Thanks to their various promising properties, bioactive peptides extracted from microalgae have recently attracted great attention from scientists. These compounds have been mostly obtained by enzymatic hydrolysis. In the present study, proteins from the marine microalga Rhodomonas sp. were hydrolysated into peptides using alcalase and pepsin. After obtaining the peptides, we characterized them and the crude protein by Fourier-transform infrared spectroscopy. Then, the biological activities of all protein preparations were evaluated. Antioxidant activity was investigated using DPPH (2,2-Diphenyl-1-picrylhydrazyl) radical-scavenging and ferric reducing power assays. The obtained results showed that crude protein presents higher antioxidant activity (74% at 1 mg/mL) compared to peptides obtained after hydrolysis by pepsin (56.5% at 1 mg/mL) and alcalase (47.5% at 1 mg/mL). The anti-inflammatory activity was also evaluated by inhibition of the denaturation of albumin assay. An interesting anti-inflammatory activity was obtained using protein extract. It was improved after enzymatic hydrolysis using pepsin to reach 89% of inhibition at 500 µg/mL. The obtained data showed that the marine microalga Rhodomonas sp. could be a potential source of valuable proteins and peptides for the pharmaceutical and cosmetic fields.

Polysaccharides from marine algae are one novel source of plant defense elicitors for alternative and eco-friendly plant protection against phytopathogens. The effect of exopolysaccharides (EPS) produced by Porphyridium sordidum on elicitation of Arabidopsis thaliana defense responses against Fusarium oxysporum was evaluated. Firstly, in order to enhance EPS production, a Box–Behnken experimental design was carried out to optimize NaCl, NaNO₃ and MgSO₄ concentrations in the culture medium of microalgae. A maximum EPS production (2.45 g/L) higher than that of the control (0.7 g/L) was observed for 41.62 g/L NaCl, 0.63 g/L NaNO₃ and 7.2 g/L MgSO₄ concentrations. Structurally, the EPS contained mainly galactose, xylose and glucose. Secondly, the elicitor effect of EPS was evaluated by investigating the plant defense-related signaling pathways that include activation of Salicylic or Jasmonic Acid-dependent pathway genes. A solution of 2 mg/mL of EPS has led to the control of fungal growth by the plant. Results showed that EPS foliar application induced phenylalaline ammonia lyase and H₂O₂ accumulation. Expression profile analysis of the defense-related genes using qRT-PCR revealed the up-regulation of Superoxide dismutases (SOD), Peroxidase (POD), Pathogenesis-related protein 1 (PR-1) and Cytochrome P450 monooxyge-nase (CYP), while Catalase (CAT) and Plant defensin 1.2 (PDF1.2) were not induced. Results suggest that EPS may induce the elicitation of A. thaliana’s defense response against F. oxysporum, activating the Salicylic Acid pathway.

Microalgae are photoautotrophic microorganisms known as producers of a large variety of metabolites. The taxonomic diversity of these microorganisms has been poorly explored. In this study, a newly isolated strain was identified based on the 18S rRNA encoding gene. The phylogenetic analysis showed that the isolated strain was affiliated with the Rhodomonas genus. This genus has greatly attracted scientific attention according to its capacity to produce a large variety of metabolites, including phycoerythrin. Growth and phycoerythrin production conditions were optimized using a Plackett–Burman design and response surface methodology. An expression profile analysis of the cpeB gene, encoding the beta subunit of phycoerythrin, was performed by qRT-PCR under standard and optimized culture conditions. The optimization process showed that maximum cell abundance was achieved under the following conditions: CaCl₂ = 2.1328 g/L, metal solution = 1 mL/L, pH = 7 and light intensity = 145 μmol photons/m²/s, whereas maximum phycoerythrin production level occurred when CaCl₂ = 1.8467 g/L, metal solution = 1 mL/L, pH = 7 and light intensity = 157 μmol/m²/s. In agreement, positive transcriptional regulation of the cpeB gene was demonstrated using qRT-PCR. This study showed the successful optimization of abiotic conditions for highest growth and phycoerythrin production, making Rhodomonas sp. suitable for several biotechnological applications.