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

Abstract

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.

Life Cycle Assessment of Exopolysaccharides and Phycocyanin Production with Arthrospira platensis

“…Upstream processing consists of preparing the culture media, sterilization of the reactor and media, and the cultivation in a laboratory horizontal tubular airlift photobioreactor (PBR). The procedure was meticulously upheld and controlled to adhere to predetermined growth conditions studied previously [32]. The initial stage of downstream processing involves the separation of biomass from the supernatant.…”

“…These factors lead this process to a particularly significant degree of importance-in terms of parameter dependence-since almost all the variables are linked to the harvesting duration in days and the volume needed for harvesting. Additionally, it must be kept in mind that the highest product yield of both aimed-on products is in the stationary phase [32].…”

“…Regarding the input flows, the sole supplementary source is deionized water for washing, consistently set at a fixed volume of 30 L across all scenarios. The first product obtained from this added-value process is the EPS, whose EPS yield is dependent on process-specific parameters [32] and scenarios, as shown in Table 2. Along with this outflow, the residual fluid from the process is directed towards membrane electrodialysis for additional treatment, which will be elaborated upon in the following section.…”

Agro-Industrial Wastewaters for Algal Biomass Production, Bio-Based Products, and Biofuels in a Circular Bioeconomy

“…These compounds possess bioactivity and can be applied in structuring an integrated system as building blocks for various commercial applications [229]. Exopolysaccharide recovery systems have already been evaluated in effluents such as POME and the microalgae Phaeodactylum tricornutum [230] and in systems with the microalgae Arthrospira platensis and Chlamydomonas asymmetrica with CO 2 injection in the culture [231]. The integration of processes with liquid effluents and gas injections to produce algal biomass and the recovery of exopolysaccharides can be targeted.…”

Decay of Trichomes of Arthrospira platensis After Permeabilization Through Pulsed Electric Fields (PEFs) Causes the Release of Phycocyanin

“…Since this is degraded under nitrogen deficiency and serves as a nitrogen source for the cells (Boussiba and Richmond, 1980), nitrogen deficiency is very likely the reason for the variation between the experiments. It has been reported in the literature that A. platensis forms more exopolysaccharides (EPSs) under poor conditions such as nitrogen deficiency or high light radiation (Li et al, 2001;Jung et al, 2022). EPSs form a layer around trichomes and protect them from environmental stress such as dehydration.…”