Photosynthesis at the forefront of a sustainable life

The impact of polystyrene nanoplastics (PSNPs) on physiological and biochemical parameters of the microalgae Spirulina platensis

Nanoplastics, as emerging pollutants, have harmful effects on living organisms and the environment, the mechanisms and extent of which remain unclear. Microalgae, as one of the most important biological groups in the food chain and sensitive environmental indicators to various pollutants, are considered a suitable option for investigating the effects of nanoplastics. In this study, the effects of polystyrene nanoplastics on the growth rate, dry weight, chlorophyll a and carotenoid levels, proline, and lipid peroxidation in the Spirulina platensis were examined. Three concentrations of 0.1, 1, and 10 mg L-1 of PSNPs were used alongside a control sample with zero concentration, with four repetitions in one-liter containers for 20 days under optimal temperature and light conditions. Various analyses, including growth rate, dry weight, proline, chlorophyll a and carotenoid levels, and lipid peroxidation, were performed. The results indicated that exposure to PSNP stress led to a significant decrease in growth rate, dry weight, and chlorophyll a and carotenoid levels compared to the control sample. Furthermore, this stress increased the levels of proline and lipid peroxidation in Spirulina platensis. Morphological analysis via microscopy supported these findings, indicating considerable environmental risks associated with PSNPs.

Breathing life into Mars: Terraforming and the pivotal role of algae in atmospheric genesis

The Martian environment, characterized by extreme aridity, frigid temperatures, and a lack of atmospheric oxygen, presents a formidable challenge for potential terraforming endeavors. This review article synthesizes current research on utilizing algae as biocatalysts in the proposed terraforming of Mars, assessing their capacity to facilitate Martian atmospheric conditions through photosynthetic bioengineering. We analyze the physiological and genetic traits of extremophile algae that equip them for survival in extreme habitats on Earth, which serve as analogs for Martian surface conditions. The potential for these organisms to mediate atmospheric change on Mars is evaluated, specifically their role in biogenic oxygen production and carbon dioxide sequestration. We discuss strategies for enhancing algal strains' resilience and metabolic efficiency, including genetic modification and the development of bioreactors for controlled growth in extraterrestrial environments. The integration of algal systems with existing mechanical and chemical terraforming proposals is also examined, proposing a synergistic approach for establishing a nascent Martian biosphere. Ethical and ecological considerations concerning introducing terrestrial life to extra-planetary bodies are critically appraised. This appraisal includes an examination of potential ecological feedback loops and inherent risks associated with biological terraforming. Biological terraforming is the theoretical process of deliberately altering a planet's atmosphere, temperature, and ecosystem to render it suitable for Earth-like life. The feasibility of a phased introduction of life, starting with microbial taxa and progressing to multicellular organisms, fosters a supportive atmosphere on Mars. By extending the frontier of biotechnological innovation into space, this work contributes to the foundational understanding necessary for one of humanity's most audacious goals-the terraforming of another planet.

Integrating the multiple functions of CHLH into chloroplast-derived signaling fundamental to plant development and adaptation as well as fruit ripening

Chlorophyll (Chl)-mediated oxygenic photosynthesis sustains life on Earth. Greening leaves play fundamental roles in plant growth and crop yield, correlating with the idea that more Chls lead to better adaptation. However, they face significant challenges from various unfavorable environments. Chl biosynthesis hinges on the first committed step, which involves inserting Mg2+ into protoporphyrin. This step is facilitated by the H subunit of magnesium chelatase (CHLH) and features a conserved mechanism from cyanobacteria to plants. For better adaptation to fluctuating land environments, especially drought, CHLH evolves multiple biological functions, including Chl biosynthesis, retrograde signaling, and abscisic acid (ABA) responses. Additionally, it integrates into various chloroplast-derived signaling pathways, encompassing both retrograde signaling and hormonal signaling. The former comprises ROS (reactive oxygen species), heme, GUN (genomes uncoupled), MEcPP (methylerythritol cyclodiphosphate), β-CC (β-cyclocitral), and PAP (3'-phosphoadenosine-5'-phosphate). The latter involves phytohormones like ABA, ethylene, auxin, cytokinin, gibberellin, strigolactone, brassinolide, salicylic acid, and jasmonic acid. Together, these elements create a coordinated regulatory network tailored to plant development and adaptation. An intriguing example is how drought-mediated improvement of fruit quality provides insights into chloroplast-derived signaling, aiding the shift from vegetative to reproductive growth. In this context, we explore the integration of CHLH's multifaceted roles into chloroplast-derived signaling, which lays the foundation for plant development and adaptation, as well as fruit ripening and quality. In the future, manipulating chloroplast-derived signaling may offer a promising avenue to enhance crop yield and quality through the homeostasis, function, and regulation of Chls.

