The current linear economy model relies on fossil energy and increases CO₂ emissions, which contributes to global warming and environmental pollution. Therefore, there is an urgent need to develop and deploy technologies for carbon capture and utilization to establish a circular economy. The use of acetogens for C1-gas (CO and CO₂) conversion is a promising technology due to high metabolic flexibility, product selectivity, and diversity of the products including chemicals and fuels. This review focuses on the physiological and metabolic mechanisms, genetic and metabolic engineering modifications, fermentation process optimization, and carbon atom economy in the process of C1-gas conversion by acetogens, with the aim to facilitate the industrial scale-up and carbon negative production through acetogen gas fermentation.
Fermentation ; Gases/metabolism* ; Carbon Dioxide/metabolism* ; Metabolic Engineering ; Carbon/metabolism*

The use of light energy to drive carbon dioxide (CO₂) reduction for production of chemicals is of great significance for relieving environmental pressure and solving energy crisis. Photocapture, photoelectricity conversion and CO₂ fixation are the key factors affecting the efficiency of photosynthesis, and thus also affect the efficiency of CO₂ utilization. To solve the above problems, this review systematically summarizes the construction, optimization and application of light-driven hybrid system from the perspective of combining biochemistry and metabolic engineering. We introduce the latest research progress of light-driven CO₂ reduction for biosynthesis of chemicals from three aspects: enzyme hybrid system, biological hybrid system and application of these hybrid system. In the aspect of enzyme hybrid system, many strategies were adopted such as improving enzyme catalytic activity and enhancing enzyme stability. In the aspect of biological hybrid system, many methods were used including enhancing biological light harvesting capacity, optimizing reducing power supply and improving energy regeneration. In terms of the applications, hybrid systems have been used in the production of one-carbon compounds, biofuels and biofoods. Finally, the future development direction of artificial photosynthetic system is prospected from the aspects of nanomaterials (including organic and inorganic materials) and biocatalysts (including enzymes and microorganisms).
Carbon Dioxide/metabolism* ; Photosynthesis ; Metabolic Engineering

Human activities increase the concentration of atmospheric carbon dioxide (CO₂), which leads to global climate warming. Microbial CO₂ fixation is a promising green approach for carbon neutral. In contrast to autotrophic microorganisms, heterotrophic microorganisms are characterized by fast growth and ease of genetic modification, but the efficiency of CO₂ fixation is still limited. In the past decade, synthetic biology-based enhancement of heterotrophic CO₂ fixation has drawn wide attention, including the optimization of energy supply, modification of carboxylation pathway, and heterotrophic microorganisms-based indirect CO₂ fixation. This review focuses on the research progress in CO₂ fixation by heterotrophic microorganisms, which is expected to serve as a reference for peaking CO₂ emission and achieving carbon neutral by microbial CO₂ fixation.
Carbon Cycle ; Carbon Dioxide/metabolism* ; Heterotrophic Processes ; Humans ; Synthetic Biology

Carboxysomes are extremely efficient microcompartments committed to CO2 fixation due to tailored CO2-concentrating mechanism (CCM). In cyanobacteria and some chemoautotrophs, carboxysomes as organelle-like microbodies encapsulate ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) and carbonic anhydrase (CA). Together with active inorganic carbon uptake transporters, carboxysomes accumulate HCO3(-) in the cytoplasm, leading to high efficiency of carbon fixation. Based on the elucidation of structures and functionalities, heterologous production of carboxysomes has been achieved so far. In fact, the genes encoding either vacant carboxysome shell or only interior components have been characterized. This review summarizes the discovery along with types, showcases molecular structures and roles of carboxysomes in CCM, and presents their broad applications in metabolic engineering.
Biological Transport ; Carbon ; metabolism ; Carbon Cycle ; Carbon Dioxide ; metabolism ; Cyanobacteria ; metabolism ; Metabolic Engineering

OBJECTIVETo compare the photosynthetic characteristics difference of different ploidy Rhodiola sachalinensis germplasm and provide the scientific basis for their cultivation.

METHODLI-6400/XT photosynthesis system was used to measure leaf light response curve and CO2 response curve of diploid and autotetraploid. Biomass, leaf area, stomatal characteristics and chlorophyll content differences were compared in the study.

RESULTStomata of the two germplasms were open during daytime obviously, and stomata conductance responded to the changes of light intensity and CO2 concentration which was not consistent with the characteristics of CAM (crassulacean acid metabolism) plants. Light compensation point of autotetraploid was significantly lower than that of the diploid, and light saturation points of both germplam were close, and their light saturation points were near 500 micromol x m(-2) x s(-1). Quantum efficiency of autotetraploid was significantly higher than the diploid, and the net photosynthetic rate of autotetraploid significantly higher than the diploid when light intensity was higher than 500 micromol x m(-2) x s(-1). Stomata conductance, transpiration rate of autotetraploid was also significantly higher than that of diploid. Biomass, leaf area, stomata diameter and chlorophyll content of autotetraploid were much higher than that of diploid, while the stomata density of autotetraploid was less than diploid.

CONCLUSIONThe results above provide scientific basis for the cultivation of different ploidy Rh. sachalinensi germplasm.

OBJECTIVETo study the diurnal variation of net photosynthetic rate (P(n)) and main influencing factors in different types of Pueraria thomsonii, aimed at providing the theoretical basis for breeding the fine varieties of P. thomsonii suitable for the local light condition.

