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BACKGROUND: Tyrosinase, a copper‐containing metalloenzyme with catalytic activity, is widely found in mammals. It is the key rate‐limiting enzyme that catalyzes melanin synthesis. For humans, tyrosinase is beneficial to the darkening of eyes and hair. However, excessive deposition of melanin in the skin can lead to dull skin color and lead to pigmentation. Therefore, many skin‐whitening compounds have been developed to decrease tyrosinase activity. This study aimed to identify a new tyrosinase inhibitory peptide through enzymatic hydrolysis, in vitro activity verification, molecular docking, and molecular dynamics (MD) simulation. RESULTS: A tripeptide Asp‐Glu‐Arg (DER) was identified, with a '‐CDOCKER_Energy' value of 121.26 Kcal mol−1. DER has effective tyrosinase inhibitory activity. Research shows that its half maximal inhibitory concentration value is 1.04 ± 0.01 mmol L−1. In addition, DER binds to tyrosinase residues His85, His244, His259, and Asn260, which are key residues that drive the interaction between the peptide and tyrosinase. Finally, through MD simulation, the conformational changes and structural stability of the complexes were further explored to verify and supplement the results of molecular docking. CONCLUSION: This experiment shows that DER can effectively inhibit tyrosinase activity. His244, His259, His260, and Asn260 are the critical residues that drive the interaction between the peptide and tyrosinase, and hydrogen bonding is an important force. DER from Spirulina has the potential to develop functional products with tyrosinase inhibition. © 2024 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

The aim of this study was to examine how light intensity and quality affect the photosynthetic apparatus of Cyanidioschyzon merolae cells by modulating the structure and function of phycobilisomes. Cells were grown in equal amounts of white, blue, red, and yellow light of low (LL) and high (HL) intensity. Biochemical characterization, fluorescence emission, and oxygen exchange were used to investigate selected cellular physiological parameters. It was found that the allophycocyanin content was sensitive only to light intensity, whereas the phycocynin content was also sensitive to light quality. Furthermore, the concentration of the PSI core protein was not affected by the intensity or quality of the growth light, but the concentration of the PSII core D1 protein was. Finally, the amount of ATP and ADP was lower in HL than LL. In our opinion, both light intensity and quality are main factors that play an important regulatory role in acclimatization/adaptation of C. merolae to environmental changes, and this is achieved by balancing the amounts of thylakoid membrane and phycobilisome proteins, the energy level, and the photosynthetic and respiratory activity. This understanding contributes to the development of a mix of cultivation techniques and genetic changes for a future large-scale synthesis of desirable biomolecules. [ABSTRACT FROM AUTHOR]

Phycobilisomes, the light‐harvesting complexes of cyanobacteria and red algae, are a resource for photosynthetic, photonic and fluorescence labeling elements. They cover an exceptionally broad spectral range, but the complex superstructure and assembly have been an obstacle. By replacing in Synechocystis sp. PCC 6803 the biliverdin reductases, we studied the role of chromophores in the assembly of the phycobilisome core. Introduction of the green‐absorbing phycoerythrobilin instead of the red‐absorbing phycocyanobilin inhibited aggregation. A novel, trimeric allophycocyanin (Dic‐APC) was obtained. In the small (110 kDa) unit, the two chromophores, phycoerythrobilin and phytochromobilin, cover a wide spectral range (550 to 660 nm). Due to efficient energy transfer, it provides an efficient artificial light‐harvesting element. Dic‐APC was generated in vitro by using the contained core‐linker, LC, for template‐assisted purification and assembly. Labeling the linker provides a method for targeting Dic‐APC. [ABSTRACT FROM AUTHOR]

Some cyanobacteria species have a high capacity for accumulating phycobiliprotein contents in their cells. However, there is a lack of information on screening tropical freshwater cyanobacteria, particularly phycobiliproteins. In addition, it is unclear which characteristics of cyanobacteria (morphological and/or growth) could affect phycobiliprotein contents. This study aimed to screen and characterise Malaysian indigenous freshwater cyanobacteria for the growth, biomass, and pigment contents and determine the major characteristic that contributed to the variation of phycobiliproteins. The surface/volume (S/V) ratio, specific growth rate, biomass productivity, and pigment contents of the isolated cyanobacteria were analysed. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) were applied to distinguish the factor responsible for phycobiliprotein variations in cyanobacteria. For the phycobiliprotein contents, Arthrospira sp., Pseudanabaena sp., and Synechococcus elongatus showed significantly higher (p < 0.05) amounts of cyanobacterial phycocyanin (C-PC), phycoerythrin (C-PE), and allophycocyanin (C-APC), respectively, than other studied cyanobacteria. This study showed no apparent trend of similarity and difference between the unicellular and filamentous cyanobacteria. In addition, carotenoid contents demonstrated a positive correlation with total phycobiliproteins, C-PC and C-APC. Based on the current findings, Arthrospira sp., Pseudanabaena sp. and Synechococcus elongatus might be the promising candidate to be the C-PC, C-PE and C-APC sources, respectively, for commercial production purposes. The selection of optimal cyanobacterial strain is crucial for efficient phycobiliprotein production. This study underlined the potential of freshwater cyanobacteria in producing respective and total phycobiliproteins. Future studies such as the optimization process should be adopted to improve the phycobiliprotein production of these cyanobacteria significantly. [ABSTRACT FROM AUTHOR]

The research in the field of food storage and preservation intensified in recent years to develop alternative preservatives and colorants to chemical ones. The algal preservatives and colorants have emerged as a viable green alternative in this context. The primary food preservatives from the algae are phycobiliproteins (PBPs) and their primary constituents: allophycocyanin (APC), phycocyanin (PC), and phycoerythrin (PE). As the foods have been subjected to the adverse environmental conditions during the production, storage, and utilization stages, it is important to research the determinants of the thermal, acidic, light, and color stability of the PBPs in these adverse environmental conditions such as light and acid exposure as well as elevated and sub-zero temperatures relevant to the food storage. Although there have been around 60 papers published in this research field, there has been no review of the research on the stability of the PBPs in these adverse environmental conditions relevant to the food storage. Hence, this paper reviews the research in this field as a first-ever population study. These studies reveal that these PBPs are stable at a wide range of acid and light exposure, and temperatures, making them perfect for the foods and beverages as a green alternative to chemical preservatives. Furthermore, a wide range of preservatives improve the stability of these PBPs through their close interaction with the PBPs and encapsulation of the PBPs is an efficient way to improve their stability, potentially using the nanotechnology. A couple of recommendations were made for the further research. [ABSTRACT FROM AUTHOR]

