Using an innovative pH-stat CO 2 feeding strategy to enhance cell growth and C-phycocyanin production from Spirulina platensis

Phycocyanin from microalgae: A comprehensive review covering microalgal culture, phycocyanin sources and stability

As food safety continues to gain prominence, phycocyanin (PC) is increasingly favored by consumers as a natural blue pigment, which is extracted from microalgae and serves the dual function of promoting health and providing coloration. Spirulina-derived PC demonstrates exceptional stability within temperature ranges below 45 °C and under pH conditions between 5.5 and 6.0. However, its application is limited in scenarios involving high-temperature processing due to its sensitivity to heat and light. This comprehensive review provides insights into the efficient production of PC from microalgae, covers the metabolic engineering of microalgae to increase PC yields and discusses various strategies for enhancing its stability in food applications. In addition to the most widely used Spirulina, some red algae and Thermosynechococcus can serve as good source of PC. The genetic and metabolic manipulation of microalgae strains has shown promise in increasing PC yield and improving its quality. Delivery systems including nanoparticles, hydrogels, emulsions, and microcapsules offer a promising solution to protect and extend the shelf life of PC in food products, ensuring its vibrant color and health-promoting properties are preserved. This review highlights the importance of metabolic engineering, multi-omics applications, and innovative delivery systems in unlocking the full potential of this natural blue pigment in the realm of food applications, provides a complete overview of the entire process from production to commercialization of PC, including the extraction and purification.

Reforming CO2 bio-mitigation utilizing Bacillus cereus from hypersaline realms in pilot-scale bubble column bioreactor

The bubble column reactor of 10 and 20 L capacity was designed to bio-mitigate 10% CO2 (g) with 90% air utilizing thermophilic bacteria (Bacillus cereus SSLMC2). The maximum biomass yield during the growth phase was obtained as 9.14 and 10.78 g L-1 for 10 and 20 L capacity, respectively. The maximum removal efficiency for CO2 (g) was obtained as 56% and 85% for the 10 and 20 L reactors, respectively. The FT-IR and GC-MS examination of the extracellular and intracellular samples identified value-added products such as carboxylic acid, fatty alcohols, and hydrocarbons produced during the process. The total carbon balance for CO2 utilization in different forms confirmed that B. cereus SSLMC2 utilized 1646.54 g C in 10 L and 1587 g of C in 20 L reactor out of 1696.13 g of total carbon feed. The techno-economic assessment established that the capital investment required was $286.21 and $289.08 per reactor run of 11 days and $0.167 and $0.187 per gram of carbon treated for 10 and 20 L reactors, respectively. The possible mechanism pathways for bio-mitigating CO2 (g) by B. cereus SSLMC2 were also presented utilizing the energy reactions. Hence, the work presents the novelty of utilizing thermophilic bacteria and a bubble column bioreactor for CO2 (g) bio-mitigation.

Engineering strategies and applications of cyanobacterial exopolysaccharides: A review on past achievements and recent perspectives

Cyanobacteria are ideally suited for developing sustainable biological products but are underdeveloped due to a lack of genetic tools. Exopolysaccharide (EPS) is one of the essential bioproducts with widespread industrial applications. Despite their unique structural characteristics associated with distinct biological and physicochemical aspects, EPS from cyanobacteria has been underexplored. However, it is expected to accelerate in the near future due to the utilization of low-cost cyanobacterial platforms and readily available information on the structural data and specific features of these biopolymers. In recent years, cyanobacterial EPSs have attracted growing scientific attention due to their simple renewability, rheological characteristics, massive production, and potential uses in several biotechnology domains. This review focuses on the most recent research on potential new EPS producers and their distinct compositions responsible for novel biological activities. Additionally, nutritional and process parameters discovered recently for enhancing EPS production and engineering strategies applied currently to control the biosynthetic pathway for enhanced EPS production are critically highlighted. The process intensification of previously developed EPS extraction and purification processes from cyanobacterial biomass is also extensively explained. Furthermore, the newly reported biotechnological applications of cyanobacterial exopolysaccharides are also discussed.