Nanoreactor Engineering Can Unlock New Possibilities for CO2 Tandem Catalytic Conversion to C-C Coupled Products

Climate change is becoming increasingly more pronounced every day while the amount of greenhouse gases in the atmosphere continues to rise. CO₂ reduction to valuable chemicals is an approach that has gathered substantial attention as a means to recycle these gases. Herein, some of the tandem catalysis approaches that can be used to achieve the transformation of CO₂ to C-C coupled products are explored, focusing especially on tandem catalytic schemes where there is a big opportunity to improve performance by designing effective catalytic nanoreactors. Recent reviews have highlighted the technical challenges and opportunities for advancing tandem catalysis, especially highlighting the need for elucidating structure-activity relationships and mechanisms of reaction through theoretical and in situ/operando characterization techniques. In this review, the focus is on nanoreactor synthesis strategies as a critical research direction, and discusses these in the context of two main tandem pathways (CO-mediated pathway and Methanol-mediated pathway) to C-C coupled products.

Nanodiamond Particles Reduce Oxidative Stress Induced by Methyl Viologen and High Light in the Green Alga Chlamydomonas reinhardtii

Widely used in biomedical and bioanalytical applications, the detonation nanodiamonds (NDs) are generally considered to be biocompatible and non-toxic to a wide range of eukaryotic cells. Due to their high susceptibility to chemical modifications, surface functionalisation is often used to tune the biocompatibility and antioxidant activity of the NDs. The response of photosynthetic microorganisms to redox-active NDs is still poorly understood and is the focus of the present study. The green microalga Chlamydomonas reinhardtii was used to assess the potential phytotoxicity and antioxidant activity of NDs hosting hydroxyl functional groups at concentrations of 5–80 μg NDs/mL. The photosynthetic capacity of microalgae was assessed by measuring the maximum quantum yield of PSII photochemistry and the light-saturated oxygen evolution rate, while oxidative stress was assessed by lipid peroxidation and ferric-reducing antioxidant capacity. We demonstrated that hydroxylated NDs might reduce cellular levels of oxidative stress, protect PSII photochemistry and facilitate the PSII repair under methyl viologen and high light associated stress conditions. Factors involved in this protection may include the low phytotoxicity of hydroxylated NDs in microalgae and their ability to accumulate in cells and scavenge reactive oxygen species. Our findings could pave the way for using hydroxylated NDs as antioxidants to improve cellular stability in algae-based biotechnological applications or semi-artificial photosynthetic systems.

Microorganisms as New Sources of Energy

The use of fossil energy sources has a negative impact on the economic and socio-political stability of specific regions and countries, causing environmental changes due to the emission of greenhouse gases. Moreover, the stocks of mineral energy are limited, causing the demand for new types and forms of energy. Biomass is a renewable energy source and represents an alternative to fossil energy sources. Microorganisms produce energy from the substrate and biomass, i.e., from substances in the microenvironment, to maintain their metabolism and life. However, specialized microorganisms also produce specific metabolites under almost abiotic circumstances that often do not have the immediate task of sustaining their own lives. This paper presents the action of biogenic and biogenic–thermogenic microorganisms, which produce methane, alcohols, lipids, triglycerides, and hydrogen, thus often creating renewable energy from waste biomass. Furthermore, some microorganisms acquire new or improved properties through genetic interventions for producing significant amounts of energy. In this way, they clean the environment and can consume greenhouse gases. Particularly suitable are blue-green algae or cyanobacteria but also some otherwise pathogenic microorganisms (E. coli, Klebsiella, and others), as well as many other specialized microorganisms that show an incredible ability to adapt. Microorganisms can change the current paradigm, energy–environment, and open up countless opportunities for producing new energy sources, especially hydrogen, which is an ideal energy source for all systems (biological, physical, technological). Developing such energy production technologies can significantly change the already achieved critical level of greenhouse gases that significantly affect the climate.

Analysis of Physiological Variations and Genetic Architecture for Photosynthetic Capacity of Japanese Soybean Germplasm

The culmination of conventional yield improving parameters has widened the margin between food demand and crop yield, leaving the potential yield productivity to be bridged by the manipulation of photosynthetic processes in plants. Efficient strategies to assess photosynthetic capacity in crops need to be developed to identify suitable targets that have the potential to improve photosynthetic efficiencies. Here, we assessed the photosynthetic capacity of the Japanese soybean mini core collection (GmJMC) using a newly developed high-throughput photosynthesis measurement system "MIC-100" to analyze physiological mechanisms and genetic architecture underpinning photosynthesis. K-means clustering of light-saturated photosynthesis (A_sat ) classified GmJMC accessions into four distinct clusters with Cluster2 comprised of highly photosynthesizing accessions. Genome-wide association analysis based on the variation of A_sat revealed a significant association with a single nucleotide polymorphism (SNP) on chromosome 17. Among the candidate genes related to photosynthesis in the genomic region, variation in expression of a gene encoding G protein alpha subunit 1 (GPA1) showed a strong correlation (r = 0.72, p < 0.01) with that of A_sat . Among GmJMC accessions, GmJMC47 was characterized by the highest A_sat , stomatal conductance (g_s ), stomatal density (S_Density ), electron transfer rate (ETR), and light use efficiency of photosystem II (Fv'/Fm') and the lowest non-photochemical quenching [NPQ(t)], indicating that GmJMC47 has greater CO₂ supply and efficient light-harvesting systems. These results provide strong evidence that exploration of plant germplasm is a useful strategy to unlock the potential of resource use efficiencies for photosynthesis.

