Photosynthetic CO2 Fixation Research Articles

From biogas to biomethane: Evaluating the role of microalgae in sustainable energy production – A review

Methane, predominantly derived from fossil resources, is a highly utilised energy source due to its high energy density. However, the rapid consumption of fossil fuels has precipitated anthropogenic climate change and resource depletion, compelling the necessity for a transition towards sustainable and climate-compatible energy sources. This review examines biogas upgrading technologies, encompassing physical, chemical, and biological methods, with a particular focus on photosynthetic CO2 fixation to enhance methane purity and meet biomethane purity standards. Biological processes, in particular those utilising microalgae, demonstrate considerable potential for CO2 sequestration and have the capacity to reduce emissions while simultaneously generating valuable byproducts. The review investigates key process parameters, including pH, liquid-to-gas (L/G) ratio, temperature, and gas retention time (GRT), along with the removal efficiency of CO2. The mass transfer of CO2 and the role of microorganisms are also examined. Furthermore, biological, and chemical/physical upgrading technologies are economically and ecologically compared.

Dramatic changes in mitochondrial subcellular location and morphology accompany activation of the CO2 concentrating mechanism

Dynamic changes in intracellular ultrastructure can be critical for the ability of organisms to acclimate to environmental conditions. Microalgae, which are responsible for ~50% of global photosynthesis, compartmentalize their Ribulose 1,5 Bisphosphate Carboxylase/Oxygenase (Rubisco) into a specialized structure known as the pyrenoid when the cells experience limiting CO2 conditions; this compartmentalization is a component of the CO2 Concentrating Mechanism (CCM), which facilitates photosynthetic CO2 fixation as environmental levels of inorganic carbon (Ci) decline. Changes in the spatial distribution of mitochondria in green algae have also been observed under CO2 limitation, although a role for this reorganization in CCM function remains unclear. We used the green microalga Chlamydomonas reinhardtii to monitor changes in mitochondrial position and ultrastructure as cells transition between high CO2 and Low/Very Low CO2 (LC/VLC). Upon transferring cells to VLC, the mitochondria move from a central to a peripheral cell location and orient in parallel tubular arrays that extend along the cell's apico-basal axis. We show that these ultrastructural changes correlate with CCM induction and are regulated by the CCM master regulator CIA5. The apico-basal orientation of the mitochondrial membranes, but not the movement of the mitochondrion to the cell periphery, is dependent on microtubules and the MIRO1 protein, with the latter involved in membrane-microtubule interactions. Furthermore, blocking mitochondrial respiration in VLC-acclimated cells reduces the affinity of the cells for Ci. Overall, our results suggest that mitochondrial repositioning functions in integrating cellular architecture and energetics with CCM activities and invite further exploration of how intracellular architecture can impact fitness under dynamic environmental conditions.

Interplay between photosynthetic electron flux and organic carbon sinks in sucrose-excreting Synechocystis sp. PCC 6803 revealed by omics approaches

BackgroundAdvancing the engineering of photosynthesis-based prokaryotic cell factories is important for sustainable chemical production and requires a deep understanding of the interplay between bioenergetic and metabolic pathways. Rearrangements in photosynthetic electron flow to increase the efficient use of the light energy for carbon fixation must be balanced with a strong carbon sink to avoid photoinhibition. In the cyanobacterium Synechocystis sp. PCC 6803, the flavodiiron protein Flv3 functions as an alternative electron acceptor of photosystem I and represents an interesting engineering target for reorganizing electron flow in attempts to enhance photosynthetic CO2 fixation and increase production yield.ResultsWe have shown that inactivation of Flv3 in engineered sucrose-excreting Synechocystis (S02:Δflv3) induces a transition from photoautotrophic sucrose production to mixotrophic growth sustained by sucrose re-uptake and the formation of intracellular carbon sinks such as glycogen and polyhydroxybutyrate. The growth of S02:Δflv3 exceeds that of the sucrose-producing strain (S02) and demonstrates unforeseen proteomic and metabolomic changes over the course of the nine-day cultivation. In the absence of Flv3, a down-regulation of proteins related to photosynthetic light reactions and CO2 assimilation occurred concomitantly with up-regulation of those related to glycolytic pathways, before any differences in sucrose production between S02 and S02:Δflv3 strains were observed. Over time, increased sucrose degradation in S02:Δflv3 led to the upregulation of respiratory pathway components, such as the plastoquinone reductase complexes NDH-11 and NDH-2 and the terminal respiratory oxidases Cyd and Cox, which transfer electrons to O2. While glycolytic metabolism is significantly up-regulated in S02:Δflv3 to provide energy for the cell, the accumulation of intracellular storage compounds and the increase in respiration serve as indirect sinks for photosynthetic electrons.ConclusionsOur results show that the presence of strong carbon sink in the engineered sucrose-producing Synechocystis S02 strain, operating under high light, high CO2 and salt stress, cannot compensate for the lack of Flv3 by directly balancing the light transducing source and carbon fixing sink reactions. Instead, the cells immediately sense the imbalance, leading to extensive reprogramming of cellular bioenergetic, metabolic and ion transport pathways that favor mixotrophic growth rather than enhancing photoautotrophic sucrose production.

