Biomass and phycobiliprotein production of Galdieria sulphuraria, immobilized on a twin-layer porous substrate photobioreactor

Significance and Applications of the Thermo-Acidophilic Microalga Galdieria sulphuraria (Cyanidiophytina, Rhodophyta)

Galdieria sulphuraria is a thermo-acidophilic microalga belonging to the Cyanidiophyceae (Rhodophyta) class. It thrives in extreme environments, such as geothermal sulphuric springs, with low pH, high temperatures, and high salinity. This microalga utilises various growth modes, including autotrophic, heterotrophic, and mixotrophic, enabling it to exploit diverse organic carbon sources. Remarkably, G. sulphuraria survives and produces a range of bioactive compounds in these harsh conditions. Moreover, it plays a significant role in environmental remediation by removing nutrients, pathogens, and heavy metals from various wastewater sources. It can also recover rare earth elements from mining wastewater and electronic waste. This review article explores the diverse applications and significant contributions of G. sulphuraria.

Contribution to a Sustainable Society: Biosorption of Precious Metals Using the Microalga Galdieria

The red microalga Galdieria sp. is an extremophile that inhabits acidic hot sulphur springs and grows heterotrophically to a high cell density. These characteristics make Galdieria suitable for commercial applications as stable mass production is the key to success in the algae business. Galdieria has great potential as a precious metal adsorbent to provide a sustainable, efficient and environmentally benign method for urban mining and artisanal small-scale gold mining. The efficiency and selectivity in capturing precious metals, gold and palladium from metal solutions by a Galdieria-derived adsorbent was assessed relative to commercially used adsorbents, ion exchange resin and activated charcoal. As it is only the surface of Galdieria cells that affect metal adsorption, the cell content was analysed to determine the manner of utilisation of those metabolites. Galdieria was shown to be protein-rich and contain beneficial metabolites, the levels of which could shift depending on the growth conditions. Separating the cell content from the adsorbent could improve the adsorption efficiency and reduce CO2 emissions during the metal collection process. The commercial applications of Galdieria appear promising: growth is quick and dense; the precious metal adsorption capacity is highly efficient and selective in acidic conditions, especially at low metal concentrations; and the cell content is nutrient-rich.

Phycobiliproteins from microalgae: research progress in sustainable production and extraction processes

Phycobiliproteins (PBPs), one of the functional proteins from algae, are natural pigment-protein complex containing various amino acids and phycobilins. It has various activities, such as anti-inflammatory and antioxidant properties. And are potential for applications in food, cosmetics, and biomedicine. Improving their metabolic yield is of great interest. Microalgaes are one of the important sources of PBPs, with high growth rate and have the potential for large-scale production. The key to large-scale PBPs production depends on accumulation and recovery of massive productive alga in the upstream stage and the efficiency of microalgae cells breakup and extract PBPs in the downstream stage. Therefore, we reviewed the status quo in the research and development of PBPs production, summarized the advances in each stage and the feasibility of scaled-up production, and demonstrated challenges and future directions in this field.

Potential of Porous Substrate Bioreactors for Removal of Pollutants from Wastewater Using Microalgae

Porous substrate bioreactors (PSBRs) are a new technology to grow microalgae immobilized in a dense culture and solve some problems linked to suspended cultivation. During recent years, this technology has been used in laboratory and pilot setups in different fields of environmental biotechnology, such as wastewater treatment. The aim of this short review is to introduce the PSBR technology, summarize the results obtained in removing some pollutants from wastewater, provide an assessment of the potential of PSBRs for wastewater treatment, and the subsequent use of the algal biomass for other purposes.

Phycobiliproteins from algae: Current updates in sustainable production and applications in food and health

Phycobiliproteins are light-harvesting complexes found mainly in cyanobacteria and red algae, playing a key role in photosynthesis. They are extensively applied in food, cosmetics, and biomedical industry due to bright color, unique fluorescence characteristics and diverse physiological activities. They have received much attention in the past few decades because of their green and sustainable production, safe application, and functional diversity. This work aimed to provide a comprehensive summary of parameters affecting the whole bioprocess with a special focus on the extraction and purification, which directly determines the application of phycobiliproteins. Food grade phycobiliproteins are easy to prepare, whereas analytical grade phycobiliproteins are extremely complex and costly to produce. Most phycobiliproteins are denatured and inactivated at high temperatures, severely limiting their application. Inspired by recent advances, future perspectives are put forward, including (1) the mutagenesis and screening of algal strains for higher phycobiliprotein productivity, (2) the application of omics and genetic engineering for stronger phycobiliprotein stability, and (3) the utilization of synthetic biology and heterologous expression systems for easier phycobiliprotein isolation. This review will give a reference for exploring more phycobiliproteins for food and health application development.

Bioenergy, Biofuels, Lipids and Pigments—Research Trends in the Use of Microalgae Grown in Photobioreactors

This scientometric review and bibliometric analysis aimed to characterize trends in scientific research related to algae, photobioreactors and astaxanthin. Scientific articles published between 1995 and 2020 in the Web of Science and Scopus bibliographic databases were analyzed. The article presents the number of scientific articles in particular years and according to the publication type (e.g., articles, reviews and books). The most productive authors were selected in terms of the number of publications, the number of citations, the impact factor, affiliated research units and individual countries. Based on the number of keyword occurrences and a content analysis of 367 publications, seven leading areas of scientific interest (clusters) were identified: (1) techno-economic profitability of biofuels, bioenergy and pigment production in microalgae biorefineries, (2) the impact of the construction of photobioreactors and process parameters on the efficiency of microalgae cultivation, (3) strategies for increasing the amount of obtained lipids and obtaining biodiesel in Chlorella microalgae cultivation, (4) the production of astaxanthin on an industrial scale using Haematococcus microalgae, (5) the productivity of biomass and the use of alternative carbon sources in microalgae culture, (6) the effect of light and carbon dioxide conversion on biomass yield and (7) heterotrophy. Analysis revealed that topics closely related to bioenergy production and biofuels played a dominant role in scientific research. This publication indicates the directions and topics for future scientific research that should be carried out to successfully implement economically viable technology based on microalgae on an industrial scale.

