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In cyanobacteria, phycobilisomes serve as peripheral light-harvesting complexes of the two photosystems, extending their antenna size and the wavelength range of photons available for photosynthesis. The abundance of phycobilisomes, the number of phycobiliproteins they contain, and their light-harvesting function are dynamically adjusted in response to the physiological conditions. Phycobilisomes are also thought to be involved in state transitions that maintain the excitation balance between the two photosystems. Unlike its eukaryotic counterpart, PSI is trimeric in many cyanobacterial species and the physiological significance of this is not well understood. Here we compared the composition and light-harvesting function of phycobilisomes in cells of Synechocystis sp. PCC 6803, which has primarily trimeric PSI, and the ΔpsaL mutant unable to form trimers. We also investigated a mutant additionally lacking the PsaJ and PsaF subunits of PSI. Both strains with monomeric PSI accumulated significantly more allophycocyanin per chlorophyll, indicating higher abundance of phycobilisomes. On the other hand, a higher phycocyanin:allophycocyanin ratio in WT suggests larger phycobilisomes or the presence of APC-less phycobilisomes (CpcL-type), that are not assembled in cells with monomeric PSI. Steady-state and time-resolved fluorescence spectroscopy at room temperature and 77 K revealed that PSII receives more energy from the phycobilisomes at the expense of PSI in cells with monomeric PSI, regardless of the presence of PsaF. Taken together, these results show that the oligomeric state of PSI has an impact on the excitation energy flow in Synechocystis.One-sentence summaryCyanobacterial mutants with monomeric PSI show changes in the composition and abundance of phycobilisomes and in the excitation energy transfer to PSII and PSI.

Phycobilisomes in cyanobacteria and red algae are large protein complexes that absorb light and transfer energy for use in photosynthesis. The light energy absorbed by chromophores binding to phycobiliproteins in the peripheral rods can be funneled to the core through chromophores at very high efficiency. The molecular mechanism of excitation energy transfer within a phycobilisome is an example of a higher and unique function in a living organism. However, the mechanism underlying the high efficiency remains unclear. Thus, this study was carried out as a step to resolve this mechanism theoretically. The three-dimensional structure of phycobilisomes containing the linker proteins of the red alga Porphyridium purpureum was determined by cryoelectron microscopy at 2.82 Å resolution in 2020. Using these data, the absorption wavelength of each β82 chromophore in the phycocyanin hexamer located next to the core was calculated using quantum chemical treatment, considering the electric effect from its surrounding phycocyanin proteins and two linker proteins. In addition to unaffected chromophores, chromophores that were redshifted and blueshifted under the electrical influence of the two linker proteins were found. Namely, the chromophore serving as the energy sink in the rod was determined.

Phycobiliproteins are a class of light-harvesting fluorescent proteins existing in cyanobacteria and microalgae, which harvest light and convert it into electricity. Owing to recent demands on environmental-friendly and renewable apparatuses, phycobiliproteins have attracted substantial interest in bioenergy and sustainable devices. However, converting energy from biological materials remains challenging to date. Herein, we report a novel scheme to enhance biological light-harvesting through light-matter interactions at the biointerface of whispering-gallery modes (WGMs), where phycobiliproteins were employed as the active gain material. By exploiting microdroplets as a carrier for light-harvesting biomaterials, strong local electric field enhancement and photon confinement at the cavity interface resulted in significantly enhanced bio-photoelectricity. A threshold-like behavior was discovered in photocurrent enhancement and the WGM modulated fluorescence. Systematic studies of biologically produced photoelectricity and optical mode resonance were carried out to illustrate the impact of the cavity quality factor, structural geometry, and refractive indices. Finally, a biomimetic system was investigated by exploiting cascade energy transfer in phycobiliprotein assembly composed of three light-harvesting proteins. The key findings not only highlight the critical role of optical cavity in light-harvesting but also offer deep insights into light energy coupling in biomaterials. Ministry of Education (MOE) Nanyang Technological University This research is supported by the Ministry of Education Singapore (Tier 1-RG 158/19(S)). We would like to thank Internal Grant NAP SUG -M4082308.040 from NTU.

Currently, the food additive industry has interest in replacing artificial dyes with natural pigments, trying to maintain consumer interest and increase their awareness towards healthy diets. Phycobiliproteins are light-harvesting and water-soluble proteins extracted from cyanobacteria and red algae that can be employed as natural additives. In the present work, a C-phycocyanin extract from the cyanobacterium Arthrospira platensis was tested as blue colorant in beverages to demonstrate that samples containing the protein extract have a color similar to marketed beverages containing synthetic dyes. Using spectroscopy and colorimetry, the extract was characterized and gave evidence of having good properties and good stability in the pH range between 3.0 and 9.0. The staining factors, representing the amount of blue protein needed to reproduce the color of bluish commercial samples, ranged between 15.6 and 111.7 mg·L−1, being sufficiently low in all samples. Additionally, color stability during a short period of cold storage was studied: it demonstrated that isotonic and tonic beverages remained stable throughout the 11-days analysis period with no significant changes. These results prove that the C-phycocyanin extract has potential applications in food as natural colorant, being an alternative option to synthetic coloring molecules.