Shining a Light on Wastewater Treatment with Microalgae

Microalgae can produce biofuels, nutriceuticals, pigments and many other products, but commercialization has been limited by the cost of growing, harvesting and processing algal biomass. Nutrients, chiefly nitrogen and phosphorus, are a key cost for growing microalgae, but these nutrients are present in abundance in municipal wastewater where they pose environmental problems if not removed. This is not a traditional review article; rather, it is a fact-based set of suggestions that will have to be investigated by scientists and engineers. It is suggested that if microalgae were grown as biofilms rather than as planktonic cells, and if internal illumination rather than external illumination were employed, then the use of microalgae may provide useful improvements to the wastewater treatment process. The use of microalgae to remove nutrients from wastewater has been demonstrated, but has not yet been widely implemented due to cost, and because microalgae derived from wastewater treatment has not yet been demonstrated as a commercial source for value-added products. Future facilities are likely to be called Municipal Resource Recovery Facilities as wastewater will increasingly be viewed as a resource for water, biofuels, fertilizer, monitoring public health and value-added products. Advances in photonics will accelerate this transition.

The induction of pyrenoid synthesis by hyperoxia and its implications for the natural diversity of photosynthetic responses in Chlamydomonas

In algae, it is well established that the pyrenoid, a component of the carbon-concentrating mechanism (CCM), is essential for efficient photosynthesis at low CO₂. However, the signal that triggers the formation of the pyrenoid has remained elusive. Here, we show that, in Chlamydomonas reinhardtii, the pyrenoid is strongly induced by hyperoxia, even at high CO₂ or bicarbonate levels. These results suggest that the pyrenoid can be induced by a common product of photosynthesis specific to low CO₂ or hyperoxia. Consistent with this view, the photorespiratory by-product, H₂O₂, induced the pyrenoid, suggesting that it acts as a signal. Finally, we show evidence for linkages between genetic variations in hyperoxia tolerance, H₂O₂ signaling, and pyrenoid morphologies.

Expression of cyanobacterial genes enhanced CO2 assimilation and biomass production in transgenic Arabidopsis thaliana

Background

Photosynthesis is a key process in plants that is compromised by the oxygenase activity of Rubisco, which leads to the production of toxic compound phosphoglycolate that is catabolized by photorespiratory pathway. Transformation of plants with photorespiratory bypasses have been shown to reduce photorespiration and enhance plant biomass. Interestingly, engineering of a single gene from such photorespiratory bypasses has also improved photosynthesis and plant productivity. Although single gene transformations may not completely reduce photorespiration, increases in plant biomass accumulation have still been observed indicating an alternative role in regulating different metabolic processes. Therefore, the current study was aimed at evaluating the underlying mechanism (s) associated with the effects of introducing a single cyanobacterial glycolate decarboxylation pathway gene on photosynthesis and plant performance.

Methods

Transgenic Arabidopsis thaliana plants (GD, HD, OX) expressing independently cyanobacterial decarboxylation pathway genes i.e., glycolate dehydrogenase, hydroxyacid dehydrogenase, and oxalate decarboxylase, respectively, were utilized. Photosynthetic, fluorescence related, and growth parameters were analyzed. Additionally, transcriptomic analysis of GD transgenic plants was also performed.

Results

The GD plants exhibited a significant increase (16%) in net photosynthesis rate while both HD and OX plants showed a non-significant (11%) increase as compared to wild type plants (WT). The stomatal conductance was significantly higher (24%) in GD and HD plants than the WT plants. The quantum efficiencies of photosystem II, carbon dioxide assimilation and the chlorophyll fluorescence-based photosynthetic electron transport rate were also higher than WT plants. The OX plants displayed significant reductions in the rate of photorespiration relative to gross photosynthesis and increase in the ratio of the photosynthetic electron flow attributable to carboxylation reactions over that attributable to oxygenation reactions. GD, HD and OX plants accumulated significantly higher biomass and seed weight. Soluble sugars were significantly increased in GD and HD plants, while the starch levels were higher in all transgenic plants. The transcriptomic analysis of GD plants revealed 650 up-regulated genes mainly related to photosynthesis, photorespiratory pathway, sucrose metabolism, chlorophyll biosynthesis and glutathione metabolism.