Phycocyanin and allophycocyanin are important active substances in Arthrospira platensis, because of their fluorescent characteristic and antioxidant capacity. In order to solve the problem of insufficient production and inconvenient modification of natural protein, recombinant expression was performed and the fluorescence activity and antioxidant activity was analyzed to meet the demand for phycocyanin and allophycocyanin. A total of seven recombinant strains were constructed in this study, including individual phycocyanin or allophycocyanin, co-expression of phycocyanin-allophycocyanin, and their co-expression with chromophore, and the expression strain for individual chromophore. Different molecular weights of phycocyanin and allophycocyanin were detected in the recombinant strains, which indicated the different polymers expressed. Through mass spectrometry identification, phycocyanin and allophycocyanin may form a dimer of 66 kDa and a polymer of 300 kDa. The results of fluorescence detection showed that phycocyanin and allophycocyanin combined with phycocyanobilin to show fluorescence activity. The fluorescence peak of recombinant phycocyanin was mainly concentrated at 640 nm, which was similar to natural phycocyanin, the fluorescence peak of purified recombinant allophycocyanin was at about 642 nm. The fluorescence peak of the co-expressed recombinant phycocyanin-allophycocyanin is located at 640 nm, and the fluorescence intensity is between the recombinant phycocyanin and the recombinant allophycocyanin. After purification, the fluorescence peak of the recombinant phycocyanin is more concentrated and the fluorescence intensity is higher, which is about 1.3 times of recombinant phycocyanin-allophycocyanin, 2.8 times of recombinant allophycocyanin, indicating that phycocyanin may be more suitable to be used as fluorescence probe in medicine. The antioxidant capacity was measured by using total antioxidant capacity (T-AOC) and DPPH (2,2'-diphenyl-1-triphenylhydrazino) free radical scavenging method, and the recombinant phycobiliprotein showed antioxidant activity. Phycocyanobilin also has certain antioxidant activity and could enhance the antioxidant activity of phycobiliprotein to a certain extent. Recombinant phycocyanin-allophycocyanin polymer has stronger T-AOC, which is about 1.17–2.25 times that of the other five recombinant proteins. And recombinant phycocyanin has stronger DPPH antioxidant activity, which is about 1.2–2.5 times that of the other five recombinant proteins. This study laid the foundation for the application of recombinant phycocyanin and allophycocyanin in medical detection and drug development.

The molecular structure of mBDFP, a far‐red fluorescent protein (FPs) derived from an allophycocyanin homolog was resolved to 2.52 Å. Its biliverdin chromophore was found to be attached to the protein in an unusual way that was never observed in natural phycobiliproteins, and only once in a sub‐population of artificial bacteriophytochrome‐derived FPs. One of the biliverdin's vinyl groups had two cysteine residues covalently bound to its two carbon atoms. This reduces the conjugation length of the biliverdin π‐electron system, which shifts the absorption and emission spectra by about 40 nm, from the near‐infrared to the far‐red region of the spectrum. By spectrally characterizing a set of mBDFP mutants, we show that such spectral shifts can be induced by modifying a single residue in either one of two critical positions in the vicinity of the binding cysteines. This changes the reactivity of biliverdin and the cysteine's thiols towards forming one, or two thioether bonds to the vinyl group. The ability to control the spectral properties of BDFP by specific point mutations opens many possibilities for rational design of far‐red and near‐infrared FPs that are of great interest to the development of fluorescence markers for bioimaging since most biological tissues are transparent in this spectral window. PDB Code(s): 6HRK; [ABSTRACT FROM AUTHOR]

Depending upon their growth responses to high and low irradiance, respectively, thermophilic Synechococcus sp. isolates from microbial mats associated with the effluent channels of Mushroom Spring, an alkaline siliceous hot spring in Yellowstone National Park, can be described as either high-light (HL) or low-light (LL) ecotypes. Strains isolated from the bottom of the photic zone grow more rapidly at low irradiance compared to strains isolated from the uppermost layer of the mat, which conversely grow better at high irradiance. The LL-ecotypes develop far-red absorbance and fluorescence emission features after growth in LL. These isolates have a unique gene cluster that encodes a putative cyanobacteriochrome denoted LcyA, a putative sensor histidine kinase; an allophycocyanin (FRL-AP; ApcD4-ApcB3) that absorbs far-red light; and a putative chlorophyll a-binding protein, denoted IsiX, which is homologous to IsiA. The emergence of FRL absorbance in LL-adapted cells of Synechococcus sp. strain A1463 was analyzed in cultures responding to differences in light intensity. The far-red absorbance phenotype arises from expression of a novel antenna complex containing the FRL-AP, ApcD4-ApcB3, which is produced when cells were grown at very low irradiance. Additionally, the two GAF domains of LcyA were shown to bind phycocyanobilin and a [4Fe-4S] cluster, respectively. These ligands potentially enable this photoreceptor to respond to a variety of environmental factors including irradiance, redox potential, and/or oxygen concentration. The products of the gene clusters specific to LL-ecotypes likely facilitate growth in low-light environments through a process called Low-Light Photoacclimation. [ABSTRACT FROM AUTHOR]

Metastasis is a major challenge in aggressive endometrial cancer treatment accounting for the high recurrence risk and poor prognosis of epithelial–mesenchymal transition (EMT), regulated by the transforming growth factor beta (TGFβ) signaling pathway, facilitates tumor metastasis. Spirulina phycocyanin extract (SPE) and its purified products allophycocyanin (APC) and C-phycocyanin (C-PC), derived from Spirulina platensis, can be considered a nutraceutical compound with the ability to inhibit tumor growth and metastasis. Current study aims to investigate the anti-metastatic potential of SPE, and its purified products APC, and C-PC on endometrial cancer both in vitro and in vivo. Firstly, human endometrial cancer cell lines (HEC-1A and Ishikawa) as an in vitro model. Secondly, HEC-1A cells transfected with luminescence gene were implanted into female nude mice as a xenograft model. MTT assay, transwell migration assay, immunoblotting assay, quantitative real-time polymerase chain reaction assay, and IVIS XRMS analysis techniques were used. The in vitro results showed that SPE and its purified products APC and C-PC inhibited cell migration, and altered the expression of EMT-related phenotypes by reversing the TGFβ/SMADs signaling pathway. The in vivo results indicated that SPE repressed the metastasis of HEC-1A-LUC cells through modulating EMT-related markers expression. Overall, SPE and its efficient components APC and C-PC reversed the EMT through targeting the TGFβ/SMADs signaling pathway, suggesting an effective therapeutic strategy for metastatic endometrial cancer.

