The green alga Dictyosphaerium chlorelloides biomass and polysaccharides production determined using cultivation in crossed gradients of temperature and light

Structural properties of the biologically active Dictyosphaerium chlorelloides exopolysaccharide α-d-manno-α-l-rhamno-α-d-(2-O-methyl)-galactan

Structure of biopolymers produced by microalgae plays an important role for their potential biological activity prediction and applications. Previously isolated and well characterized dominant fractions (Dch5-8) from ion-exchange chromatography separation of the biologically active microalga Dictyosphaerium chlorelloides exopolysaccharide (Dch) were pooled and partially acid hydrolyzed. The dominant sugar components in the combined Dch5-8 fraction were Gal and its 2-O-methyl derivative, Rha and Man, all accounting for about 94 mol% of total amount of sugars. Separation of obtained hydrolysate on Bio-Gel P-2 afforded ten fractions. Their main components were identified by NMR. Based on oligosaccharide structures, the repeating unit of the polysaccharide backbone was identified as →2)-α-L-Rhap-(1→4)-2-O-methyl-[3-O-β-D-Galp]-α-D-Galp-(1→ branched by Man. Furthermore, the higher molecular weight fraction contained glucuronorhamnan. NMR data indicate 1,4-linked Rha units in the backbone in α and β configuration, branched at O2 by 2,4-di-O-methyl-β-d-glucuronic acid.

Isolation and identification of the molybdenum-resistant strain Raoultella ornithinolytica A1 and its effect on MoO42- in the environment

The mining and leakage of molybdenum (Mo) can cause environmental contamination which has not been realized until recently. Bacteria that can mitigate Mo-contamination was enriched and isolated. The low temperature and different pH conditions were considered to analysis its feasibility in Northern China which suffers from a long time of low temperatures every year. The result showed that the removal rate of MoO₄^2- by Raoultella ornithinolytica A1 reached 30.46% at 25 °C and pH 7.0 in Luria-Bertani medium (LB). Meanwhile, A1 also showed some efficiency in the reduction of MoO₄^2- in low phosphate molybdate medium (LPM), which reached optimum at the MoO₄^2- concentration of 10 mM. The results of FTIR indicated that the cell wall performed an essential role in the MoO₄^2- removal process, which was illustrated by the distribution of Mo in A1 (Mo bound to cell wall accounted for 92.29% of the total MoO₄^2- removed). In addition, low temperature (10 °C) effect the removal rate of MoO₄^2- by - 8.38 to 11.66%, indicating the potential for the in-situ microbial remediation of Mo-contaminated environments in low temperature areas.

Production and characterization of exopolysaccharides from salinity-induced Auxenochlorella protothecoides and the analysis of anti-inflammatory activity

The set scenario of this work was to investigate the production, physicochemical characteristics, and anti-inflammatory activities of exopolysaccharides from salinity-induced Auxenochlorella protothecoides. The results demonstrated that 10 ‰ salinity manipulation endowed preferable exopolysaccharide production by A. protothecoides. Under this salinity stress, ACPEPS1A and ACPEPS2A were purified from exopolysaccharide production by anion chromatography and molecular exclusion chromatography. ACPEPS1A exhibited a molecular weight (Mw) of 132 kDa and mainly consisted of galactose. ACPEPS2A was a heteropolysaccharide with an Mw of 170 kDa and the main monosaccharides of galactose and rhamnose with separate molar percents of 42.41 % and 35.29 %, respectively. FTIR, ¹H and ¹³C NMR supported that monosaccharide components of ACPEPS1A and ACPEPS2A possessed both α- and β-configuration pyranose rings. Further evidence indicated that ACPEPS1A and ACPEPS2A could effectively inhibit the inflammatory response in lipopolysaccharide (LPS) induced RAW264.7 cells by quenching inflammatory factor levels such as ROS, iNOS, TNF-α, and IL-6. The potential anti-inflammatory possibilities were that the monosaccharides of ACPEPS1A and ACPEPS2A possessed higher affinity with receptors on the macrophage surface than LPS and hampered LPS-induced inflammation. The findings of this work would favor innovative applications of exopolysaccharides from microalgae in complementary medicines or functional foods.