Conclusion

This study revealed the potential of introduced cyanobacterial pathway genes to enhance photosynthetic and growth-related parameters. The upregulation of genes related to different pathways provided evidence of the underlying mechanisms involved particularly in GD plants. However, transcriptomic profiling of HD and OX plants can further help to identify other potential mechanisms involved in improved plant productivity.

Photosynthesis Z-Scheme biomimicry: Photosystem I/BiVO4 photo-bioelectrochemical cell for donor-free bias-free electrical power generation

Photo-bioelectrochemical cells that are based on photosynthetic proteins are drawing increased attention for both fundamental and applied research. While novel photosynthetic based systems have been introduced, further optimization in terms of stability and efficiency is required. Photosystem I has been utilized extensively in bioelectronic devices, often in conjugation with viologen moieties which act as electron acceptors. It has been shown previously that a partial reduction of oxygen to H₂O₂ can facilitate damage to proteins hence, limits their long-term activation. Here, we show a newly developed bias-free, donor-free photo-bioelectrochemical system that mimics the natural photosynthetic Z-scheme. Polymethylene blue and polybutyl-viologen were tailored to fit the photosystem I donor and acceptor sides, respectively. Furthermore, we show that by coupling the developed biocathode with a BiVO₄/CoP photoanode, a power output of 25 μW/cm² can be achieved. We further show that our configuration can minimize the damaging effect of H₂O₂ by two different pathways, oxidation at the photoanode or reduction by the polymethylene blue layer at the biocathode.

Engineering of NADPH Supply Boosts Photosynthesis-Driven Biotransformations

Light-driven biocatalysis in recombinant cyanobacteria provides highly atom-efficient cofactor regeneration via photosynthesis, thereby remediating constraints associated with sacrificial cosubstrates. However, despite the remarkable specific activities of photobiocatalysts, self-shading at moderate-high cell densities limits efficient space-time-yields of heterologous enzymatic reactions. Moreover, efficient integration of an artificial electron sink into the tightly regulated network of cyanobacterial electron pathways can be highly challenging. Here, we used C=C bond reduction of 2-methylmaleimide by the NADPH-dependent ene-reductase YqjM as a model reaction for light-dependent biotransformations. Time-resolved NADPH fluorescence spectroscopy allowed direct monitoring of in-cell YqjM activity and revealed differences in NADPH steady-state levels and oxidation kinetics between different genetic constructs. This effect correlates with specific activities of whole-cells, which demonstrated conversions of >99%. Further channelling of electrons toward heterologous YqjM by inactivation of the flavodiiron proteins (Flv1/Flv3) led to a 2-fold improvement in specific activity at moderate cell densities, thereby elucidating the possibility of accelerating light-driven biotransformations by the removal of natural competing electron sinks. In the best case, an initial product formation rate of 18.3 mmol h^–1 L^–1 was reached, allowing the complete conversion of a 60 mM substrate solution within 4 h.

Do HOMO-LUMO Energy Levels and Band Gaps Provide Sufficient Understanding of Dye-Sensitizer Activity Trends for Water Purification?

A dye-sensitized solar cell assembly can be used to harvest solar energy, while suitable dye sensitizers can be used to purify water. Here, we characterized the activity trends of four dye sensitizers, namely, PORPC-1, PORPC-2, PORPC-3, and PORPC-4, for water purification applications using density functional theory (DFT) with the Perdew-Burke-Ernzerhof (PBE), B3LYP, and PBE0 functionals, ΔSCF, time-dependent DFT (TD-DFT), and quasiparticle Green's function (GW) methods. The energy levels of the highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) were calculated using gas-phase and aqueous-phase methods in order to understand charge-injection abilities and the dye regeneration processes. PBE, B3LYP, PBE0, and TD-DFT methods failed to predict PORPC-4 to be the best sensitizer, while PORPC-2 and PORPC-4 were predicted to be the best sensitizers using ΔSCF coupled with the implicit solvation method, and HOMO-LUMO energies were corrected for the aqueous environment in the GW calculations. However, none of these methods accurately predicted the performance trend of all four dye sensitizers. Consequently, we used the aggregation assembly patterns of the dye molecules in an aqueous environment to further probe the activity trends and found that PORPC-3 and PORPC-4 prefer J-aggregated assembly patterns, whereas PROPC-1 and PORPC-2 prefer to be H-aggregated. Therefore, the performance of these dye molecules can be determined by combining HOMO-LUMO energy levels with aggregate-assembly patterns, with the activity trend predicted to be PORPC-4 > PORPC-2 > PORPC-3 > PORPC-1, which is in good agreement with experimental findings.