The aim of this study was to examine how light intensity and quality affect the photosynthetic apparatus of Cyanidioschyzon merolae cells by modulating the structure and function of phycobilisomes. Cells were grown in equal amounts of white, blue, red, and yellow light of low (LL) and high (HL) intensity. Biochemical characterization, fluorescence emission, and oxygen exchange were used to investigate selected cellular physiological parameters. It was found that the allophycocyanin content was sensitive only to light intensity, whereas the phycocynin content was also sensitive to light quality. Furthermore, the concentration of the PSI core protein was not affected by the intensity or quality of the growth light, but the concentration of the PSII core D1 protein was. Finally, the amount of ATP and ADP was lower in HL than LL. In our opinion, both light intensity and quality are main factors that play an important regulatory role in acclimatization/adaptation of C. merolae to environmental changes, and this is achieved by balancing the amounts of thylakoid membrane and phycobilisome proteins, the energy level, and the photosynthetic and respiratory activity. This understanding contributes to the development of a mix of cultivation techniques and genetic changes for a future large-scale synthesis of desirable biomolecules.

The present study evaluated the effect of multiple variables (drying time, drying temperature, biomass/solvent ratio, glass beads/biomass ratio, extraction time, and extraction speed) in the solubilization of three different phycobiliproteins (C-PC, APC, and PE) from a thermotolerant Oscillatoria sp. The strain was grown in BG11 media (28 °C, light: dark cycle of 12:12 h at 100 µmol·m−2·s−1, 20 days) and the experiments were conducted according to a two-level randomized factorial design with six center points (38 runs). Results show that biomass/solvent ratio, glass beads/biomass ratio, and extraction time, are the most significant variables in the extraction of all three proteins, whereas the glass beads/biomass ratio and extraction time significantly affect their purity. The optimized conditions allow a statistical increase in the concentration of C-PC, APC, and PE extracted from the biomass; however, the purity was lower in comparison with the expected value. The latter occurs due to a larger biomass/solvent ratio and longer extraction times, which enhanced the solubility of other hydrophilic metabolites (proteins and carbohydrates, etc.). [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The loss of density and elasticity, the appearance of wrinkles and hyperpigmentation are among the first noticeable signs of skin aging. Beyond UV radiation and oxidative stress, matrix metalloproteinases (MMPs) assume a preponderant role in the process, since their deregulation results in the degradation of most extracellular matrix components. In this survey, four cyanobacteria strains were explored for their capacity to produce secondary metabolites with biotechnological potential for use in anti-aging formulations. Leptolyngbya boryana LEGE 15486 and Cephalothrix lacustris LEGE 15493 from freshwater ecosystems, and Leptolyngbya cf. ectocarpi LEGE 11479 and Nodosilinea nodulosa LEGE 06104 from marine habitats were sequentially extracted with acetone and water, and extracts were analyzed for their toxicity in cell lines with key roles in the skin context (HaCAT, 3T3L1, and hCMEC). The non-toxic extracts were chemically characterized in terms of proteins, carotenoids, phenols, and chlorophyll a, and their anti-aging potential was explored through their ability to scavenge the physiological free radical superoxide anion radical (O2•−), to reduce the activity of the MMPs elastase and hyaluronidase, to inhibit tyrosinase and thus avoid melanin production, and to block UV-B radiation (sun protection factor, SPF). Leptolyngbya species stood out for anti-aging purposes: L. boryana LEGE 15486 presented a remarkable SPF of 19 (at 200 µg/mL), being among the best species regarding O2•− scavenging, (IC50 = 99.50 µg/mL) and also being able to inhibit tyrosinase (IC25 = 784 µg/mL), proving to be promising against UV-induced skin-aging; L. ectocarpi LEGE 11479 was more efficient in inhibiting MMPs (hyaluronidase, IC50 = 863 µg/mL; elastase, IC50 = 391 µg/mL), thus being the choice to retard dermal density loss. Principal component analysis (PCA) of the data allowed the grouping of extracts into three groups, according to their chemical composition; the correlation of carotenoids and chlorophyll a with MMPs activity (p < 0.01), O2•− scavenging with phenolic compounds (p < 0.01), and phycocyanin and allophycocyanin with SPF, pointing to these compounds in particular as responsible for UV-B blockage. This original survey explores, for the first time, the biotechnological potential of these cyanobacteria strains in the field of skin aging, demonstrating the promising, innovative, and multifactorial nature of these microorganisms. [ABSTRACT FROM AUTHOR]

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.

Far-red and near-infrared fluorescent proteins have regions of maximum transmission in most tissues and can be widely used as fluorescent biomarkers. We report that fluorescent phycobiliproteins originating from the phycobilisome core subunit ApcF2 can covalently bind biliverdin, named BDFPs. To further improve BDFPs, we conducted a series of studies. Firstly, we mutated K53Q and T144A of BDFPs to increase their effective brightness up to 190 % in vivo. Secondly, by homochromatic tandem fusion of high-brightness BDFPs to achieve monomerization, which increases the effective brightness by up to 180 % in vivo, and can effectively improve the labeling effect. By combining the above two approaches, the brightness of the tandem BDFPs was much improved compared with that of the previously reported fluorescent proteins in a similar spectral range. The tandem BDFPs were expressed stably while maintaining fluorescence in mammalian cells and Caenorhabditis elegans. They were also photostable and resistant to high temperature, low pH, and chemical denaturation. The tandem BDFPs advantages were proved in applications as biomarkers for imaging in super-resolution microscopy., (© 2024 Wiley-VCH GmbH.)

