A thermophilic C-phycocyanin with unprecedented biophysical and biochemical properties

C-Phycocyanin improves the quality of goat oocytes after in vitro maturation and vitrification

In vitro maturation (IVM) and cryopreservation of goat oocytes are important for establishing a valuable genetic bank for domesticated female animals and improving livestock reproductive efficiency. C-Phycocyanin (PC) is a Spirulina extract with antioxidant, antiinflammatory, and radical scavenging properties. However, whether PC has positive effect on goat oocytes IVM or developmental competence after vitrification is still unknown. In this study, we found that first polar body extrusion (n = 293), cumulus expansion index (n = 269), and parthenogenetic blastocyst formation (n = 281) were facilitated by adding 30 μg/mL PC to the oocyte maturation medium when compared with the control groups and that supplemented with 3, 10, 100 or 300 μg/mL PC (P < 0.05). Although PC supplementation did not affect spindle formation or chromosome alignment (n = 115), it facilitated or improved cortical granules migration (n = 46, P < 0.05), mitochondria distribution (n = 39, P < 0.05), and mitochondrial membrane potential (n = 46, P < 10-4). Meanwhile, supplementation with 30 μg/mL PC in the maturation medium could significantly inhibit the reactive oxygen species accumulation (n = 65, P < 10-4), and cell apoptosis (n = 42, P < 0.05). In addition, PC increased the oocyte mRNA levels of GPX4 (P < 0.01), and decreased the mRNA and protein levels of BAX (P < 0.01). Next, we investigated the effect of PC supplementation in the vitrification solution on oocyte cryopreservation. When compared with the those equilibrate in the vitrification solution without PC, recovered oocytes in the 30 μg/mL PC group showed higher ratios of normal morphology (n = 85, P < 0.05), survival (n = 85, P < 0.05), first polar body extrusion (n = 62, P < 0.05), and parthenogenetic blastocyst formation (n = 107, P < 0.05). Meanwhile, PC supplementation of the vitrification solution increased oocyte mitochondrial membrane potential (n = 53, P < 0.05), decreased the reactive oxygen species accumulation (n = 73, P < 0.05), promoted mitochondria distribution (n = 58, P < 0.05), and inhibited apoptosis (n = 46, P < 10-3). Collectively, our findings suggest that PC improves goat oocyte IVM and vitrification by reducing oxidative stress and early apoptosis, which providing a novel strategy for livestock gamete preservation and utilization.

Investigation of the Potential of Selected Food-Derived Antioxidants to Bind and Stabilise the Bioactive Blue Protein C-Phycocyanin from Cyanobacteria Spirulina

Blue C-phycocyanin (C-PC), the major Spirulina protein with innumerable health-promoting benefits, is an attractive colourant and food supplement. A crucial obstacle to its more extensive use is its relatively low stability. This study aimed to screen various food-derived ligands for their ability to bind and stabilise C-PC, utilising spectroscopic techniques and molecular docking. Among twelve examined ligands, the protein fluorescence quenching revealed that only quercetin, coenzyme Q10 and resveratrol had a moderate affinity to C-PC (Ka of 2.2 to 3.7 × 105 M-1). Docking revealed these three ligands bind more strongly to the C-PC hexamer than the trimer, with the binding sites located at the interface of two (αβ)3 trimers. UV/VIS absorption spectroscopy demonstrated the changes in the C-PC absorption spectra in a complex with quercetin and resveratrol compared to the spectra of free protein and ligands. Selected ligands did not affect the secondary structure content, but they induced changes in the tertiary protein structure in the CD study. A fluorescence-based thermal stability assay demonstrated quercetin and coenzyme Q10 increased the C-PC melting point by nearly 5 °C. Our study identified food-derived ligands that interact with C-PC and improve its thermal stability, indicating their potential as stabilising agents for C-PC in the food industry.