Linear tetrapyrrole compounds (bilins) are chromophores of the phytochrome and cyanobacteriochrome classes of photosensors and light-harvesting phycobiliproteins. Various spectroscopic techniques, such as resonance Raman, Fourier transform-infrared and nuclear magnetic resonance, have been used to elucidate the structures underlying their remarkable spectral diversity, in which the signals are experimentally assigned to specific structures using isotopically labeled bilin. However, current methods for isotopic labeling of bilins require specialized expertise, time-consuming procedures and/or expensive reagents. To address these shortcomings, we established a method for pressurized liquid extraction of phycocyanobilin (PCB) from the phycobiliprotein powder Lina Blue and also the cyanobacterium Synechocystis sp. PCC 6803 (Synechocystis). PCB was efficiently cleaved in ethanol with three extractions (5 min each) under nitrogen at 125�C and 100 bars. A prewash at 75�C was effective for removing cellular pigments of Synechocystis without PCB cleavage. Liquid chromatography and mass spectrometry suggested that PCB was cleaved in the C3-E (majority) and C3-Z (partial) configurations. 15N- and 13C/15N-labeled PCBs were prepared from Synechocystis cells grown with NaH13CO3 and/or Na15NO3, the concentrations of which were optimized based on cell growth and pigmentation. Extracted PCB was reconstituted with a recombinant apoprotein of the cyanobacteriochrome-class photosensor RcaE. Yield of the photoactive holoprotein was improved by optimization of the expression conditions and cell disruption in the presence of Tween 20. Our method can be applied for the isotopic labeling of other PCB-binding proteins and for the commercial production of non-labeled PCB for food, cosmetic and medical applications.

The paper studies the possibility of bioconversion of waste water from recirculating aquaculture systems (RAS). For this purpose, cyanobacteria Nostoc linckia (Roth.) Born. et Flah. was grown on waste water from RAS. In the process of cultivation, indicators of total mineralization, pH, and culture density were monitored. In the waste water, the content of various forms of nitrogen (NH4+, NO3-, NO2-), the content of P and S before and after the growth of cyanobacteria were determined It was noted that as a result of growing N. linckia in RAS waste water, a decrease in the content of various forms of nitrogen, sulfur and phosphorus is observed. Also, the content of phosphates decreased from 35×10-3 to 5×10-3 mg.L-1 and the content of sulfates from 95×10-3 to 25×10-3 mg.L-1. Moreover, the resulting biomass of cyanobacteria contained 57 % of proteins, 20 % of lipids and 11% of carbohydrates. It was found that N. linckia biomass is a promising source of phycobiliprotein pigments: phycocyanin, allophycocyanin and phycoerythrin.

Phycocyanin is a light-blue water-soluble natural pigment with wide application in fields including pharmaceutical, cosmetic and food industry. Arthrospira platensis is considered a natural bio-factory for obtaining phycocyanin, and although suitable cultivation conditions can enhance the pigment content, the importance of extraction and purification should not be overlooked, because the chemicals used in those steps can affect the quality of phycocyanin. Further, changes in temperature, or approaches used to extract other protein types from biomass, have been reported to degrade phycocyanin, influencing its final quality, while also contributing to higher energy consumption in the extraction process. Hence, this work compares several approaches for phycocyanin extraction, and analyzed the effects of changes in operating conditions, such as exposure time, application of solvent buffer, and ultrasonication, on the extraction yield, the extracts purity, and the process energy use efficiency. Experimental results point to promising improvements in the extraction yield with high purity of phycocyanin (44.24 mg/g with purity ratio of 0.34), when suitable operating parameters were used (2 h exposure to potassium phosphate buffer with 20 min of ultrasonication).

Phycobilisomes (PBS), the major light-harvesting antenna in cyanobacteria, are supramolecular complexes of colorless linkers and heterodimeric, pigment-binding phycobiliproteins. Phycocyanin and phycoerythrin commonly comprise peripheral rods, and a multi-cylindrical core is principally assembled from allophycocyanin (AP). Each AP subunit binds one phycocyanobilin (PCB) chromophore, a linear tetrapyrrole that predominantly absorbs in the orange-red region of the visible spectrum (600–700 nm). AP facilitates excitation energy transfer from PBS peripheral rods or from directly absorbed red light to accessory chlorophylls in the photosystems. Paralogous forms of AP that bind PCB and are capable of absorbing far-red light (FRL; 700–800 nm) have recently been identified in organisms performing two types of photoacclimation: FRL photoacclimation (FaRLiP) and low-light photoacclimation (LoLiP). The FRL-absorbing AP (FRL-AP) from the thermophilic LoLiP strain Synechococcus sp. A1463 was chosen as a platform for site-specific mutagenesis to probe the structural differences between APs that absorb in the visible region and FRL-APs and to identify residues essential for the FRL absorbance phenotype. Conversely, red light-absorbing allophycocyanin-B (AP-B; ~ 670 nm) from the same organism was used as a platform for creating a FRL-AP. We demonstrate that the protein environment immediately surrounding pyrrole ring A of PCB on the alpha subunit is mostly responsible for the FRL absorbance of FRL-APs. We also show that interactions between PCBs bound to alpha and beta subunits of adjacent protomers in trimeric AP complexes are responsible for a large bathochromic shift of about ~ 20 nm and notable sharpening of the long-wavelength absorbance band.