Alkaline hydrogenotrophic methanogenesis in Methanococcus vannielii at low carbon dioxide concentrations

Capture of carbon dioxide from the atmosphere is challenging and thermodynamically expensive because of its dilute concentration (421 ppm, December 2023). Utilizing the concentrating effect of dissolving atmospheric CO2 in alkaline solution to form dissolved inorganic carbon (DIC), we explored the potential of an alkalotolerant hydrogenotrophic methanogen, Methanococcus vannielii, to capture and convert CO2 at low partial pressures to methane. Kinetic constants for CO2 reduction to CH4 were determined from experiments in serum bottles at low pCO2 at 30˚C. At pH 7, 8, and 9, the apparent KM is 0.4, 1.2, and 1.2 mM DIC and the apparent vmax is 5.6, 7.8, and 2.9 mmol CH4 L−1 OD−1 hr−1, respectively. Using atmosphere-equilibrated DIC concentrations at pH 7, 8, and 9, methane formation rates were 1.1, 2.3, and 2.1 mmol CH4 L−1 OD−1 hr−1, respectively. Our data show that alkaline hydrogenotrophic methanogenesis is an alternative to photosynthetic CO2 fixation for biological capture and conversion of CO2 at atmospheric concentrations at reasonable rates.

Molecular mechanism of dissolvable metal nanoparticles-enhanced CO2 fixation by algae: Metal-chlorophyll synthesis

Algae-driven photosynthetic CO2 fixation is a promising strategy to mitigate global climate changes and energy crises. Yet, the presence of metal nanoparticles (NPs), particularly dissolvable NPs, in aquatic ecosystems introduces new complexities due to their tendency to release metal ions that may perturb metabolic processes related to algal CO2 fixation. This study selected six representative metal NPs (Fe3O4, ZnO, CuO, NiO, MgO, and Ag) to investigate their impacts on CO2 fixation by algae (Chlorella vulgaris). We discovered an intriguing phenomenon that bivalent metal ions released from the metal NPs, especially from ZnO NPs, substituted Mg2+ within the porphyrin ring. This interaction led to 81.8% and 76.1% increases in Zinc-chlorophyll and Magnesium-chlorophyll contents within algal cells at 0.01 mM ZnO NPs, respectively. Integrating metabolomics and transcriptomics analyses revealed that ZnO NPs mainly promoted the photosynthesis-antenna protein pathway, porphyrin and chlorophyll metabolism, and carbon fixation pathway, thereby mitigating the adverse effects of Zn2+ substitution in light harvesting and energy transfer for CO2 fixation. Ultimately, the genes encoding Rubisco large subunit (rbcL) responsible for CO2 fixation were upregulated to 2.60-fold, resulting in a 76.3% increase in carbon fixation capacity. Similar upregulations of rbcL expression (1.13-fold) and carbon fixation capacity (76.1%) were observed in algal cells even at 0.001 mM ZnO NPs, accompanied by valuable lipid accumulation. This study offers novel insights into the molecular mechanism underlying NPs on CO2 fixation by algae and potentially introduces strategies for global carbon sequestration.