SUMMARY: The phycobilisomes (PBSs) of cyanobacteria and red‐algae are unique megadaltons light‐harvesting protein‐pigment complexes that utilize bilin derivatives for light absorption and energy transfer. Recently, the high‐resolution molecular structures of red‐algal PBSs revealed how the multi‐domain core‐membrane linker (LCM) specifically organizes the allophycocyanin subunits in the PBS's core. But, the topology of LCM in these structures was different than that suggested for cyanobacterial PBSs based on lower‐resolution structures. Particularly, the model for cyanobacteria assumed that the Arm2 domain of LCM connects the two basal allophycocyanin cylinders, whereas the red‐algal PBS structures revealed that Arm2 is partly buried in the core of one basal cylinder and connects it to the top cylinder. Here, we show by biochemical analysis of mutations in the apcE gene that encodes LCM, that the cyanobacterial and red‐algal LCM topologies are actually the same. We found that removing the top cylinder linker domain in LCM splits the PBS core longitudinally into two separate basal cylinders. Deleting either all or part of the helix‐loop‐helix domain at the N‐terminal end of Arm2, disassembled the basal cylinders and resulted in degradation of the part containing the terminal emitter, ApcD. Deleting the following 30 amino‐acids loop severely affected the assembly of the basal cylinders, but further deletion of the amino‐acids at the C‐terminal half of Arm2 had only minor effects on this assembly. Altogether, the biochemical data are consistent with the red‐algal LCM topology, suggesting that the PBS cores in cyanobacteria and red‐algae assemble in the same way. [ABSTRACT FROM AUTHOR]

Cyanobacteria harvest light by using architecturally complex, soluble, light-harvesting complexes known as phycobilisomes (PBSs). PBS diversity includes specialized subunit paralogs that are tuned to specific regions of the light spectrum; some cyanobacterial lineages can even absorb far-red light. In a recent issue of the Journal of Biological Chemistry, Gisriel et al. reported the cryo-electron microscopic structure of a far-red PBS core, showing how bilin binding in the α-subunits of allophycocyanin paralogs can modify the bilin-binding site to red shift the absorbance spectrum. This work helps explain how cyanobacteria can grow in environments where most of the visible light has been filtered out., Competing Interests: Conflict of interest The author declares no conflicts of interest with the contents of this article., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

C-phycocyanin (C-PC), allophycocyanin (APC) and carbonic anhydrase (CA) are intracellular bioproducts produced by Spirulina platensis LEB-52. In order to extract them, a cell rupture step is required. The influence of extraction time on ultrasound-assisted extraction (UAE) was evaluated at two biomass concentrations (0.2 and 23 g/L). At biomass concentration of 0.2 g/L, 12-min UAE was sufficient to simultaneously obtain phycobiliproteins (C-PC and APC) and esterase-expressed CA. Enzyme activity of hydratase-expressed CA in cyanobacteria is very low. Therefore, to determine the activity of hydratase-expressed CA, biomass concentration of 23 g/L and 8-min extraction time were needed. UAE is an efficient method of rapid determination of phycobiliproteins in wet biomass, even though it is not a selective method which extracts an array of contaminants from biomass.

Cyanobacteria are gram-negative photosynthetic organisms and one of the most successful groups of organisms this planet has ever seen. They include some of the first life forms to evolve on Earth. During their long evolutionary history, cyanobacteria have undergone functional modifications, and these are responsible for their versatile physiology and wide ecological tolerance. The ability of cyanobacteria to tolerate high temperature, UV radiation, desiccation, and water and salt stresses contributes to their competitive success in a wide range of environments. Various species of cyanobacteria utilize different combinations of chromophores and phycobiliproteins to optimize their light-harvesting capabilities for photosynthesis. Phycobilisomes serve as the primary light-harvesting antennae for photosystem II in cyanobacteria and red algae. The aim of this research was to investigate phycobiliproteins in isolated heterocystous cyanobacteria from paddy fields in western Mazandaran. After collecting soil samples, cyanobacteria cultures were cultivated on a typical BG110. In addition to purification process, there were repeated sub-culturing on the solidified and liquid medium before the strains were characterized morphologically. Results indicated that because of adaptation of strains under accessible light condition, different species of cyanobacteria employ a high diversity of phycobiliprotein to optimize their light harvesting process in photosynthesis. Moreover, significant differences in the amounts of phycocyanin, allophycocyanin, and phycoerythrin were observed in various species. Maximum level of these protein compounds belonged to MGCY372 (Plectonema boryanum).

• Endolithic Chroococcidiopsis sp. can grow autotrophically in a minimum mineral medium. • Dry biomass contains 45 % carbohydrates, 36 % proteins and 6 % lipids. • It presents an unusual high content of capric (6.29 %) and palmitoleic (12.75 %) fatty acids. • The cells accumulate phycobiliproteins (204 mg g dw−1) at low light intensity. • Chroococcidiopsis sp. accumulates high APC content (95.0 mg g dw−1). 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 2 -enriched air (2.5 % v/v), and continuously illuminated with a white light of 70 μmol photons m–2 s–1. The obtained biomass (productivity of 0.21 g L–1 d–1) 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–1, under incident light of 10 μmol photons·m–2·s–1, 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−1), which are of interest for pharmacological, cosmetic, and food industries. [ABSTRACT FROM AUTHOR]

Phycobiliproteins (PBPs) are pigment proteins that comprise phycobilisomes (PBS), major light-harvesting antenna complexes of cyanobacteria and red algae. PBS core substructures are made up of allophycocyanins (APs), a subfamily of PBPs. Five paralogous AP subunits are encoded by the Far-Red Light Photoacclimation (FaRLiP) gene cluster, which is transcriptionally activated in cells grown in far-red light (FRL; λ = 700 to 800 nm). FaRLiP gene expression enables some terrestrial cyanobacteria to remodel their PBS and photosystems and perform oxygenic photosynthesis in far-red light (FRL). Paralogous AP genes encoding a putative, FRL-absorbing AP (FRL-AP) are also found in an operon associated with improved low-light growth (LL; < 50 μmol photons m–2 s–1) in some thermophilic Synechococcus spp., a phenomenon termed low-light photoacclimation (LoLiP). In this study, apc genes from FaRLiP and LoLiP gene clusters were heterologously expressed individually and in combinations in Escherichia coli. The resulting novel FRL-APs were characterized and identified as major contributors to the FRL absorbance observed in whole cells after FaRLiP and potentially LoLiP. Post-translational modifications of native FRL-APs from FaRLiP cyanobacterium, Leptolyngbya sp. strain JSC-1, were analyzed by mass spectrometry. The PBP complexes made in two FaRLiP organisms were compared, revealing strain-specific diversity in the FaRLiP responses of cyanobacteria. Through analyses of native and recombinant proteins, we improved our understanding of how different cyanobacterial strains utilize specialized APs to acclimate to FRL and LL. We discuss some insights into structural changes that may allow these APs to absorb longer light wavelengths than their visible-light-absorbing paralogs. [ABSTRACT FROM AUTHOR]