Molecular and microscopic studies were performed to identify Chroococcidiopsis sp., an endolithic cyanobacterium, isolated from gypsum rocks of Atacama Desert (Chile). It was adapted to grow in mineral liquid medium, with 9 mM nitrate, bubbled with CO-enriched air (2.5 % v/v), and continuously illuminated with a white light of 70 μmol photons m s. The obtained biomass (productivity of 0.21 g L d) had a C/N ratio of 6.67, and it contained carbohydrates (45.40 % of dry weight), proteins (36.72 %), lipids (5.60 %) nucleic acids (3.90 %) and ashes (8.28 %). The lipid fraction was particularly rich in palmitic (29.86 % of total fatty acids), linoleic (18.20 %), palmitoleic (12.75 %), linolenic (10.92 %), stearic (9.64 %) and capric acid (6.29 %). Chroococcidiopsis sp. accumulated phycobiliproteins in a light-dependent process and produced 204 mg g, under incident light of 10 μmol photons·m·s, with a relative abundance of 40.9 % for phycocyanin, 23.3 % for phycoerythrin, and 35.8 % for allophycocyanin. The biomass from this cyanobacterium can be a good source of these pigments, especially APC (maximum of 95 mg g dw), which are of interest for pharmacological, cosmetic, and food industries., This work was funded by MCIU/AEI (Spain) and FEDER (UE) (grantreference PGC2018–094076-B-I00) and by a PhD-Grant from the R&DPlan of the University of Huelva, Spain, for Zaida Montero.

Phycocyanin (PC) is one of the phycobiliproteins, pigments found in cyanobacteria, which can be used as natural dyes, antioxidants and fluorescent markers. This study aimed to investigate the effect of supplementation of the basal culture medium (BG110) of the cyanobacterium Anabaena variabilis with different sources of organic carbon in concentration of 1 g?L-1, evaluating the production of biomass and PC. The best condition obtained was the medium supplemented with glucose that produced 75.36 mg?g-1 PC, about 5 times greater than the control with 14.57 mg?g-1 PC. All supplemented media also showed higher biomass production compared to the basal medium, again to stand out for the glucose medium, presenting 0.29 g?L-1 of dry biomass. A ficocianina (FC) é uma das ficobiliproteínas, pigmentos encontrados nas cianobactérias, que podem ser usadas como corantes naturais, antioxidantes e marcadores fluorescentes. Este estudo teve como objetivo investigar o efeito da suplementação do meio de cultura basal (BG110) da cianobactéria Anabaena variabilis com diferentes fontes de carbono orgânico em concentração de 1 g?L-1, de modo a avaliar à produção de biomassa e FC. A melhor condição obtida foi o meio suplementado com glicose que produziu 75,36 mg?g-1 FC, cerca de 5 vezes maior que o controle com 14,57 mg?g-1 FC. Todos os meios suplementados também apresentaram maior produção de biomassa em comparação com o meio basal, novamente para destaque para o meio com glicose, apresentando 0,29 g?L-1 de biomassa seca.

R-phycoerythrin and R-phycocyanin are the main light-harvesting pigment-protein complexes in Pyropia yezoensis. They have bright colors and a high degree of fluorescence, and are now widely used in biomedicine, food, and cosmetic industries. Therefore, membrane chromatography was used to isolate and purify phycobiliprotein from P. yezoensis. Algal cells were disrupted by repeated freeze-thaw cycles. Then ammonium sulfate was added into the crude phycobiliprotein extract, so that the saturation of ammonium sulfate in the solution reached 20%, 30%, and 40% in sequence. At 30% and 40% ammonium sulfate saturation, precipitates of R-phycoerythrin and R-phycocyanin mixture in different proportions were obtained. The precipitates were ultra-filtrated to remove the salt, and then, the retentate was taken for membrane chromatographic treatment. In the membrane chromatographic treatment, salt-sensitive PVDF (polyvinyl difluoride) membranes were used for the follow-up experiments. By adjusting the concentration of ammonium sulfate, the membrane system changed the binding strength of various proteins, and then separated different types of phycobiliproteins. The final products of R-phycoerythrin (Aλmax/A280 purity 4.25, yield 45%) and R-phycocyanin (two purity grades: purity 5.8, yield 14.70% and purity 4.18, yield 39.89%) were obtained and then characterized by spectrophotometric and fluorometric measurements and SDS-PAGE. However, the large-scale production of R-phycocyanin and R-phycoerythrin remains a bottleneck as the column chromatography is difficult to be applied for industrial production. This method avoids the problem of easy clogging of column chromatography and can be useful for mass-production of R-phycoerythrin and R-phycocyanin in the future based on the laboratory results.

