Short CommunicationOptimisation of culture parameters for exopolysaccharides production by the microalga Rhodella violacea
Introduction
Autotrophic microalgae require a light energy source to convert inorganic compounds such as CO2, N, S, P into biomass via photosynthesis with high efficiencies. The growing interest of the scientific community for microalgae is linked to their ability to produce high-value compounds (Pignolet et al., 2013). Among them, red marine microalgae (Rhodophyta) encapsulated within a high molecular weight sulphated polysaccharide are an interesting source of hydrocolloids (Pignolet et al., 2013). They are composed of numerous monosaccharides, most abundant one being xylose. Methylated sugars, deoxy-monosaccharides, uronic acids and non-sugar substituents have been also identified (Pignolet et al., 2013, Capek et al., 2008, Geresh et al., 2009). The main species of microalgae described for exopolysaccharide production are Porphyridium and Rhodella ones (Pignolet et al., 2013, Geresh et al., 2009, Capek et al., 2008, Nosálová et al., 2012). At this time, only a partial structure of exopolysaccharide from Porphyridium sp. has been described (Geresh et al., 2009) and revealed a complex and ramified heteropolymer. Although all these red marine microalgae were widely studied for their photosynthetic apparatus (Lichtlé et al. 1996), a low number of articles focus on the implementation of culture parameters (composition of culture media and physico-chemical environment) for the biomass and exopolysaccharide productions.
In the present work, the autotrophic growth of a R. violacea strain was studied in batch photobioreactors with the objective to analyse the incidence of modified culture medium and physico-chemical parameters of cultures on photosynthetic activity, biomass and exopolysaccharide productions. In a preliminary study, the effect of irradiance, temperature and pH on the photosynthetic rate of the strain were also investigated.
Section snippets
Microbial strain: culture and identification
The R. violacea strain (LMGEIP 001) was obtained from the collection of culture of microalgae, Clermont Université, Université Blaise Pascal, France, “Laboratoire Microorganismes Génome et Environnement”. The microalgae was grown photoautotrophically in flask (50−1000 mL) stirred at 110 rpm at 24 °C for one month, in a 16 h−8 h light–dark regime (150 μE/m2/s) or in continuously lightened photobioreactor. Photobioreactors were built with a double jacketed Glass Roux culture flask of 700 mL vertically
Molecular phylogenetic characterisation
The PCR amplification of chromosomal DNA of the microalgae with Euk-1F and Euk-1520R primers revealed an efficient amplification. The length of the 18S rRNA region encoding gene amplified was 976-bp (accession number KC515354). The result of PCR blasted with other sequenced microalgae in NCBI showed similarity to the gene encoding for 18S small subunit rRNA of other microalgae. Edited sequences were used as queries in tBlastn (http://blast.ncbi.nlm.nih.gov/Blast.cgi) searches to determine the
Conclusion
The red marine microalgae LMGEIP001 strain was identified as belonging to the R. violacea species. The characterisation of its ability for CO2 capture led us to adapt its physico-chemical environment to optimise its photosynthetic activity. The elementary analysis of f/2 medium showed that it could be easily modified by supplementation of N and P to increase biomass production. Cultures using these new parameters validated their positive impacts on biomass but also on exopolysaccharide
Acknowledgements
Pr. Jean François Cornet is gratefully acknowledged for his help during this study.
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