Photosynthetic Oxygen Research Articles

Mesoproterozoic biomineralization: Cyanobacterium-like filamentous siderite sheaths ∼1.4 Ga

Biomineralization was a key development in a wide variety of organisms, yet its history prior to the Ediacaran remains poorly understood. In this paper, we describe ∼1420–1330 million year old microscopic tubes preserved as siderite (FeCO3). In size and shape these tubes closely resemble cyanobacterial sheaths forming mineralized mats. We consider two competing explanations for their formation. First, the tubes and associated sediment were originally composed of Ca-carbonate that was subsequently replaced by siderite. In this case, siderite mineralization was early, but post-mortem, as in early silicification, and preferentially preserved the more resilient sheath. However, no relict calcite is observed. Second, the Fe-carbonate mineralogy of the tubes and sediment is synsedimentary. In this case, photosynthetic oxygen may have precipitated Fe-oxyhydroxide that was promptly converted to siderite by dissimilatory iron reduction (DIR). Primary siderite mineralization of cyanobacteria has not been described before. Both explanations link photosynthetic processes to preferential sheath mineralization during the life of the cyanobacteria, as observed in present-day calcified cyanobacteria. This process might include CO2-concentrating mechanisms (CCMs) linked to relatively low levels of atmospheric CO2, consistent with empirical estimates of mid-Proterozoic CO2 levels based on paleosols and weathering rinds. In either case, these cyanobacterium-like fossils preserved in siderite provide an early example of biomineralization and suggest the interactive influences of both metabolic processes and ambient seawater chemistry.

The decrease in diurnal oxygen production in Elodea under the influence of high geomagnetic variability: the role of light, temperature and atmospheric pressure

Epidemiological studies have indicated adverse effects of geomagnetic disturbance on human health, including increased mortality. There is evidence from plant and animal studies that help to elucidate this interaction. This study tests the hypothesis that geomagnetic disturbance affects living systems, by modifying the metabolic process of photosynthesis, in the natural environment.Continuous 24-h measurements of dissolved oxygen in flasks containing Holtfreiter’s solution and strands of healthy Elodea were recorded from May 1996, until September 1998, in an electromagnetically quiet, purpose built, garden shed environment, without mains electricity. Sensormeter recordings of oxygen, light, temperature and air pressure were uploaded weekly to a PC. The hourly total geomagnetic field measurements were obtained from the nearest observatory.Significant decrease in oxygen (diurnal volume of oxygen divided by plant mass and diurnal light), (O/WL), was found on days of high geomagnetic field variability throughout 11 recorded months of the year 1997. This result was independent of temperature and atmospheric pressure. No significant decrease in O/WL during high geomagnetic variability was found for the 7 months recorded in 1996. The 1996 and 1997 data both showed a significant decrease in the diurnal time lag between peak light and peak oxygen for diurnal high geomagnetic variability compared with low geomagnetic variability. Cross correlation analysis for 1997 and 1998 data showed a decrease in positive correlation of oxygen with light in high geomagnetic variability, compared with low geomagnetic variability, and increased positive correlation with the geomagnetic field instead. These experiments support a hypothesis of high geomagnetic field variability as a weak zeitgeber, and a metabolic depressant for photosynthetic oxygen production in plants.

Photorespiration plays an important role in H2 production by marine Chlorella pyrenoidosa

Marine Chlorella pyrenoidosa was previously reported to produce H2 under nitrogen-deprived condition. In this study, the role of photorespiration in H2 production by C. pyrenoidosa was investigated. It was found that the expression level of genes encoding three enzymes involved in photorespiration decreased, but the expression level of gene encoding glutamate synthase increased in nitrogen-deprived culture compared with control, indicating a complex adjustment of photorespiration activity during H2 production by C. pyrenoidosa. The use of a photorespiration inhibitor led not only to a decrease in H2 production by 15 % under nitrogen deprivation condition, but also to a 16 % decrease in O2 evolution in the complete medium. Moreover, it was demonstrated that the total photosynthetic oxygen evolution and Fv/Fm declined when photorespiration was blocked. This suggested that, the photorespiration pathway does not directly participate in the production of photosynthetic electrons and the transfer of hydrogen producing electrons. However, it played an important role in photoprotection of PSII during H2 production by C. pyrenoidosa, which enabled PSII to provide more photosynthetic electrons to hydrogenase.