Spirulina maxima is a blue-green microalga that rich in pigment. The pigments in S. maxima grouped into primary pigment (Chlorophyll a) and accessory pigments (carotenoid & phycobiliprotein). Phycocyanin is an accessory pigment that belongs to phycobiliprotein, blue colored, and can be used as natural food coloring and drugs. Phycocyanin has activities as antibacterial, antioxidant, anti-inflammatory, antihyperalgesic, and many more. Because of that, phycocyanin usually used in the pharmaceutical industry. However, phycocyanin is a protein that unstable under lights, high temperature, and pH in the storage. This study aims to obtain information about the effect of pH on the stability of phycocyanin extracted from S. maxima that cultivated in indoor and semi-outdoor. The steps are cultivation, extraction using different solutions to get blue pigment phycocyanin, and stability test. Phycocyanin was dissolved in a buffer solution at pH 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, and 7.0 for 7 days. Color observations based on visualization and concentration measurements are carried out every day to see changes in phycocyanin. Growth in indoor cultivation with 24 hours light is faster than semi-outdoor a that uses only sunlight. Cultivation gets the optical density value 0,6 at day 20 with indoor cultivation and day 34 with semi-outdoor cultivation. Results show that phycocyanin can be extracted using a buffer phosphate solution. The stability of the pigments can be seen from the color changes and relative concentration using a spectrophotometer. Phycocyanin shows stable in the storage of pH 4 until pH 5.5. The highest relative concentration (CR) was shown in pH 5.

Cyanobacteria are able to absorb light over a wide spectral range due to the presence of photoreceptors, making it possible to modulate the production of high-value compounds by inducing specific pathways. In order to evaluate the influence of light quality in cyanobacteria metabolism, Cyanobium sp. was grown in five different light conditions, by using low-pressure sodium vapor lamp (SOX) supplemented with low irradiances of green, red, and blue light and UV radiation compared to a control with only SOX. The effects of light supplementation on biomass productivity, photosynthetic activity, biochemical composition, and total antioxidant capacity were evaluated. No changes in biomass productivity were induced by any light supplements. The supplementation of red light triggered the production of lipids, phycocyanin, carotenoids, and total antioxidant compounds, while supplementation of green light increased the content of carbohydrates and chlorophyll a. Thus, supplementation of blue light and UV radiation showed little or no improvements to the culture, whereas under UV radiation the photosynthetic activity was reduced. Overall, Cyanobium sp. is a promising strain, mainly due to its accessibility to metabolism photoregulation as to produce various bioactive compounds. This work was financially co-supported by the COST Action ES1408 European network for algal bioproducts (EUALGAE); by the ZEBRALGRE (PTDC/CVT-WEL/5207/2014), funded by national funds through FCT supported by COMPETE 2020: POCI-01-0145-FEDER-016797; and by the strategical funding from FCT (UIDB/04423/2020 and UIDP/04423/2020) and the Atlantic Interreg Project - Enhance MicroAlgae - High added-value industrial opportunities for microalgae in the Atlantic Area (EAPA_338/2016). We also acknowledge the Junta de Andalucía for financing the RNM295 research group in University of Malaga.

Blue-green microalgae are the source of many commercially important products such as protein, amino acids, fatty acids, carotenoids and phycobiliproteins, and biotechnological studies on this issue has been profoundly increasing.Arthrospira (Spirulina) platensisis the main source of cyanobacterial phycocyanin, used as a natural colorant that is called as "Lina blue" in the commercial area. The purity ratio and quantity of phycocyanin may vary depending on the processing method, also the purity of the phycocyanin is an important factor that determines its application area. Food-grade phycocyanin is utilized safely as a natural dye in the food formulation without offering health risk. Many conventional methods are used in several to obtain crude extracts of C-PC, such as freezing and thawing, sonication and mechanical disruption. Also, for the purification stage high-speed centrifugation, precipitation with ammonium sulphate, and ion-exchange chromatography methods are used. The aim of this study is to investigate the effects of a modified and combined extraction and purification method, including precipitation, chilling and centrifugation, at different centrifuge speeds, temperature and time on phycocyanin concentration to obtain a food grade phycocyanin fromSpirulina platensis. As a result, centrifugation at 25 °C was found the higher purity ratio, above 0.7.