Allophycocyanin (APC) is a pigment-protein with optical activity in the core of phycobilisomes of cyanobacteria and red algae. Its wide application prospects make it necessary to carry out the recombinant expression of allophycocyanin with optical activity. In this study, apcA and apcB genes encoding two subunits of allophycocyanin were cloned from Gracilariopsis lemaneiformis. Then apcA and apcB genes expressed in Escherichia coli to obtain allophycocyanin. In order to investigate the active sites of allophycocyanin to bind with phycocyanobilin, the Cys-81 and Cys-138 of α subunit and Cys-81 and Cys-157 of β subunit were mutated. SDS-PAGE and Western blotting results verified the expression of allophycocyanin. The fluorescence emission spectra showed the characteristic fluorescence peak of allophycocyanin, which indicated that the recombinant allophycocyanin had optical activity. The recombinant strains with chromophore lyases—CpcU and CpcS—had the higher fluorescence emission peak, indicating that chromophore lyases would catalyze the combination of phycocyanobilin and apo-allophycocyanin more effectively. The binding sites were Cys-81 and Cys138 of allophycocyanin α subunit, and Cys-81 and Cys-157 of allophycocyanin β subunit. The catalytic effect of CpeT was not obvious. This research provides an experimental foundation for understanding the synthesis mechanism of optically active allophycocyanin in G. lemaneiformis. [ABSTRACT FROM AUTHOR]

The allophycocyanin (APC) protein purified from Phormidium sp. A09DM was investigated for its in vivo antioxidant and anti-aging potential in Caenorhabditis elegans. An increased mean lifespan of APC-treated (100 μg/ml) worms (wild type) were observed from 16 ± 0.2 days (control) to 20 ± 0.1 days (treated). APC-treated worms also showed improved physiological marker of aging such as the rate of pharyngeal pumping and higher rate of survival against oxidative and thermal stress. Furthermore, APC was found to moderate the expression of human amyloid beta (Aβ1–42) as well as associated Aβ-induced paralysis in the transgenic C. elegans CL4176 upon increase in temperature. Furthermore, RNA interference (RNAi)-mediated studies revealed the dependence of downstream regulator daf-16, independent of stress-induced resistance gene skn-1 in the APC treated C. elegans. In the present study, we tried to demonstrate the anti-aging activity, longevity and protective effects of APC against cellular stress in C. elegans, which can lead to the use of this biomolecule in drug development for age-related disorders. [ABSTRACT FROM AUTHOR]

Excitation energy transfer (EET) and trapping in Anabaena variabilis (PCC 7120) intact cells, isolated phycobilisomes (PBS) and photosystem I (PSI) complexes have been studied by picosecond time-resolved fluorescence spectroscopy at room temperature. Global analysis of the time-resolved fluorescence kinetics revealed two lifetimes of spectral equilibration in the isolated PBS, 30–35 ps and 110–130 ps, assigned primarily to energy transfer within the rods and between the rods and the allophycocyanin core, respectively. An additional intrinsic kinetic component with a lifetime of 500–700 ps was found, representing non-radiative decay or energy transfer in the core. Isolated tetrameric PSI complexes exhibited biexponential fluorescence decay kinetics with lifetimes of about 10 ps and 40 ps, representing equilibration between the bulk antenna chlorophylls with low-energy "red" states and trapping of the equilibrated excitations, respectively. The cascade of EET in the PBS and in PSI could be resolved in intact filaments as well. Virtually all energy absorbed by the PBS was transferred to the photosystems on a timescale of 180–190 ps. [ABSTRACT FROM AUTHOR]

Far-red light photoacclimation, or FaRLiP, is a facultative response exhibited by some cyanobacteria that allows them to absorb and utilize lower energy light (700-800 nm) than the wavelengths typically used for oxygenic photosynthesis (400-700 nm). During this process, three essential components of the photosynthetic apparatus are altered: photosystem I, photosystem II, and the phycobilisome. In all three cases, at least some of the chromophores found in these pigment-protein complexes are replaced by chromophores that have red-shifted absorbance relative to the analogous complexes produced in visible light. Recent structural and spectroscopic studies have elucidated important features of the two photosystems when altered to absorb and utilize far-red light, but much less is understood about the modified phycobiliproteins made during FaRLiP. We used single-particle, cryo-EM to determine the molecular structure of a phycobiliprotein core complex comprising allophycocyanin variants that absorb far-red light during FaRLiP in the marine cyanobacterium Synechococcus sp. PCC 7335. The structure reveals the arrangement of the numerous red-shifted allophycocyanin variants and the probable locations of the chromophores that serve as the terminal emitters in this complex. It also suggests how energy is transferred to the photosystem II complexes produced during FaRLiP. The structure additionally allows comparisons with other previously studied allophycocyanins to gain insights into how phycocyanobilin chromophores can be tuned to absorb far-red light. These studies provide new insights into how far-red light is harvested and utilized during FaRLiP, a widespread cyanobacterial photoacclimation mechanism., Competing Interests: Conflict of interest The authors declare that they have no conflicts of interest with the contents of this article., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Blue green alga Spirulina platensis was subjected to different concentrations of NaCl, i.e. (0.1, 0.5, 5 and 10g/l) by using 1g/l (as stock salt) that considered to be the control of the experiments according to their concentration in Zarrouk medium, in order to study the effect of NaCl concentrations on the photosynthesis pigments which are chlorophyll a, chlorophyll b, total chlorophyll, carotenoids, phycocyanin, allophycocyanin and phycobiliproteins. Sodium chloride caused different effects on photosynthetic pigments of the studied algae. In 10g/l NaCl, the maximum reduction of chlorophyll a, chlorophyll b, and total chlorophyll were 2.540, 0.808, and 3.349mg/1, respectively, while maximum reduction of phycocyanin, allophycocynin, and phycobiliproteins were 0.303, 0.232, and 0.535mg/1, respectively. Moreover, carotenoids induced to reach 1.182mg/l in 10g/l NaCl. Rising NaCl concentration up to 5 and 10g/l caused the induction of carotenoids as well as the inhibition of chlorophyll a, chlorophyll b, total chlorophyll, phycocyanin, allophycocyanin and phycobiliproteins and vice versa happen when NaCl concentration decreased to 0.1 and 0.5g/l. [ABSTRACT FROM AUTHOR]