Microfluidic encapsulation of photosynthetic cyanobacteria in hydrogel microparticles augments oxygen delivery to rescue ischemic myocardium

Cardiovascular disease, primarily caused by coronary artery disease, is the leading cause of death in the United States. While standard clinical interventions have improved patient outcomes, mortality rates associated with eventual heart failure still represent a clinical challenge. Macrorevascularization techniques inadequately address the microvascular perfusion deficits that persist beyond primary and secondary interventions. In this work, we investigate a photosynthetic oxygen delivery system that rescues the myocardium following acute ischemia. Using a simple microfluidic system, we encapsulated Synechococcus elongatus into alginate hydrogel microparticles (HMPs), which photosynthetically deliver oxygen to ischemic tissue in the absence of blood flow. We demonstrate that HMPs improve the viability of S.elongatus during the injection process and allow for simple oxygen diffusion. Adult male Wistar rats (n= 45) underwent sham surgery, acute ischemia reperfusion surgery, or a chronic ischemia reperfusion surgery, followed by injection of phosphate buffered saline (PBS), S.elongatus suspended in PBS, HMPs, or S.elongatus encapsulated in HMPs. Treatment with S.elongatus-HMPs mitigated cellular apoptosis and improved left ventricular function. Thus, delivery of S.elongatus encapsulated in HMPs improves clinical translation by utilizing a minimally invasive delivery platform that improves S.elongatus viability and enhances the therapeutic benefit of a novel photosynthetic system for the treatment of myocardial ischemia.

Novel ZIF-8@CHs catalysts for photocatalytic degradation of tetracycline hydrochloride

A novel ZIF-8@CHs photocatalyst, which was generated using the metal organic framework ZIF-8 and intact chloroplasts (CHs) from Chlorella sp. in a one-pot synthesis, was used in this study for the first time to degrade tetracycline hydrochloride (TCH) through photocatalysis. The results of systematic characterization demonstrated that ZIF-8@CHs was successfully p0repared. Meanwhile, ZIF-8@CHs exhibited excellent photocatalytic performance and good adaptability. Under the condition of simulated sunlight, the high porosity ZIF-8 shell enabled CHs to maintain typical photosynthetic oxygen evolution behavior in vitro, and using CHs as the core produced significant ROS, significantly improving the efficiency of TCH photocatalytic degradation. In addition, the radical trapping test and EPR spectra proved that O2–, 1O2, and •OH were the key active species for TCH degradation. Eventually, the ZIF-8@CHs system can not only expand the new concept of organic pollutant degradation in water bodies, but also offer recommendations for live organ envelope modification..

Effects of calcification on air-water CO2 fluxes in tropical seagrass meadows: A mesocosm experiment

Seagrass meadows deliver a range of ecosystem services, where one of the more important is the capacity to store carbon and serve as sinks for atmospheric carbon dioxide. The capacity of seagrass meadows for carbon storage might, however, be modified and complicated by several factors; one important factor is the possible effects of calcification within the meadows. In tropical areas, seagrass meadows can contain high proportions of calcareous organisms, which through their calcification may cause release of CO2. To study this aspect of the CO2 balance within tropical seagrass systems, we investigated the air-water CO2 flux in seagrass mesocosms with different plant community compositions, i.e. mixtures of seagrass and calcifying macroalgae, having similar overall photosynthetic oxygen evolution rates. The measured CO2 fluxes changed both in rate and direction over the day and were significantly related to plant community composition. Downward fluxes of CO2 were found only over vegetation with high proportion of seagrass and in the afternoon, whereas occurrence of calcifying algae appeared to reverse the flow. A partial least squares (PLS) regression model indicated that pH, pCO2 and dissolved inorganic carbon (DIC) were the primary environmental variables predicting the CO2 fluxes. Our findings show that algal calcification might partly counteract the carbon sequestration in seagrass meadows.

