RESUMO
Carbon fixation is the process by which CO2 is converted from a gas into biomass. The Calvin-Benson-Bassham cycle (CBB) is the dominant carbon-consuming pathway on Earth, driving >99.5% of the â¼120 billion tons of carbon that are converted to sugar by plants, algae, and cyanobacteria. The carboxylase enzyme in the CBB, ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco), fixes one CO2 molecule per turn of the cycle into bioavailable sugars. Despite being critical to the assimilation of carbon, rubisco's kinetic rate is not very fast, limiting flux through the pathway. This bottleneck presents a paradox: Why has rubisco not evolved to be a better catalyst? Many hypothesize that the catalytic mechanism of rubisco is subject to one or more trade-offs and that rubisco variants have been optimized for their native physiological environment. Here, we review the evolution and biochemistry of rubisco through the lens of structure and mechanism in order to understand what trade-offs limit its improvement. We also review the many attempts to improve rubisco itself and thereby promote plant growth.
Assuntos
Dióxido de Carbono , Ribulose-Bifosfato Carboxilase , Ribulose-Bifosfato Carboxilase/genética , Ribulose-Bifosfato Carboxilase/química , Ribulose-Bifosfato Carboxilase/metabolismo , Dióxido de Carbono/metabolismo , FotossínteseRESUMO
It is challenging to convert a heterotrophic organism that loves sugars and other multicarbon compounds as energy and carbon sources into an autotroph that builds all biomass from carbon dioxide. In this issue, Gleizer et al. demonstrate how this can be achieved.
Assuntos
Processos Autotróficos/fisiologia , Escherichia coli/fisiologia , Biomassa , Dióxido de Carbono/metabolismo , Ribulose-Bifosfato Carboxilase/metabolismoRESUMO
The living world is largely divided into autotrophs that convert CO2 into biomass and heterotrophs that consume organic compounds. In spite of widespread interest in renewable energy storage and more sustainable food production, the engineering of industrially relevant heterotrophic model organisms to use CO2 as their sole carbon source has so far remained an outstanding challenge. Here, we report the achievement of this transformation on laboratory timescales. We constructed and evolved Escherichia coli to produce all its biomass carbon from CO2. Reducing power and energy, but not carbon, are supplied via the one-carbon molecule formate, which can be produced electrochemically. Rubisco and phosphoribulokinase were co-expressed with formate dehydrogenase to enable CO2 fixation and reduction via the Calvin-Benson-Bassham cycle. Autotrophic growth was achieved following several months of continuous laboratory evolution in a chemostat under intensifying organic carbon limitation and confirmed via isotopic labeling.
Assuntos
Biomassa , Dióxido de Carbono/metabolismo , Carbono/metabolismo , Escherichia coli/metabolismo , Adaptação Fisiológica/genética , Aminoácidos/metabolismo , Processos Autotróficos/fisiologia , Isótopos de Carbono , Evolução Molecular Direcionada , Escherichia coli/genética , Marcação por Isótopo , Engenharia Metabólica , Análise do Fluxo Metabólico , Mutação/genéticaRESUMO
Approximately 30%-40% of global CO2 fixation occurs inside a non-membrane-bound organelle called the pyrenoid, which is found within the chloroplasts of most eukaryotic algae. The pyrenoid matrix is densely packed with the CO2-fixing enzyme Rubisco and is thought to be a crystalline or amorphous solid. Here, we show that the pyrenoid matrix of the unicellular alga Chlamydomonas reinhardtii is not crystalline but behaves as a liquid that dissolves and condenses during cell division. Furthermore, we show that new pyrenoids are formed both by fission and de novo assembly. Our modeling predicts the existence of a "magic number" effect associated with special, highly stable heterocomplexes that influences phase separation in liquid-like organelles. This view of the pyrenoid matrix as a phase-separated compartment provides a paradigm for understanding its structure, biogenesis, and regulation. More broadly, our findings expand our understanding of the principles that govern the architecture and inheritance of liquid-like organelles.
