Production of exopolymer substances from the thermophilic chlorophyte Graesiella: industrial and ecological applications

Abstract

Microalgal extracellular polymeric substances (EPSs) are heteropolysaccharides that have characteristics suitable for industrial and biotechnological applications. Notably, they have strong anionic nature and high hydrophobicity. Nevertheless, systematic studies to demonstrate the viability of the production of EPSs on an industrial scale are still crucial. In this research, the chlorophyte Graesiella was grown on a raceway pond to view its EPS valorization. The biomass production achieved a maximum of 1.98 g L −1 and an EPS production of 1.6 g L −1 after six production days. The Graesiella EPSs with a molecular weight above 100 kDa are sulfated exopolymers containing mainly polysaccharide (70%) and protein (16%). The EPSs produced more stable emulsions with hydrocarbons and oils than Tween-20. The emulsification indices with n-hexane (88%) and maize oil (28%) indicate the EPSs' strong emulsion-stabilizing capacity. The EPSs showed a peak flocculating percentage of 95% to kaolin suspension, with better flocculation performance than Al 2 (SO 4 ) 3 and alginate. Moreover, Graesiella EPSs had a significant effect on antimicrobial activity, significantly inhibiting fungal growth (71% for Botytis cinerea and 87% for Fusarium oxysporum), spore germination (100% of inhibition at a concentration of 1.8 g L −1 ), and mycelium growth (68% of inhibition). Also, Graesiella EPSs acted as a bactericide against Vibrio anguilaruim and Listonella anguilaruim (100% inhibition). EPSs were also found to have potent antioxidant activity compared with L-ascorbic acid. The obtained results open new perspectives to the further exploration of Graesiella sp. as a potential EPS producer, making it a promising candidate for numerous industrial applications.

Characterization of biodegradable films based on extracellular polymeric substances extracted from the thermophilic microalga Graesiella sp.

“…In a previous work [13], results showed that Graesiella sp., is found amongst the most efficient EPSs producers reaching values close to 1.62 g⋅L − 1 in laboratory cultures. The native Graesiella sp., EPS are hetero-sulphated polysaccharides of anionic nature composed mainly with polysaccharides (80%) and proteins (14%), presenting a high crystalline nature.…”

“…The strain was isolated from a hot-spring (60 • C; North of Tunisia at 36 • 49 ′′ N, 10 • 34 ′′ E) and grown in Bold's Basal Medium (BBM) at a temperature of 30 ± 1 • C and a light intensity of 120 μmol photons m − 2 s − 1 . Extracellular Polymeric Substances (EPS) were extracted from a stationary phase culture as described by Gongi et al [13]. The recovered EPS solution was freeze-dried and stored in dark and dry conditions for edible film preparation.…”

“…Structural analysis of Graesiella sp., EPS film was performed by the Fourier Transform Infrared spectroscopy (FTIR) analysis and the surface microstructure characterization using atomic force microscopy (AFM) and scanning electron microscopy (SEM). FTIR spectra were obtained by pressing into a 16 mm-diameter mold with a Perkin-Elmer spectrum GX FTIR system (Perkin-Elmer, USA) according to Gongi et al [13].…”

“…EPS obtained from microalgae are versatile biopolymers produced at a high amount by several microalgae species, particularly thermophilic ones [12,13].…”

“…EPS have been utilized as additives, thickeners, emulsifiers, gelling agents, and stabilizers in several industrial sectors such as food products, pharmacy, petroleum industry, and bioremediation agents [14]. Furthermore, EPS provides high intrinsic bioactive properties such as antioxidant, anti-inflammatory, antiviral, antifungal, and antibacterial [13,14] and therefore have a high potential for use as biodegradable active packaging, especially for meat products.…”