External-loop split-type dynamic membrane photobioreactor for the treatment of high-strength pyridine wastewater: Improved photosynthetic oxygenation and mitigated membrane fouling

In order to avoid pyridine volatilization in the conventional aerobic system based on bubble aeration, an algal-bacterial symbiotic system based on photosynthetic oxygenation was developed. Nonetheless, pyridine at high concentration would inhibit algal growth and photosynthetic activity, and thus decrease oxygen production efficiency. An external-loop split-type dynamic membrane photobioreactor system was proposed for treating high-strength pyridine wastewater, which consisted of a pyridine degrading reactor (R 1-1 ), and an algal-bacterial dynamic membrane bioreactor (R 1-2 ) for the photosynthetic oxygenation. The results showed that pyridine could be effectively removed at the influent concentration as high as 500 mg·L -1 at the hydraulic retention time of 48 h. Preferable algal growth and photosynthetic activity were retained in R 1-2 , with Fv/Fm maintained at 0.502±0.013 at the influent pyridine concentration of 500 mg·L -1 . The decreased reactive oxygen species and malondialdehyde level as well as the relative low catalase and superoxide dismutase activities also revealed the alleviation of oxidative stress in algae. The mitigated membrane fouling was due to reduced protein/polysaccharide ratio in the extracellular polymeric substances in the mixed liquor and fouling layer in R 1-2 . Rhodobacter and Rhodococcus were the dominant genus in R 1-1 and R 1-2 , and Chlorella was enriched in R 1-2 , responsible for pyridine degradation and oxygen production. • ESDMPBR was developed to alleviate the inhibitory effects of pyridine to algae. • Pyridine removal, nitrogen removal and oxygen production were enhanced in ESDMPBR. • Membrane fouling could be alleviated at high PS concentration and low PN/PS ratio. • Mechanism for enhanced pyridine removal involved in ESDMPBR was proposed. • Algal-bacterial symbiotic system was promising in treating high-strength pyridine.

Light-triggered photosynthetic engineered bacteria for enhanced-photodynamic therapy by relieving tumor hypoxic microenvironment.

Background: Singlet oxygen (1O2) has received considerable research attention in photodynamic therapy (PDT) due to its cytotoxic solid features. However, the inherent hypoxic state of the tumor microenvironment (TME) leads to the meager 1O2 quantum yield of inorganic PDT reagents, and their application in vivo remains elusive. Methods: We developed a novel strategy to fabricate active photosynthetic bacteria/photosensitizer/photothermal agent hybrids for photosynthetic tumor oxygenation and PDT and PTT tumor therapy under different laser irradiation sources. Photosynthetic bacteria combined with Ce6 photosensitizer and Au NPs photothermal agent, the obtained Bac@Au-Ce6 effectively targets tumor tissues and further enhances the tumor accumulation of Au-Ce6. Results: The results showed that the Au-Ce6-loaded engineered bacteria (Bac@Au-Ce6) maintained the photosynthetic properties of Syne. After i.v. injection, Bac@Au-Ce6 efficiently aggregates at tumor sites due to the tumor-targeting ability of active Syne. With 660 nm laser irradiation at the tumor site, the photoautotrophic Syne undergoes sustained photosynthetic O2 release and immediately activates O2 to 1O2 via a loaded photosensitizer. PTT was subsequently imparted by 808 laser irradiations to enhance tumor killing further. Conclusions: This work provides a new platform for engineering bacteria-mediated photosynthesis to promote PDT combined with PTT multi-faceted anti-tumor.

Catalytic metal-nucleotide coordinative cytoskeleton on algae cell towards photosynthetic hydrogen production under air.

A metal-nucleotide coordinative cytoskeleton with ascorbate oxidase-like catalytic behavior was constructed on an individual algae cell wall, which endows the engineered cells with the capability of self-generating a localized hypoxic microenvironment around the cell surface, and thus allows the functionality switching from photosynthetic oxygen production to efficient hydrogen evolution for over one month.