Assuntos
Chlamydomonas reinhardtii/citologia , Cloroplastos/ultraestrutura , Proteínas de Algas/metabolismo , Dióxido de Carbono/metabolismo , Chlamydomonas reinhardtii/química , Chlamydomonas reinhardtii/metabolismo , Cloroplastos/química , Cloroplastos/metabolismo , Microscopia Crioeletrônica , Biogênese de Organelas , Ribulose-Bifosfato Carboxilase/metabolismoRESUMO
Approximately one-third of global CO2 fixation is performed by eukaryotic algae. Nearly all algae enhance their carbon assimilation by operating a CO2-concentrating mechanism (CCM) built around an organelle called the pyrenoid, whose protein composition is largely unknown. Here, we developed tools in the model alga Chlamydomonas reinhardtii to determine the localizations of 135 candidate CCM proteins and physical interactors of 38 of these proteins. Our data reveal the identity of 89 pyrenoid proteins, including Rubisco-interacting proteins, photosystem I assembly factor candidates, and inorganic carbon flux components. We identify three previously undescribed protein layers of the pyrenoid: a plate-like layer, a mesh layer, and a punctate layer. We find that the carbonic anhydrase CAH6 is in the flagella, not in the stroma that surrounds the pyrenoid as in current models. These results provide an overview of proteins operating in the eukaryotic algal CCM, a key process that drives global carbon fixation.
Assuntos
Proteínas de Algas/metabolismo , Ciclo do Carbono , Chlamydomonas reinhardtii/citologia , Chlamydomonas reinhardtii/metabolismo , Cloroplastos/metabolismo , Proteínas de Algas/química , Dióxido de Carbono/metabolismo , Anidrases Carbônicas/metabolismo , Chlamydomonas reinhardtii/química , Cloroplastos/química , Proteínas Luminescentes/análise , Microscopia Confocal , Fotossíntese , Proteínas de Plantas/metabolismo , Ribulose-Bifosfato Carboxilase/química , Ribulose-Bifosfato Carboxilase/metabolismoRESUMO
Nitrogenase is a versatile metalloenzyme that is capable of catalyzing two important reactions under ambient conditions: the reduction of nitrogen (N2) to ammonia (NH3), a key step in the global nitrogen cycle; and the reduction of carbon monoxide (CO) and carbon dioxide (CO2) to hydrocarbons, two reactions useful for recycling carbon waste into carbon fuel. The molybdenum (Mo)- and vanadium (V)-nitrogenases are two homologous members of this enzyme family. Each of them contains a P-cluster and a cofactor, two high-nuclearity metalloclusters that have crucial roles in catalysis. This review summarizes the progress that has been made in elucidating the biosynthetic mechanisms of the P-cluster and cofactor species of nitrogenase, focusing on what is known about the assembly mechanisms of the two metalloclusters in Mo-nitrogenase and giving a brief account of the possible assembly schemes of their counterparts in V-nitrogenase, which are derived from the homology between the two nitrogenases.
Assuntos
Azotobacter vinelandii/enzimologia , Proteínas de Bactérias/metabolismo , Coenzimas/metabolismo , Molibdênio/metabolismo , Nitrogenase/metabolismo , Subunidades Proteicas/metabolismo , Sequência de Aminoácidos , Amônia/química , Amônia/metabolismo , Azotobacter vinelandii/genética , Proteínas de Bactérias/química , Proteínas de Bactérias/genética , Biocatálise , Dióxido de Carbono/química , Dióxido de Carbono/metabolismo , Monóxido de Carbono/química , Monóxido de Carbono/metabolismo , Coenzimas/química , Ferro/química , Ferro/metabolismo , Molibdênio/química , Nitrogênio/química , Nitrogênio/metabolismo , Nitrogenase/química , Nitrogenase/genética , Oxirredução , Subunidades Proteicas/química , Subunidades Proteicas/genética , Alinhamento de Sequência , Homologia de Sequência de Aminoácidos , Vanádio/química , Vanádio/metabolismoRESUMO
Can a heterotrophic organism be evolved to synthesize biomass from CO2 directly? So far, non-native carbon fixation in which biomass precursors are synthesized solely from CO2 has remained an elusive grand challenge. Here, we demonstrate how a combination of rational metabolic rewiring, recombinant expression, and laboratory evolution has led to the biosynthesis of sugars and other major biomass constituents by a fully functional Calvin-Benson-Bassham (CBB) cycle in E. coli. In the evolved bacteria, carbon fixation is performed via a non-native CBB cycle, while reducing power and energy are obtained by oxidizing a supplied organic compound (e.g., pyruvate). Genome sequencing reveals that mutations in flux branchpoints, connecting the non-native CBB cycle to biosynthetic pathways, are essential for this phenotype. The successful evolution of a non-native carbon fixation pathway, though not yet resulting in net carbon gain, strikingly demonstrates the capacity for rapid trophic-mode evolution of metabolism applicable to biotechnology. PAPERCLIP.
