Tectonically-driven oxidant production in the hot biosphere

Microplastic distribution and its implications for human health through marine environments

Microplastics are pervasive pollutants in the ocean, threatening ecosystems and human health through bioaccumulation and toxicological effects. This review synthesizes recent findings on microplastic distribution, trophic transfer, and human health impacts. Key findings indicate that microplastic abundance is highest in the Indian and Pacific Oceans, particularly in seawater and sediment. Morphologically, fibers and fragments dominate, with polypropylene, polyethylene, and polyester being the most prevalent polymers. Smaller particles (<1 mm) undergo long-range transport via ocean currents, while biofouling accelerates vertical sinking. Trophic transfer studies confirm microplastic ingestion across marine food webs. Human exposure is associated with seafood consumption, inhalation of airborne particles, and potential dermal contact, particularly in marine environments. These exposures can lead to adverse health effects, including inflammation, organ damage, respiratory issues, oxidative stress, and metabolic disruptions. Finally, this review explores potential strategies for minimizing human exposure to microplastic pollution in marine environments, paving the way for further research in this critical area.

A geological timescale for bacterial evolution and oxygen adaptation

Microbial life has dominated Earth's history but left a sparse fossil record, greatly hindering our understanding of evolution in deep time. However, bacterial metabolism has left signatures in the geochemical record, most conspicuously the Great Oxidation Event (GOE). We combine machine learning and phylogenetic reconciliation to infer ancestral bacterial transitions to aerobic lifestyles, linking them to the GOE to calibrate the bacterial time tree. Extant bacterial phyla trace their diversity to the Archaean and Proterozoic, and bacterial families prior to the Phanerozoic. We infer that most bacterial phyla were ancestrally anaerobic and adopted aerobic lifestyles after the GOE. However, in the cyanobacterial ancestor, aerobic metabolism likely predated the GOE, which may have facilitated the evolution of oxygenic photosynthesis.

Three enzymes governed the rise of O2 on Earth

Current views of O2 accumulation in Earth history depict three phases: The onset of O2 production by ∼2.4 billion years ago; 2 billion years of stasis at ∼1 % of modern atmospheric levels; and a rising phase, starting about 500 million years ago, in which oxygen eventually reached modern values. Purely geochemical mechanisms have been proposed to account for this tripartite time course of Earth oxygenation. In particular the second phase, the long period of stasis between the advent of O2 and the late rise to modern levels, has posed a puzzle. Proposed solutions involve Earth processes (geochemical, ecosystem, day length). Here we suggest that Earth oxygenation was not determined by geochemical processes. Rather it resulted from emergent biological innovations associated with photosynthesis and the activity of only three enzymes: 1) The oxygen evolving complex of cyanobacteria that makes O2; 2) Nitrogenase, with its inhibition by O2 causing two billion years of oxygen level stasis; 3) Cellulose synthase of land plants, which caused mass deposition and burial of carbon, thus removing an oxygen sink and therefore increasing atmospheric O2. These three enzymes are endogenously produced by, and contained within, cells that have the capacity for exponential growth. The catalytic properties of these three enzymes paved the path of Earth's atmospheric oxygenation, requiring no help from Earth other than the provision of water, CO2, salts, colonizable habitats, and sunlight.

Widespread occurrence of dissolved oxygen anomalies, aerobic microbes, and oxygen-producing metabolic pathways in apparently anoxic environments

Nearly all molecular oxygen (O2) on Earth is produced via oxygenic photosynthesis by plants or photosynthetically active microorganisms. Light-independent O2 production, which occurs both abiotically, e.g. through water radiolysis, or biotically, e.g. through the dismutation of nitric oxide or chlorite, has been thought to be negligible to the Earth system. However, recent work indicates that O2 is produced and consumed in dark and apparently anoxic environments at a much larger scale than assumed. Studies have shown that isotopically light O2 can accumulate in old groundwaters, that strictly aerobic microorganisms are present in many apparently anoxic habitats, and that microbes and metabolisms that can produce O2 without light are widespread and abundant in diverse ecosystems. Analysis of published metagenomic data reveals that the enzyme putatively capable of nitric oxide dismutation forms four major phylogenetic clusters and occurs in at least 16 bacterial phyla, most notably the Bacteroidota. Similarly, a re-analysis of published isotopic signatures of dissolved O2 in groundwater suggests in situ production in up to half of the studied environments. Geochemical and microbiological data support the conclusion that "dark oxygen production" is an important and widespread yet overlooked process in apparently anoxic environments with far-reaching implications for subsurface biogeochemistry and ecology.