Circular economy approaches for the production of high-value polysaccharides from microalgal biomass grown on industrial fish processing wastewater: A review

The discharge of high-strength wastewater from the fish-processing industries, comprising undefined blends of toxic and organic compounds, has always been a subject of great disquiet worldwide. Despite a large number of effluent treatment methodologies known to date, biosorption with the aid of naturally grown microalgae has been recognized recently to possess promising outcomes in eradicating pollutants comprising organic compounds from liquid effluents. Interestingly, the microalgal biomass harvested from phytoremediation of fish effluent was identified to be abundant in bio compounds that exhibited potential application in pharmaceutical, nutraceutical, and, aquaculture feed, generating a circular economy. In this context, the focus of the review is to emphasize the applications of microalgal species as naturally occurring and zero-cost adsorbents for the elimination of organic contaminants from fish liquid effluents. The summary of the literature encompassed in this work is supposed to benefit the readers to comprehend the primary mechanisms by which microalgae uptakes the organic matter from fish processing effluents and converts them into various biological molecules. From the scientific works assessed through this review, the most promising microalgae species regards to nutrient uptake and removal efficiency from fish effluent, were identified as Chlorella sp. > Spirulina sp. > Scenedesmus sp. The review further revealed supercritical fluid extraction as the robust extraction tool for the extraction of targeted bioproducts from microalgal biomass grown within fish effluents. Eventually, the information presented through this review establishes phytoremediation using microalgal biomass to be a natural cost-effective, sustainable circular bio-economy approach that could be robustly applied for the efficient treatment of wastewater discharged from food processing industries.

Effects of Culture Conditions on the Performance of Arthrospira platensis and Its Production of Exopolysaccharides

Exopolysaccharides (EPS) produced by Arthrospira platensis (A. platensis) has been widely applied in industry and commerce for its various activities but the accumulation of EPS in culture medium may influence the growth of A. platensis reversely. This work aims to explore the impacts of initial pH, nitrogen source and concentration, phosphate concentration and recycle times of the culture medium on the growth of A. platensis and the secretion of its EPS. The results showed that EPS accumulated with the increase in recycle times of culture medium. The optimal initial pH for the growth of A. platensis was 8.50, and high pH of 11.5 inhibited the growth of biomass while resulting in highest EPS content of 92.87 mg/g DW. Excessive and limited nitrogen (NaNO3 of 25.00 g/L and NaNO3 < 2.50 g/L) and phosphate (K2HPO4 of 5.00 g/L and K2HPO4 < 0.50 g/L) inhibited the biomass production of A. platensis by 1.28−30.77% and 14.29−45.05%, respectively. EPS yield of 97.57 mg/g DW and 40.90 mg/g DW were obtained under NaNO3 of 25.00 g/L and K2HPO4 of 5.00 g/L due to salt stress. These findings are beneficial in providing a theoretical basis for high yield EPS from A. platensis without affecting biomass yield.

Commercial Potential of the Cyanobacterium Arthrospira maxima: Physiological and Biochemical Traits and the Purification of Phycocyanin

Simple Summary

Arthrospira maxima is an unbranched, filamentous cyanobacterium rich in important cellular products such as vitamins, minerals, iron, essential amino acids, essential fatty acids, and protein, which has made it one of the most important commercial photoautotrophs. To optimize the growth conditions for the production of target compounds and to ensure profitability in commercial applications, the effects of pH and temperature were investigated. A. maxima has been shown to be tolerant to a range of pH conditions and to exhibit hyper-accumulation of phycoerythrin and allophycocyanin at low temperatures. These traits may offer significant advantages for future exploitation, especially in outdoor cultivation with fluctuating pH and temperature. Our study also demonstrated a new method for the purification of phycocyanin from A. maxima by using by ultrafiltration, ion-exchange chromatography, and gel filtration, producing PC at 1.0 mg·mL⁻¹ with 97.6% purity.

Abstract

Arthrospira maxima is a natural source of fine chemicals for multiple biotechnological applications. We determined the optimal environmental conditions for A. maxima by measuring its relative growth rate (RGR), pigment yield, and photosynthetic performance under different pH and temperature conditions. RGR was highest at pH 7–9 and 30 °C. Chlorophyll a, phycocyanin, maximal quantum yield (F_v/F_m), relative maximal electron transport rate (rETR_max), and effective quantum yield (Φ_PSII) were highest at pH 7–8 and 25 °C. Interestingly, phycoerythrin and allophycocyanin content was highest at 15 °C, which may be the lowest optimum temperature reported for phycobiliprotein production in the Arthrospira species. A threestep purification of phycocyanin (PC) by ultrafiltration, ion-exchange chromatography, and gel filtration resulted in a 97.6% purity of PC.