Assuntos
Dióxido de Carbono/metabolismo , Evolução Molecular Direcionada , Escherichia coli/genética , Escherichia coli/metabolismo , Gluconeogênese , Redes e Vias Metabólicas , Processos Autotróficos , Carboidratos/biossíntese , Escherichia coli/crescimento & desenvolvimento , Espectrometria de MassasRESUMO
The capacity for terrestrial ecosystems to sequester additional carbon (C) with rising CO2 concentrations depends on soil nutrient availability1,2. Previous evidence suggested that mature forests growing on phosphorus (P)-deprived soils had limited capacity to sequester extra biomass under elevated CO2 (refs. 3-6), but uncertainty about ecosystem P cycling and its CO2 response represents a crucial bottleneck for mechanistic prediction of the land C sink under climate change7. Here, by compiling the first comprehensive P budget for a P-limited mature forest exposed to elevated CO2, we show a high likelihood that P captured by soil microorganisms constrains ecosystem P recycling and availability for plant uptake. Trees used P efficiently, but microbial pre-emption of mineralized soil P seemed to limit the capacity of trees for increased P uptake and assimilation under elevated CO2 and, therefore, their capacity to sequester extra C. Plant strategies to stimulate microbial P cycling and plant P uptake, such as increasing rhizosphere C release to soil, will probably be necessary for P-limited forests to increase C capture into new biomass. Our results identify the key mechanisms by which P availability limits CO2 fertilization of tree growth and will guide the development of Earth system models to predict future long-term C storage.
Assuntos
Dióxido de Carbono , Sequestro de Carbono , Florestas , Fósforo , Microbiologia do Solo , Árvores , Biomassa , Dióxido de Carbono/metabolismo , Dióxido de Carbono/análise , Fósforo/metabolismo , Rizosfera , Solo/química , Árvores/crescimento & desenvolvimento , Árvores/metabolismo , Mudança ClimáticaRESUMO
The uptake of carbon dioxide (CO2) by terrestrial ecosystems is critical for moderating climate change1. To provide a ground-based long-term assessment of the contribution of forests to terrestrial CO2 uptake, we synthesized in situ forest data from boreal, temperate and tropical biomes spanning three decades. We found that the carbon sink in global forests was steady, at 3.6 ± 0.4 Pg C yr-1 in the 1990s and 2000s, and 3.5 ± 0.4 Pg C yr-1 in the 2010s. Despite this global stability, our analysis revealed some major biome-level changes. Carbon sinks have increased in temperate (+30 ± 5%) and tropical regrowth (+29 ± 8%) forests owing to increases in forest area, but they decreased in boreal (-36 ± 6%) and tropical intact (-31 ± 7%) forests, as a result of intensified disturbances and losses in intact forest area, respectively. Mass-balance studies indicate that the global land carbon sink has increased2, implying an increase in the non-forest-land carbon sink. The global forest sink is equivalent to almost half of fossil-fuel emissions (7.8 ± 0.4 Pg C yr-1 in 1990-2019). However, two-thirds of the benefit from the sink has been negated by tropical deforestation (2.2 ± 0.5 Pg C yr-1 in 1990-2019). Although the global forest sink has endured undiminished for three decades, despite regional variations, it could be weakened by ageing forests, continuing deforestation and further intensification of disturbance regimes1. To protect the carbon sink, land management policies are needed to limit deforestation, promote forest restoration and improve timber-harvesting practices1,3.