Physiological responses of low- and high-cadmium accumulating Robinia pseudoacacia-rhizobium symbioses to cadmium stress

The role of rhizobia in alleviating cadmium (Cd) stress in woody legumes is still unclear. Therefore, two types of black locust (Robinia pseudoacacia L.) with high and low Cd accumulation abilities were selected from 11 genotypes in China, and the effects of rhizobium (Mesorhizobium huakuii GP1T11) inoculation on the growth, CO2 and H2O gas exchange parameters, Cd accumulation, and the absorption of mineral elements of the high (SX) and low Cd-accumulator (HB) were compared. The results showed that rhizobium-inoculation significantly increased biomass, shoot Cd contents, Cd accumulation, root-to-shoot translocation factor (TF) and the absorption and accumulation of mineral elements in both SX and HB. Rhizobium-inoculation increased chlorophyll a and carotenoid contents, and the intercellular carbon dioxide concentrations in HB plants. Under Cd exposure, the high-accumulator SX exhibited a significant decrease in photosynthetic CO2 fixation (Pn) and an enhanced accumulation of Cd in leaves, but coped with Cd exposure by increasing chlorophyll synthesis, regulating stomatal aperture (Gs), controlling transpiration (Tr), and increasing the absorption and accumulation of mineral elements. In contrast, the low-accumulator HB was more sensitive to Cd exposure despite preferential accumulation of Cd in roots, with decreased chlorophyll and carotenoid contents, but significantly increased root biomass. Compared to the low-accumulator HB, non-inoculated Cd-exposed SX plants had higher chlorophyll contents, and rhizobium-inoculated Cd-exposed SX plants had higher Pn, Tr, and Gs as well as higher levels of P, K, Fe, Ca, Zn, and Cu. In conclusion, the high- and low-Cd-accumulator exhibited different physiological responses to Cd exposure. Overall, rhizobium-inoculation of black locust promoted the growth and heavy metal absorption, providing an effective strategy for the phytoremediation of heavy metal-contaminated soils by this woody legume.

Integrative Physiological, Transcriptome, and Proteome Analyses Provide Insights into the Photosynthetic Changes in Maize in a Maize-Peanut Intercropping System.

Intercropping is a traditional and sustainable planting method that can make rational use of natural resources such as light, temperature, fertilizer, water, and CO2. Due to its efficient resource utilization, intercropping, in particular, maize and legume intercropping, is widespread around the world. However, the molecular details of these pathways remain largely unknown. In this study, physiological, transcriptome, and proteome analyses were compared between maize monocropping and maize-peanut intercropping. The results show that an intercropping system enhanced the ability of carbon fixation and carboxylation of maize leaves. Apparent quantum yield (AQY), the light-saturated net photosynthetic rate (LSPn), the light saturation point (LSP), and the light compensation point (LCP) were increased by 11.6%, 9.4%, 8.9%, and 32.1% in the intercropping system, respectively; carboxylation efficiency (CE), the CO2 saturation point (Cisat), the Rubisco maximum carboxylation rate (Vcmax), the maximum electron transfer rate (Jmax), and the triose phosphate utilization rate (TPU) were increased by 28.5%, 7.3%, 18.7%, 29.2%, and 17.0%, respectively; meanwhile, the CO2 compensation point (Γ) decreased by 22.6%. Moreover, the transcriptome analysis confirmed the presence of 588 differentially expressed genes (DEGs), and the numbers of up-regulated and down-regulated genes were 383 and 205, respectively. The DEGs were primarily concerned with ribosomes, plant hormone signal transduction, and photosynthesis. Furthermore, 549 differentially expressed proteins (DEPs) were identified in the maize leaves in both the maize monocropping and maize-peanut intercropping systems. Bioinformatics analysis revealed that 186 DEPs were related to 37 specific KEGG pathways in each of the two treatment groups. Based on the physiological, transcriptome, and proteome analyses, it was demonstrated that the photosynthetic characteristics in maize leaves can be improved by maize-peanut intercropping. This may be related to PS I, PS II, cytochrome b6f complex, ATP synthase, and photosynthetic CO2 fixation, which is caused by the improved CO2 carboxylation efficiency. Our results provide a more in-depth understanding of the high yield and high-efficiency mechanism in maize and peanut intercropping.

Machine Learning-Supported Enzyme Engineering toward Improved CO2-Fixation of Glycolyl-CoA Carboxylase.

Glycolyl-CoA carboxylase (GCC) is a new-to-nature enzyme that catalyzes the key reaction in the tartronyl-CoA (TaCo) pathway, a synthetic photorespiration bypass that was recently designed to improve photosynthetic CO2 fixation. GCC was created from propionyl-CoA carboxylase (PCC) through five mutations. However, despite reaching activities of naturally evolved biotin-dependent carboxylases, the quintuple substitution variant GCC M5 still lags behind 4-fold in catalytic efficiency compared to its template PCC and suffers from futile ATP hydrolysis during CO2 fixation. To further improve upon GCC M5, we developed a machine learning-supported workflow that reduces screening efforts for identifying improved enzymes. Using this workflow, we present two novel GCC variants with 2-fold increased carboxylation rate and 60% reduced energy demand, respectively, which are able to address kinetic and thermodynamic limitations of the TaCo pathway. Our work highlights the potential of combining machine learning and directed evolution strategies to reduce screening efforts in enzyme engineering.