Abstract Biliproteins have extended the spectral range of fluorescent proteins into the near-infrared region (NIR, 700–770 nm) of maximal transmission of most tissues and are also favorable for multiplex labeling. Their application, however, presents considerable challenges to increase their stability under physiological conditions and, in particular, to increase their brightness while maintaining the emission in near-infrared regions: their fluorescence yield generally decreases with increasing wavelengths, and their effective brightness depends strongly on the environmental conditions. We report a fluorescent biliprotein triad, termed BDFP1.1:3.1:1.1, that combines a large red-shift (722 nm) with high brightness in mammalian cells and high stability under changing environmental conditions. It is fused from derivatives of the phycobilisome core subunits, ApcE2 and ApcF2. These two subunits are induced by far-red light (FR, 650–700 nm) in FR acclimated cyanobacteria. Two BDFP1.1 domains engineered from ApcF2 covalently bind biliverdin that is accessible in most cells. The soluble BDFP3 domain, engineered from ApcE2, binds phytochromobilin non-covalently, generating BDFP3.1. This phytochromobilin chromophore was added externally; it is readily generated by an improved synthesis in E. coli and subsequent extraction. Excitation energy absorbed in the FR by covalently bound biliverdins in the two BDFP1.1 domains is transferred via fluorescence resonance energy transfer to the non-covalently bound phytochromobilin in the BDFP3.1 domain fluorescing in the NIR around 720 nm. Labeling of a variety of proteins by fusion to the biliprotein triad is demonstrated in prokaryotic and mammalian cells, including human cell lines. Highlights • A near-infrared fluorescent biliprotein triad (BDFP1.1:3.1:1.1, λ Fmax ~ 722 nm) is reported. • The triad is 2.7-fold brighter than the known brightest near-infrared fluorescent biliprotein, iRFP720. • Labeling using the triad is demonstrated in prokaryotic and mammalian cells. • A method for conveniently isolating phytochromobilin for the labeling is established. [ABSTRACT FROM AUTHOR]

Abstract Phycobiliproteins are natural additives in food industry and essential fluorescent probes in biotechnology. Various algal species may be suitable for their extraction, therefore, it is important to study different seaweeds to determine the highest-yielding species. Furcellaria lumbricalis , a red algal species primarily harvested from Canadian, Danish and Estonian waters, has been utilized for merely furcellaran extraction in Estonia on a commercial scale for over 50 years. To further valorize the bioresource it is vital to study whether additional products, such as phycobiliproteins, can be extracted. In the given study, optimal phycobiliprotein extraction conditions from F. lumbricalis were determined for the first time. For quantification, a novel high-pressure liquid chromatography method with fluorescence and photodiode array detection was developed. Considering R-phycoerythrin, citrate pH 6 buffer gave the highest yields (0.13% using fluorescence detector and 0.43% using photodiode array detector) after an extraction for 24 h at 20 °C. Different enzymes (cellulases, xylanases, galactosidases) and their combinations, lowering the extraction temperature or ultrasonication increased the yield further. In addition, red-coloured low-molecular fraction (with similar absorption characteristics to R-phycoerythrin) was separated. For allophycocyanin phosphate pH 6 buffer gave slightly higher yield (0.09% using fluorescence detector and 0.12% using photodiode array detector), compared to citrate or acetate buffer at the same pH. However, the tested enzyme combination, temperature variation and ultrasonication were not so advantageous for allophyocyanin recovery. The phycocyanin concentration from the red algae was below the limit of detection. Graphical abstract Unlabelled Image Highlights • Chromatography method with fluorescence and photodiode array detectors was developed. • Buffers at pH 6 give higher phycobiliprotein yields from Furcellaria lumbricalis. • Yields are increased at lower temperatures and with enzymolysis or ultrasonication. • Low molecular-weight fraction with akin absorption to phycoerythrin was obtained. • Phycocyanin is not detected in Furcellaria lumbricalis with the tested criteria. [ABSTRACT FROM AUTHOR]

Fusion protein of streptavidin and allophycocyanin holo-α subunit (ApcA) is fluorescent and is able to bind biotin. This fusion protein (SLA) can be used as fluorescent label in immunofluorescence assay. In this study, one or two repeats of ApcA were fused to the protein SLA, with the aim to improve its brightness. The fusion proteins SLA2 (two repeats of ApcA) and SLA3 (three repeats of ApcA), together with lyase (cpcS) and phycoerythrobilin synthesizing enzymes (Ho1 and PebS), were co-expressed in Escherichia coli. These fusion proteins were purified by affinity chromatography. While SLA2 and SLA3 shared similar absorbance spectra, fluorescence spectra and biotin-binding activities with SLA, their brightness were much higher than that of SLA. When used as fluorescent labels in immunofluorescence assay, SLA2 and SLA3 showed higher detection sensitivity than SLA. These results suggested that SLA2 and SLA3 were the preferable fluorescent labels in immunofluorescence assays. [ABSTRACT FROM AUTHOR]

Arthrospira platensis (spirulina) is a cyanobacterium, which contains mainly two phycobiliproteins (PBP), i.e., C-phycocyanin (C-PC) and allophycocyanin (APC). In this study, PBP were hydrolyzed using trypsin, and the composition of the hydrolysate was characterized by HPLC-ESI-MS/MS. Furthermore, the potential anti-diabetic activity was assessed by using either biochemical or cellular techniques. Findings suggest that PBP peptides inhibit DPP-IV activity in vitro with a dose-response trend and an IC50 value falling in the range between 0.5 and 1.0 mg/mL. A lower inhibition of the DPP-IV activity expressed by Caco-2 cells was observed, which was explained by a secondary metabolic degradation exerted by the same cells.

Abstract—: A method using chromatography on DEAE-Toyopearl 650M was developed for the simultaneous extraction of water-soluble chromoproteins from Arthrospira platensis cyanobacteria cells. These chromoproteins were C-phycocyanin, allophycocyanin, and carotenoid- and chlorophyll-binding proteins. The purity of the isolated C-phycocyanin was 4.42 (A620/A280). The allophycocyanin purity was 3.40 (A652/A280). The phycocyanin purity was confirmed by the presence of only two bands obtained during SDS-PAGE: α-subunit (17 kDa) and β-subunit (18 kDa). The isolated carotenoid- and chlorophyll-binding proteins were analyzed by high-performance exclusion chromatography on TSK-GEL 2000SW (XL) with detection at three wavelengths (280, 480, and 678 nm). The spectral, chromatographic, and electrophoretic analyses of chromoproteins, as well as pigment analysis, made it possible to conclude that the carotenoid—chlorophyll a binding protein was a xanthophyll-chlorophyll a protein complex, and the chlorophyll a binding protein was a chlorophyll a protein complex. The molecular weight of the proteins was determined by high-performance exclusion chromatography and SDS-PAGE to be 57 and 16 kDa, respectively. The photoprotective properties of these proteins and their possible functioning as part of evolutionary precursors of photosynthetic systems are discussed. [ABSTRACT FROM AUTHOR]