Valuable pigments from microalgae: phycobiliproteins, primary carotenoids, and fucoxanthin

Phycobiliproteins, carotenoids and fucoxanthin are photosynthetic pigments extracted from microalgae and cyanobacteria with great potential biotechnological applications, as healthy food colorants and cosmetics. Phycocyanin possesses a brilliant blue color, with fluorescent properties making it useful as a reagent for immunological essays. The most important source of phycocyanin is the cyanobacterium Arthrospira platensis, however, recently, the Rhodophyta Galdieria sulphuraria has also been identified as such. The main obstacle to the commercialization of phycocyanin is represented by its chemical instability, strongly reducing its shelf-life. Moreover, the high level of purity needed for pharmaceutical applications requires several steps which increase both the production time and cost. Microalgae (Chlorella, Dunaliella, Nannochloropsis, Scenedesmus) produce several light harvesting carotenoids, and are able to manage with oxidative stress, due to their free radical scavenging properties, which makes them suitable for use as source of natural antioxidants. Many studies focused on the selection of the most promising strains producing valuable carotenoids and on their extraction and purification. Among carotenoids produced by marine microalgae, fucoxanthin is the most abundant, representing more than 10% of total carotenoids. Despite the abundance and diversity of fucoxanthin producing microalgae only a few species have been studied for commercial production, the most relevant being Phaeodactylum tricornutum. Due to its antioxidant activity, fucoxanthin can bring various potential benefits to the prevention and treatment of lifestyle-related diseases. In this review, we update the main results achieved in the production, extraction, purification, and commercialization of these important pigments, motivating the cultivation of microalgae as a source of natural pigments.

An Alternative Exploitation of Synechocystis sp. PCC6803: A Cascade Approach for the Recovery of High Added-Value Products

Microalgal biomass represents a very interesting biological feedstock to be converted into several high-value products in a biorefinery approach. In this study, the cyanobacterium Synechocystis sp. PCC6803 was used to obtain different classes of molecules: proteins, carotenoids and lipids by using a cascade approach. In particular, the protein extract showed a selective cytotoxicity towards cancer cells, whereas carotenoids were found to be active as antioxidants both in vitro and on a cell-based model. Finally, for the first time, lipids were recovered from Synechocystis biomass as the last class of molecules and were successfully used as an alternative substrate for the production of polyhydroxyalkanoate (PHA) by the native PHA producer Pseudomonas resinovorans. Taken together, our results lead to a significant increase in the valorization of Synechocystis sp. PCC6803 biomass, thus allowing a possible offsetting of the process costs.

Impact of Hydrophobic Chains in Five-Coordinate Glucoconjugate Pt(II) Anticancer Agents

This study describes new platinum(II) cationic five-coordinate complexes (1-R,R') of the formula [PtR(NHC)(dmphen)(ethene)]CF₃SO₃ (dmphen = 2,9-dimethyl-1,10-phenanthroline), containing in their axial positions an alkyl group R (methyl or octyl) and an imidazole-based NHC-carbene ligand with a substituent R' of variable length (methyl or octyl) on one nitrogen atom. The Pt-carbene bond is stable both in DMSO and in aqueous solvents. In DMSO, a gradual substitution of dmphen and ethene is observed, with the formation of a square planar solvated species. Octanol/water partitioning studies have revealed the order of hydrophobicity of the complexes (1-Oct,Me > 1-Oct,Oct > 1-Me,Oct > 1-Me,Me). Their biological activity was investigated against two pairs of cancer and non-cancer cell lines. The tested drugs were internalized in cancer cells and able to activate the apoptotic pathway. The reactivity of 1-Me,Me with DNA and protein model systems was also studied using UV-vis absorption spectroscopy, fluorescence, and X-ray crystallography. The compound binds DNA and interacts in various ways with the model protein lysozyme. Remarkably, structural data revealed that the complex can bind lysozyme via non-covalent interactions, retaining its five-coordinate geometry.