Living Chinese Herbal Scaffolds from Microfluidic Bioprinting for Wound Healing.

Biological scaffolds have been widely employed in wound healing applications, while their practical efficiency is compromised by insufficient oxygen delivery to the 3-dimensional constructs and inadequate nutrient supply for the long-term healing process. Here, we present an innovative living Chinese herbal scaffold to provide a sustainable oxygen and nutrient supply for promoting wound healing. Through a facile microfluidic bioprinting strategy, a traditional Chinese herbal medicine (Panax notoginseng saponins [PNS]) and a living autotrophic microorganism (microalgae Chlorella pyrenoidosa [MA]) were successfully encapsulated into the scaffolds. The encapsulated PNS could be gradually released from the scaffolds, which promoted cell adhesion, proliferation, migration, and tube formation invitro. In addition, benefiting from the photosynthetic oxygenation of the alive MA, the obtained scaffolds would produce sustainable oxygen under light illumination, exerting a protective effect against hypoxia-induced cell death. Based on these features, we have demonstrated through invivo experiments that these living Chinese herbal scaffolds could efficiently alleviate local hypoxia, enhance angiogenesis, and thereby accelerate wound closure in diabetic mice, indicating their great potential in wound healing and other tissue repair applications.

Transcriptomic Analysis of Ulva prolifera in Response to Salt Stress

Since 2007, Ulva prolifera, a green macroalgal species that blooms periodically in the Yellow Sea of China, has caused the world’s biggest green tide, which induced harmful ecological impacts and economic losses. When the alga is subject to prolonged exposure to air, it suffers abiotic stresses. To explore the physiological and molecular mechanisms of salt stress, the transcriptome data of U. prolifera at different salinities (30, 50, and 90 psu) were obtained by high-throughput sequencing using the Illumina HiSeq platform, and photosynthetic physiological parameters were also measured. The results showed that a total of 89,626 unigenes were obtained after de novo assembly, of which 60,441 unigenes were annotated in the databases (NR, NT, KO, SWISS-PROT, PFAM, GO, and KOG). GO functional enrichment analysis revealed that the enrichment of differentially expressed genes (DEGs) was mainly in cellular, cell, and binding processes. KEGG metabolic pathway enrichment analysis showed that the most frequently enriched pathways of DEGs included glycolysis, pyruvate metabolism, peroxisome, and fatty acid biosynthesis. In addition, resistance-associated proteins, such as heat-shock proteins, microtubule-associated proteins, ubiquitin-associated proteins, abscisic-acid-signaling-pathway-associated proteins, and antioxidant-related proteins are upregulated under salt stress. Genes associated with photosynthesis and carbon fixation pathways are also upregulated, accompanied by an increase in photosynthetic oxygen release rates. These findings provide a basis for understanding the molecular mechanisms of the response of U. prolifera to salinity change, thus providing a theoretical basis for the analysis of the green tide outbreak mechanism.

Performance of a novel rotating membrane photobioreactor based on indigenous microalgae-bacteria consortia for wastewater reclamation

Performance of a novel a rotating membrane photobioreactor (R-MPBR) for wastewater reclamation under photosynthetic oxygenation was investigated. The unit was operated in dead-end mode with an alternative physical cleaning strategy based in membrane module rotation. It was found that the carbon loading rate applied (CLR) (9.1–36.6 g DOC·m−3·d-1) determined the dissolved oxygen concentration, affecting nutrient removal, bioflocculation and membrane fouling. Indigenous microalgae-bacteria consortia were effectively developed under each condition. At high CLR values, the dissolved inorganic nitrogen removal was significantly enhanced (81.2 ± 13.9 %), probably due to a simultaneous nitrification–denitrification process as a result of the negligible dissolved oxygen concentration. Decreasing CLR from 36.6 to 9.1 g DOC·m−3·d-1, increased particle size (D(0.5) from 61.9 to 92.8 μm) and decreased biopolymer clusters content (from 50.0 to 2.3 mg DOC·L-1). It also revealed that membrane rotation does not compromise bioflocculation. Cake filtration model showed that fouling was associated to the supernatant fraction, particularly to the biopolymer clusters. Sustainable long-term operation was achieved at a permeate flux of 10 L·h−1·m−2 and CLR ≤ 11.4 g DOC·m−3·d-1. The proposed configuration effectively controlled membrane fouling, allowing to further process optimization.

