Phycobiliproteins Production Enhancement and Lipidomic Alteration by Titanium Dioxide Nanoparticles in Synechocystis sp. PCC 6803 Culture

Exploring engineering reduced graphene oxide-titanium dioxide (RGO-TiO2) nanoparticles treatment to effectively enhance lutein biosynthesis with Chlorella sorokiniana F31 under different light intensity

The Chlorella sorokiniana F31 is a promising lutein producer with high lutein content. Herein, different graphene/TiO₂ nanoparticles (NPs) were designed and synthesized by hydrothermal method. Through the UV-vis diffuse reflectance spectra (DRS) analysis, the results showed that RGO-TiO₂ NPs can effectively expand visible light absorption compared with TiO₂ NPs. Subsequently, the effects of these NPs on light utilization and lutein accumulation of C. sorokiniana F31 were investigated, and the RGO-TiO₂ NPs treatment exhibited the higher lutein production and content than that of TiO₂ and control group. As the optimal RGO-TiO₂ (0.5 wt%) NPs concentration of 50 mg/L and light intensity of 211 μmol/m²/s, the supreme lutein content (15.55 mg/g), production (77.2 mg/L) and productivity (12.87 mg/L/d) were achieved. The performances are higher than most of reported values in previous study, indicated that RGO-TiO₂ (0.5 wt%) NPs treatment is a promised strategy to enhance microalgal growth and lutein accumulation.

Single-cell Raman micro-spectroscopy for tracking of carotenoids in cyanobacteria exposed to Mn and Zn doped ferrite nanoparticles

Ferrite nanoparticles are increasingly produced and exploited as adsorbents for environmental pollutants. However, their impact on the aquatic microbiota such as cyanobacteria, are not yet investigated. Targeting the environmental monitoring context, in this paper we explored for the first time if any change in the carotenoid signal from cyanobacteria Coelomoron pussilum (AICB 1012) exposed to non-lethal doses of Mn and Zn doped ferrite nanoparticles (NPs) can be associated with the nano-aggression on single-cell level, using micro-Raman spectroscopy. UV-Vis absorption spectroscopy of the bulk culture and single-cell Raman microscopy showed that the carotenoid signal increases relative to the chlorophyll contribution upon exposure of the cells to the Mn-ferrite NPs throughout the 7 days of the experiment. The red-shift and broadening of the strongest carotenoid Raman band arising from (CC) stretching modes indicates the change of carotenoid profile towards increased amount of β-carotene in answer to the NPs stress. The increase of this band intensity relative to the fluorescence background was also observed in Zn-ferrite NPs treatment. Using a simplified and rapid sample preparation procedure, electron microscopy in both transmission and scanning modes, showed greater coverage of the cells by the stable colloidal AgNPs than by the magnetic ferrite NPs. The latter mostly clumped together rather than adhering to the cells. The combined single-cell micro-Raman tracking of physiological response of the unicellular photosynthetic microorganisms coupled with electron microscopy approach to visualise cell-NPs interaction and the extracellular polymeric substance secretion holds the promise for rapid assessment of the NPs-induced environmental stress acting on the unicellular organisms.

Ultrasound-Assisted Extraction and Assessment of Biological Activity of Phycobiliprotein-Rich Aqueous Extracts from Wild Cyanobacteria (Aphanizomenon flos-aquae)

Cyanobacteria are photosynthetic microorganisms that are considered as an important source of bioactive metabolites, among which phycobiliproteins (PBPs) are a class of water-soluble macromolecules of cyanobacteria with a wide range of applications. Massive proliferation of cyanobacteria can lead to excessive surface water blooms, of which removal, as a management measure, should be prioritized. In this study, the utilization of wild cyanobacteria biomass (Aphanizomenon flos-aquae) for extraction of phycobiliproteins is reported. Extraction of phycobiliproteins by conventional methods, such as homogenization, freeze-thaw cycles, and solid-liquid extraction, were optimized prior to ultrasound-assisted extraction. Standardization of ultrasonication for different parameters, such as ultrasonication amplitude (38, 114, and 190 μm) and ultrasonication time (1, 5.5, and 10 min), was carried out using a central composite design and response surface methodology for each of the primary techniques. A substantial increase on the individual and total phycobiliprotein yields was observed after ultrasonic treatment. The highest total PBP yield (115.37 mg/g of dry weight) was observed with samples treated with a homogenizer (30 min, 30 °C, and 1 cycle) combined with ultrasound treatment (8.7 min at 179 μm). Moreover, in vitro antioxidant capacity was observed for the obtained extracts in the Folin-Ciocalteu and ABTS^* + assays. In addition, a cytotoxic effect against C6 glioma cells was observed for A. flos-aquae PBPs. Conclusively, wild cyanobacteria could be considered as an alternative feedstock for recovery of PBPs.