Phycobiliproteins, the pigment-protein complex form of natural food colorants and bioactive ingredients

Currently, the use of synthetic pigments in foods is restricted since synthetic pigments are proven and suspected to be harmful to human health. Phycobiliproteins (PBPs), existed in phycobilisomes (PBSs) of algae, are a kind of pigment-proteins with intense color. The specific color of PBPs (red and blue) is given by the water-soluble open-chained tetrapyrrole chromophore (phycobilin) that covalently attaches to the apo-protein via thioether linkages to cysteine residues. According to the spectral characteristics of PBPs, they can be categorized as phycoerythrins (PEs), phycocyanins (PCs), allophycocyanins (APCs), and phycoerythrocyanins (PECs). PBPs can be used as natural food colorants, fluorescent substances, and bioactive ingredients in food applications owing to their color characteristics and physiological activities. This paper mainly summarizes the extraction and purification methods of the PBPs and reviews their characteristics and applications. Moreover, the use of several strategies such as additives, microencapsulation, electrospray, and cross-linking to improve the stability and bioavailability of PBPs as well as the future outlooks of PBPs as natural colorants in food commercialization are elucidated.

Fabrication and characterization of phycocyanin-alginate-pregelatinized corn starch composite gel beads: Effects of carriers on kinetic stability of phycocyanin

Composite gel beads using calcium alginate and different concentrations of pregelatinized corn starch (PCS) were produced to encapsulate phycocyanin (PC). Rheological properties of different sodium alginate/PCS/PC mixtures, structural and morphological properties of beads, and kinetic stability of encapsulated PC (upon heating at various time-temperature combinations) were then assessed. Rheological properties of the mixtures exhibited shear thinning behaviors. Aquagram revealed that the PC-containing beads had more water structure with weak‑hydrogen bonds. Morphological images represented less subsidence in the structures of composite gel beads, unlike PCS-free beads. Kinetic study showed that degradation rate constant values of PC encapsulated in composite gel beads (1.08-3.45 × 10^-4, 3.38-4.43 × 10^-4, and 5.57-15.32 × 10^-4 s^-1) were lower than those in PCS-free alginate gel beads (4.45 × 10^-4, 9.20 × 10^-4, and 18.04 × 10^-4 s^-1) at 40, 50, and 60 °C, respectively. This study suggests that the composite gel beads can improve PC stability.

Preparation, Characterization, and Antioxidant Properties of Phycocyanin Complexes Based on Sodium Alginate and Lysozyme

In this study, phycocyanin-sodium alginate/lysozyme complex (PC-SLC) was prepared for the first time and characterized by UV spectroscopy, Fourier transform infrared spectroscopy (FT-IR), and circular dichroism spectroscopy (CD). The stability of PC-SLC under light, temperature, pH and simulated gastrointestinal fluid was investigated. The scavenging ability of the complexes against DPPH and ABTS radicals was determined. The results showed that the complex formed by the mass ratio of SA-LZM of 0.1 showed the highest PC encapsulation rate (89.9 ± 0.374%). The combination of SA and LZM changed the secondary conformation of PC. The PC-SLC complex shows an irregular spherical structure and the spheres are clustered together. Compared with phycocyanin (PC), its thermal stability was obviously improved, but it was still greatly influenced by light. It could exist stably in simulated gastric fluid (SGF) for 2 h and be slowly digested in simulated intestinal fluid (SIF), which helped to promote the absorption of nutrients in the intestinal tract. Meanwhile, the complex PC-SLC showed high scavenging ability for DPPH and ABTS radicals. It can be concluded that the complexes have good antioxidant activity. This study provides an idea for the construction of PC delivery system and makes it more widely used in food industry and other fields.

Acid Tolerant and Acidophilic Microalgae: An Underexplored World of Biotechnological Opportunities