A kinetic model for redox-active film based biophotoelectrodes

Redox-active films are advantageous matrices for the immobilization of photosynthetic proteins, due to their ability to mediate electron transfer as well as to achieve high catalyst loading on an electrode for efficient generation of electricity or solar fuels. A general challenge arises from various charge recombination pathways along the light-induced electron transfer chain from the electrode to the charge carriers for electricity production or to the final electron acceptors for solar fuel formation. Experimental methods based on current measurement or product quantification are often unable to discern between the contributions from the photocatalytic process and the detrimental effect of the short-circuiting reactions. Here we report on a general electrochemical model of the reaction-diffusion processes to identify and quantify the "bottlenecks" present in the fuel or current generation. The model is able to predict photocurrent-time curves including deconvolution of the recombination contributions, and to visualize the corresponding time dependent concentration profiles of the product. Dimensionless groups are developed for straightforward identification of the limiting processes. The importance of the model for quantitative understanding of biophotoelectrochemical processes is highlighted with an example of simulation results predicting the effect of the diffusion coefficient of the charge carrier on photocurrent generation for different charge recombination kinetics.

Chlorophyll fluorescence induction and relaxation system for the continuous monitoring of photosynthetic capacity in photobioreactors

The development of high-performance photobioreactors equipped with automatic systems for non-invasive real-time monitoring of cultivation conditions and photosynthetic parameters is a challenge in algae biotechnology. Therefore, we developed a chlorophyll (Chl) fluorescence measuring system for the online recording of the light-induced fluorescence rise and the dark relaxation of the flash-induced fluorescence yield (Qa^- - re-oxidation kinetics) in photobioreactors. This system provides automatic measurements in a broad range of Chl concentrations at high frequency of gas-tight sampling, and advanced data analysis. The performance of this new technique was tested on the green microalgae Chlamydomonas reinhardtii subjected to a sulfur deficiency stress and to long-term dark anaerobic conditions. More than thousand fluorescence kinetic curves were recorded and analyzed during aerobic and anaerobic stages of incubation. Lifetime and amplitude values of kinetic components were determined, and their dynamics plotted on heatmaps. Out of these data, stress-sensitive kinetic parameters were specified. This implemented apparatus can therefore be useful for the continuous real-time monitoring of algal photosynthesis in photobioreactors.

CO2 Signaling through the Ptc2-Ssn3 Axis Governs Sustained Hyphal Development of Candida albicans by Reducing Ume6 Phosphorylation and Degradation

Candida albicans is the most common cause of invasive fungal infections in humans. Its ability to sense and adapt to changing carbon dioxide levels is crucial for its pathogenesis. Carbon dioxide promotes hyphal development. The hypha-specific transcription factor Ume6 is rapidly degraded in air, but is stable under physiological CO₂ and hypoxia to sustain hyphal elongation. Here, we show that Ume6 stability is regulated by two parallel E3 ubiquitin ligases, SCF^Grr1 and Ubr1, in response to CO₂ and O₂, respectively. To uncover the CO₂ signaling pathway that regulates Ume6 stability, we performed genetic screens for mutants unable to respond to CO₂ for sustained filamentation. We find that the type 2C protein phosphatase Ptc2 is specifically required for CO₂-induced stabilization of Ume6 and hyphal elongation. In contrast, the cyclin-dependent kinase Ssn3 is found to be required for Ume6 phosphorylation and degradation in atmospheric CO₂ Furthermore, we find that Ssn3 is dephosphorylated in 5% CO₂ in a Ptc2-dependent manner, whereas deletion of PTC2 has no effect on Ssn3 phosphorylation in air. Our study uncovers the Ptc2-Ssn3 axis as a new CO₂ signaling pathway that controls hyphal elongation by regulating Ume6 stability in C. albicans IMPORTANCE The capacity to sense and adapt to changing carbon dioxide levels is crucial for all organisms. In fungi, CO₂ is a key determinant involved in fundamental biological processes, including growth, morphology, and virulence. In the pathogenic fungus Candida albicans, high CO₂ is directly sensed by adenylyl cyclase to promote hyphal growth. However, little is known about the mechanism by which hyphal development is maintained in response to physiological levels of CO₂ Here we report that a signal transduction system mediated by a phosphatase-kinase pair controls CO₂-responsive Ume6 phosphorylation and stability that in turn dictate hyphal elongation. Our results unravel a new regulatory mechanism of CO₂ signaling in fungi.

Photosensitization of electro-active microbes for solar assisted carbon dioxide transformation

Tandem bio-inorganic platform by combining efficient light harvesting properties of nano-inorganic semiconductor cadmium sulfide (CdS) with biocatalytic ability of electro-active bacteria (EAB) towards carbon dioxide (CO₂) conversion is reported. Sulfur was obtained from either cysteine (EAB-Cys-CdS) or hydrogen sulfide (EAB-H₂S-CdS) and experiments were carried out under similar conditions. Anchoring of the nano CdS cluster on the microbe surface was confirmed using electronic microscope. Bio-inorganic hybrid system was able to produce single and multi-carbon compounds from CO₂ in visible spectrum (λ > 400 nm). Though, acetic acid was dominant (EAB-Cys-CdS, 1.46 g/l and EAB-H₂S-CdS, 1.55 g/l) in both the microbe-CdS hybrids, its concentration as well as product slate varied significantly. EAB-H₂S-CdS produced hexanoic acid and less methanol fraction, while the EAB-Cys-CdS produced no hexanoic acid along with almost double the concentration of methanol. Due to easy harvesting process, this bio-inorganic hybrid represents unique sustainable approach for solar-to-chemical production via CO₂ transformation.