Productivity and nutrient removal by the microalga Chlamydopodium fusiforme grown outdoors in BG-11 and piggery wastewater

The objective of this work was to test the growth of the freshwater microalgaChlamydopodium fusiformeMACC-430 in diluted piggery wastewater (PWW) for biomass production which is a potential producer of biostimulating and antimicrobial compounds. The productivity and effectiveness in removing nitrogen and phosphorus by the cultures were tested outdoors in open ponds by comparing the mineral medium BG-11 medium (control) and piggery wastewater (PWW). Daily biomass yields were found 14.7 ± 4.6g m-2d-1in BG-11 and 17.6 ± 6.7g m-2d-1in 10-fold diluted wastewater (PWW10) with deionized water. Further increase in the biomass productivity yield (33.1 ± 5.6g m-2d-1) was achieved with more concentrated PWW (5-fold dilution – PWW5). Nitrogen removal rate (N-NH4+) reached 21.4 ± 2.9mg L-1d-1in cultures grown in PWW10 and increased to 38.4±16.3mg L-1d-1using the PWW5. The use of undiluted PWW strongly increased the bacterial load, which caused the loss of the culture. The photosynthetic performance measured as the maximum fluorescence yield Fv/Fmratio in both the PWW10 and BG-11 cultures showed a cyclic behavior, as it decreased during the day and recovered at night. However, in the cultures grown in diluted PWW the Fv/Fmratio slightly increased throughout the cultivation. Between PWW10 and BG-11, no significant differences were observed in photosynthetic oxygen evolution; on the contrary, PWW5 showed a 30% reduction compared to PWW10 and BG-11. Significantly lower chlorophyll and carotenoid contents were found in the cultures grown in PWW compared to BG-11. Biochemical composition showed a slightly higher protein content in biomass grown in PWW10 (53.4%) compared to BG-11 (52.7%). The protein content further increased (61.3%) when the more concentrated PWW5 was used. The biomass, particularly that produced on PWW, revealed antimicrobial activity against plant pathogens, including fungi, and oomycete, while rather weak biostimulant activity was determined for theC. fusiformebiomass independently of the cultivation medium. Results demonstrated thatC. fusiformeis a robust strain suitable to be grown in diluted PWW outdoors with a high nutrient removal rate.

Tuning photosynthetic oxygen for hydrogen evolution in synergistically integrated, sulfur deprived consortia of Coccomyxa chodatii and Rhodobium gokarnense at dim and high light

In this work, tuning oxygen tension was targeted to improve hydrogen evolution. To achieve such target, various consortia of the chlorophyte Coccomyxa chodatii with a newly isolated photosynthetic purple non-sulfur bacterium (PNSB) strain Rhodobium gokarnense were set up, sulfur replete/deprived, malate/acetate fed, bicarbonate/sulfur added at dim/high light. C. chodatii and R. gokarnense are newly introduced to biohydrogen studies for the first time. Dim light was applied to avoid the inhibitory drawbacks of photosynthetic oxygen evolution, values of hydrogen are comparable with high light or even more and thus economically feasible to eliminate the costs of artificial illumination. Particularly, the consortium of 2n− (n = 1.9 × 105 cell/ml, sulfur deprived) demonstrated its perfection for the target, i.e., the highest possible cumulative hydrogen. This consortium exhibited negative photosynthesis, i.e., oxygen uptake in the light. Most hydrogen in consortia is from bacterial origin, although algae evolved much more hydrogen than bacteria on per cell basis, but for only one day (the second 24 h), as kinetics revealed. The higher hydrogen in unibacterial culture or consortia results from higher bacterial cell density (20 times). Consortia evolved more hydrogen than their respective separate cultures, further enhanced when bicarbonate and sulfur were supplemented at higher light. The share of algae relatively increased as bicarbonate or sulfur were added at higher light intensity, i.e., PSII activity partially recovered, resulting in a transient autotrophic hydrogen evolution. The addition of acetic acid in mixture with malic acid significantly enhanced the cumulative hydrogen levels, mostly decreased cellular ascorbic acid indicating less oxidative stress and relief of PSII, relative to malic acid alone. Starch, however, decreased, indicating the specificity of acetic acid. Exudates (reducing sugars, amino acids, and soluble proteins) were detected, indicating mutual utilization. Yet, hydrogen evolution is limited; tuning PSII activity remains a target for sustainable hydrogen production.