Co-evolution of early Earth environments and microbial life

Two records of Earth history capture the evolution of life and its co-evolving ecosystems with interpretable fidelity: the geobiological and geochemical traces preserved in rocks and the evolutionary histories captured within genomes. The earliest vestiges of life are recognized mostly in isotopic fingerprints of specific microbial metabolisms, whereas fossils and organic biomarkers become important later. Molecular biology provides lineages that can be overlayed on geologic and geochemical records of evolving life. All these data lie within a framework of biospheric evolution that is primarily characterized by the transition from an oxygen-poor to an oxygen-rich world. In this Review, we explore the history of microbial life on Earth and the degree to which it shaped, and was shaped by, fundamental transitions in the chemical properties of the oceans, continents and atmosphere. We examine the diversity and evolution of early metabolic processes, their couplings with biogeochemical cycles and their links to the oxygenation of the early biosphere. We discuss the distinction between the beginnings of metabolisms and their subsequent proliferation and their capacity to shape surface environments on a planetary scale. The evolution of microbial life and its ecological impacts directly mirror the Earth's chemical and physical evolution through cause-and-effect relationships.

The radical impact of oxygen on prokaryotic evolution-enzyme inhibition first, uninhibited essential biosyntheses second, aerobic respiration third

Molecular oxygen is a stable diradical. All O2-dependent enzymes employ a radical mechanism. Generated by cyanobacteria, O2 started accumulating on Earth 2.4 billion years ago. Its evolutionary impact is traditionally sought in respiration and energy yield. We mapped 365 O2-dependent enzymatic reactions of prokaryotes to phylogenies for the corresponding 792 protein families. The main physiological adaptations imparted by O2-dependent enzymes were not energy conservation, but novel organic substrate oxidations and O2-dependent, hence O2-tolerant, alternative pathways for O2-inhibited reactions. Oxygen-dependent enzymes evolved in ancestrally anaerobic pathways for essential cofactor biosynthesis including NAD+, pyridoxal, thiamine, ubiquinone, cobalamin, heme, and chlorophyll. These innovations allowed prokaryotes to synthesize essential cofactors in O2-containing environments, a prerequisite for the later emergence of aerobic respiratory chains.

Marine Science Can Contribute to the Search for Extra-Terrestrial Life

Life on our planet likely evolved in the ocean, and thus exo-oceans are key habitats to search for extraterrestrial life. We conducted a data-driven bibliographic survey on the astrobiology literature to identify emerging research trends with marine science for future synergies in the exploration for extraterrestrial life in exo-oceans. Based on search queries, we identified 2592 published items since 1963. The current literature falls into three major groups of terms focusing on (1) the search for life on Mars, (2) astrobiology within our Solar System with reference to icy moons and their exo-oceans, and (3) astronomical and biological parameters for planetary habitability. We also identified that the most prominent research keywords form three key-groups focusing on (1) using terrestrial environments as proxies for Martian environments, centred on extremophiles and biosignatures, (2) habitable zones outside of "Goldilocks" orbital ranges, centred on ice planets, and (3) the atmosphere, magnetic field, and geology in relation to planets' habitable conditions, centred on water-based oceans.

Reaction with Water Vapor Defines Surface Reconstruction and Membranolytic Activity of Quartz Milled in Different Molecular Environments

Industrial processing of quartz (SiO2) and quartz-containing materials produces toxic dust. Fracturing quartz crystals opens the Si‒O bond and produces highly reactive surface species which mainly react with molecules like water and oxygen. This surface-reconstruction process forms silanol (Si‒OH) on the quartz surface, which can damage biological membranes under specific configurations. To comprehend the impact of the quartz surface restructuring on membranolytic activity, the formation and reactivity of quartz radicals produced in four distinct molecular environments with electron paramagnetic resonance (EPR) spectroscopy are evaluated and their membranolytic activity is measured through in vitro hemolysis test. The four molecular environments are formulated with and without molecular water vapor and oxygen (±H2O/±O2). The absence of water favored the formation of surface radical species. In water-rich environments, diamagnetic species prevailed due to radical recombination. Quartz milled in -H2O/±O2 acquired membranolytic activity when exposed to water vapor, unlike quartz milled in +H2O/±O2. After being stabilized by reaction with water vapor, the membranolytic activity of quartz is maintained over time. It is demonstrated that the type and the reactivity of radical sites on quartz are modulated by the outer molecular environment, ultimately determining the biological activity of milled quartz dust.

