Algal photosynthesis as the primary driver for a sustainable development in energy, feed, and food production

Restoration of mitochondrial function by Spirulina polysaccharide via upregulated SOD2 in aging fibroblasts

Reactive oxygen species (ROS), such as superoxide, are crucial factors involved in the stimulation of cellular aging. Mitochondria, which are important organelles responsible for various metabolic processes in cells, produce ROS. These ROS impair mitochondrial function, thereby accelerating aging-related cellular dysfunction. Herein, we demonstrated that the Spirulina polysaccharide complex (SPC) restores mitochondrial function and collagen production by scavenging superoxide via the upregulation of superoxide dismutase 2 (SOD2) in aging fibroblasts. We observed that SOD2 expression was linked to inflammatory pathways; however, SPC did not upregulate the expression of most inflammatory cytokines produced as a result of induction of LPS in aging fibroblasts, indicating that SPC induces SOD2 without activation of inflammatory pathways. Furthermore, SPC stimulated endoplasmic reticulum (ER) protein folding by upregulating ER chaperones expression. Thus, SPC is proposed to be an antiaging material that rejuvenates aging fibroblasts by increasing their antioxidant potential via the upregulation of SOD2.

Physiological Properties of Photoautotrophic Microalgae and Cyanobacteria Relevant to Industrial Biomass Production

Photoautotrophic mass culture of microalgae is currently under investigation for social implementation, since such organisms are anticipated to be resources of alternative fuels and materials for reducing global warming. Production scale-up of culture systems and economy balance are great barriers for practical usage. In order to develop new culture systems such as attachment on solid surfaces or biofilms, we investigated various characteristics of photosynthesis in Chlorella, not only in liquid but also on filter membranes. In aquatic cultures, the photosynthetic rate was almost the same as the specific exponential growth rate at over 32 °C, suggesting that highly efficient cell growth was achieved at that temperature. The algal cells could fix about 50 mmol carbons per mole photons, at cloudy-day-level light intensities, which result to produce 1.2 g dry cell weight in calculation. Moreover, Chlorella could grow on a membrane surface at almost the same rate as in liquid. Similar tolerance to water deficiency was observed in a cyanobacterium, Synechocystis, in which gene expression responded in 30 min after the stress. Such a tolerance was also observed in other species of microalgae and cyanobacteria in photosynthesis.

Carbon-free production of 2-deoxy-scyllo-inosose (DOI) in cyanobacterium Synechococcus elongatus PCC 7942

Owing to their photosynthetic capabilities, there is increasing interest in utilizing cyanobacteria to convert solar energy into biomass. 2-Deoxy-scyllo-inosose (DOI) is a valuable starting material for the benzene-free synthesis of catechol and other benzenoids. DOI synthase (DOIS) is responsible for the formation of DOI from d-glucose-6-phosphate (G6P) in the biosynthesis of 2-deoxystreptamine-containing aminoglycoside antibiotics such as neomycin and butirosin. DOI fermentation using a recombinant Escherichia coli strain has been reported, although a carbon source is necessary for high-yield DOI production. We constructed DOI-producing cyanobacteria toward carbon-free and sustainable DOI production. A DOIS gene derived from the butirosin producer strain Bacillus circulans (btrC) was introduced and expressed in the cyanobacterium Synechococcus elongatus PCC 7942. We ultimately succeeded in producing 400 mg/L of DOI in S. elongatus without using a carbon source. DOI production by cyanobacteria represents a novel and efficient approach for producing benzenoids from G6P synthesized by photosynthesis.

Selective degradation of the recalcitrant cell wall of Scenedesmus quadricauda CASA CC202

An eco-friendly cell wall digestion strategy was developed to enhance the availability of nutritionally important bio molecules of edible microalgae and exploit them for cloning, transformation, and expression of therapeutic proteins. Microalgae are the source for many nutritionally important bioactive compounds and potential drugs. Even though edible microalgae are rich in nutraceutical, bioavailability of all these molecules is very less due to their rigid recalcitrant cell wall. For example, the cell wall of Scenedesmus quadricauda CASA CC202 is made up of three layers comprising of rigid outer pectin and inner cellulosic layer separated by a thin middle layer. In the present investigation, a comprehensive method has been developed for the selective degradation of S. quadricauda CASA CC202 cell wall, by employing both mechanical and enzymatic treatments. The efficiency of cell wall removal was evaluated by measuring total reducing sugar (TRS), tannic acid-ferric chloride staining, calcoflour white staining, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) analysis. It was confirmed that the yield of TRS increased from 129.82 mg/g in 14 h from pectinase treatment alone to 352.44 mg/g by combined sonication and enzymatic treatment within 12 h. As a result, the combination method was found to be effective for the selective degradation of S. quadricauda CASA CC202 cell wall. This study will form a base for our future works, where this will help to enhance the digestibility and availability of nutraceutically important proteins.