Employing newly developed plastic bubble wrap technique for biofuel production from diatoms cultivated in discarded plastic waste

Algal culturing in photobioreactors for biofuel and other value-added products is a challenge globally specifically due to expensive closed or open photobioreactors associated with the high cost, problems of water loss and contamination. Among the wide varieties of microalgae, diatoms have come out as potential source for crude oil in the form of Diafuel™ (biofuel from diatoms). However, culturing diatoms at large scale hypothesized as diatom solar panels for biofuel production is still facing a need for facile and economical production of value-added products. The aim of this work was to culture diatom (microalgae) in a closed system by sealing the reactor rim tightly with very cheap priced and used plastic bubble wrap material which is generally discarded in a lodging and transportation of goods. To optimize it, different plastic wraps discarded from a plastic industry were tested first for their permeability to gases and impermeability to water loss. It was found that among different varieties of plastic bubble wraps, low density polyethylene (LDPE) bubble wrap material which was used to seal glass containers as photobioreactors allowed harvest of maximum Diafuel™ (37%), lipid (35 μgmL^-1), highest cell count (1152 × 10² cells mL^-1), maximum CO₂ absorbance (0.084) with almost no water loss and nutrient uptake for 40 days of experiments. This was due to its permeability to gases and impermeability to water. To check usability of such LDPE bubble wrap on other microalgae it was therefore tested on the red-green microalgae Haematococcus pluvialis, which showed scope to be scaled up for astaxanthin production using discarded bubble wrap packing material. This study thus would open up a new way for decreasing plastic disposal and with reuse for sustainable development and application of diatom in biofuel production which could find applications in environmental and industrial sectors.

Anti-Dengue Activity of ZnO Nanoparticles of Crude Fucoidan from Brown Seaweed S.marginatum

Dengue fever is a rapidly spreading infection that affects people all over the tropics and subtropics, posing a significant public health threat. The brown seaweed Stoechospermum marginatum was found all over the world, from South Africa (Indian Ocean) to Australia (Pacific Ocean), among other places. In India, it is only available along the coast of the Bay of Bengal, which is a small region. Various metal oxides were proved to be successful in the formation of nanoparticles and zinc is one among them. In this present study, an attempt was made to study the anti-dengue activity of green synthesized zinc oxide nanoparticles of crude fucoidan isolated from brown seaweed S. marginatum. The fucoidan was isolated from the seaweed by acid extraction method and then characterized by UV, HPLC, and Fourier Transform Infra-Red (FT-IR) Spectroscopy. Then it was biosynthesized into ZnO nanoparticles and characterized by SEM-EDAX analysis. The results showed the formation of fucoidans and SEM studies showed the crystalline nature of the synthesized nanoparticles. The size of nanoparticles was in the range of 80-126 nm. The synthesized nanoparticles were tested with the C6/36 cell line and it was shown 99.09% of anti-dengue activity against the tested cell line. As an antiviral agent, the ZnO nanoparticles of fucoidans have been shown to be an excellent lead molecule for the treatment of dengue fever.

Evaluation of Microalgae Antiviral Activity and Their Bioactive Compounds

During the last year, science has been focusing on the research of antivirally active compounds overall after the SARS-CoV-2 pandemic, which caused a great amount of deaths and the downfall of the economy in 2020. Photosynthetic organisms such as microalgae are known to be a reservoir of bioactive secondary metabolites; this feature, coupled with the possibility of achieving very high biomass levels without excessive energetic expenses, make microalgae worthy of attention in the search for new molecules with antiviral effects. In this work, the antiviral effects of microalgae against some common human or animal viruses were considered, focusing our attention on some possible effects against SARS-CoV-2. We summed up the data from the literature on microalgae antiviral compounds, from the most common ones, such as lectins, polysaccharides and photosynthetic pigments, to the less known ones, such as unidentified proteins. We have discussed the effects of a microalgae-based genetic engineering approach against some viral diseases. We have illustrated the potential antiviral benefits of a diet enriched in microalgae.

Comparison of Galdieria growth and photosynthetic activity in different culture systems

In the last years, the acidothermophilic red microalga Galdieria sulphuraria has been increasingly studied for industrial applications such as wastewater treatment, recovery of rare earth elements, production of phycobilins. However, even now it is not possible an industrial cultivation of this organism because biotechnological research on G. sulphuraria and allied species is relatively recent and fragmented. Having in mind a possible scale-up for commercial applications, we have compared the growth and photosynthetic performance of G. sulphuraria in four suspended systems (Inclined bubble column, Decanter Laboratory Flask, Tubular Bioreactor, Ultra-flat plate bioreactor) and one immobilized system (Twin Layer Sytem). The results showed that G. sulphuraria had the highest growth, productivity and photosynthetic performance, when grown on the immobilized system, which also offers some economics advantages.