Die Strukturaufklärung des ersten sex‐induzierenden Pheromons einer Kieselalge

AbstractKieselalgen sind weit verbreitete einzellige Mikroalgen, die für ≈20 % der globalen photosynthetischen CO2 Fixierung verantwortlich sind. Unser Wissen über die fundamentalen Aspekte ihrer Biologie, zu denen auch die sexuelle Fortpflanzung gehört, ist jedoch begrenzt. Für eine erfolgreiche Paarung der Einzeller ist die chemische, Pheromonvermittelte Kommunikation von höchster Wichtigkeit. Mit Hilfe von Pheromonen kann die sexuelle Aktivität synchronisiert und der Prozess der Partnerfindung mediiert werden. In der Diatomee Seminavis robusta wurde bereits der Lockstoff, der die Suchbewegung zum Partner vermittelt, identifiziert. Die Strukturen weiterer Metaboliten, welche die Zellen sexuell synchronisieren blieben allerdings unbekannt. Diese sex‐induzierenden Pheromone (SIP) lösen eine Zellzyklusarretierung aus und induzieren zusätzlich die Freisetzung des richtungsweisenden Lockstoffs. Im Folgenden beschreiben wir die anspruchsvolle Strukturaufklärung eines SIPs von S. robusta. Dafür wurde ein potentieller aktiver Metabolit in einer Metabolomstudie identifiziert und durch Isotopenmarkierungsexperimente, NMR, Elektrospray MSn Analysen und chemische Umsetzungen aufgeklärt. Die Verwendung der Massenspektrometrie im negativen Ionenmodus war von essentieller Bedeutung bei der Entschlüsselung des zyklischen Heptapeptids, welches Hydroxyprolin‐ und ein neuartiges β‐sulfatiertes Aspartat enthält. Das SIP ist bereits in femtomolaren Konzentrationen wirksam.

Structure Elucidation of the First Sex-Inducing Pheromone of a Diatom.

Diatoms are abundant unicellular microalgae, responsible for ≈20 % of global photosynthetic CO2 fixation. Nevertheless, we know little about fundamental aspects of their biology, such as their sexual reproduction. Pheromone-mediated chemical communication is crucial for successful mating. An attraction pheromone was identified in the diatom Seminavis robusta, but metabolites priming cells for sex and synchronizing search and mating behavior remained elusive. These sex-inducing pheromones (SIP) induce cell cycle arrest and trigger the production of the attraction pheromone. Here we describe the challenging structure elucidation of an S. robusta SIP. Guided by metabolomics, a candidate metabolite was identified and elucidated by labeling experiments, NMR, ESI MSn analyses, and chemical transformations. The use of negative ion mode MS was essential to decipher the unprecedented hydroxyproline and β-sulfated aspartate-containing cyclic heptapeptide that acts in femtomolar concentrations.

Review of Marine Cyanobacteria and the Aspects Related to Their Roles: Chemical, Biological Properties, Nitrogen Fixation and Climate Change.

Marine cyanobacteria are an ancient group of photosynthetic microbes dating back to 3.5 million years ago. They are prolific producers of bioactive secondary metabolites. Over millions of years, natural selection has optimized their metabolites to possess activities impacting various biological targets. This paper discusses the historical and existential records of cyanobacteria, and their role in understanding the evolution of marine cyanobacteria through the ages. Recent advancements have focused on isolating and screening bioactive compounds and their respective medicinal properties, and we also discuss chemical property space and clinical trials, where compounds with potential pharmacological effects, such as cytotoxicity, anticancer, and antiparasitic properties, are highlighted. The data have shown that about 43% of the compounds investigated have cytotoxic effects, and around 8% have anti-trypanosome activity. We discussed the role of different marine cyanobacteria groups in fixing nitrogen percentages on Earth and their outcomes in fish productivity by entering food webs and enhancing productivity in different agricultural and ecological fields. The role of marine cyanobacteria in the carbon cycle and their outcomes in improving the efficiency of photosynthetic CO2 fixation in the chloroplasts of crop plants, thus enhancing the crop plant's yield, was highlighted. Ultimately, climate changes have a significant impact on marine cyanobacteria where the temperature rises, and CO2 improves the cyanobacterial nitrogen fixation.