Combined effect of bicarbonate and water in photosynthetic oxygen evolution and carbon neutrality

Combined effect of bicarbonate and water in photosynthetic oxygen evolution and carbon neutrality

Physiological Responses of a Diazotrophic Cyanobacterium to Acidification of Paddy Floodwater: N2 Fixation, Photosynthesis, and Oxidative-Antioxidative Characteristics.

Long-term of excessive fertilization using nitrogen (N) chemical fertilizer caused the acidification of paddy soils. Presently, the impacts of soil acidification on physiological characteristics of diazotrophic cyanobacteria remain unknown. In order to elucidate this issue, the effects of paddy floodwater acidification on activities of respiration, photosynthetic oxygen evolution, and N2 fixation of a paddy diazotrophic cyanobacterium Aliinostoc sp. YYLX235 were investigated in this study. In addition, the origination and quenching of intracellular reactive oxygen species (ROS) were analyzed. The acidification of paddy floodwater decreased intracellular pH and interfered in energy flux from light-harvesting chlorophyll antenna to the reaction center of photosystem II (PS II). Activities of respiration, photosynthetic oxygen evolution, and N2 fixation were decreased by the acidification of paddy floodwater. Accompanied with an increase in ROS, the level of antioxidative system increased. Superoxide dismutase (SOD) and catalase (CAT) were the main enzymatic ROS scavengers in the cells of YYLX235; reduced glutathione (GSH) was the main non-enzymatic antioxidant. Antioxidants and oxidants in the cells of YYLX235 lost balance when the pH of paddy floodwater fell to 5.0 and 4.0, and lipid oxidative damage happened. The results presented in this study suggest that the acidification of paddy soil severely interfered in the photosynthesis of diazotrophic cyanobacteria and induced the production of ROS, which in turn resulted in oxidative damage on diazotrophic cyanobacteria and a decrease in cell vitality.

Towards an In Vitro 3D Model for Photosynthetic Cancer Treatment: A Study of Microalgae and Tumor Cell Interactions.

As hypoxic tumors show resistance to several clinical treatments, photosynthetic microorganisms have been recently suggested as a promising safe alternative for oxygenating the tumor microenvironment. The relationship between organisms and the effect microalgae have on tumors is still largely unknown, evidencing the need for a simple yet representative model for studying photosynthetic tumor oxygenation in a reproducible manner. Here, we present a 3D photosynthetic tumor model composed of human melanoma cells and the microalgae Chlamydomonas reinhardtii, both seeded into a collagen scaffold, which allows for the simultaneous study of both cell types. This work focuses on the biocompatibility and cellular interactions of the two cell types, as well as the study of photosynthetic oxygenation of the tumor cells. It is shown that both cell types are biocompatible with one another at cell culture conditions and that a 10:1 ratio of microalgae to cells meets the metabolic requirement of the tumor cells, producing over twice the required amount of oxygen. This 3D tumor model provides an easy-to-use in vitro resource for analyzing the effects of photosynthetically produced oxygen on a tumor microenvironment, thus opening various potential research avenues.