Growth and secretome analysis of possible synergistic interaction between green algae and cyanobacteria

Synergistic coexistence of nitrogen fixing cyanobacteria such as Anabaena variabilis, Nostoc muscorum and Westiellopsis prolifica with green algae namely Scenedesmus obliquus, Chlorella vulgaris and Botryococcus braunii was studied under nitrogen deficient conditions. The effect of these interactions was investigated on growth, fixed nitrogen content, lipid content and their secretomes in individual cultures and cocultures. Based on the cocultivation studies, it was found that out of the nine interactions studied, B. braunii-N. muscorum synergism was best established. This interaction resulted in a maximum of 50% enhancement in nitrogen fixation in B. braunii-N. muscorum co-culture leading to 27% enhancement in lipid content (membrane and neutral lipid). In general, B. braunii co-cultures showed an enhancement in biomass content of up to 38%. Secretome analysis showed presence of new and modified secondary metabolites having roles in quorum sensing/quenching, interspecies signaling, N-fixation, carbon metabolism, lipid metabolism, antimicrobial activity. Compounds such as trichloroacetic acid and hexadecane were identified that are known to have roles in nitrogen assimilation and carbon metabolism, respectively, were present in some of the co-culture secretomes. The combination of B. braunii-N. muscorum led to the formation of new compounds such as triacontanol which have role in improvement of glucose-lipid metabolism and 9-octadecenamide that is known to be a phytohormone.

Features of cues and processes during chloroplast-mediated retrograde signaling in the alga Chlamydomonas

Retrograde signaling is an intracellular communication process defined by cues generated in chloroplast and mitochondria which traverse membranes to their destination in the nucleus in order to regulate nuclear gene expression and protein synthesis. The coding and decoding of such organellar message(s) involve gene medleys and metabolic components about which more is known in higher plants than the unicellular organisms such as algae. Chlamydomonas reinhardtii is an oxygenic microalgal model for genetic and physiological studies. It harbors a single chloroplast and is amenable for generating mutants. The focus of this review is on studies that delineate retrograde signaling in Chlamydomonas vis a vis higher plants. Thus, communication networks between chloroplast and nucleus involving photosynthesis- and ROS-generated signals, functional tetrapyrrole biosynthesis intermediates, and Ca²⁺-signaling that modulate nuclear gene expression in this alga are discussed. Conceptually, different signaling components converge to regulate either the same or functionally-overlapping gene products.

Metabolic regulation of photosynthesis

Photosynthesis is fundamental to biomass production, but is a dynamic process sensitive to environmental constraints. In recent years, approaches to increase biomass and grain yield by altering photosynthetically related processes in the plant have received considerable attention. However, improving biomass yield requires a predictive understanding of the molecular mechanisms that allow photosynthesis to be adjusted. The important roles of metabolic reactions external to those directly involved in photosynthesis are highlighted in this review; however, our major focus is on the routes taken to improve photosynthetic carbon assimilation and to increase photosynthetic efficiency and consequently biomass yield.

Production of Industrial Chemicals from CO2 by Engineering Cyanobacteria

As photosynthetic prokaryotes, cyanobacteria can directly convert CO₂ to organic compounds and grow rapidly using sunlight as the sole source of energy. The direct biosynthesis of chemicals from CO₂ and sunlight in cyanobacteria is therefore theoretically more attractive than using glucose as carbon source in heterotrophic bacteria. To date, more than 20 different target chemicals have been synthesized from CO₂ in cyanobacteria. However, the yield and productivity of the constructed strains is about 100-fold lower than what can be obtained using heterotrophic bacteria, and only a few products reached the gram level. The main bottleneck in optimizing cyanobacterial cell factories is the relative complexity of the metabolism of photoautotrophic bacteria. In heterotrophic bacteria, energy metabolism is integrated with the carbon metabolism, so that glucose can provide both energy and carbon for the synthesis of target chemicals. By contrast, the energy and carbon metabolism of cyanobacteria are separated. First, solar energy is converted into chemical energy and reducing power via the light reactions of photosynthesis. Subsequently, CO₂ is reduced to organic compounds using this chemical energy and reducing power. Finally, the reduced CO₂ provides the carbon source and chemical energy for the synthesis of target chemicals and cell growth. Consequently, the unique nature of the cyanobacterial energy and carbon metabolism determines the specific metabolic engineering strategies required for these organisms. In this chapter, we will describe the specific characteristics of cyanobacteria regarding their metabolism of carbon and energy, summarize and analyze the specific strategies for the production of chemicals in cyanobacteria, and propose metabolic engineering strategies which may be most suitable for cyanobacteria.

