Evolution and unique bioenergetic mechanisms in oxygenic photosynthesis

Limiting factors in the operation of photosystems I and II in cyanobacteria

Cyanobacteria are important targets for biotechnological applications due to their ability to grow in a wide variety of environments, rapid growth rates, and tractable genetic systems. They and their bioproducts can be used as bioplastics, biofertilizers, and in carbon capture and produce important secondary metabolites that can be used as pharmaceuticals. However, the photosynthetic process in cyanobacteria can be limited by a wide variety of environmental factors such as light intensity and wavelength, exposure to UV light, nutrient limitation, temperature, and salinity. Carefully considering these limitations, modifying the environment, and/or selecting cyanobacterial species will allow cyanobacteria to be used in biotechnological applications.

Study on high-CO2 tolerant Dunaliella salina and its mechanism via transcriptomic analysis

Microalgae has been regarded as a promising method for reducing CO2 emission. High CO2 concentration generally inhibits algal growth, and previous studies have mostly focused on breeding freshwater algae with high CO2 tolerance. In this study, one marine algal strain Dunaliella salina (D. salina) was grown under 0.03%-30 % CO2 and 3% NaCl conditions, and was evaluated to determine its potential for CO2 assimilation. The results showed that D. salina could tolerate 30% CO2 , and its maximum biomass concentration could reach 1.13 g·L-1 after 8 days incubation, which was 1.85 times higher than that of incubation in air (0.03%). The phenomenon of high-CO2 tolerance in D. salina culture was discussed basing on transcriptome analysis. The results showed that D. salina was subjected to oxidative stress under 30% CO2 conditions, and the majority genes involving in antioxidant system, such as SOD, CAT, and APX genes were up-regulated to scavenge ROS. In addition, most of the key enzyme genes related to photosynthesis, carbon fixation and metabolism were up-regulated, which are consistent with the higher physiological and biochemical values for D. salina incubation under 30% CO2 .

Genes encoding the photosystem II proteins are under purifying selection: an insight into the early evolution of oxygenic photosynthesis

The molecular evolution concerns coding sequences (CDSs) of genes and may affect the structure and function of proteins. Non-uniform use of synonymous codons during translation, known as codon usage bias (CUB), depends on the balance between mutations bias and natural selection. We estimated different CUB indices, i.e. the effective number of codons (ENC), G + C content in the 3rd codon positions (GC₃), and codon adaptation index for CDSs of intrinsic proteins of photosystem II (PSII), such as psbA (D1), psbD (D2), psbB (CP47), psbC (CP43), and CDSs of the extrinsic protein psbO (PsbO). These genes occur in all organisms that perform oxygenic photosynthesis (OP) on Earth: cyanobacteria, algae and plants. Comparatively, a similar analysis of codon bias for CDSs of L and M subunits that constitute the core proteins of the type II reaction centre (RCII) in anoxygenic bacteria was performed. Analysis of CUB indices and determination of the number of synonymous (d_S) and nonsynonymous substitutions (d_N) in all analysed CDSs indicated that the crucial PSII and RCII proteins were under strong purifying (negative) selection in course of evolution. Purifying selection was also estimated for CDSs of atpA, the α subunit of ATP synthase, an enzyme that was most likely already present in the last universal common ancestor (LUCA). The data obtained point to an ancient origin of OP, even in the earliest stages of the evolution of life on Earth.

Effect of Magnetopriming on Photosynthetic Performance of Plants

Magnetopriming has emerged as a promising seed-priming method, improving seed vigor, plant performance and productivity under both normal and stressed conditions. Various recent reports have demonstrated that improved photosynthesis can lead to higher biomass accumulation and overall crop yield. The major focus of the present review is magnetopriming-based, improved growth parameters, which ultimately favor increased photosynthetic performance. The plants originating from magnetoprimed seeds showed increased plant height, leaf area, fresh weight, thick midrib and minor veins. Similarly, chlorophyll and carotenoid contents, efficiency of PSII, quantum yield of electron transport, stomatal conductance, and activities of carbonic anhydrase (CA), Rubisco and PEP-carboxylase enzymes are enhanced with magnetopriming of the seeds. In addition, a higher fluorescence yield at the J-I-P phase in polyphasic chlorophyll a fluorescence (OJIP) transient curves was observed in plants originating from magnetoprimed seeds. Here, we have presented an overview of available studies supporting the magnetopriming-based improvement of various parameters determining the photosynthetic performance of crop plants, which consequently increases crop yield. Additionally, we suggest the need for more in-depth molecular analysis in the future to shed light upon hidden regulatory mechanisms involved in magnetopriming-based, improved photosynthetic performance.

Reconstructing the Origin of Oxygenic Photosynthesis: Do Assembly and Photoactivation Recapitulate Evolution?

Due to the great abundance of genomes and protein structures that today span a broad diversity of organisms, now more than ever before, it is possible to reconstruct the molecular evolution of protein complexes at an incredible level of detail. Here, I recount the story of oxygenic photosynthesis or how an ancestral reaction center was transformed into a sophisticated photochemical machine capable of water oxidation. First, I review the evolution of all reaction center proteins in order to highlight that Photosystem II and Photosystem I, today only found in the phylum Cyanobacteria, branched out very early in the history of photosynthesis. Therefore, it is very unlikely that they were acquired via horizontal gene transfer from any of the described phyla of anoxygenic phototrophic bacteria. Second, I present a new evolutionary scenario for the origin of the CP43 and CP47 antenna of Photosystem II. I suggest that the antenna proteins originated from the remodeling of an entire Type I reaction center protein and not from the partial gene duplication of a Type I reaction center gene. Third, I highlight how Photosystem II and Photosystem I reaction center proteins interact with small peripheral subunits in remarkably similar patterns and hypothesize that some of this complexity may be traced back to the most ancestral reaction center. Fourth, I outline the sequence of events that led to the origin of the Mn4CaO5 cluster and show that the most ancestral Type II reaction center had some of the basic structural components that would become essential in the coordination of the water-oxidizing complex. Finally, I collect all these ideas, starting at the origin of the first reaction center proteins and ending with the emergence of the water-oxidizing cluster, to hypothesize that the complex and well-organized process of assembly and photoactivation of Photosystem II recapitulate evolutionary transitions in the path to oxygenic photosynthesis.