Assuntos
Dióxido de Carbono , Sequestro de Carbono , Florestas , Internacionalidade , Árvores , Dióxido de Carbono/metabolismo , Dióxido de Carbono/análise , Mudança Climática , Conservação dos Recursos Naturais , Ecossistema , Agricultura Florestal/legislação & jurisprudência , Agricultura Florestal/estatística & dados numéricos , Agricultura Florestal/tendências , Combustíveis Fósseis/efeitos adversos , Combustíveis Fósseis/provisão & distribuição , Taiga , Árvores/metabolismo , Árvores/crescimento & desenvolvimento , Clima TropicalRESUMO
The linear production and consumption of plastics today is unsustainable. It creates large amounts of unnecessary and mismanaged waste, pollution and carbon dioxide emissions, undermining global climate targets and the Sustainable Development Goals. This Perspective provides an integrated technological, economic and legal view on how to deliver a circular carbon and plastics economy that minimizes carbon dioxide emissions. Different pathways that maximize recirculation of carbon (dioxide) between plastics waste and feedstocks are outlined, including mechanical, chemical and biological recycling, and those involving the use of biomass and carbon dioxide. Four future scenarios are described, only one of which achieves sufficient greenhouse gas savings in line with global climate targets. Such a bold system change requires 50% reduction in future plastic demand, complete phase-out of fossil-derived plastics, 95% recycling rates of retrievable plastics and use of renewable energy. It is hard to overstate the challenge of achieving this goal. We therefore present a roadmap outlining the scale and timing of the economic and legal interventions that could possibly support this. Assessing the service lifespan and recoverability of plastic products, along with considerations of sufficiency and smart design, can moreover provide design principles to guide future manufacturing, use and disposal of plastics.
Assuntos
Poluição Ambiental , Objetivos , Plásticos , Reciclagem , Desenvolvimento Sustentável , Biomassa , Dióxido de Carbono/análise , Dióxido de Carbono/química , Dióxido de Carbono/metabolismo , Poluição Ambiental/economia , Poluição Ambiental/legislação & jurisprudência , Poluição Ambiental/prevenção & controle , Poluição Ambiental/estatística & dados numéricos , Combustíveis Fósseis , Aquecimento Global/prevenção & controle , Gases de Efeito Estufa/análise , Plásticos/síntese química , Plásticos/economia , Plásticos/metabolismo , Plásticos/provisão & distribuição , Reciclagem/economia , Reciclagem/legislação & jurisprudência , Reciclagem/métodos , Reciclagem/tendências , Energia Renovável , Desenvolvimento Sustentável/economia , Desenvolvimento Sustentável/legislação & jurisprudência , Desenvolvimento Sustentável/tendências , Tecnologia/economia , Tecnologia/legislação & jurisprudência , Tecnologia/métodos , Tecnologia/tendênciasRESUMO
Mosquitoes are a great threat to human health. Fortunately, they have a weakness: they utilize their sense of smell to target a human host. Recent studies examine the effectiveness of protecting humans from attack by ablating or odorant targeting mosquito olfactory receptors. The results are both promising and alarming.
Assuntos
Culicidae/efeitos dos fármacos , Culicidae/fisiologia , Mordeduras e Picadas de Insetos , Controle de Mosquitos , Animais , Dióxido de Carbono/metabolismo , Humanos , Proteínas de Insetos/metabolismo , Neurônios Receptores Olfatórios/efeitos dos fármacos , Neurônios Receptores Olfatórios/metabolismo , Receptores Odorantes/metabolismo , OlfatoRESUMO
Photosystems II and I (PSII, PSI) are the reaction centre-containing complexes driving the light reactions of photosynthesis; PSII performs light-driven water oxidation and PSI further photo-energizes harvested electrons. The impressive efficiencies of the photosystems have motivated extensive biological, artificial and biohybrid approaches to 're-wire' photosynthesis for higher biomass-conversion efficiencies and new reaction pathways, such as H2 evolution or CO2 fixation1,2. Previous approaches focused on charge extraction at terminal electron acceptors of the photosystems3. Electron extraction at earlier steps, perhaps immediately from photoexcited reaction centres, would enable greater thermodynamic gains; however, this was believed impossible with reaction centres buried at least 4 nm within the photosystems4,5. Here, we demonstrate, using in vivo ultrafast transient absorption (TA) spectroscopy, extraction of electrons directly from photoexcited PSI and PSII at early points (several picoseconds post-photo-excitation) with live cyanobacterial cells or isolated photosystems, and exogenous electron mediators such as 2,6-dichloro-1,4-benzoquinone (DCBQ) and methyl viologen. We postulate that these mediators oxidize peripheral chlorophyll pigments participating in highly delocalized charge-transfer states after initial photo-excitation. Our results challenge previous models that the photoexcited reaction centres are insulated within the photosystem protein scaffold, opening new avenues to study and re-wire photosynthesis for biotechnologies and semi-artificial photosynthesis.