Intracellular spectral recompositioning of light enhances algal photosynthetic efficiency

Diatoms, considered as one of the most diverse and largest groups of algae, can provide the means to reach a sustainable production of petrochemical substitutes and bioactive compounds. However, a prerequisite to achieving this goal is to increase the solar-to-biomass conversion efficiency of photosynthesis, which generally remains less than 5% for most photosynthetic organisms. We have developed and implemented a rapid and effective approach, herein referred to as intracellular spectral recompositioning (ISR) of light, which, through absorption of excess blue light and its intracellular emission in the green spectral band, can improve light utilization. We demonstrate that ISR can be used chemogenically, by using lipophilic fluorophores, or biogenically, through the expression of an enhanced green fluorescent protein (eGFP) in the model diatom Phaeodactylum tricornutum. Engineered P. tricornutum cells expressing eGFP achieved 28% higher efficiency in photosynthesis than the parental strain, along with an increased effective quantum yield and reduced nonphotochemical quenching (NPQ) induction levels under high-light conditions. Further, pond simulator experiments demonstrated that eGFP transformants could outperform their wild-type parental strain by 50% in biomass production rate under simulated outdoor sunlight conditions. Transcriptome analysis identified up-regulation of major photosynthesis genes in the engineered strain in comparison with the wild type, along with down-regulation of NPQ genes involved in light stress response. Our findings provide a proof of concept for a strategy of developing more efficient photosynthetic cell factories to produce algae-based biofuels and bioactive products.

In silico screening for candidate chassis strains of free fatty acid-producing cyanobacteria

BACKGROUND

Finding a source from which high-energy-density biofuels can be derived at an industrial scale has become an urgent challenge for renewable energy production. Some microorganisms can produce free fatty acids (FFA) as precursors towards such high-energy-density biofuels. In particular, photosynthetic cyanobacteria are capable of directly converting carbon dioxide into FFA. However, current engineered strains need several rounds of engineering to reach the level of production of FFA to be commercially viable; thus new chassis strains that require less engineering are needed. Although more than 120 cyanobacterial genomes are sequenced, the natural potential of these strains for FFA production and excretion has not been systematically estimated.

RESULTS

Here we present the FFA SC (FFASC), an in silico screening method that evaluates the potential for FFA production and excretion of cyanobacterial strains based on their proteomes. A literature search allowed for the compilation of 64 proteins, most of which influence FFA production and a few of which affect FFA excretion. The proteins are classified into 49 orthologous groups (OGs) that helped create rules used in the scoring/ranking of algorithms developed to estimate the potential for FFA production and excretion of an organism. Among 125 cyanobacterial strains, FFASC identified 20 candidate chassis strains that rank in their FFA producing and excreting potential above the specifically engineered reference strain, Synechococcus sp. PCC 7002. We further show that the top ranked cyanobacterial strains are unicellular and primarily include Prochlorococcus (order Prochlorales) and marine Synechococcus (order Chroococcales) that cluster phylogenetically. Moreover, two principal categories of enzymes were shown to influence FFA production the most: those ensuring precursor availability for the biosynthesis of lipids, and those involved in handling the oxidative stress associated to FFA synthesis.

CONCLUSION

To our knowledge FFASC is the first in silico method to screen cyanobacteria proteomes for their potential to produce and excrete FFA, as well as the first attempt to parameterize the criteria derived from genetic characteristics that are favorable/non-favorable for this purpose. Thus, FFASC helps focus experimental evaluation only on the most promising cyanobacteria.