Seasonal changes in gas exchange, water and macro-nutrient content differ between Citrus cultivars

Citrus is an evergreen broad-leaved fruit tree including numerous species and cultivars with an extensive global planting area. However, the relationship between physiological parameters and seasonal fruit ripening of different citrus cultivars has not been reported. With the aim to obtain information on this relationship, we selected two late-maturing (Newhall Navel and Ponkan) and two middle-maturing citrus cultivars (Fertile orange and Tarocco) and compared the seasonal patterns of foliar CO2 and H2O gas exchange, leaf water content and macro-nutrient concentrations in leaves and roots. Our results showed that seasonal changes of foliar CO2 and H2O gas exchange and water content greatly differed between cultivars at defined developmental stages, but especially during fruit ripening. For example, in December, the net rates of photosynthetic CO2 fixation (Pn) of the late-maturing cultivars were significantly higher than in middle-maturing cultivars. Seasonal fluctuations of total nitrogen (N), total phosphorus (P), and inorganic phosphorus (Pi), as well as C/N, C/P, and N/P ratios in leaves and roots differed between middle and late-maturing cultivars. These differences were most obvious at fruit ripening compared to other developmental stages and were significantly higher in leaves than in roots. We conclude that seasonal differences in foliar Pn and macro-nutrient contents between leaves of citrus cultivars are largely determined by seasonal fruit ripening. In addition, seasonal changes in root macro-nutrient contents were also affected by seasonal fruit ripening of citrus cultivars. However, this effect was much lower compared to the leaves, but still indicates particular shoot-root interactions during fruit ripening.

Photosynthetic Fixation of CO2 in Alkenes by Heterogeneous Photoredox Catalysis with Visible Light.

Light-driven fixation of CO2 in organics has emerged as an appealing alternative for the synthesis of value-added fine chemicals. Challenges remain in the transformation of CO2 as well as product selectivity due to its thermodynamic stability and kinetic inertness. Here we develop a boron carbonitride (BCN) with the abundant terminal B/N defects around the mesoporous walls, which essentially enhances surface active sites as well as charge transfer kinetics, boosting the overall rate of CO2 adsorption and activation. In this protocol, anti-Markovnikov hydrocarboxylation of alkenes with CO2 to an extended carbon chain is achieved with good functional group tolerance and specific regioselectivity under visible-light irradiation. The mechanistic studies demonstrate the formation of CO2 radical anion intermediate on defective boron carbonitride, leading to the anti-Markovnikov carboxylation. Gram-scale reaction, late-stage carboxylation of natural products and synthesis of anti-diabetic GPR40 agonists reveal the utility of this method. This study sheds new insight on the design and application of metal-free semiconductors for the conversion of CO2 in an atom-economic and sustainable manner.

Structural basis of metabolite transport by the chloroplast outer envelope channel OEP21

Triose phosphates (TPs) are the primary products of photosynthetic CO2 fixation in chloroplasts, which need to be exported into the cytosol across the chloroplast inner envelope (IE) and outer envelope (OE) membranes to sustain plant growth. While transport across the IE is well understood, the mode of action of the transporters in the OE remains unclear. Here we present the high-resolution nuclear magnetic resonance (NMR) structure of the outer envelope protein 21 (OEP21) from garden pea, the main exit pore for TPs in C3 plants. OEP21 is a cone-shaped β-barrel pore with a highly positively charged interior that enables binding and translocation of negatively charged metabolites in a competitive manner, up to a size of ~1 kDa. ATP stabilizes the channel and keeps it in an open state. Despite the broad substrate selectivity of OEP21, these results suggest that control of metabolite transport across the OE might be possible.