The feasibility of the semi-continuous cultivation of Arthrospira (Spirulina) sp. and Nostoc sp. PCC 7413, using the centrate from the anaerobic digestion of wastewater from a seafood canning industry as a nutrient source, was assessed. Semi-continuous cultures were carried out in aerated tubular culture units of 250 mL by replacing a 10–20% of the volume with the centrate every 2 days. Growth, ammonium, and nitrate removal were monitored, as well as phycobiliprotein and protein production by Arthrospira sp. and released exopolysaccharides production by Nostoc sp. PCC 7413. The ammonium removal efficiency by Arthrospira sp. was 84.9 ± 1.9% in a culture maintained with an ammonium concentration of 11.3 mM. Lower ammonium concentrations (4.9 mM) could be applied to Nostoc sp. PCC 7413, reaching similar relative removal efficiency (84.1%). Taking into account the high ammonium stripping that occurs at the high pH required in Arthrospira sp. cultures, results indicate a better nutrient removal by Nostoc sp., although Arthrospira sp. is more suitable for working at high ammonium concentrations. Since all the ammonium was removed during the first 24 h for both species, much lower residence time could be supported by the cultures. High concentrations of protein (2.5 ± 0.2 mg mL−1), phycobiliprotein (allophycocyanin, 84.3 ± 10.2 mg g−1; phycocyanin, 73.7 ± 7.7 mg g−1) were obtained by Arthrospira sp. cultures. A high concentration of released exopolysaccharides (962.7 ± 26.7 mg L−1) was also obtained for Nostoc sp. PCC 7413 when cultured in the anaerobic centrate. The results indicate the possibility of the use of filamentous cyanobacteria for the treatment of industrial effluents rich in ammonium, with different possibilities of valorization of the biomass produced.

Cyanobacteria are a group of microorganisms that have been studied for pigment production. Among these pigments, phycobiliproteins, especially the phycocyanin (PC), of blue color, are found in grea...

The light-harvesting phycobilisome complex is an important component of photosynthesis in cyanobacteria and red algae. Phycobilisomes are composed of phycobiliproteins, including the blue phycobiliprotein phycocyanin, that are considered high-value products with applications in several industries. Remarkably, several cyanobacteria and red algal species retain the capacity to harvest light and photosynthesise under highly selective environments such as hot springs, and flourish in extremes of pH and elevated temperatures. These thermophilic organisms produce thermostable phycobiliproteins, which have superior qualities much needed for wider adoption of these natural pigment–proteins in the food, textile, and other industries. Here we review the available literature on the thermostability of phycobilisome components from thermophilic species and discuss how a better appreciation of phycobiliproteins from extreme environments will benefit our fundamental understanding of photosynthetic adaptation and could provide a sustainable resource for several industrial processes.

Photosynthesis is an ancient and important chemical reaction process. Under light conditions, plants, algae, and certain bacteria convert solar energy into chemical energy. And then, chemical energy is directly used by living cells. A special light-harvesting pigment protein, phycobiliprotein (PBP), exists in red algae, cyanobacteria (blue-green algae), and some cryptophytes to capture light energy in the water environment. Since the first discovered of PBP, scientists have conducted in-depth research on the structure, function and application of PBP. PBP is a water-soluble protein. It is formed by the covalent connection of apoprotein and phycobilin. According to the spectral characteristics, PBP can be divided into four types: Phycoerythrin (PE), phycocyanin (PC), allophycocyanin (APC) and phycoerythrocyanin (PEC). Through the coordination of four PBPs, more than 95% of the energy can be efficiently transmitted. PE is the beginning of the energy transfer of the PBP system. It is composed of three subunits α, β and γ, and the molecular weight is about 240 kD. Among them, the γ subunit has the function of connecting and stabilizing, so that PE can exist in a stable (αβ) 6γ form. PE can covalently connect chromophores such as phycoerythrobilin (PEB) and phycourobilin (PUB), and has a strong absorption efficiency for short-wavelength blue and green light. It enables red algae and cyanobacteria to efficiently capture and transfer light energy in the deep blue and green light environment. PE is a bright red fluorescent protein. When excited by a specific wavelength, PE will emit strong fluorescence. Food-grade PE can be used as a natural colorant in food, cosmetics and other fields. High-purified PE is combined with proteins such as biotin and monoclonal antibodies to make fluorescent probes for immunodetection and other technologies; PE can also be used as a new photosensitizer for photodynamic therapy of deep tissues. In addition, PE has also been proven to have anti-oxidant and anti-inflammatory biological activities, and has a certain therapeutic effect on Alzheimer’s disease, cancer, diabetes, liver and kidney toxicity and other diseases. But there is no doubt that PE has great potential in the field of biotechnology. The application of PE is closely related to its purity. China’s abundant red algae resources provide a large amount of raw materials for large-scale preparation of PE. However, there are many obstacles in the preparation of high-purified PE. The most commonly used column chromatography has the problem of expansion, while other purification processes are not mature. In view of the above problems, this review highlights an overview on the structure, function and purification process of PE. Then the applications of PE in optical and biological activities are reviewed and prospected. This article provides a reference for the high value processing and application of marine algae.