Microalgae Cultivation on Anaerobic Digestate of Municipal Wastewater, Sewage Sludge and Agro-Waste

Microalgae are fast-growing photosynthetic organisms which have the potential to be exploited as an alternative source of liquid fuels to meet growing global energy demand. The cultivation of microalgae, however, still needs to be improved in order to reduce the cost of the biomass produced. Among the major costs encountered for algal cultivation are the costs for nutrients such as CO₂, nitrogen and phosphorous. In this work, therefore, different microalgal strains were cultivated using as nutrient sources three different anaerobic digestates deriving from municipal wastewater, sewage sludge or agro-waste treatment plants. In particular, anaerobic digestates deriving from agro-waste or sewage sludge treatment induced a more than 300% increase in lipid production per volume in Chlorella vulgaris cultures grown in a closed photobioreactor, and a strong increase in carotenoid accumulation in different microalgae species. Conversely, a digestate originating from a pilot scale anaerobic upflow sludge blanket (UASB) was used to increase biomass production when added to an artificial nutrient-supplemented medium. The results herein demonstrate the possibility of improving biomass accumulation or lipid production using different anaerobic digestates.

Photobioreactors for microalgal cultures: A Lagrangian model coupling hydrodynamics and kinetics

Closed photobioreactors have to be optimized in terms of light utilization and overall photosynthesis rate. A simple model coupling the hydrodynamics and the photosynthesis kinetics has been proposed to analyze the photosynthesis dynamics due to the continuous shuttle of microalgae between dark and lighted zones of the photobioreactor. Microalgal motion has been described according to a stochastic Lagrangian approach adopting the turbulence model suitable for the photobioreactor configuration (single vs. two-phase flows). Effects of light path, biomass concentration, turbulence level and irradiance have been reported in terms of overall photosynthesis rate. Different irradiation strategies (internal, lateral and rounding) and several photobioreactor configurations (flat, tubular, bubble column, airlift) have been investigated. Photobioreactor configurations and the operating conditions to maximize the photosynthesis rate have been pointed out. Results confirmed and explained the common experimental observation that high concentrated cultures are not photoinhibited at high irradiance level.

Photosynthesis at the forefront of a sustainable life

The development of a sustainable bio-based economy has drawn much attention in recent years, and research to find smart solutions to the many inherent challenges has intensified. In nature, perhaps the best example of an authentic sustainable system is oxygenic photosynthesis. The biochemistry of this intricate process is empowered by solar radiation influx and performed by hierarchically organized complexes composed by photoreceptors, inorganic catalysts, and enzymes which define specific niches for optimizing light-to-energy conversion. The success of this process relies on its capability to exploit the almost inexhaustible reservoirs of sunlight, water, and carbon dioxide to transform photonic energy into chemical energy such as stored in adenosine triphosphate. Oxygenic photosynthesis is responsible for most of the oxygen, fossil fuels, and biomass on our planet. So, even after a few billion years of evolution, this process unceasingly supports life on earth, and probably soon also in outer-space, and inspires the development of enabling technologies for a sustainable global economy and ecosystem. The following review covers some of the major milestones reached in photosynthesis research, each reflecting lasting routes of innovation in agriculture, environmental protection, and clean energy production.

An overview: biomolecules from microalgae for animal feed and aquaculture

Despite being more popular for biofuel, microalgae have gained a lot of attention as a source of biomolecules and biomass for feed purposes. Algae farming can be established using land as well as sea and strategies can be designed in order to gain the products of specific interest in the optimal way. A general overview of the contributions of Algae to meet the requirements of nutrients in animal/aquaculture feed is presented in this study. In addition to its applications in animal/aquaculture feed, algae can produce a number of biomolecules including astaxanthin, lutein, beta-carotene, chlorophyll, phycobiliprotein, Polyunsaturated Fatty Acids (PUFAs), beta-1,3-glucan, and pharmaceutical and nutraceutical compounds which have been reviewed with respect to their commercial importance and current status. The review is further extended to highlight the adequate utilization of value added products in the feeds for livestock, poultry and aquaculture (with emphasis in shrimp farming).