Cyanobacteria are unique prokaryotes, which are capable to perform oxygenic photosynthesis. Within these organisms, phycobilisomes (PBS) act as an antenna of the photosynthetic pigment apparatus. Phycobilisomes contain several phycobiliproteins (PBP): phycoerythrin (PE), phycocyanin (PC), allophycocyanin (APC) and phycoerythrocyanin (PEC). The application of phycobiliproteins in the biotechnology, food industry and medicine during the last years is rapidly increasing. The aim of our study was to assess the qualitative and quantitative content of phycoerythrin, phycocyanin, allophycocyanin and phycoerythrocyanin in 14 cyanobacterial strains kept in Plovdiv Algal Culture Collection (PACC) and 4 strains purchased from the Culture Collection of Autotrophic Organisms (CCALA). Our data demonstrated that three strains of Microcoleus autumnalis (PACC 5505, PACC 5522 and PACC 5527) have high potential to produce phycoerythrins (0.132, 0.201 and 0.136 mg/mL, respectively). Similarly, one Microcoleus autumnalis strain (PACC 5522) and one strain of Leptolyngbya boryana (CCALA 084) are suitable for biotechnological production of phycocyanins (0.051 and 0.264 mg/mL, respectively) as well as allophycocyanins (0.102 and 0.171 mg/mL, respectively). In addition, the data about the pigment content could be used as a biochemical marker for taxonomic purposes within the group. [ABSTRACT FROM AUTHOR]

Abstract The cyanobacterium Arthrospira platensis is an important source of phycocyanin, which has many commercial applications in foods, cosmetics and pharmaceutics. In this study, hydrophobic interaction membrane chromatography (HIMC) was used for the first time to separate phycocyanin from allophycocyanin and obtain analytical grade phycocyanin, avoiding packed bed (i.e., packed column) chromatography steps. The extraction of phycobiliproteins was carried out on freeze-dried biomass samples suspended in NaCl 0.1 M, and the phycobiliprotein crude extract was obtained by centrifuging the suspension to eliminate cell debris. The crude extract, after the addition of an appropriate amount of ammonium sulphate, was loaded on an ammonium sulphate responsive commercial hydrophilic polyvinylidene fluoride (PVDF) membrane for the HIMC purification process. Applying a two-step HIMC purification procedure, a phycocyanin purity ratio of 4.20 and a yield of 67.0% was attained. Graphical abstract Unlabelled Image Highlights • Analytical grade phycocyanin (PC) can be obtained using a salt responsive polyvinylidene fluoride (PVDF) membrane. • Hydrophobic interaction membrane chromatography (HIMC) allows to achieve high PC purity and yield applying a simple procedure. • HIMC could be a new route for large scale and cost-effective PC production. [ABSTRACT FROM AUTHOR]

Conventional extraction methods are able to extract only 50–60% of the total allophycocyanin (A-PC) present in a given biomass. One of the reasons is the resistance offered by the cell membrane for its disruption. The present study is aimed at screening different conventional methods and their combinations (to explore synergy) to arrive at the most suitable methodology for the primary extraction of A-PC from dry biomass of Arthrospira platensis . A synergistic effect was observed on employing ultrasonication in combination with other conventional methods. Ultrasonication with freezing and thawing resulted in the highest A-PC extraction efficiency of 93.11%. The problem of purification of A-PC when extracted along with c-phycocyanin (C-PC), due to same biochemical properties, could be overcome by carrying out ‘ultrasonication followed by sequential extraction employing freezing and thawing’. A-PC with an yield of 40% (devoid of C-PC) with a purity of 1.15 could be extracted, the highest reported till date during primary extraction itself. [ABSTRACT FROM AUTHOR]

Abstract: The simultaneous production of carbonic anhydrase and the phycobiliproteins, C‐phycocyanin and allophycocyanin, was evaluated during the cultivation of Spirulina platensis using Zarrouk's medium in its non‐diluted (100 % ZM) and diluted to 20 % (v/v) (20 % ZM) forms. In both media, Spirulina simultaneously produced carbonic anhydrase and phycobiliproteins. For the phycobiliproteins’ production, higher concentrations (mg/g) of C‐phycocyanin and allophycocyanin were obtained when 100 % ZM was used. For carbonic anhydrase production, higher concentrations (U/g) were obtained on the 6th day of cultivation in both culture media. 100 % ZM promoted greater productions of these bioproducts, and, for simultaneous obtainment, the cells should be harvested after 21 days, obtaining concentrations of 137.4 mg/g C‐phycocyanin, 104.4 mg/g allophycocyanin, and 26.6 U/g carbonic anhydrase. [ABSTRACT FROM AUTHOR]

Five red algae, Agardhiella subulata, Gracilariopsis longissima, Gracilaria vermiculophylla, Polysiphonia morrowii, and Pyropia elongata were sampled in winter for the extraction of phycoerythrin. The extracted phycoerythrin molecules were compared with the commercial phycoerythrin to determine the intrinsic fluorescence characteristics of the single pigments. An improved selective method for phycoerythrin extraction was set up for routinary investigation. The use of the mortar and pestle method for tissue homogenization with a freeze-thawing cycle allowed a simple and complete homogenization of the red algae. The extraction of phycoerythrin with diluted EDTA solutions (1 mM) at pH 9 enabled a selective and easy extraction of the pigment with 95-98% extraction efficiency. The way pH affected the phycoerythrin, phycocyanin, and allophycocyanin selective extraction was also evaluated. The 3D fingerprint of each pigment was recorded, and a comparison of different phycoerythrin spectra was performed by fluorescence spectroscopy highlighting differences in A. subulata and P. morrowii phycoerythrins in comparison with commercial standards purified from Pyropia. The productivity and the advantages of phycoerythrin that was extracted from unattached red algal species are discussed. [ABSTRACT FROM AUTHOR]