Despite their large number and diversity, microalgae from only four genera are currently cultivated at large-scale. Three of those share common characteristics: they are cultivated mainly autotrophically and are extremophiles or tolerate “extreme conditions.” Extreme growth conditions aid in preventing contamination and predation of microalgae, therefore facilitating outdoor cultivation. In search for new extremophilic algae suitable for large-scale production, we investigated six microalgal strains able to grow at pH below 3 and belonging to four genera; Stichococcus bacillaris ACUF158, Chlamydomonas acidophila SAG 2045, and Chlamydomonas pitschmannii ACUF238, Viridiella fridericiana ACUF035 and Galdieria sulphuraria ACUF064 and ACUF074. All strains were cultivated autotrophically at light intensity of 100 and 300 μmol m−2 s−1 and pH between 1.9 and 2.9. The autotrophic biomass productivities were compared with one of the most productive microalgae, Chlorella sorokiniana SAG 211-8K, grown at pH 6.8. The acid tolerant strains have their autotrophic biomass productivities reported for the first time. Mixotrophic and heterotrophic properties were investigated when possible. Five of the tested strains displayed autotrophic biomass productivities 10–39% lower than Chlorella sorokiniana but comparable with other commercially relevant neutrophilic microalgae, indicating the potential of these microalgae for autotrophic biomass production under acidic growth conditions. Two acid tolerant species, S. bacillaris and C. acidophila were able to grow mixotrophically with glucose. Chlamydomonas acidophila and the two Galdieria strains were also cultivated heterotrophically with glucose at various temperatures. Chlamydomonas acidophila failed to grow at 37°C, while G. sulphuraria ACUF64 showed a temperature optimum of 37°C and G. sulphuraria ACUF74 of 42°C. For each strain, the biomass yield on glucose decreased when cultivated above their optimal temperature. The possible biotechnological applications of our findings will be addressed.

Thermo resistant antioxidants from photoautotrophic microorganisms: screening and characterization

The demand for natural antioxidants to be used in food industry is increasing, as synthetic antioxidants are toxic and have high production costs. Specifically, food processing and preservation require antioxidants resistant to thermal sterilization processes. In this study, twenty-five strains among microalgae and cyanobacteria were screened as antioxidants producers. The species Enallax sp., Synechococcus bigranulatus and Galdieria sulphuraria showed the highest content of chlorophyll a and total carotenoids. In vitro stability and antioxidant activity of the ethanolic extracts were performed. The results revealed that pigments present in the extracts, obtained from the previously mentioned species, were stable at room temperature and exhibited in vitro free radical scavenging potential with IC₅₀ values of 0.099 ± 0.001, 0.048 ± 0.001 and 0.13 ± 0.02 mg mL^-1, respectively. Biocompatibility assay showed that the extracts were not toxic on immortalized cell lines. The antioxidant activity was also tested on a cell-based model by measuring intracellular ROS levels after sodium arsenite treatment. Noteworthy, extracts were able to exert the same protective effect, before and after the pasteurization process. Results clearly indicate the feasibility of obtaining biologically active and thermostable antioxidants from microalgae. Green solvents can be used to obtain thermo-resistant antioxidants from cyanobacteria and microalgae which can be used in the food industry. Thus, the substitution of synthetic pigments with natural ones is now practicable.

Production of thermostable phycocyanin in a mesophilic cyanobacterium

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.

X-ray structure of C-phycocyanin from Galdieria phlegrea: Determinants of thermostability and comparison with a C-phycocyanin in the entire phycobilisome

Galdieria phlegrea is a polyextremophilic red alga belonging to Cyanidiophyceae. Galdieria phlegrea C-phycocyanin (GpPC), an abundant light-harvesting pigment with an important role in energy capture and transfer to photosystems, is the C-phycocyanin (C-PC) with the highest thermal stability described so far. GpPC also presents interesting antioxidant and anticancer activities. The X-ray structure of the protein was here solved. GpPC is a [(αβ)₃]₂ hexamer, with the phycocyanobilin chromophore attached to Cys84α, Cys82β and Cys153β. Details of geometry and interaction with solvent of the chromophores are reported. Comparison with the structure of a C-PC in the entire Porphyridium purpureum phycobilisome system reveals that linker polypeptides have a significant effect on the local structure of the chromophores environment. Comparative analyses with the structures of other purified C-PCs, which were carried out including re-refined models of G. sulphuraria C-PC, reveal that GpPC presents a significantly higher number of inter-trimer salt bridges. Notably, the higher number of salt bridges at the (αβ)₃/(αβ)₃ interface is not due to an increased number of charged residues in this region, but to subtle conformational variations of their side chains, which are the result of mutations of close polar and non-polar residues.