Structural features of biologically active extracellular polysaccharide produced by green microalgae Dictyosphaerium chlorelloides

Ion-exchange chromatography of the biologically active extracellular biopolymer produced by D. chlorelloides yielded ten fractions differing in yield, protein content, monosaccharide composition and molecular weight distribution. Their sugar compositional analyses showed rhamnogalactans, substituted to different extent by mannose and glucose, as a dominant EPS component in all fractions (91 %) except one containing arabinogalactan (7 %). In highly branched rhamnogalactans the quantity of linear (1,3-; 1,4- and 1,6-linked) and branched β-D-galactose units (1,3,6-, 1,4,6- and 1,3,4,6-linked) was nearly equal. From various α-L-rhamnose linkages the 1,2,4-linkage was dominant. Data indicate a rhamnogalactan backbone of EPS, branched by terminal mannose and glucose units, and a lot of O-methylated derivatives of galactose residues (2-O-methyl, 2,3-O-dimethyl, 3-O-methyl and 6-O-methyl). In individual fractions their content and type varied. Detail study of the arabinogalactan showed that its backbone consists of 1,3-linked β-D-Galp units; some of them are branched through O-4 by 6-OMe-α-D-Galp- (1 → 2) -α-L-Araf side chain, other through O-6 by 3-OMe-β-D-Galp, 6-OMe-β-D-Galp, β-D-Galp and β-D-Galf.

Influence of Process Operation on the Production of Exopolysaccharides in Arthrospira platensis and Chlamydomonas asymmetrica

Extracellular polysaccharides, or exopolysaccharides are high–molecular weight sugar-based polymers expressed and secreted by many microorganisms. As host organisms, the functions of exopolysaccharides are diverse, ranging from physical protection via biofilm formation, adhesion, and water retention to biological functions that are not entirely understood such as viral attachment inhibition. Industrial applications of exopolysaccharides can be found in food texture modification; for example, utilizing the hydrocolloidal properties of exopolysaccharides for thickening and gelling purposes to improve food quality and texture. Over the last decade, biologically active exopolysaccharides produced by microalgae have received attention for their potential as antiviral, antibacterial and antioxidative compounds and in the applications. However, relatively low yield and productivity are the limiting factors for full-scale industrial application. In this study, the well-known prokaryotic phototrophic microorganism Arthrospira platensis and the comparatively unknown eukaryotic unicellular green alga Chlamydomonas asymmetrica were used to evaluate the influence of different process parameters on exopolysaccharides formation and productivity. In addition to the essential control variables (light and temperature), the influence of operational techniques (batch and turbidostat) were also investigated. Although the two studied algae are differently affected by above parameters. The light intensity was the most influential parameter observed in the study, leading to differences in exopolysaccharides concentrations by a factor of 10, with the highest measured concentration for A. platensis of cEPS = 0.138 g L−1 at 180 μmol m−2 s−1 and for C. asymmetrica of cEPS = 1.2 g L−1 at 1,429 μmol m−2 s−1. In continuous systems, the achieved exopolysaccharides concentrations were low compared to batch process, however, slightly higher productivities were reached. Regardless of all screened process parameters, C. asymmetrica is the better organism in terms of exopolysaccharides concentrations and productivity.

Recent Advances of Microalgae Exopolysaccharides for Application as Bioflocculants

Microalgae are used in flocculation processes because biopolymers are released into the culture medium. Microalgal cell growth under specific conditions (temperature, pH, luminosity, nutrients, and salinity) provides the production and release of exopolysaccharides (EPS). These biopolymers can be recovered from the medium for application as bioflocculants or used directly in cultivation as microalgae autoflocculants. The optimization of nutritional parameters, the control of process conditions, and the possibility of scaling up allow the production and industrial application of microalgal EPS. Therefore, this review addresses the potential use of EPS produced by microalgae in bioflocculation. The recovery, determination, and quantification techniques for these biopolymers are also addressed. Moreover, other technological applications of EPS are highlighted.

Extracellular Polymeric Substances (EPS) as Microalgal Bioproducts: A Review of Factors Affecting EPS Synthesis and Application in Flocculation Processes

Microalgae are natural resources of intracellular compounds with a wide spectrum of applications in, e.g., the food industry, pharmacy, and biofuel production. The extracellular polymeric substances (EPS) released by microalgal cells are a valuable bioproduct. Polysaccharides, protein, lipids, and DNA are the main constituents of EPS. This review presents the recent advances in the field of the determinants of the synthesis of extracellular polymeric substances by microalgal cells and the EPS structure. Physical and chemical culture conditions have been analyzed to achieve useful insights into the development of a strategy optimizing EPS production by microalgal cells. The application of microalgal EPS for flocculation and mechanisms involved in this process are also discussed in terms of biomass harvesting. Additionally, the ability of EPS to remove toxic heavy metals has been analyzed. With their flocculation and sorption properties, microalgal EPS are a promising bioproduct that can potentially be used in harvesting algal biomass and wastewater management.