The objective of the present study is to investigate the physiological responses of three soil strains of cyanobacteria (collected from areas contaminated with oil in southern Iran and from paddyfields in north of Iran) to crude oil concentrations in limited salinity (NaCl) and irradiance conditions. Three cyanobacteria species of Fischerella sp. ISC107, Nostoc sp. ISC101, Phormidium sp. ISC108 were assayed. After purification, samples were grown in BG11 and BG110 media. The results showed that the efficiency of hydrocarbon source utilization of Phormidium sp. ISC108 was higher than in other cyanobacteria in crude oil treatment. The highest growth rate was observed at 3% crude oil concentration in Phormidium sp. ISC108. Also, the highest levels of allophycocyanin, phycocyanin, phycoerythrin, chlorophyll, carbohydrate, protein and phycobiliprotein were obtained from cyanobacteria Phormidium sp. ISC108 had larger phycobilisomes than the other strains (3.99 μg/gdw). The highest ratio of PSII/PSI was observed in Fischerella sp. ISC107. The highest levels of photosynthetic indices were assigned to 3% crude oil. In fact, reducing photosynthetic efficiency in higher levels of crude oil could be related to the toxic effect of organic hydrocarbons on algae growth. It can be concluded that the cyanobacteria can be used as a bioremediation for decomposing crude oil especially in the coastal area of the Persian Gulf and the Caspian Sea. The results of this research can be valuable for reducing the contamination which affects the fauna and flora of the marine ecosystems in Iran. [ABSTRACT FROM AUTHOR]

Seven days exposure to 10 µM Cu showed reduction in growth in terms of chlorophyll a and protein concentration by 38% and 21% in Nostoc muscorum Meg 1. Same period of exposure to 10 µM Cd recorded reduction in these two parameters by 89% and 71%. Photosynthetic pigments carotenoids, phycocyanin, allophycocyanin and phycoerythrin were compromised > 75% in Cd as against ~ 14-21% in Cu. Nitrogenase and glutamine synthetase activities were down by ~ 75% in Cd, whereas the adverse effect of Cu was ~ 13%. The photosystem II activity and respiration were reduced by 44% and 53% in Cu but toxicity was more pronounced (> 70%) in Cd. Energy dispersion X-ray analysis established Cu and Cd binding to cell surface and Fourier Transform Infrared spectroscopic analysis determined the involvement of hydroxyl, carboxylic, carbonyl, nitro and amino groups in metal binding. Langmuir isotherm study established higher metal sorption capability with Qmax of 69.7 mg/g of biomass for Cd against 17.4 mg/g of biomass for Cu. Bright Field and Scanning Electron microscopy showed severity of Cd on filaments morphology compared to Cu. The cyanobacterium showed high efficiency (> 90%) for binding both metals making it a potential organism for research in the field of bioremediation. [ABSTRACT FROM AUTHOR]

Summary: Phycobilisomes, the macromolecular light harvesting complexes of cyanobacteria are degraded under nutrient‐limiting conditions. This crucial response is required to adjust light excitation to the metabolic status and avoid damage by excess excitation. Phycobilisomes are comprised of phycobiliproteins, apo‐proteins that covalently bind bilin chromophores. In the cyanobacterium Synechococcus elongatus, the phycobiliproteins allophycocyanin and phycocyanin comprise the core and the rods of the phycobilisome, respectively. Previously, NblB was identified as an essential component required for phycocyanin degradation under nutrient starvation. This protein is homologous to bilin‐lyases, enzymes that catalyze the covalent attachment of bilins to apo‐proteins. However, the nblB‐inactivated strain is not impaired in phycobiliprotein synthesis, but rather is characterized by aberrant phycocyanin degradation. Here, using a phycocyanin‐deficient strain, we demonstrate that NblB is required for degradation of the core pigment, allophycocyanin. Furthermore, we show that the protein NblB is expressed under nutrient sufficient conditions, but during nitrogen starvation its level decreases about two‐fold. This finding is in contrast to an additional component essential for degradation, NblA, the expression of which is highly induced under starvation. We further identified NblB residues required for phycocyanin degradation in vivo. Finally, we demonstrate phycocyanin degradation in a cell‐free system, thereby providing support for the suggestion that NblB directly mediates pigment degradation by chromophore detachment. The dependence of NblB function on NblA revealed using this system, together with the results indicating presence of NblB under nutrient sufficient conditions, suggests a rapid mechanism for induction of pigment degradation, which requires only the expression of NblA. [ABSTRACT FROM AUTHOR]

A new method that combines ultrasonic assisted extraction (UAE) with ionic liquids (ILs) was proposed to extract phycobiliproteins from the microalgae Spirulina ( Arthrospira ) platensis . Extraction of the pigments was carried out in an ultrasonic bath at 25 °C and at a frequency of 25 kHz. The effects of pH and solvent:biomass ratio were evaluated through a central rotational composite design and response surface methodology were used to determine the best extraction conditions. Solvents used were protic ionic liquids (PILs) 2-hydroxy ethylammonium acetate (2-HEAA), 2-hydroxy ethylammonium formate (2-HEAF), their equimolar mixture (2-HEAA+2-HEAF) (1:1  v /v) and the commercial ionic liquid, 1-butyl-3-methylimidazolium chloride [Bmim][Cl] and sodium phosphate buffer (0.1 M) as a control. Results showed that the PILs were able to extract the phycobiliproteins from microalgae. The pH was the most significant variable. Solvent:biomass ratio was also significant in the extraction process. The highest concentrations of phycobiliproteins were observed using 2-HEAA +2-HEAF as solvent at pH 6.50 and solvent:biomass ratio 7.93 mL·g −1 within 30 min of extraction. Allophycocyanin was the pigment extracted in greater quantity (6.34 mg·g −1 ), followed by phycocyanin (5.95 mg·g −1 ) and phycoerythrin (2.62 mg·g −1 ). Scanning electron microscopy (SEM) revealed that the ultrasound affect the cellular structure of the microalgae. [ABSTRACT FROM AUTHOR]

Abstract: C‐Phycocyanin is the major phycobiliprotein in Arthrospira platensis, also known as Spirulina, which is a cyanobacterium used as a dietary supplement because of its powerful effects on body and brain. C‐phycocyanin is a blue‐colored accessory photosynthetic pigment with multiple applications in food industry as natural dye or additive, and in pharmaceuticals. This study presents a simple protocol for the extraction and purification of food‐grade C‐phycocyanin from Arthrospira platensis. The cell lysis of cyanobacterium was performed by sonication combined with repeated freezing and thawing cycles. The purification of the crude extract of C‐phycocyanin was carried out by ammonium sulfate precipitation followed by ion exchange chromatography resulting in 2.5 purity. The purity of phycocyanobilin chromophore has been tested by UV‐visible spectrophotometry by monitoring the absorption after each stage of purification. A high‐performance liquid chromatography method has been developed and validated for the determination of food‐grade C‐phycocyanin. Intra‐ and interday precision values less than 5.6% and recovery greater than 91.2% indicated high precision and accuracy of the method for analysis of C‐phycocyanin. The method has been applied to commercial confectionery of blue color and to the purified protein obtained in the first stage of the study. [ABSTRACT FROM AUTHOR]