Cytochrome c Provides an Electron-Funneling Antenna for Efficient Photocurrent Generation in a Reaction Center Biophotocathode

The high quantum efficiency of photosynthetic reaction centers (RCs) makes them attractive for bioelectronic and biophotovoltaic applications. However, much of the native RC efficiency is lost in communication between surface-bound RCs and electrode materials. The state-of-the-art biophotoelectrodes utilizing cytochrome c (cyt c) as a biological wiring agent have at best approached 32% retained RC quantum efficiency. However, bottlenecks in cyt c-mediated electron transfer have not yet been fully elucidated. In this work, protein film voltammetry in conjunction with photoelectrochemistry is used to show that cyt c acts as an electron-funneling antennae that shuttle electrons from a functionalized rough silver electrode to surface-immobilized RCs. The arrangement of the two proteins on the electrode surface is characterized, revealing that RCs attached directly to the electrode via hydrophobic interactions and that a film of six cyt c per RC electrostatically bound to the electrode. We show that the additional electrical connectivity within a film of cyt c improves the high turnover demands of surface-bound RCs. This results in larger photocurrent onset potentials, positively shifted half-wave reduction potentials, and higher photocurrent densities reaching 100 μA cm^-2. These findings are fundamental for the optimization of bioelectronics that utilize the ubiquitous cyt c redox proteins as biological wires to exploit electrode-bound enzymes.

CO2 sensing in fungi: at the heart of metabolic signaling

Adaptation to the changing environmental CO₂ levels is essential for all living cells. In particular, microorganisms colonizing and infecting the human body are exposed to highly variable concentrations, ranging from atmospheric 0.04 to 5% and more in blood and specific host niches. Carbonic anhydrases are highly conserved metalloenzymes that enable fixation of CO₂ by its conversion into bicarbonate. This process is not only crucial to ensure the supply of adequate carbon amounts for cellular metabolism, but also contributes to several signaling processes in fungi, including morphology and communication. The fungal specific carbonic anhydrase gene NCE103 is transcribed in response to CO₂ availability. As recently shown, this regulation relies on the ATF/CREB transcription factor Cst6 and the AGC family protein kinase Sch9. Here, we review the regulatory mechanisms which control NCE103 expression in the model organism Saccharomyces cerevisiae and the pathogenic yeasts Candida albicans and Candida glabrata and discuss which additional factors might contribute in this novel CO₂ sensing cascade.

Toward biotechnology in space: High-throughput instruments for in situ biological research beyond Earth

Space biotechnology is a nascent field aimed at applying tools of modern biology to advance our goals in space exploration. These advances rely on our ability to exploit in situ high throughput techniques for amplification and sequencing DNA, and measuring levels of RNA transcripts, proteins and metabolites in a cell. These techniques, collectively known as "omics" techniques have already revolutionized terrestrial biology. A number of on-going efforts are aimed at developing instruments to carry out "omics" research in space, in particular on board the International Space Station and small satellites. For space applications these instruments require substantial and creative reengineering that includes automation, miniaturization and ensuring that the device is resistant to conditions in space and works independently of the direction of the gravity vector. Different paths taken to meet these requirements for different "omics" instruments are the subjects of this review. The advantages and disadvantages of these instruments and technological solutions and their level of readiness for deployment in space are discussed. Considering that effects of space environments on terrestrial organisms appear to be global, it is argued that high throughput instruments are essential to advance (1) biomedical and physiological studies to control and reduce space-related stressors on living systems, (2) application of biology to life support and in situ resource utilization, (3) planetary protection, and (4) basic research about the limits on life in space. It is also argued that carrying out measurements in situ provides considerable advantages over the traditional space biology paradigm that relies on post-flight data analysis.

Water Collective Dynamics in Whole Photosynthetic Green Algae as Affected by Protein Single Mutation

In the context of the importance of water molecules for protein function/dynamics relationship, the role of water collective dynamics in Chlamydomonas green algae carrying both native and mutated photosynthetic proteins has been investigated by neutron Brillouin scattering spectroscopy. Results show that single point genetic mutation may notably affect collective density fluctuations in hydrating water providing important insight on the transmission of information possibly correlated to biological functionality. In particular, we highlight that the damping factor of the excitations is larger in the native compared to the mutant algae as a signature of a different plasticity and structure of the hydrogen bond network.

From cyanochemicals to cyanofactories: a review and perspective

Engineering cyanobacteria for production of chemicals from solar energy, CO₂ and water is a potential approach to address global energy and environment issues such as greenhouse effect. To date, more than 20 chemicals have been synthesized by engineered cyanobacteria using CO₂ as raw materials, and these studies have been well reviewed. However, unlike heterotrophic microorganisms, the low CO₂ fixation rate makes it a long way to go from cyanochemicals to cyanofactories. Here we review recent progresses on improvement of carbon fixation and redistribution of intercellular carbon flux, and discuss the challenges for developing cyanofactories in the future.