Enhancing photosynthetic CO2 fixation in microbial electrolysis cell (MEC)-based anaerobic digestion for the in-situ biogas upgrading

Biogas from anaerobic digestion usually contains 30%–50% of CO2, which needs to be upgraded before industrial utilization. However, current upgrading techniques typically consume large amounts of chemicals and energy. This study designed a green and low-energy-consumption microbial electrolysis cell (MEC)-based anaerobic digester for in-situ biogas upgrading, in which the cathode with photosynthetic bacteria (PSB) was used to fix CO2. Results showed that charged MEC-AD increased photosynthetic CO2 fixation by 83.3% and CH4 production by 62.8% compared with uncharged open-circuit MEC-AD. Adding an extracellular electron uptake inhibitor to the cathode decreased the CO2 fixation, accompanied by the decline of current between the two electrodes, which suggested that the cathode electron uptake was the main reason for the facilitated CO2 fixation of PSB. The electrically-stimulated PSB fixed CO2 more efficiently than unstimulated PSB even under power off, likely related to their enhanced electroactivity and photoactivity that could acquire more extracellular electrons and light energy for CO2 fixation. The carbonyl-related hydrogen bonds in the LH1 complex of photosynthetic reaction centers increased under electrical stimulation, resulting in a red shift of absorbance spectra to improve the energy utilization of PSB. This upgrading technique consumed about 0.37 kWh/Nm3 CO2removed of electric energy, much lower than other MEC-based techniques, providing a green and feasible strategy for in-situ biogas upgrading.

A novel simulation calculation model based on photosynthetic electron transfer for microalgal growth prediction in any photobioreactor

The microalgal research field is currently lacking a unified theoretical computing system to explain various experimental results related to microalgal growth. Thus a novel universal theoretical model was created to predict microalgal growth with carbon dioxide (CO2) fixation in any cultivation system. First, a new “light-effect colorimetric method” was proposed to estimate the actual f2 value of suspended microalgal cells during regular experimentation using a formula explaining the photosynthetic effective electron transfer rate (ETR = PFD·ΦII·f1·f2), which only requires the use of a simple spectrophotometer. A mathematical relationship between photosynthetic electron transfer and the microalgal growth rate was then identified based on this modified ETR by simplifying factors influencing the cultivation conditions (e.g., nutrients and CO2) into the slope and intercept of this formula. Subsequently, software was written to allow the above relationship to stimulate any 3-D microalgal cultivation system. Many example cases were conducted to clarify the significance and application of this theoretical model. It was found that the average ETR of a cultivation system describes microalgal tolerance to high CO2 concentrations. A photobioreactor at any given location under a certain light condition has a theoretical maximum yield of microalgal biomass, irrespective of how the other cultivation conditions change. A new concept of “biological similarity” is proposed as a basic principle for scaling up microalgal experiments with photosynthetic CO2 fixation to perform a repeated growth curve with < 5 % error. Finally, a “multi-batch dilution method” was demonstrated to increase the microalgal biomass yield by 64.4 % over a short cultivation period. General application of this calculation model would change the empirical status of microalgal engineering designs.

No effect of ocean acidification on growth, photosynthesis, or dissolved organic carbon release by three temperate seaweeds with different dissolved inorganic carbon uptake strategies

AbstractIn a future ocean, dissolved organic carbon (DOC) release by seaweed has been considered a pathway for organic carbon that is not incorporated into growth under carbon dioxide (CO2) enrichment/ocean acidification (OA). To understand the influence of OA on seaweed DOC release, a 21-day experiment compared the physiological responses of three seaweed species, two which operate CO2 concentrating mechanisms (CCMs), Ecklonia radiata (C. Agardh) J. Agardh and Lenormandia marginata (Hooker F. and Harvey) and one that only uses CO2 (non-CCM), Plocamium cirrhosum (Turner) M.J. Wynne. These two groups (CCM and non-CCM) are predicted to respond differently to OA dependent on their affinities for Ci (defined as CO2 + bicarbonate, HCO3−). Future ocean CO2 treatment did not drive changes to seaweed physiology—growth, Ci uptake, DOC production, photosynthesis, respiration, pigments, % tissue carbon, nitrogen, and C:N ratios—for any species, regardless of Ci uptake method. Our results further showed that Ci uptake method did not influence DOC release rates under OA. Our results show no benefit of elevated CO2 concentrations on the physiologies of the three species under OA and suggest that in a future ocean, photosynthetic CO2 fixation rates of these seaweeds will not increase with Ci concentration.

Transcriptome and metabolome profiling provide insights into hormone-mediated enhanced growth in autotetraploid seedlings of banana (Musa spp.)