Assuntos
Fotossíntese , Complexo de Proteína do Fotossistema I , Complexo de Proteína do Fotossistema II , Clorofila/metabolismo , Oxirredução , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo , Fatores de Tempo , Ciclo do Carbono , Dióxido de Carbono/metabolismo , Hidrogênio/metabolismo , Cianobactérias/metabolismo , Elétrons , TermodinâmicaRESUMO
Terrestrial ecosystems have taken up about 32% of the total anthropogenic CO2 emissions in the past six decades1. Large uncertainties in terrestrial carbon-climate feedbacks, however, make it difficult to predict how the land carbon sink will respond to future climate change2. Interannual variations in the atmospheric CO2 growth rate (CGR) are dominated by land-atmosphere carbon fluxes in the tropics, providing an opportunity to explore land carbon-climate interactions3-6. It is thought that variations in CGR are largely controlled by temperature7-10 but there is also evidence for a tight coupling between water availability and CGR11. Here, we use a record of global atmospheric CO2, terrestrial water storage and precipitation data to investigate changes in the interannual relationship between tropical land climate conditions and CGR under a changing climate. We find that the interannual relationship between tropical water availability and CGR became increasingly negative during 1989-2018 compared to 1960-1989. This could be related to spatiotemporal changes in tropical water availability anomalies driven by shifts in El Niño/Southern Oscillation teleconnections, including declining spatial compensatory water effects9. We also demonstrate that most state-of-the-art coupled Earth System and Land Surface models do not reproduce the intensifying water-carbon coupling. Our results indicate that tropical water availability is increasingly controlling the interannual variability of the terrestrial carbon cycle and modulating tropical terrestrial carbon-climate feedbacks.
Assuntos
Ciclo do Carbono , Dióxido de Carbono , Mudança Climática , Ecossistema , Análise Espaço-Temporal , Clima Tropical , Água , Atmosfera/química , Carbono/análise , Carbono/metabolismo , Dióxido de Carbono/análise , Dióxido de Carbono/metabolismo , Água/análise , Água/química , Sequestro de Carbono , Chuva , El Niño Oscilação Sul , RetroalimentaçãoRESUMO
The transfer of photosynthetically produced organic carbon from surface to mesopelagic waters draws carbon dioxide from the atmosphere1. However, current observation-based estimates disagree on the strength of this biological carbon pump (BCP)2. Earth system models (ESMs) also exhibit a large spread of BCP estimates, indicating limited representations of the known carbon export pathways3. Here we use several decades of hydrographic observations to produce a top-down estimate of the strength of the BCP with an inverse biogeochemical model that implicitly accounts for all known export pathways. Our estimate of total organic carbon (TOC) export at 73.4 m (model euphotic zone depth) is 15.00 ± 1.12 Pg C year-1, with only two-thirds reaching 100 m depth owing to rapid remineralization of organic matter in the upper water column. Partitioned by sequestration time below the euphotic zone, τ, the globally integrated organic carbon production rate with τ > 3 months is 11.09 ± 1.02 Pg C year-1, dropping to 8.25 ± 0.30 Pg C year-1 for τ > 1 year, with 81% contributed by the non-advective-diffusive vertical flux owing to sinking particles and vertically migrating zooplankton. Nevertheless, export of organic carbon by mixing and other fluid transport of dissolved matter and suspended particles remains regionally important for meeting the respiratory carbon demand. Furthermore, the temperature dependence of the sequestration efficiency inferred from our inversion suggests that future global warming may intensify the recycling of organic matter in the upper ocean, potentially weakening the BCP.