Phycocyanin, a super functional ingredient from algae; properties, purification characterization, and applications

Phycocyanins (PCYs) are a group of luxuriant bioactive compounds found in blue-green algae with an estimated global market of about US$250 million within this decade. The multifarious markets of PCYs noted by form (e.g. powder or aqueous forms), by grade (e.g. analytical, cosmetic, or food grades), and by application (such as biomedical, diagnostics, beverages, foods, nutraceuticals and pharmaceuticals), show that the importance of PCYs cannot be undermined. In this comprehensive study, an overview on PCY, its structure, and health-promoting features are diligently discussed. Methods of purification including chromatography, ammonium sulfate precipitation and membrane filtration, as well as characterization and measurement of PCYs are described. PCYs could have many applications in food colorants, fluorescent markers, nanotechnology, nutraceutical and pharmaceutical industries. It is concluded that PCYs offer significant potentials, although more investigations regarding its purity and safety are encouraged.

Isolation of Industrial Important Bioactive Compounds from Microalgae

Microalgae are known as a rich source of bioactive compounds which exhibit different biological activities. Increased demand for sustainable biomass for production of important bioactive components with various potential especially therapeutic applications has resulted in noticeable interest in algae. Utilisation of microalgae in multiple scopes has been growing in various industries ranging from harnessing renewable energy to exploitation of high-value products. The focuses of this review are on production and the use of value-added components obtained from microalgae with current and potential application in the pharmaceutical, nutraceutical, cosmeceutical, energy and agri-food industries, as well as for bioremediation. Moreover, this work discusses the advantage, potential new beneficial strains, applications, limitations, research gaps and future prospect of microalgae in industry.

Microalgae Biomolecules: Extraction, Separation and Purification Methods

Several microalgae species have been exploited due to their great biotechnological potential for the production of a range of biomolecules that can be applied in a large variety of industrial sectors. However, the major challenge of biotechnological processes is to make them economically viable, through the production of commercially valuable compounds. Most of these compounds are accumulated inside the cells, requiring efficient technologies for their extraction, recovery and purification. Recent improvements approaching physicochemical treatments (e.g., supercritical fluid extraction, ultrasound-assisted extraction, pulsed electric fields, among others) and processes without solvents are seeking to establish sustainable and scalable technologies to obtain target products from microalgae with high efficiency and purity. This article reviews the currently available approaches reported in literature, highlighting some examples covering recent granted patents for the microalgae’s components extraction, recovery and purification, at small and large scales, in accordance with the worldwide trend of transition to bio-based products.

A novel CO2 steady feeding based on the pH steady strategy data in the Haematococcus pluvialis cultivation to maximize the cell growth and carbon bio-sequestration

Two common strategies to feed the CO₂ are pH steady (PS) and CO₂ steady (CS). An innovative strategy called ''CSBPS (CS feeding based on PS data)" in comparison to the 0.04% CS, 5% CS, and PS approaches improved the Haematococcus pluvialis growth and carbon bio-sequestration. The optimum concentration of CO₂ was estimated based on the PS cultivation data and fed to culture media using the CS approach with no buffering agent. The biomass productivity, CO₂ bio-fixation rate, and rubisco activity under CSBPS strategy were 127, 121, and 65% higher than 0.04% CS strategy, respectively. The DIC concentration 177-230 (mg/L) and C/N ratio 0.48-0.76 were found promising for cell growth through increasing the rubisco activities under CSBPS strategy by 65, 54 and, 4% higher than 0.04% CS, 5% CS and PS strategies, respectively. The presented strategy provides a promising eco-friendly approach to reduce the CO₂ losses and the production cost.

Extraction Methods for Obtaining Natural Blue Colorants

Background:

Blue is a color not often present in food. Even so, it is especially attractive to children. Today, most blue coloring agents used by the food industry are synthetic. With increasing health issues concern by the scientific community and the general population, there is a trend to look for natural alternatives to most synthetic products. There only exist few natural blue colorants, which are presented in a literature survey, along with the methods currently used for their recovery from natural sources. The best extraction methods and process parameters for the extraction of blue anthocyanins, iridoids and phycocyanin are discussed.