Comments on "was hydrogen peroxide present before the arrival of oxygenic photosynthesis? The important role of iron(II) in the archean ocean"

Recent research has hypothesized that hydrogen peroxide (H2O2) may have emerged from abiotic geochemical processes during the Archean eon (4.0-2.5 Ga), stimulating the evolution of an enzymatic antioxidant system in early life. This eventually led to the evolution of cyanobacteria, and in turn, the accumulation of oxygen on Earth. In the latest issue of Redox Biology, Koppenol and Sies (vol. 29, no. 103012, 2024) argued against this hypothesis and suggested instead that early organisms would not have been exposed to H2O2 due to its short half-life in the ferruginous oceans of the Archean. We find these arguments to be factually incomplete because they do not consider that freshwater or some coastal marine environments during the Archean could indeed have led to H2O2 generation and accumulation. In these environments, abiotic oxidants could have interacted with early life, thus steering its evolutionary course.

Hydrogeological controls on microbial activity and habitability in the Precambrian continental crust

Earth's deep continental subsurface is a prime setting to study the limits of life's relationship with environmental conditions and habitability. In Precambrian crystalline rocks worldwide, deep ancient groundwaters in fracture networks are typically oligotrophic, highly saline, and locally inhabited by low-biomass communities in which chemolithotrophic microorganisms may dominate. Periodic opening of new fractures can lead to penetration of surface water and/or migration of fracture fluids, both of which may trigger changes in subsurface microbial composition and activity. These hydrogeological processes and their impacts on subsurface communities may play a significant role in global cycles of key elements in the crust. However, to date, considerable uncertainty remains on how subsurface microbial communities may respond to these changes in hydrogeochemical conditions. To address this uncertainty, the biogeochemistry of Thompson mine (Manitoba, Canada) was investigated. Compositional and isotopic analyses of fracture waters collected here at ~1 km below land surface revealed different extents of mixing between subsurface brine and (paleo)meteoric waters. To investigate the effects this mixing may have had on microbial communities, the Most Probable Number technique was applied to test community response for a total of 13 different metabolisms. The results showed that all fracture waters were dominated by viable heterotrophic microorganisms which can utilize organic materials associated with aerobic/facultative anaerobic processes, sulfate reduction, or fermentation. Where mixing between subsurface brines and (paleo)meteoric waters occurs, the communities demonstrate higher cell densities and increased viable functional potentials, compared to the most saline sample. This study therefore highlights the connection between hydrogeologic heterogeneity and the heterogeneity of subsurface ecosystems in the crystalline rocks, and suggests that hydrogeology can have a considerable impact on the scope and scale of subsurface microbial communities on Earth and potentially beyond.

Inorganic Fe-O and Fe-S oxidoreductases: paradigms for prebiotic chemistry and the evolution of enzymatic activity in biology

Oxidoreductases play crucial roles in electron transfer during biological redox reactions. These reactions are not exclusive to protein-based biocatalysts; nano-size (<100 nm), fine-grained inorganic colloids, such as iron oxides and sulfides, also participate. These nanocolloids exhibit intrinsic redox activity and possess direct electron transfer capacities comparable to their biological counterparts. The unique metal ion architecture of these nanocolloids, including electron configurations, coordination environment, electron conductivity, and the ability to promote spontaneous electron hopping, contributes to their transfer capabilities. Nano-size inorganic colloids are believed to be among the earliest 'oxidoreductases' to have 'evolved' on early Earth, playing critical roles in biological systems. Representing a distinct type of biocatalysts alongside metalloproteins, these nanoparticles offer an early alternative to protein-based oxidoreductase activity. While the roles of inorganic nano-sized catalysts in current Earth ecosystems are intuitively significant, they remain poorly understood and underestimated. Their contribution to chemical reactions and biogeochemical cycles likely helped shape and maintain the balance of our planet's ecosystems. However, their potential applications in biomedical, agricultural, and environmental protection sectors have not been fully explored or exploited. This review examines the structure, properties, and mechanisms of such catalysts from a material's evolutionary standpoint, aiming to raise awareness of their potential to provide innovative solutions to some of Earth's sustainability challenges.

Was hydrogen peroxide present before the arrival of oxygenic photosynthesis? The important role of iron(II) in the Archean ocean

We address the chemical/biological history of H2O2 back at the times of the Archean eon (2.5-3.9 billion years ago (Gya)). During the Archean eon the pO2 was million-fold lower than the present pO2, starting to increase gradually from 2.3 until 0.6 Gya, when it reached ca. 0.2 bar. The observation that some anaerobic organisms can defend themselves against O2 has led to the view that early organisms could do the same before oxygenic photosynthesis had developed at about 3 Gya. This would require the anaerobic generation of H2O2, and here we examine the various mechanisms which were suggested in the literature for this. Given the concentration of Fe2+ at 20-200 μM in the Archean ocean, the estimated half-life of H2O2 is ca. 0.7 s. The oceanic H2O2 concentration was practically zero. We conclude that early organisms were not exposed to H2O2 before the arrival of oxygenic photosynthesis.