Deep soils store over half of terrestrial organic carbon, yet the viral mechanisms governing carbon persistence in subsurface contexts remain unclear. Here, by conducting a soil profile survey (0–700 cm) across four agroecosystems and a global synthesis of subsurface metagenomes, we established the Deep Soil Viral Resources Database, comprising 50,949 viral operational taxonomic units and 3,902 auxiliary metabolic genes (AMGs). Viral richness increased significantly with depth, accompanied by a shift towards lysogeny driven by declining carbon availability. The deep-soil virome carried AMGs and lysozymes involved in polymer degradation and cell endolysis. Viral endolysin significantly promoted necromass carbon accumulation, which contributed to increases in mineral-associated organic carbon. A synthesis of 138 global soil profiles further revealed a positive effect of viral abundance on soil organic carbon. Our findings establish a framework where viruses strengthen the microbial carbon pump in deep soils by facilitating host carbon scavenging via AMGs and promoting necromass formation via endolysin activity. Combining a metagenomic analysis of agroecosystem soils along a 7-metre depth profile with microcosm incubations and a global synthesis, the authors find increases in viral diversity, lysogeny and necromass carbon accumulation in deeper soils.
Non-ribosomal peptides play important roles in microbial ecology and medicine, for example as toxins and antibiotics such as penicillin. Like ordinary proteins, non-ribosomal peptides are subject to evolutionary change, which is driven by rampant recombinations of their synthetases. The evolutionary dynamics and causes of non-ribosomal peptide diversification are not well understood, because recombinations complicate phylogenetic analysis and statistical tests for natural selection and drift. Here we study the non-ribosomal GameXPeptides, which entomopathogenic bacteria use to kill their insect prey. We use recombination-aware phylogenetics, ancestral sequence reconstruction and statistical analysis of historical recombination patterns to retrace the evolution of GameXPeptides. This uncovers dozens of new GameXPeptides, including striking patterns of structural convergence. We provide statistical and experimental evidence that this diversity is shaped by selection, but also that GameXPeptides experience substantial genetic drift and biased recombination rates that limit the space of accessible peptide variants. Our work illuminates the complex interplay of adaptive and non-adaptive evolutionary forces acting on some of the most versatile chemical weapons in nature. The structural diversity of non-ribosomal peptides is largely determined by recombination. This study shows that selection, genetic drift and biased recombination rates contribute to the diversity of GameXPeptides, non-ribosomal peptides used by entomopathogenic bacteria to kill their insect prey.
Photosynthetic heat tolerance constrains primary productivity and defines the upper temperature limit of the biosphere. However, current approaches to heat tolerance either overlook the duration of heat exposure or describe temperature–time relationships without characterizing causal mechanisms, constraining hypothesis testing and prediction under novel conditions. Heat inactivation of photosynthesis has been posited to result from protein denaturation or lipid membrane breakdown, but their relative contributions are not well resolved. Here we develop and test a quantitative theory of photosynthetic heat inactivation based on chemical kinetics and use the theory to evaluate these competing mechanisms. By analysing photosystem II temperature responses in 177 plant species from 157 families, we show that protein denaturation, not lipid membrane breakdown, governs heat tolerance. The theory also predicts an upper acclimatization limit of ~60 °C, set by the thermal stability of heat shock proteins and supported by global data for 826 species. Our findings provide a predictive, mechanistic basis for photosynthetic heat tolerance and the thermal limits of the biosphere in a changing climate. The authors develop a mechanistic theory for heat inactivation of photosynthesis, based on principles of chemical kinetics, that predicts a photosynthetic heat tolerance upper acclimatization limit of ~60 °C.