Assuntos
Dióxido de Carbono , Água do Mar , Água , Animais , Dióxido de Carbono/metabolismo , Fotossíntese , Água do Mar/química , Água/química , Água/metabolismo , Zooplâncton/metabolismo , Aquecimento Global , Oceanos e MaresRESUMO
Global net land carbon uptake or net biome production (NBP) has increased during recent decades1. Whether its temporal variability and autocorrelation have changed during this period, however, remains elusive, even though an increase in both could indicate an increased potential for a destabilized carbon sink2,3. Here, we investigate the trends and controls of net terrestrial carbon uptake and its temporal variability and autocorrelation from 1981 to 2018 using two atmospheric-inversion models, the amplitude of the seasonal cycle of atmospheric CO2 concentration derived from nine monitoring stations distributed across the Pacific Ocean and dynamic global vegetation models. We find that annual NBP and its interdecadal variability increased globally whereas temporal autocorrelation decreased. We observe a separation of regions characterized by increasingly variable NBP, associated with warm regions and increasingly variable temperatures, lower and weaker positive trends in NBP and regions where NBP became stronger and less variable. Plant species richness presented a concave-down parabolic spatial relationship with NBP and its variability at the global scale whereas nitrogen deposition generally increased NBP. Increasing temperature and its increasing variability appear as the most important drivers of declining and increasingly variable NBP. Our results show increasing variability of NBP regionally that can be mostly attributed to climate change and that may point to destabilization of the coupled carbon-climate system.
Assuntos
Sequestro de Carbono , Carbono , Mudança Climática , Ecossistema , Mapeamento Geográfico , Plantas , Carbono/análise , Carbono/metabolismo , Dióxido de Carbono/análise , Dióxido de Carbono/metabolismo , Sequestro de Carbono/fisiologia , Estações do Ano , Atmosfera/química , Oceano Pacífico , Temperatura , Nitrogênio/metabolismo , Plantas/classificação , Plantas/metabolismo , Medição de RiscoRESUMO
The Amazon forest carbon sink is declining, mainly as a result of land-use and climate change1-4. Here we investigate how changes in law enforcement of environmental protection policies may have affected the Amazonian carbon balance between 2010 and 2018 compared with 2019 and 2020, based on atmospheric CO2 vertical profiles5,6, deforestation7 and fire data8, as well as infraction notices related to illegal deforestation9. We estimate that Amazonia carbon emissions increased from a mean of 0.24 ± 0.08 PgC year-1 in 2010-2018 to 0.44 ± 0.10 PgC year-1 in 2019 and 0.52 ± 0.10 PgC year-1 in 2020 (± uncertainty). The observed increases in deforestation were 82% and 77% (94% accuracy) and burned area were 14% and 42% in 2019 and 2020 compared with the 2010-2018 mean, respectively. We find that the numbers of notifications of infractions against flora decreased by 30% and 54% and fines paid by 74% and 89% in 2019 and 2020, respectively. Carbon losses during 2019-2020 were comparable with those of the record warm El Niño (2015-2016) without an extreme drought event. Statistical tests show that the observed differences between the 2010-2018 mean and 2019-2020 are unlikely to have arisen by chance. The changes in the carbon budget of Amazonia during 2019-2020 were mainly because of western Amazonia becoming a carbon source. Our results indicate that a decline in law enforcement led to increases in deforestation, biomass burning and forest degradation, which increased carbon emissions and enhanced drying and warming of the Amazon forests.
Assuntos
Dióxido de Carbono , Sequestro de Carbono , Conservação dos Recursos Naturais , Política Ambiental , Aplicação da Lei , Floresta Úmida , Biomassa , Brasil , Dióxido de Carbono/análise , Dióxido de Carbono/metabolismo , Política Ambiental/legislação & jurisprudência , Atmosfera/química , Incêndios Florestais/estatística & dados numéricos , Conservação dos Recursos Naturais/estatística & dados numéricos , El Niño Oscilação Sul , Secas/estatística & dados numéricosRESUMO
Phosphorus is a limiting nutrient that is thought to control oceanic oxygen levels to a large extent1-3. A possible increase in marine phosphorus concentrations during the Ediacaran Period (about 635-539 million years ago) has been proposed as a driver for increasing oxygen levels4-6. However, little is known about the nature and evolution of phosphorus cycling during this time4. Here we use carbonate-associated phosphate (CAP) from six globally distributed sections to reconstruct oceanic phosphorus concentrations during a large negative carbon-isotope excursion-the Shuram excursion (SE)-which co-occurred with global oceanic oxygenation7-9. Our data suggest pulsed increases in oceanic phosphorus concentrations during the falling and rising limbs of the SE. Using a quantitative biogeochemical model, we propose that this observation could be explained by carbon dioxide and phosphorus release from marine organic-matter oxidation primarily by sulfate, with further phosphorus release from carbon-dioxide-driven weathering on land. Collectively, this may have resulted in elevated organic-pyrite burial and ocean oxygenation. Our CAP data also seem to suggest equivalent oceanic phosphorus concentrations under maximum and minimum extents of ocean anoxia across the SE. This observation may reflect decoupled phosphorus and ocean anoxia cycles, as opposed to their coupled nature in the modern ocean. Our findings point to external stimuli such as sulfate weathering rather than internal oceanic phosphorus-oxygen cycling alone as a possible control on oceanic oxygenation in the Ediacaran. In turn, this may help explain the prolonged rise of atmospheric oxygen levels.
