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

The extremophile red alga Galdieria sulphuraria was successfully grown immobilized in a twin-layer porous substrate bioreactor (TL-PSBR). A maximal biomass growth rate of 10 g dry weight m-2 day-1 was measured at a photon fluence rate of 200 µmol photons m-2 s-1 with addition of 1% CO2 and a temperature of 34 °C. Under these conditions, a maximal biomass value of 232 g m-2 was attained after 33 days of growth. Phycobilin productivity, however, was highest at a lower photon fluence rate of 100 µmol photons m-2 s-1 and reached a phycobilin value of 14 g m-2, a phycobilin content in the biomass of 63 mg g-1 and a phycobilin growth rate of 0.28 g m-2 day-1 for phycocyanin and 0.23 g m-2 day-1 for allophycocyanin. Addition of CO2 was essential to enhance growth and phycobilin production in G. sulphuraria and further optimization of the cultivation process in the TL-PSBR appears possible using a multi-phase approach, higher growth temperatures and optimization of nutrient supply. It is concluded that autotrophic cultivation of G. sulphuraria in a TL-PSBR is an attractive alternative to suspension cultivation for phycobilin production and applications in bioremediation.

Growth and biomass productivity of Scenedesmus vacuolatus on a twin layer system and a comparison with other types of cultivations.

Scenedesmus is a genus of microalgae employed for several industrial uses. Industrial cultivations are performed in open ponds or in closed photobioreactors (PBRs). In the last years, a novel type of PBR based on immobilized microalgae has been developed termed porous substrate photobioreactors (PSBR) to achieve significant higher biomass density during cultivation in comparison to classical PBRs. This work presents a study of the growth of Scenedesmus vacuolatus in a Twin Layer System PSBR at different light intensities (600 µmol photons m-2 s-1 or 1000 µmol photons m-2 s-1), different types and concentrations of the nitrogen sources (nitrate or urea), and at two CO2 levels in the gas phase (2% or 0.04% v/v). The microalgal growth was followed by monitoring the attached biomass density as dry weight, the specific growth rate and pigment accumulation. The highest productivity (29 g m-2 d-1) was observed at a light intensity of 600 µmol photons m-2 s-1 and 2% CO2. The types and concentrations of nitrogen sources did not influence the biomass productivity. Instead, the higher light intensity of 1000 µmol photons m-2 s-1 and an ambient CO2 concentration (0.04%) resulted in a significant decrease of productivity to 18 and 10-12 g m-2 d-1, respectively. When compared to the performance of similar cultivation systems (15-30 g m-2 d-1), these results indicate that the Twin Layer cultivation System is a competitive technique for intensified microalgal cultivation in terms of productivity and, at the same time, biomass density.

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.

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.

Microalgal Co-Cultivation Prospecting to Modulate Vitamin and Bioactive Compounds Production.

Microalgal biotechnology is gaining importance. However, key issues in the pipeline from species selection towards large biomass production still require improvements to maximize the yield and lower the microalgal production costs. This study explores a co-cultivation strategy to improve the bioactive compounds richness of the harvested microalgal biomass. Based on their biotechnological potential, two diatoms (Skeletonema marinoi, Cyclotella cryptica) and one eustigmatophyte (Nannochloropsis oceanica) were grown alone or in combination. Concentrations of ten vitamins (A, B1, B2, B6, B12, C, D2, D3, E and H), carotenoids and polyphenols, together with total flavonoids, sterols, lipids, proteins and carbohydrates, were compared. Moreover, antioxidant capacity and chemopreventive potential in terms inhibiting four human tumor-derived and normal cell lines proliferation were evaluated. Co-cultivation can engender biomass with emergent properties regarding bioactivity or bioactive chemical profile, depending on the combined species. The high vitamin content of C. cryptica or N. oceanica further enhanced (until 10% more) when co-cultivated, explaining the two-fold increase of the antioxidant capacity of the combined C. cryptica and N. oceanica biomass. Differently, the chemopreventive activity was valuably enhanced when coupling the two diatoms C. cryptica and S. marinoi. The results obtained in this pilot study promote microalgal co-cultivation as a valuable strategy aiming to boost their application in eco-sustainable biotechnology.

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.

Prevalent pH Controls the Capacity of Galdieria maxima to Use Ammonia and Nitrate as a Nitrogen Source.

Galdieria maxima is a polyextremophilic alga capable of diverse metabolic processes. Ammonia is widely used in culture media typical of laboratory growth. Recent reports that this species can grow on wastes promote the concept that G. maxima might have biotechnological utility. Accordingly, there is a need to know the range of pH levels that can support G. maxima growth in a given nitrogen source. Here, we examined the combined effect of pH and nitrate/ammonium source on the growth and long-term response of the photochemical process to a pH gradient in different G. maxima strains. All were able to use differing nitrogen sources, despite both the growth rate and photochemical activity were significantly affected by the combination with the pH. All strains acidified the NH4+-medium (pH < 3) except G. maxima IPPAS P507. Under nitrate at pH ≥ 6.5, no strain was able to acidify the medium; noteworthy, G. maxima ACUF551 showed a good growth performance under nitrate at pH 5, despite the alkalization of the medium.

Biofilm architecture on different substrates of an Oculatella subterranea (Cyanobacteria) strain isolated from Pompeii archaeological site (Italy).

The Cyanobacterium Oculatella subterranea Zammit, Billi, Albertano inhabits hypogea and stone caves and is a pioneer of different stone substrata. In this study, a strain isolated from the House of Marco Castricio (Archaeological Park of Pompeii, Italy) was identified by a polyphasic approach and used for an in vitro colonization test to verify the influence of the substrate on the biofilm architecture. Fine structure of O. subterranea microbial mats was revealed as well as filaments orientation toward light source. This aim has been achieved through confocal laser scanner microscope microscopy and computer image analysis. Moreover, bioreceptivity of five different substrates, commonly retrieved in archaeological sites of Campania, was assessed for O. subterranea. Our results show that the three-dimensional structure of O. subterranea microbial mats is poorly affected by physical and geochemical features of substrates: in fact, the porous architecture of its biofilm was preserved, independently of the materials. On the other hand, the area/perimeter ratio relative to the O. subterranea growth on tuff, brick, and porphyry showed significant differences, indicating dissimilar levels of bioreceptivity of the three substrates.