Capture and Release of Phosphorus by Periphyton in Closed Water Systems Influenced by Illumination and Temperature

Periphyton is known to play an important role in the self-purification of aquatic ecosystems. However, little attention has been paid to the understanding of P distribution and its partitioning influenced by the physical parameters when periphyton is separated from the sediment. In this work, the effect of periphyton on the capture and release of phosphorus in closed water systems was studied and the influence of illumination and temperature conditions were investigated. Results showed that phosphorus was transferred from water to periphyton during the experiment at 15 °C, but periphyton turned from a sink to a source of phosphorus in a few days at 25 and 35 °C. Phosphorus capture in periphyton was more enhanced when illuminated at 70 than 20 μmol photons m−2 s−1 at 25 and 35 °C, but not at 15 °C. At the end of the experiment, cyanobacteria became more abundant at 25 and 35 °C and phosphorus fractionation showed that labile-P was predominant in periphyton. The release of the captured phosphorus could be related to the disaggregation of periphyton following the depletion of nutrients. Therefore, periphyton act as a temporary storage of phosphorus following nutrient input in closed water systems and the capture and release of phosphorus is strongly influenced by the environmental conditions.

Estimation of growth and exopolysaccharide production by two soil cyanobacteria, Scytonema tolypothrichoides and Tolypothrix bouteillei as determined by cultivation in irradiance and temperature crossed gradients

Two filamentous cyanobacteria of the genera Scytonema and Tolypothrix were reported to be effective for stabilizing soil in arid areas due to the production of significant amounts of extracellular polysaccharides (EPS). These EPS may also have applications in the biotechnology industry. Therefore, two cyanobacterial species, Scytonema tolypothrichoides and Tolypothrix bouteillei were examined using crossed gradients of temperature (8-40°C) and irradiance (3-21 W m^-2) to identify their temperature and irradiance optima for maximum biomass and EPS production. According to their reported temperature requirements, both strains were considered mesophilic. The optimum growth range of temperature in S. tolypothrichoides (27 to 34°C) was higher than T. bouteillei (22-32°C). The optimum irradiance range for growth of S. tolypothrichoides (9-13 W m^-2) was slightly lower than T. bouteillei (7-18 W m^-2). Maximum EPS production by S. tolypothrichoides occurred at similar temperatures (28-34°C) as T. bouteillei (27-34°C), both slightly higher than for maximum growth. The optimum irradiance range for EPS production was comparable to that for growth in S. tolypotrichoides (8-13 W m^-2), and slightly lower in T. bouteillei (7-17 W m^-2). The Redundancy Analysis confirmed that temperature was the most important controlling factor and protocols for field applications or for mass cultivation can now be developed.

Euglena gracilis growth and cell composition under different temperature, light and trophic conditions

Background

Euglena gracilis, a photosynthetic protist, produces protein, unsaturated fatty acids, wax esters, and a unique β-1,3-glucan called paramylon, along with other valuable compounds. The cell composition of E. gracilis was investigated in this study to understand how light and organic carbon (photo-, mixo- and heterotrophic conditions) affected growth and cell composition (especially lipids). Comparisons were primarily carried out in cultures grown at 23 °C, but the effect of growth at higher temperatures (27 or 30 °C) was also considered.

Cell growth

Specific growth rates were slightly lower when E. gracilis was grown on glucose in either heterotrophic or mixotrophic conditions than when grown photoautotrophically, although the duration of exponential growth was longer. Temperature determined the rate of exponential growth in all cultures, but not the linear growth rate during light-limited growth in phototrophic conditions. Temperature had less effect on cell composition.

Cell composition

Although E. gracilis was not expected to store large amounts of paramylon when grown phototrophically, we observed that phototrophic cells could contain up to 50% paramylon. These cells contained up to 33% protein and less than 20% lipophilic compounds, as expected. The biomass contained about 8% fatty acids (measured as fatty acid methyl esters), most of which were unsaturated. The fatty acid content of cells grown in mixotrophic conditions was similar to that observed in phototrophic cells, but was lower in cells grown heterotrophically. Heterotrophic cells contained less unsaturated fatty acids than phototrophic or mixotrophic cells. α-Linolenic acid was present at 5 to 18 mg g^-1 dry biomass in cells grown in the presence of light, but at < 0.5 mg g^-1 biomass in cells grown in the dark. Eicosapentaenoic and docosahexaenoic acids were detected at 1 to 5 mg g^-1 biomass. Light was also important for the production of vitamin E and phytol.