Methods:

A literature survey was conducted to detect the main sources of blue colorants found in nature. The focus was on the extraction methods used to recover such molecules, with the objective of finding efficient and environmentally safe techniques for application at industrial level, and, thus, allowing the production of natural blue colorants at scale high enough for food industry consumption.

Results:

The main natural blue colorants found in literature are anthocyanins, phycocyanin, and genipin. While anthocyanins can be recovered from a variety of plants, the source of phycocyanin are algae, and genipin can be obtained specifically from Gardenia jasminoides Ellis and Genipa americana L. Several extraction techniques have been applied to recover blue colorants from such sources, from classical methods using organic solvents, to more sophisticated technologies as ultrasoundassisted extraction, supercritical fluid extraction, pressurized liquid extraction, high-pressure extraction, and enzyme-assisted extraction.

Conclusion:

There is great potential for anthocyanins, phycocyanin and genipin use as natural food additives with health benefits, besides imparting color. However, the technologies for the colorants recovery and application are not mature enough. Therefore, this area is still developing, and it is necessary to evaluate the economic feasibility of the proposed extraction processes, along with the safety and acceptance of colored food using these additives.

Engineering salt tolerance of photosynthetic cyanobacteria for seawater utilization

Photosynthetic cyanobacteria are capable of utilizing sunlight and CO₂ as sole energy and carbon sources, respectively. With genetically modified cyanobacteria being used as a promising chassis to produce various biofuels and chemicals in recent years, future large-scale cultivation of cyanobacteria would have to be performed in seawater, since freshwater supplies of the earth are very limiting. However, high concentration of salt is known to inhibit the growth of cyanobacteria. This review aims at comparing the mechanisms that different cyanobacteria respond to salt stress, and then summarizing various strategies of developing salt-tolerant cyanobacteria for seawater cultivation, including the utilization of halotolerant cyanobacteria and the engineering of salt-tolerant freshwater cyanobacteria. In addition, the challenges and potential strategies related to further improving salt tolerance in cyanobacteria are also discussed.

A novel two-phase bioprocess for the production of Arthrospira (Spirulina) maxima LJGR1 at pilot plant scale during different seasons and for phycocyanin induction under controlled conditions

A two-phase outdoor cultivation bioprocess for Arthrospira maxima LJGR1 combined with phycocyanin induction in concentrated cultures under controlled conditions was evaluated using a modified low-cost Zarrouk medium. Growth was monitored during 4 cycles in 2018 and 4 cycles in 2019. Biomass was harvested and concentrated using membrane technology at the end of each cycle for further phycocyanin induction using blue LED light (controlled conditions, 24 h). The highest biomass productivity was observed during spring and summer cycles (13.63-18.97 g_DWm^-2 d^-1); during mid-fall and mid-end fall, a decrease was observed (9.93-7.76 g_DWm^-2 d^-1). Under favorable growth conditions, phycocyanin induction was successful. However, during cycles with unfavorable growth condition, phycocyanin induction was not observed. Reactive-grade phycocyanin (3.72 ± 0.14) was recovered and purified using microfiltration and ultrafiltration technologies.

Large-Scale Cultivation of Spirulina for Biological CO2 Mitigation in Open Raceway Ponds Using Purified CO2 From a Coal Chemical Flue Gas

In order to select excellent strains with high CO₂ fixation capability on a large scale, nine Spirulina species were cultivated in columnar photobioreactors with the addition of 10% CO₂. The two species selected (208 and 220) were optimized for pH value, total dissolved inorganic carbon (DIC), and phosphorus content with intermittent CO₂ addition in 4 m² indoor raceway ponds. On the basis of biomass accumulation and CO₂ fixation rate in the present study, the optimum pH, DIC, and phosphate concentration were 9.5, 0.1 mol L^-1, and 200 mg L^-1 for both strains, respectively. Lastly, the two strains selected were semi-continuously cultivated successfully for CO₂ mitigation in 605 m² raceway ponds aerated with food-grade CO₂ purified from a coal chemical flue gas on a large scale. The daily average biomass dry weight of the two stains reached up to 18.7 and 13.2 g m^-2 d^-1, respectively, suggesting the two Spirulina strains can be utilized for mass production.