Utilization of light energy and photodynamic therapy based on thylakoid membranes

<p indent="0mm">The thylakoid membrane, which contains photosynthetic pigments, lipids and proteins, is the main site where the photosynthetic light reaction of green plants, eukaryotic algae and cyanobacteria occurs. Water photolysis and photosynthetic electron transport are two core processes of the light reaction. The former is responsible for converting photons into electrons, and the latter then condenses the energy from the high-potential electrons into energy carriers such as adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide phosphate (NADPH). Due to the electron transport and energy conversion properties of the light reaction, thylakoid membrane can be used in biophotoelectrochemical and biophotoelectrocatalytic systems. Biophotoelectrochemical systems refer to direct or indirect extraction of electrons from the photosynthetic electron transfer chain (PETC) of the thylakoid membrane and transfer the electrons into an external electrode, eventually converting light energy into electric current. Biophotoelectrocatalytic systems refer to the use of ATP and NADPH generated in the light reaction of the thylakoid membrane to drive a series of ATP- or NADPH-dependent biocatalytic reactions. These thylakoid membrane-based light energy utilization systems are featured with material renewability and environmental compatibility. In addition, they show higher energy efficiency than that of the whole photosynthetic-cell systems. Furthermore, thylakoid membranes also hold clear advantages over sub-cellular photosystems, including retention of photosynthetic complexes in their natural environment and relatively simple and fast procedures for their extraction and purification. For biophotoelectrochemical systems, scientists have optimized the electron transfer between the thylakoid membrane and electrode, for example by developing different immobilization methods, or modifying electrode surface with redox polymers and nanomaterials. As an effective platform for cofactor regeneration, the thylakoid membrane-based biophotoelectrocatalytic systems have been used to drive the enzymatic synthesis of poly(3-hydroxybutyrate) (PHB) from acetate, as well as CO₂ fixation through a synthetic crotonyl-coenzyme A (CoA)/ethylmalonyl-CoA/hydroxybutyryl-CoA (CETCH) cycle. In addition to light energy utilization, thylakoid membranes can also be used in photodynamic therapy (PDT) of tumors. Firstly, the photosensitizer porphyrin in the chlorophyll molecules can produce singlet oxygen (¹O₂) from O₂ under visible light irradiation, which in turn kills the tumor cells. Secondly, the photosynthetic oxygen evolution of thylakoid membrane can rapidly supply O₂ <italic>in situ</italic>. Moreover, thylakoid membranes contain abundant catalase, which catalyzes the decomposition of H₂O₂ into O₂, thus further increasing the supply of O₂. This paper summarizes recent progress in the research of thylakoid membranes in these three fields, focusing on the application forms and underlying mechanisms. Moreover, the difficulties and challenges in the application of thylakoid membrane are discussed, and future research directions are prospected. Specifically, developing protective structures such as hydrogels or artificial vesicles to address the issue of short half-life of isolated thylakoid membranes will be crucial. In light of their ingenious energy conversion characteristics and amenability for potential commercialization, thylakoid membrane-based biotechnological systems will have a bright future in the fields of bioenergy, biocatalysis and biomedicine.

Environmental constraints on the photosynthetic rate of the marine flatworm Symsagittifera roscoffensis

Symsagittifera roscoffensis, an Acoel flatworm that lives within the intertidal zone, was first discovered over a century ago as a “plant animal” due to its symbiotic relationship with the alga Tetraselmis convolutae. Although commonly used as a model organism in biomedical research, there is little information regarding its life history or how environmental factors affect this organism. In this study, we investigated the effects of a range of abiotic factors on S. roscoffensis by measuring its photosynthetic oxygen production rate under different salinities, temperatures, light intensities, photoperiods, and nutrient concentrations over 6 days. Salinity (20, 30 and 40) had little effect on photosynthetic rate, whereas a temperature of 14 °C yielded significantly higher final oxygen production than 0 and 30 °C. The lowest light intensity (21 μmol m−2 s−1), the shortest photoperiod (8 L:16 D) and the intermediate nutrient concentration (f/4) resulted in the highest final oxygen production rates. Our results showed that S. roscoffensis had the ability to tolerate and remain photosynthetically active under a wide range of conditions that it is likely to experience within the intertidal zone. Using our experimental data, we estimated that S. roscoffensis was able to produce 174% body C d−1 via photosynthesis alone, which could explain the total absence of heterotrophic feeding in this organism. The organism appeared to be robust and easy to cultivate, which should open new opportunities for its wider applications.