R-phycoerythrin is a fluorescent red protein-pigment complex present in red algae. It belongs to the light-harvesting phycobiliprotein family with phycocyanin and allophycocyanin, which together make up the phycobilisome. The protein is most commonly used for its fluorescence properties in biochemistry. To determine the highest R-phycoerythrin yielding red algal species, a reliable quantification method is required. Calculating R-phycoerythrin yield from the crude extract’s absorption values has been the quickest and most widely used technique but at the same time, often misleading approach when impurities are present. Small phycoerythrin, which is often present in red algal suspensions, alters the absorption curve and leads to erroneous results. In the given study, we utilized an HPLC-SEC method with fluorescence and photo-diode array detectors, which is capable of separating the phycobiliproteins from interfering compounds. Also, the technique can detect and quantitate R-phycoerythrin yields reliably. A total of nine red algal species from Estonian and Japanese waters were tested, and small phycoerythrin was detected from most of the samples. For two of the tested species, the spectrophotometric quantification methods overestimated the yields by more than 200%.

The cyanobacterium Acaryochloris marina MBIC 11017 (A. marina 11017) possesses chlorophyll d (Chl. d) peaking at 698 nm as photosystem reaction center pigments, instead of chlorophyll a (Chl. a) peaking at 665 nm. About 95% of the total chlorophylls is Chl. d in A. marina 11017. In addition, A. marina 11017 possesses phycobilisome (PBS) supercomplex to harvest orange light and to transfer the absorbing energy to the photosystems. In this context, A. marina 11017 utilizes both far-red and orange light as the photosynthetic energy source. In the present study, we incubated A. marina 11017 cells under monochromatic orange and far-red light conditions and performed transcriptional and morphological studies by RNA-seq analysis and electron microscopy. Cellular absorption spectra, transcriptomic profiles, and microscopic observations demonstrated that PBS was highly accumulated under an orange light condition relative to a far-red light condition. Notably, transcription of one cpcBA operon encoding the phycobiliprotein of the phycocyanin was up-regulated under the orange light condition, but another operon was constitutively expressed under both conditions, indicating functional diversification of these two operons for light harvesting. Taking the other observations into consideration, we could illustrate the photoacclimation processes of A. marina 11017 in response to orange and far-red light conditions in detail.

Cyanobacteria are photosynthesizing prokaryotic microorganisms that stand out by the production of phycobiliproteins, which can be used as therapeutic agents, tools for medical diagnosis and as natural compounds for food coloring and cosmetics. Therefore, in order to purify the most relevant phycobiliproteins [phycocyanin (PC), allophycocyanin (APC) and phycoerythrin (PE)] from Anabaena variabilis and Nostoc sp., an aqueous two-phase system (ATPS) with different proportions of PEG/salt was used. The system was composed by PEG1500 and different salts, including potassium phosphate, sodium citrate and ammonium sulfate. Notably, both strains revealed high concentrations of phycobiliproteins when compared to other studies, highlighting the efficacy of the method. The highest values of the partition coefficient (K) observed in A. variabilis were obtained by 13% (w/w) PEG 14% (w/w) potassium phosphate proportion (KPC = 8.63 KAPC = 5.11 and KPE = 4,94) and for Nostoc sp., 13%PEG/14% sodium citrate proportion (KPC = 17.18, KAPC = 32,65 and KPE = 7.15).

Phycocyanin (PC) is a soluble phycobiliprotein found within the light-harvesting phycobilisome complex of cyanobacteria and red algae, and is considered a high-value product due to its brilliant blue colour and fluorescent properties. However, commercially available PC has a relatively low temperature stability. Thermophilic species produce more thermostable variants of PC, but are challenging and energetically expensive to cultivate. Here, we show that the PC operon from the thermophilic cyanobacterium Thermosynechococcus elongatus BP-1 (cpcBACD) is functional in the mesophile Synechocystis sp. PCC 6803. Expression of cpcBACD in an ‘Olive’ mutant strain of Synechocystis lacking endogenous PC resulted in high yields of thermostable PC (112 ± 1 mg g−1 DW) comparable to that of endogenous PC in wild-type cells. Heterologous PC also improved the growth of the Olive mutant, which was further supported by evidence of a functional interaction with the endogenous allophycocyanin core of the phycobilisome complex. The thermostability properties of the heterologous PC were comparable to those of PC from T. elongatus, and could be purified from the Olive mutant using a low-cost heat treatment method. Finally, we developed a scalable model to calculate the energetic benefits of producing PC from T. elongatus in Synechocystis cultures. Our model showed that the higher yields and lower cultivation temperatures of Synechocystis resulted in a 3.5-fold increase in energy efficiency compared to T. elongatus, indicating that producing thermostable PC in non-native hosts is a cost-effective strategy for scaling to commercial production., Highlights • Synechocystis sp. PCC 6803 was used as a platform to produce thermostable phycocyanin. • Phycocyanin from Thermosynechococcus elongatus BP-1 was expressed at native levels. • Heterologous phycocyanin could transfer energy to the allophycocyanin core in vivo. • A low-cost heat treatment was developed to purify heterologous phycocyanin. • Production of thermotolerant phycocyanin in Synechocystis is more energy efficient.