Multiproduct biorefinery from Arthrospira spp. towards zero waste: Current status and future trends

Considering the high- and low-value product perspectives, Arthrospira spp. are one of the most industrially exploited microalgae. However, currently, the biomass is being utilized for one specific product resulting in a steep upsurge in the overall production cost. Hence, to boost the economic viability of Arthrospira biorefinery process, every high- and low-value products from it ought to be valorized. Envisioning how costlier can be the multiproduct biorefinery concept owing to the downstream processing at an industrial scale, it is quite essential to look for new trends and encouraging solutions. This article intended to propose a sustainable biorefinery in the wake of the current understanding of the present constraints and challenges associated with Arthrospira biorefinery. The current review aimed at defining the future aspects of this biorefinery including integration and optimization of the culture strategy, and, implementation of new ingenious techniques to improve downstream processing (harvesting, extraction, fractionation, and purification).

Real time light intensity based carbon dioxide feeding for high cell-density microalgae cultivation and biodiesel production in a bubble column photobioreactor under outdoor natural sunlight

Outdoor high cell-density microalgae cultivation is highly challenging due to unavailability of appropriate CO₂ feeding strategy under diurnal sunlight intensities. Hence, a novel real time light based CO₂ feeding strategy was firstly developed under diurnal simulated sunlight (LED) to test on Chlorella sp. in a 10 L scale bubble column photobioreactor. The strategy yielded a biomass titer of 5.12 g L^-1 under simulated sunlight, far higher than existing biomass-density and pH-control based CO₂ feeding strategies. In outdoor culturing, the proposed feeding strategy yielded high biomass titers of 6.8 and 9.0 g L^-1 in growth-phase of two-stage and single-stage lipid induction studies respectively with same biomass productivity of 0.8 g L^-1 day^-1. Subsequently, two-stage lipid induction strategy of 6.8 g L^-1 titer yielded biodiesel productivity of 120 g L^-1 day^-1, whereas single-stage strategy of 9.0 g L^-1 titer was unable to induce lipid. Moreover, specific light availability affects the lipid production.

Combining light strategies with recycled medium to enhance the economic feasibility of phycocyanin production with Spirulina platensis

C-phycocyanin (C-PC) produced from Spirulina platensis is of great commercial interest due to its healthcare properties. In this study, light sources and light-dark frequency were manipulated to enhance C-PC productivity of S. platensis. Using white LED resulted in higher C-PC production efficiency when compared to using fluorescent lamps and monochromatic LEDs. Proper adjustment of light-dark efficiency further increased C-PC production efficiency with relatively lower power consumption. In addition, using recycled medium in place of fresh medium proved to be an environmental-friendly and economic strategy for C-PC production with S. platensis. Optimal nitrate supplementation was also employed to improve the C-PC productivity. When grown under optimal culture conditions (i.e., light source, white LED; light-dark frequency, 30:30; recycled medium replacement, 50%; nitrate supplement, 45mM), S. platensis could obtain the highest C-PC content (14.9%) and C-PC productivity (101.1mg/L/d). This performance appears to be superior to that obtained from most related studies.

Ability of an alkali-tolerant mutant strain of the microalga Chlorella sp. AT1 to capture carbon dioxide for increasing carbon dioxide utilization efficiency

An alkali-tolerant Chlorella sp. AT1 mutant strain was screened by NTG mutagenesis. The strain grew well in pH 6-11 media, and the optimal pH for growth was 10. The CO₂ utilization efficiencies of Chlorella sp. AT1 cultured with intermittent 10% CO₂ aeration for 10, 20 and 30min at 3-h intervals were approximately 80, 42 and 30%, respectively. In alkaline medium (pH=11) with intermittent 10% CO₂ aeration for 30min at 3-, 6- and 12-h intervals, the medium pH gradually changed to 10, and the biomass productivities of Chlorella sp. AT1 were 0.987, 0.848 and 0.710gL^-1d^-1, respectively. When Chlorella sp. AT1 was aerated with 10% CO₂ intermittently for 30min at 3-h intervals in semi-continuous cultivation for 21days, the biomass concentration and biomass productivity were 4.35gL^-1 and 0.726gL^-1d^-1, respectively. Our results show that CO₂ utilization efficiency can be markedly increased by intermittent CO₂ aeration and alkaline media as a CO₂-capturing strategy for alkali-tolerant microalga cultivation.