Effects of nutrients on the utilization pattern of photosynthetic inorganic carbon of the tropical &amp;lt;italic&amp;gt;Thalassia hemprichii&amp;lt;/italic&amp;gt;

<p indent="0mm">Studies on the utilization strategy of photosynthetic inorganic carbon of seagrass can reveal its ecological adaptation mechanism. <italic>Thalassia hemprichii</italic>, a widely distributed seagrass species in the Indo-Pacific and Atlantic coastal seas, needs to evolve several utilization patterns of inorganic carbon to adapt different environments and meet its growth, development and reproduction. However, the effect of nutrient on the photosynthetic inorganic carbon utilization strategy in seagrass is still unknown and further research is urgently needed. Therefore, using oxygen electrode technology, chlorophyll fluorescence technology, and non-invasive micro-test technology, this study examined the similarity and difference in the utilization patterns of photosynthetic inorganic carbon of <italic>T</italic>.<italic> hemprichii </italic>from two typical tropical seagrass beds (Tanmen, Hainan Island, and Yongxing Island, Xisha), that were affected by varying degrees of human activity. Experiments showed that the photosynthetic oxygen release rate, maximum relative electron transfer rate, and half-saturated light intensity of <italic>T</italic>.<italic> hemprichii</italic> in Yongxing Island waters were 24.95%, 24.54%, and 28.73% higher than the corresponding in Tanmen, Hainan Island. This indicated that the growth status of <italic>T</italic>.<italic> hemprichii</italic> in the waters of Yongxing Island was better with higher photosynthetic efficiency. The addition of acetazolamide (AZ) and ethoxyzolamide (EZ) significantly reduced the photosynthetic oxygen release rate of <italic>T</italic>.<italic> hemprichii</italic>, with an insignificant difference in the inhibition between AZ and EZ. This indicated that it mainly absorbed HCO₃⁻ via extracellular carbonic anhydrase catalysis. Meanwhile, hydroxymethyl (Tris) inhibited the photosynthetic oxygen release of <italic>T</italic>.<italic> hemprichii</italic> in Tanmen by up to 100% and decreased the maximum relative electron transfer rate and the H⁺ inward flow rate, implying a synergistic H⁺/HCO₃⁻ transport mode. On the other hand, the rate of photosynthetic oxygen release and the maximum electron transfer rate of <italic>T</italic>.<italic> hemprichii</italic> in Xisha did not change significantly with the addition of AZ and EZ, while Tris buffer inhibited photosynthetic oxygen release by up to 100% and significantly reduced the maximum electron transfer rate. This suggested <italic>T</italic>.<italic> hemprichii </italic>in Xisha mainly relied on the H⁺/HCO₃⁻ synergistic transport. Therefore, <italic>T</italic>.<italic> hemprichii </italic>could uptake inorganic carbon in an environment with greater anthropogenic activity, larger nutrient load and lower light availability on Hainan Island by catalyzing HCO₃⁻ into CO₂ with extracellular carbonic anhydrase and the H⁺/HCO₃⁻ synergistic transport. In contrast, <italic>T</italic>.<italic> hemprichii</italic> in an environment with less anthropogenic activity, lower nutrient loading, and greater light availability, relied chiefly on H⁺/HCO₃⁻ synergistic transport. Facing a relatively unfavorable high-nutrient and low-light growth environment, <italic>T</italic>.<italic> hemprichii</italic> could increase the photosynthetic inorganic carbon utilization strategy (such as the activity of extracellular carbonic anhydrase) to improve its utilization ability of inorganic carbon to overcome stress and growth limitation. This suggested that <italic>T</italic>.<italic> hemprichii</italic> could adjust its inorganic carbon utilization patterns according to its geographical environment. With the continuous development of technology, it is urgent to study the utilization mechanism of inorganic carbon of seagrass by applying seagrass omics technology and stable isotope tracing to deepen the understanding of the carbon sink function of seagrass.