Assuntos
Oceanos e Mares , Fósforo , Água do Mar , Atmosfera/química , Dióxido de Carbono/metabolismo , Isótopos de Carbono , Sedimentos Geológicos/química , História Antiga , Hipóxia/metabolismo , Oxigênio/análise , Oxigênio/história , Oxigênio/metabolismo , Fósforo/análise , Fósforo/história , Fósforo/metabolismo , Água do Mar/química , Sulfatos/metabolismo , Carbonatos/análise , Carbonatos/metabolismo , OxirreduçãoRESUMO
Autotrophy is the basis for complex life on Earth. Central to this process is rubisco-the enzyme that catalyzes almost all carbon fixation on the planet. Yet, with only a small fraction of rubisco diversity kinetically characterized so far, the underlying biological factors driving the evolution of fast rubiscos in nature remain unclear. We conducted a high-throughput kinetic characterization of over 100 bacterial form I rubiscos, the most ubiquitous group of rubisco sequences in nature, to uncover the determinants of rubisco's carboxylation velocity. We show that the presence of a carboxysome CO2 concentrating mechanism correlates with faster rubiscos with a median fivefold higher rate. In contrast to prior studies, we find that rubiscos originating from α-cyanobacteria exhibit the highest carboxylation rates among form I enzymes (≈10 s-1 median versus <7 s-1 in other groups). Our study systematically reveals biological and environmental properties associated with kinetic variation across rubiscos from nature.
Assuntos
Ribulose-Bifosfato Carboxilase , Ribulose-Bifosfato Carboxilase/metabolismo , Ribulose-Bifosfato Carboxilase/genética , Cinética , Dióxido de Carbono/metabolismo , Proteínas de Bactérias/metabolismo , Proteínas de Bactérias/genética , Cianobactérias/metabolismo , Cianobactérias/enzimologia , Cianobactérias/genética , Bactérias/enzimologia , Bactérias/metabolismo , Bactérias/genéticaRESUMO
Plants cannot move, so they must endure abiotic stresses such as drought, salinity and extreme temperatures. These stressors greatly limit the distribution of plants, alter their growth and development, and reduce crop productivity. Recent progress in our understanding of the molecular mechanisms underlying the responses of plants to abiotic stresses emphasizes their multilevel nature; multiple processes are involved, including sensing, signalling, transcription, transcript processing, translation and post-translational protein modifications. This improved knowledge can be used to boost crop productivity and agricultural sustainability through genetic, chemical and microbial approaches.
Assuntos
Produtos Agrícolas/genética , Secas , Ecossistema , Plantas/genética , Salinidade , Estresse Fisiológico/genética , Temperatura , Atmosfera/química , Dióxido de Carbono/metabolismo , Produtos Agrícolas/crescimento & desenvolvimento , Produtos Agrícolas/metabolismo , Regulação da Expressão Gênica de Plantas , Oxigênio/metabolismo , Plantas/metabolismo , Solo/químicaRESUMO
Female mosquitoes that transmit deadly diseases locate human hosts by detecting exhaled CO2 and skin odor. The identities of olfactory neurons and receptors required for attraction to skin odor remain a mystery. Here, we show that the CO2-sensitive olfactory neuron is also a sensitive detector of human skin odorants in both Aedes aegypti and Anopheles gambiae. We demonstrate that activity of this neuron is important for attraction to skin odor, establishing it as a key target for intervention. We screen ~0.5 million compounds in silico and identify several CO2 receptor ligands, including an antagonist that reduces attraction to skin and an agonist that lures mosquitoes to traps as effectively as CO2. Analysis of the CO2 receptor ligand space provides a foundation for understanding mosquito host-seeking behavior and identifies odors that are potentially safe, pleasant, and affordable for use in a new generation of mosquito control strategies worldwide.