburst, and the high-energy cosmic rays that arrive thousands of years after the explosion. In this study, we turn the focus to persistent X-ray emission, arising in certain SNe that have interactions with a dense circumstellar medium and observed months and/or years after the initial outburst. The sustained high X-ray luminosity leads to large doses of ionizing radiation out to formidable distances. We assess the threat posed by these X-ray-luminous SNe for Earth-like planetary atmospheres; our results are rooted in the X-ray SN observations from Chandra, Swift-XRT, XMM-Newton, NuSTAR, and others. We find that this threat is particularly acute for SNe showing evidence of strong circumstellar interaction, such as Type IIn explosions, which have significantly larger ranges of influence than previously expected and lethal consequences up to ∼50 pc away. Furthermore, X-ray-bright SNe could pose a substantial and distinct threat to terrestrial biospheres and tighten the Galactic habitable zone. We urge follow-up X-ray observations of interacting SNe for months and years after the explosion to shed light on the physical nature and full-time evolution of the emission and to clarify the danger that these events pose for life in our galaxy and other star-forming regions.

 

It is often important to determine the source of a microbial strain. Examples include tracking a bacterium linked to a disease epidemic, contaminating the food supply, or used in bioterrorism. Strain identification and tracking are generally approached by using cultivation-based or relatively nonspecific gene fingerprinting methods. Genomic methods have the ability to distinguish strains, but this approach typically has been restricted to isolates or relatively low-complexity communities. We demonstrate that strain-resolved metagenomics can be applied to extremely complex soil samples. We genotypically defined a soil-associated bacterium and identified it as a contaminant. By linking together snapshots of the bacterial genome over time, it was possible to estimate how long the contaminant had been diverging from a likely source population. The results are congruent with the derivation of the bacterium from a strain isolated in Germany and sequenced a decade ago and highlight the utility of metagenomics in strain tracking. 

Annually, half of all plant-derived carbon is added to soil where it is microbially respired to CO 2 . However, understanding of the microbiology of this process is limited because most culture-independent methods cannot link metabolic processes to the organisms present, and this link to causative agents is necessary to predict the results of perturbations on the system. We collected soil samples at two sub-root depths (10–20 cm and 30–40 cm) before and after a rainfall-driven nutrient perturbation event in a Northern California grassland that experiences a Mediterranean climate. From ten samples, we reconstructed 198 metagenome-assembled genomes that represent all major phylotypes. We also quantified 6,835 proteins and 175 metabolites and showed that after the rain event the concentrations of many sugars and amino acids approach zero at the base of the soil profile. Unexpectedly, the genomes of novel members of the Gemmatimonadetes and Candidate Phylum Rokubacteria phyla encode pathways for methylotrophy. We infer that these abundant organisms contribute substantially to carbon turnover in the soil, given that methylotrophy proteins were among the most abundant proteins in the proteome. Previously undescribed Bathyarchaeota and Thermoplasmatales archaea are abundant in deeper soil horizons and are inferred to contribute appreciably to aromatic amino acid degradation. Many of the other bacteria appear to breakdown other components of plant biomass, as evidenced by the prevalence of various sugar and amino acid transporters and corresponding hydrolyzing machinery in the proteome. Overall, our work provides organism-resolved insight into the spatial distribution of bacteria and archaea whose activities combine to degrade plant-derived organics, limiting the transport of methanol, amino acids and sugars into underlying weathered rock. The new insights into the soil carbon cycle during an intense period of carbon turnover, including biogeochemical roles to previously little known soil microbes, were made possible via the combination of metagenomics, proteomics, and metabolomics.