METHODDiurnal variations of photosynthesis in leaves of different types of P. thomsonii were determined with the Li-6400 Portable Photosynthesis System.

RESULT(1) Diurnal variation of P(n), transpiration Rate (T(r)), stomatal conductance (G(s)) in leaves of six varieties of P. thomsonii showed unimodal curve and asymmetric bimodal curve. Diurnal variation of water use efficiency (WUE), intercellular CO2 concentration (C(i)) showed single valley curve. Diurnal variation curve of stomatal limitation value (L(s)) was single peak and S-type. (2) P(n) in leaves of six varieties of P. thomsonii was positively correlated with photosynthetic active radiation (PAR), air temperature (T(a)), G(s), and negatively correlated with air relative humidity (RH), C(i), P(n) of all varieties were very significantly correlated with PAR, G(s).

CONCLUSIONDiurnal variations of photosynthesis in leaves of different types of P. thomsonii show significant difference. Jiuding, Chuanyu, Gange, Dijin No. 1 planted in Ya'an overcome "midday depression" phenomenon. Hechuan has the greatest photosynthetic potential, suitable for planting in forest understory and intercropping with high stalk to avoid the strong flashes. Planted in long-day region was beneficial to its growth. CO2 use efficiency of Geboshi No. 11 and Dijin No. 1 were significantly higher than that of the others. The accumulation efficiency of organics can be increased in cultivation management by fertilizing CO2.

Cyanobacteria are important photosynthetic autotrophic microorganisms and are considered as one of the most promising microbial chassises for photosynthetic cell factories. Glycogen is the most important natural carbon sink of cyanobacteria, playing important roles in regulating its intracellular carbon distributions. In order to optimize the performances of cyanobacterial photosynthetic cell factories and drive more photosynthetic carbon flow toward the synthesis of desired metabolites, many strategies and approaches have been developed to manipulate the glycogen metabolism in cyanobacteria. However, the disturbances on glycogen metabolism usually cause complex effects on the physiology and metabolism of cyanobacterial cells. Moreover, the effects on synthesis efficiencies of different photosynthetic cell factories usually differ. In this manuscript, we summarized the recent progress on engineering cyanobacterial glycogen metabolism, analyzed and compared the physiological and metabolism effects caused by engineering glycogen metabolism in different cyanobacteria species, and prospected the future trends of this strategy on optimizing cyanobacterial photosynthetic cell factories.
Carbon/metabolism* ; Carbon Dioxide/metabolism* ; Cyanobacteria/metabolism* ; Glycogen/metabolism* ; Metabolic Engineering ; Photosynthesis/physiology*

Development of "liquid sunshine" could be a key technology to deal with the issue of fossil fuel depletion. β-caryophyllene is a terpene compound with high energy density and has attracted attention for its potential application as a jet fuel. The high temperature and high light-tolerant photosynthetic cyanobacterium Synechococcus elongatus UTEX 2973 (hereafter Synechococcus 2973), whose doubling time is as short as 1.5 h, has great potential for synthesizing β-caryophyllene using sunlight and CO₂. In this study, a production of ~121.22 μg/L β-caryophyllene was achieved at 96 h via a combined strategy of pathway construction, key enzyme optimization and precursor supply enhancement. In addition, a final production of ~212.37 μg/L at 96 h was realized in a high-density cultivation. To our knowledge, this is the highest production reported for β-caryophyllene using cyanobacterial chassis and our study provide important basis for high-density fuel synthesis in cyanobacteria.
Biofuels/microbiology* ; Carbon Dioxide/metabolism* ; Light ; Photosynthesis ; Synechococcus/radiation effects*

Carbonic anhydrase, an enzyme catalysing the reversible hydration of carbon dioxide, is present in the Muller cells.Because the enzyme is not present in other uroretinal cells in the retina, it can be used as a marker for Muller cells.Carbonic anhydrase activity was demonstrated bnzymehistochemically in human and rabbit Muller cells to know a relation of metabolic functions and carbonic anhydrase activity.Human retinas were obtained from donor eyes.The eyes were enucleated immediately after death forenzymatic activity. In human retina, heavy staining was found in the inner nuclear layer and nerve fiber layer, moderate staining in the outer nuclear layer and weak or no staining in the plexiform layers.In rabbit retina, heavy staining was found in the nerve fiber layer and nuclear layers and weak reaction in the two plexiform layers. These findings suggest that Muller cells may participate in CO2 homeostasis mechanism of carbonic anhydrase in the retina.
Carbon Dioxide ; Carbon* ; Carbonic Anhydrases ; Ependymoglial Cells ; Homeostasis ; Humans ; Metabolism ; Nerve Fibers ; Retina ; Tissue Donors

In this work, datasets of water and carbon fluxes measured with eddy covariance technique above a summer maize field in the North China Plain were simulated with artificial neural networks (ANNs) to explore the fluxes responses to local environmental variables. The results showed that photosynthetically active radiation (PAR), vapor pressure deficit (VPD), air temperature (T) and leaf area index (LAI) were primary factors regulating both water vapor and carbon dioxide fluxes. Three-layer back-propagation neural networks (BP) could be applied to model fluxes exchange between cropland surface and atmosphere without using detailed physiological information or specific parameters of the plant.
Agriculture ; Carbon ; metabolism ; Carbon Dioxide ; metabolism ; China ; Models, Biological ; Neural Networks (Computer) ; Seasons ; Volatilization ; Water ; metabolism ; Zea mays ; metabolism