Microgravity-driven remodeling of the proteome reveals insights into molecular mechanisms and signal networks involved in response to the space flight environment

Space is a hostile environment characterized by high vacuum, extreme temperatures, meteoroids, space debris, ionospheric plasma, microgravity and space radiation, which all represent risks for human health. A deep understanding of the biological consequences of exposure to the space environment is required to design efficient countermeasures to minimize their negative impact on human health. Recently, proteomic approaches have received a significant amount of attention in the effort to further study microgravity-induced physiological changes. In this review, we summarize the current knowledge about the effects of microgravity on microorganisms (in particular Cupriavidus metallidurans CH34, Bacillus cereus and Rhodospirillum rubrum S1H), plants (whole plants, organs, and cell cultures), mammalian cells (endothelial cells, bone cells, chondrocytes, muscle cells, thyroid cancer cells, immune system cells) and animals (invertebrates, vertebrates and mammals). Herein, we describe their proteome's response to microgravity, focusing on proteomic discoveries and their future potential applications in space research.

BIOLOGICAL SIGNIFICANCE

Space experiments and operational flight experience have identified detrimental effects on human health and performance because of exposure to weightlessness, even when currently available countermeasures are implemented. Many experimental tools and methods have been developed to study microgravity induced physiological changes. Recently, genomic and proteomic approaches have received a significant amount of attention. This review summarizes the recent research studies of the proteome response to microgravity inmicroorganisms, plants, mammalians cells and animals. Current proteomic tools allow large-scale, high-throughput analyses for the detection, identification, and functional investigation of all proteomes. Understanding gene and/or protein expression is the key to unlocking the mechanisms behind microgravity-induced problems and to finding effective countermeasures to spaceflight-induced alterations but also for the study of diseases on earth. Future perspectives are also highlighted.

Unidirectional Photocurrent of Photosystem I on π-System-Modified Graphene Electrodes: Nanobionic Approaches for the Construction of Photobiohybrid Systems

One major vital element of the oxygenic photosynthesis is photosystem I (PSI). We report on the construction of graphene-based nanohybrid light-harvesting architectures consisting of PSI supercomplexes adsorbed onto π-system-modified graphene interfaces. The light-driven nanophotobioelectrochemical architectures have been designed on a modified carbon surface, on the basis of π-π-stacking interactions between polycyclic aromatic compounds and graphene. As a result of the remarkable features of graphene and the feasibility of purposeful surface property adjustment, well-defined photoelectrochemical responses have been displayed by the nanophotohybrid electrodes. In particular, the PSI-graphene electrodes utilizing naphthalene derivatives provided a suitable surface for the adsorption of PSI and display already at the open circuit potential (OCP) a high cathodic photocurrent output of 4.5 ± 0.1 μA/cm(2). By applying an overpotential and addition of a soluble electron acceptor (methyl viologen), the photocurrent density can be further magnified to 20 ± 0.5 μA/cm(2). On the contrary, the investigated anthracene-based PSI-graphene electrodes exhibit considerably smaller and not very directed photoelectrochemical responses. This study grants insights into the influences of different polycyclic aromatic compounds acting as an interface between the very large protein supercomplex PSI and graphene while supporting the electrochemical communication of the biomolecule with the electrode. It needs to be emphasized that solely the naphthalene-based photoelectrodes reveal unidirectional cathodic photocurrents, establishing the feasibility of utilizing this advanced approach for the construction of next-generation photovoltaic devices.

Potential of carbon nanotubes in algal biotechnology

A critical mass of knowledge is emerging on the interactions between plant cells and engineered nanomaterials, revealing the potential of plant nanobiotechnology to promote and support novel solutions for the development of a competitive bioeconomy. This knowledge can foster the adoption of new methodological strategies to empower the large-scale production of biomass from commercially important microalgae. The present review focuses on the potential of carbon nanotubes (CNTs) to enhance photosynthetic performance of microalgae by (i) widening the spectral region available for the energy conversion reactions and (ii) increasing the tolerance of microalgae towards unfavourable conditions occurring in mass production. To this end, current understanding on the mechanisms of uptake and localization of CNTs in plant cells is discussed. The available ecotoxicological data were used in an attempt to assess the feasibility of CNT-based applications in algal biotechnology, by critically correlating the experimental conditions with the observed adverse effects. Furthermore, main structural and physicochemical properties of single- and multi-walled CNTs and common approaches for the functionalization and characterization of CNTs in biological environment are presented. Here, we explore the potential that nanotechnology can offer to enhance functions of algae, paving the way for a more efficient use of photosynthetic algal systems in the sustainable production of energy, biomass and high-value compounds.