Elsevier

Bioresource Technology

Volume 146, October 2013, Pages 732-735
Bioresource Technology

Short Communication
Optimisation of culture parameters for exopolysaccharides production by the microalga Rhodella violacea

https://doi.org/10.1016/j.biortech.2013.07.030Get rights and content

Highlights

Abstract

A unicellular Rhodophyte was identified by sequencing of its 18S rRNA encoding gene as belonging to the Rhodella violacea specie. With the objective to optimise the production of biomass and exopolysaccharide by this strain, effects of irradiance, pH and temperature on its photosynthetic activity were investigated. In a second time a stoichiometric study of the well-known f/2 medium led to its supplementation in N and P to increase biomass and then exopolysaccharide yields when the strain was cultivated in photobioreactors. The use of optimal conditions of culture (irradiance of 420 μE/m2/s, pH of 8.3 and temperature of 24 °C) and f/2 supplemented medium led to significant increases of biomass and exopolysaccharide productions. The structural characterisation of the produced exopolysaccharide revealed that it was sulphated and mainly composed of xylose. The different culture conditions and culture media tested had no significant impact on the structure of produced exopolysaccharides.

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.

References (21)

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