Phycocyanin from Spirulina platensis (S. Platensis) is a pigment-complex protein belong to the light-harvesting phycobiliprotein family. The pigments have high economic value as a natural blue dye as well as the source of antioxidants and anticancer. Production of pure natural phycocyanin remains in high demand. Therefore, this study aimed to obtain phycocyanin with high purity values using modified liquid biphasic flotation (LBF) system and tested for DPPH (1,1-diphenyl-2-pycrilhydrazil) radical scavenging activity. This study produced high purity phycocyanin with purification fold 3.041 ± 0.04 and recovery yields approximately about 70.881%. Purified phycocyanin showed scavenging activity with IC50 of 338.585 mg/mL. Thus, the LBF system yielded high purity phycocyanin pigments.

Phycobilisomes are light-harvesting antenna complexes of cyanobacteria and red algae that are comprised of chromoproteins called phycobiliproteins. PBS core structures are made up of allophycocyanin subunits. Halomicronema hongdechloris (H. hongdechloris) is one of the cyanobacteria that produce chlorophyll f (Chl f) under far-red light and is regulated by the Far-Red Light Photoacclimation gene cluster. There are five genes encoding APC in this specific gene cluster, and they are responsible for assembling the red-shifted PBS in H. hongdechloris grown under far-red light. In this study, the five apc genes located in the FaRLiP gene cluster were heterologously expressed in an Escherichia coli reconstitution system. The canonical APC-encoding genes were also constructed in the same system for comparison. Additionally, five annotated phycobiliprotein lyase-encoding genes (cpcS) from the H. hongdechloris genome were phylogenetically classified and experimentally tested for their catalytic properties including their contribution to the shifted absorption of PBS. Through analysis of recombinant proteins, we determined that the heterodimer of CpcS-I and CpcU are able to ligate a chromophore to the APC-α/APC-β subunits. We discuss some hypotheses towards understanding the roles of the specialised APC and contributions of PBP lyases.

Phycocyanin (PC) is the principal pigment protein in the light-harvesting antenna of cyanobacteria. Here the biochemical characterization and the 1.51 A crystal structure of PC from cyanobacterium Nostoc sp. WR13 (Nst-PC) is reported. The P63 crystal lattice is composed of the minimal biological entities of Nst-PC, the (αβ)3 trimeric rings. The structure has been refined to R factor 11.5% (Rfree 15.4%) using anisotropic atomic B factors. A phylogenetic study shows that the α and β chains of Nst-PC are significantly clustered in a distinct clade with Acaryochloris marina. The structure was examined to look for any significant differences between Nst-PC and PC from non-desert species. Only minor differences were found in the chromophore microenvironments. The tentative energy transfer pathways in Nst-PC were modeled based on simple structural considerations.

Phycobiliproteins, which include phycocyanin, allophycocyanin and phycoerythrin, are the group of coloured accessory photosynthetic pigments present in cyanobacteria (blue-green algae). Pseudanabaena is a genus of microscopic cyanobacteria, cosmopolitan in distribution and known to be rich in phycoerythrins. Cyanobacteria are photosynthetic organisms, thus, one of the factors that influences their metabolism is the quality and quantity of incident light. In order to determine the production of phycobiliproteins (mainly phycocyanin and phycoerythrin) in this genus, the quantity of these pigments was investigated in two different strains of Pseudanabaena, P. catenata USMAC16 isolated from an Arctic location (Svalbard) and P. amphigranulata USMAC18 from a tropical location (Tasik Harapan, USM, Malaysia). The aims of this study were twofold. First, to determine the influence of different light wavelengths (white, green and red) and exposure duration (photoperiod of 12–24 h (h)) on phycocyanin and phycoerythrin production in the two strains. Second, to compare the production of phycobiliprotein between the two strains. Highest phycocyanin production was obtained under red light, while phycoerythrin production was highest under green light. Highest production was achieved with photoperiod 24:00 h L:D (L: light, D: dark) in the polar strain and 12:12 h L: D in the tropical strain. P. catenata (Arctic strain) was a good producer of phycoerythrin when grown under green light.

UV‐induced synthesis/accumulation of photoprotective pigments and antioxidant activity were investigated in the hot‐spring cyanobacterium Leptolyngbya cf. fragilis. The results indicated that UV radiation may induce biosynthesis of carotenoids, allophycocyanin, phycoerythrin, and scytonemin while phycocyanin degrades in response to longtime UV radiation. Moreover, pigment composition of L. cf. fragilis was significantly altered with increasing UV radiation times, probably due to destruction and resynthesis of accessory pigments as an adaptation strategy to UV stress. The in vitro antioxidant analysis of different extracts of UV treated cyanobacteria exhibited concentration‐dependent antioxidant activity. Ethyl acetate extract of 72 h UV treatment showed maximum total antioxidant activity (IC50 = 71.73 ± 5.3 μg mL⁻¹) followed by ethyl acetate control (non‐UV irradiated) extract (IC50 = 109.43 ± 2.76 μg mL⁻¹). This is the first report for the UV‐induced synthesis of photoprotective pigments and their antioxidant activity in L. cf. fragilis.