Enhanced CO2 sequestration by a novel microalga: Scenedesmus obliquus SA1 isolated from bio-diversity hotspot region of Assam, India

The present study aimed to isolate a high CO2 and temperature tolerant microalga capable of sequestering CO2 from flue gas. Microalga strain SA1 was isolated from a freshwater body of Assam and identified as Scenedesmus obliquus (KC733762). At 13.8±1.5% CO2 and 25 °C, maximum biomass (4.975±0.003 g L(-1)) and maximum CO2 fixation rate (252.883±0.361 mg L(-1) d(-1)) were obtained which were higher than most of the relevant studies. At elevated temperature (40 °C) and 13.8±1.5% CO2 maximum biomass (0.883±0.001 g L(-1)) was obtained. The carbohydrate, protein, lipid, and chlorophyll content of the CO2 treated SA1 were 30.87±0.64%, 9.48±1.65%, 33.04±0.46% and 6.03±0.19% respectively, which were higher than previous reports. Thus, SA1 could prove to be a potential candidate for CO2 sequestration from flue gas as well as for the production of value added substances.

Performance of photoperiod and light intensity on biogas upgrade and biogas effluent nutrient reduction by the microalgae Chlorella sp

Biogas is an environment-friendly fuel but that must be upgraded before being utilized. The method about removing CO2 from biogas by microalgal culturing using biogas effluent as nutrient medium in this study could effectively upgrade biogas and simultaneously reduce the biogas effluent nutrient. Results showed that the optimum parameters for microalgal growth and biogas effluent nutrient reduction was moderate light intensity with middle photoperiod. While low light intensity with long photoperiod and moderate light intensity with middle photoperiod obtained the best biogas CO2 removal and biogas upgrade effects. Therefore, the optimal parameters were moderate light intensity 350 μmol m(-2)s(-1) with middle photoperiod 14 h light:10h dark. Under this condition, the microalgal dry weight, CH4 concentration, reduction efficiency of chemical oxygen demand, total nitrogen, and total phosphorus was 615.84 ± 33.07 mg L(-1), 92.16 ± 2.83% (v/v), 88.74 ± 3.45%, 83.94 ± 3.51%, and 80.43 ± 4.17%, respectively.

Photobioreactor strategies for improving the CO2 fixation efficiency of indigenous Scenedesmus obliquus CNW-N: statistical optimization of CO2 feeding, illumination, and operation mode

Statistical experimental design and bioreactor strategies were applied to enhance CO(2) fixation ability of microalga Scenedesmus obliquus CNW-N. Four operating parameters strongly influencing microalgal CO(2) fixation efficiency (namely, CO(2) concentration, CO(2) flow rate, magnesium concentration, and light intensity) were optimized with response surface methodology. The optimal range of parameters achieving the best overall performance of specific growth rate and CO(2) fixation rate was determined with overlay counter plot techniques. Optimal ranges of CO(2) concentration, CO(2) flow rate, magnesium concentration and light intensity were 2.0-2.5%, 0.3-0.5 vvm, 1.7-2.7 mM and 180-250 μmol m(-2) s(-1), respectively, achieving a specific growth rate of >1.22 d(-1) and CO(2) fixation rate of >800 mg L(-1) d(-1). Semi-batch operations further enhanced the biomass productivity, photosynthesis efficiency, and CO(2) fixation rate to 1030 mg L(-1) d(-1), 10.5%, and 1782 mg L(-1) d(-1), respectively. This performance is better than the results reported by most related studies.

Perspectives on microalgal CO₂-emission mitigation systems--a review

The problem of climate change arising mainly from CO₂ emission is currently a critical environmental issue. Biofixation using microalgae has recently become an attractive approach to CO₂ capture and recycling with additional benefits of downstream utilization and applications of the resulting microalgal biomass. This review summarizes the history and strategies of microalgal mitigation of CO₂ emissions, photobioreactor systems used to cultivate microalgae for CO₂ fixation, current microalgae harvesting methods, as well as applications of valuable by-products. It is of importance to select appropriate microalgal species to achieve an efficient and economically feasible CO₂-emission mitigation process. The desired microalgae species should have a high growth rate, high CO₂ fixation ability, low contamination risk, low operation cost, be easy to harvest and rich in valuable components in their biomass.

Artificial photoactive proteins

Solar power is the most abundant source of renewable energy. In this respect, the goal of making photoactive proteins is to utilize this energy to generate an electron flow. Photosystems have provided the blueprint for making such systems, since they are capable of converting the energy of light into an electron flow using a series of redox cofactors. Protein tunes the redox potential of the cofactors and arranges them such that their distance and orientation are optimal for the creation of a stable charge separation. The aim of this review is to present an overview of the literature with regard to some elegant functional structures that protein designers have created by introducing cofactors and photoactivity into synthetic proteins.