IntroductionReconstructive breeding based on autotetraploids to generate triploid varieties is a promising breeding strategy in banana (Musa spp.). Therefore understanding the molecular mechanisms underlying the phenotypic differences between the original diploid and its autopolyploid derivatives is of significant importance in such breeding programs of banana.MethodsIn this study, a number of non-chimeric autotetraploid plants, confirmed by flow cytometry and chromosome counting were obtained using colchicine treatment of ‘Pisang Berlin' (AA Group), a diploid banana cultivar highly resistant to Fusarium wilt Tropical Race 4 (Foc TR4) and widely cultivated in Asia.Results and discussionThe autotetraploids showed significant increase in plant height, pseudostem diameter, root length, leaf thickness, leaf area, and leaf chlorophyll content. Transcriptomic analysis indicated that differentially expressed genes were mainly enriched in plant hormone signal transduction, mitogen-activated protein kinase (MAPK) signaling pathway, and carbon fixation in photosynthetic organelles. The genes related to the metabolism, transport or signaling of auxin, abscisic acid (ABA), cytokinin (CTK) and gibberellin (GA), as well as the genes encoding essential enzymes in photosynthetic CO2 fixation were differentially expressed in leaves of autotetraploids and most of them were up-regulated. Metabolomic analysis revealed that the differentially accumulated metabolites were mainly involved in plant hormone signal transduction, porphyrin and chlorophyll metabolism, indole alkaloid biosynthesis, and carbon fixation in photosynthetic organelles. The results therefore, demonstrate that the hormones IAA, ABA, and photosynthetic regulation may play a vital role in the observed enhancement in the autotetraploids. These could be used as molecular and biochemical markers to facilitate the generation of triploid progenies as suitable new varieties for cultivation.

Advancements on process regulation for microalgae-based carbon neutrality and biodiesel production

Microalgae biotechnology is a promising pathway to cope with CO2 emission and energy crisis due to high CO2 fixation rate and lipids productivity. However, bottlenecks of high energy cost, low photosynthetic efficiency and poor economic feasibility severely hinder its commercialization. Understanding process mechanisms of microalgae photosynthetic CO2 fixation and lipids production, and thus seeking possible regulations to enhance weak links are potential process regulation strategy for augmented competitiveness. Firstly, mass transfer and conversion processes of microalgae photosynthesis involving CO2 and light were comprehensively illuminated in this review. In detail, mechanisms of CO2 and light transfer in microalgae suspension, bioavailable carbon and photon assimilation by microalgae cells, as well as intracellular mass conversion were illustrated. Besides, synergistic effects of light and CO2 on microalgae photosynthesis were depicted from perspective of electrons and protons supply-demand relationships between photosynthetic photo-reaction and dark-reaction steps in chlorophyll. Possible weak links in these processes were emphasized to provide guideline for regulation. Secondly, available regulation strategies for CO2 and light mass transfer, cellular assimilation and intracellular conversion were summarized. Subsequently, economic and environmental impacts of process regulation on microalgae CO2 fixation and biodiesel output were evaluated to lit up large-scale applicability. Finally, challenges and future directions of microalgae biotechnology were described to inspire in-depth research and engineering practice. This review may provide a novel process regulation standpoint for operating microalgae-based CO2 fixation and biodiesel production in the most efficient manner, further facilitating the applicability of microalgae biotechnology towards carbon neutrality and biodiesel production.

Phase Separation of Rubisco by the Folded SSUL Domains of CcmM in Beta-Carboxysome Biogenesis.

Carboxysomes are large, cytosolic bodies present in all cyanobacteria and many proteobacteria that function as the sites of photosynthetic CO2 fixation by the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). The carboxysome lumen is enriched with Rubisco and carbonic anhydrase (CA). The polyhedral proteinaceous shell allows the passage of HCO3- ions into the carboxysome, where they are converted to CO2 by CA. Thus, the carboxysome functions as a CO2-concentrating mechanism (CCM), enhancing the efficiency of Rubisco in CO2 fixation. In β-cyanobacteria, carboxysome biogenesis first involves the aggregation of Rubisco by CcmM, a scaffolding protein that exists in two isoforms. Both isoforms contain a minimum of three Rubisco small subunit-like (SSUL) domains, connected by flexible linkers. Multivalent interaction between these linked SSUL domains with Rubisco results in phase separation and condensate formation. Here, we use Rubisco and the short isoform of CcmM (M35) of the β-cyanobacterium Synechococcus elongatus PCC7942 to describe the methods used for in vitro analysis of the mechanism of condensate formation driven by the SSUL domains. The methods include turbidity assays, bright-field and fluorescence microscopy, as well as transmission electron microscopy (TEM) in both negative staining and cryo-conditions.