Selection and evaluation of CO2 tolerant indigenous microalga Scenedesmus dimorphus for unsaturated fatty acid rich lipid production under different culture conditions

Five indigenous microalgal strains of Scenedesmus, Chlorococcum, Coelastrum, and Ankistrodesmus genera, isolated from Indian fresh water habitats, were studied for carbon-dioxide tolerance and its effect on growth, lipid and fatty acid profile. Scenedesmus dimorphus strain showed maximum growth (1.5 g/L) and lipid content (17.83% w/w) under CO2 supplementation, hence selected for detailed evaluation. The selected strain was alkaline adapted but tolerated (i) wide range of pH (5-11); (ii) elevated salinity levels (up to 100 mM, NaCl) with low biomass yields and increased carotenoids (19.34 mg/g biomass); (iii) elevated CO2 levels up to 15% v/v with enhancement in specific growth rate (0.137 d(-1)), biomass yield (1.57 g/L), lipid content (19.6% w/w) and CO2 biofixation rate (0.174 g L(-1) d(-1)). Unsaturated fatty acid content (alpha linolenic acid) increased with CO2 supplementation in the strain.

Development of a process for the production of L-amino-acids concentrates from microalgae by enzymatic hydrolysis

A process for the production of l-amino-acids concentrates from microalgae biomass by enzymatic hydrolysis has been developed. The process includes pre-treatment for cell-disruption, enzymatic hydrolysis and final separation by centrifugation. Thermal and mechanical cell-disruption methods have been tested, selecting mechanical disruption using bead milling for 30 min. The enzymatic hydrolysis was done using the commercial enzymes Alcalase and Flavourzyme. Maximum hydrolysis was obtained for biomass concentrations under 270 g/l and previous additional treatment with Viscozyme, reaching a 42% hydrolysis. Repeated reaction steps increased the hydrolysis from 42% (4h) with a single step to 59% (8h) after two successive steps. Further increase of the number of steps had a meagre impact on the global yield. The process widens the portfolio of products that can be obtained from microalgae biomass and is a new possibility to enhance the economic viability of microalgae-based biofuels production processes.

Production of chiral alcohols from prochiral ketones by microalgal photo-biocatalytic asymmetric reduction reaction

Microalgal photo-biocatalysis is a green technique for asymmetric synthesis. Asymmetric reduction of nonnatural prochiral ketones to produce chiral alcohols by microalgal photo-biocatalysis was studied in this work. Acetophenone (ACP) and ethyl acetoacetate (EAA) were chosen as model substrates for aromatic ketones and β-ketoesters, respectively. Two prokaryotic cyanophyta and two eukaryotic chlorophyta were selected as photo-biocatalysts. The results proved that nonnatural prochiral ketones can be reduced by microalgal photo-biocatalysis with high enantioselectivity. Illumination is indispensable to the photo-biocatalysis. For aromatic ketone, cyanophyta are eligible biocatalysts. For ACP asymmetric reduction reaction, about 45% yield and 97% e.e. can be achieved by the photo-biocatalysis reaction with Spirulina platensis as biocatalyst. On the contrary, chlorophyta are efficient biocatalysts for β-ketoester asymmetric reduction reaction among the four tested algae. For EAA asymmetric reduction reaction, about 70% yield and 90% e.e. can be achieved with Scenedesmus obliquus as biocatalyst. The microalgae used in this study outperformed other characterized biocatalysts such as microbial and plant cells.

Reduction of exogenous ketones depends upon NADPH generated photosynthetically in cells of the cyanobacterium Synechococcus PCC 7942

Effective utilization of photosynthetic microorganisms as potential biocatalysts is favorable for the production of useful biomaterials and the reduction of atmospheric CO2. For example, biocatalytic transformations are used in the synthesis of optically active alcohols. We previously found that ketone reduction in cells of the cyanobacterium Synechococcus PCC 7942 is highly enantioselective and remarkably enhanced under light illumination. In this study, the mechanism of light-enhanced ketone reduction was investigated in detail using several inhibitors of photosynthetic electron transport and of enzymes of the Calvin cycle. It is demonstrated that light intensity and photosynthesis inhibitors significantly affect the ketone reduction activity in Synechococcus. This indicates that the reduction correlates well with photosynthetic activity. Moreover, ketone reduction in Synechococcus specifically depends upon NADPH and not NADH. These results also suggest that cyanobacteria have the potential to be utilized as biocatalytic systems for direct usage of light energy in various applications such as syntheses of useful compounds and remediation of environmental pollutants.