Background Phycobiliproteins (PBPs) are light-harvesting protein found in cyanobacteria, red algae and the cryptomonads. They have been widely used as fluorescent labels in cytometry and immunofluorescence analysis. A number of PBPs has been produced in metabolically engineered Escherichia coli. However, the recombinant PBPs are incompletely chromophorylated, and the underlying mechanisms are not clear. Results and discussion In this work, a pathway for SLA-PEB [a fusion protein of streptavidin and allophycocyanin that covalently binds phycoerythrobilin (PEB)] biosynthesis in E. coli was constructed using a single-expression plasmid strategy. Compared with a previous E. coli strain transformed with dual plasmids, the E. coli strain transformed with a single plasmid showed increased plasmid stability and produced SLA-PEB with a higher chromophorylation ratio. To achieve full chromophorylation of SLA-PEB, directed evolution was employed to improve the catalytic performance of lyase CpcS. In addition, the catalytic abilities of heme oxygenases from different cyanobacteria were investigated based on biliverdin IXα and PEB accumulation. Upregulation of the heme biosynthetic pathway genes was also carried out to increase heme availability and PEB biosynthesis in E. coli. Fed-batch fermentation was conducted for the strain V5ALD, which produced recombinant SLA-PEB with a chromophorylation ratio of 96.7%. Conclusion In addition to reporting the highest chromophorylation ratio of recombinant PBPs to date, this work demonstrated strategies for improving the chromophorylation of recombinant protein, especially biliprotein with heme, or its derivatives as a prosthetic group. Electronic supplementary material The online version of this article (10.1186/s12934-019-1100-6) contains supplementary material, which is available to authorized users.

Diverse phycocyanin (PC) extraction and purification methods for cyanobacteria have been reported in literature. A particular method is not applicable to all cyanobacteria and the best method seems to be genus/species specific. Here, we report PC extraction and purification method for the filamentous cyanobacterium Anabaena fertilissima, a hyperproducer of phycobiliproteins. PC was also characterised in terms of unit assembly and stability. PC was extracted by freeze-thawing in distilled water, concentrated by ammonium sulphate fractionation and purified by size exclusion chromatography. The purification process resulted in 5.85-fold increase in PC purity reaching to 3.28. SDS-PAGE of purified PC demonstrated two bands of 19 and 21 kDa. Based on analysis of non-denaturing PAGE, the native PC from this organism is suggested to be a hexamer (αβ)6 of 240 kDa. Lyophilised PC in powder form was more stable compared to PC in the solution. Half-life of dry PC is 110 days when stored at 4 °C in dark. Storage of PC in light at elevated temperature decreased its half life. When added to milk products, PC was stable up to 9 days when stored at 4 °C. Aqueous solution of PC also exhibited significant free radical scavenging activity. The PC from this organism has potential applications in food as a natural pigment and conservative due to its antioxidant properties.

Digital, Phycobiliproteins (PBPs) are a group of brilliant pigment proteins found in cyanobacteria and red algae; their synthesis and accumulation depend on several factors such as the type of strain employed, nutrient concentration, light intensity, light regimes, and others. This study evaluates the effect of macronutrients (citrate buffer, NaNO3, K2HPO4, MgSO4, CaCl2, Na2CO3, and EDTA) and the concentration of trace metals in BG-11 media on the accumulation of PBPs in a thermotolerant strain of Oscillatoria sp. The strain was grown in BG-11 media at 28 °C with a light:dark cycle of 12:12 h at 100 μmol m–2 s–1 for 15 days, and the effect of nutrients was evaluated using a Plackett–Burman Design followed by optimization using a response surface methodology. Results from the concentration of trace metals show that it can be reduced up to half-strength in its initial concentration without affecting both biomass and PBPs. Results from the Plackett–Burman Design revealed that only NaNO3, Na2CO3, and K2HPO4 show a significant increase in PBP production. Optimization employed a central Non-Factorial Response Surface Design with three levels and four factors (34) using NaNO3, Na2CO3, K2HPO4, and trace metals as variables, while the other components of BG-11 media (citrate buffer, MgSO4, CaCl2, and EDTA) were used in half of their initial concentration. Results from the optimization show that interaction between Na2CO3 and K2HPO4 highly increased PBPs’ concentration, with values of 15.21, 3.95, and 1.89 (% w/w), respectively. These results demonstrate that identifying and adjusting the concentration of critical nutrients can increase the concentration of PBPs up to two times for phycocyanin and allophycocyanin while four times for phycoerythrin. Finally, the reduction in non-key nutrients’ concentration will reduce the production costs of colorants at an industrial scale and increase the sustainability of the process., Ingeniería Ambiental