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Survey of growth and lipid profiles in eustigmatophytes

Tiago S. Lima1*, Mariana F.G. Assunção1 and Lília M.A. Santos1
  • 1 Algoteca de Coimbra (ACOI), Departamento de Ciências da Vida, Universidade de Coimbra, Portugal

Eustigmatophytes are yellow-green microalgae that became the focus of attention and intensive research recently due to the potential commercial production of biofuels and bioproducts by some high lipid productive species (Krienitz & Wirth 2006; Li et al. 2011). A combination of parameters such as easy growth at large scale, high lipid content, new genomic information and innovation of genetic transformation techniques has led to the stabilization of Nannochloropsis as a model organism to obtain lipids (Jinkerson et al. 2013). Species from other genera have been investigated to a lesser extent, for example Monodopsis subterranea and Trachydiscus minutus known to produce large amounts of EPA (Rezanka et al. 2010; Jo & Hur 2015; Cepák et al. 2014). Some microalgae species produce large quantities of lipids as a storage product that can achieve 75% of the dry weight (D’Alessandro & Filho 2016), depending on the environmental conditions and cells growth phase. Two types of lipids are produced by microalgae, the polar structural membrane phospholipids and glycolipids, and the neutral storage lipids that include triacylglycerols (TAGs). TAGs are considered the most interesting lipids for the biotechnology sectors (Pignolet et al. 2013) since they can be converted in fatty acid methyl esters (FAMEs) and used as biofuel. Substantial TAG production and accumulation take place during the stationary phase of growth (Huerlimann et al. 2010). Considering that the Coimbra Collection of Algae (ACOI) holds a relic group of strains covering the majority of eustigmatophyte genera, the present work aims to unveil the biotechnological potential of these strains, regarding growth and lipid profiles. Fourteen strains from nine different genera of ACOI eustigmatophytes were studied. The strains were cultivated in M7 and F/2 culture media during 10 and 30 days, under defined conditions of 23˚C room temperature, 51 µmol/m2/s cool white light intensity, 16:8 light:dark photoperiod and air bubbling. Growth was determined by dry weight (DW) and cell counting and the total lipid extracted. For total lipid determination freeze-dried biomass was extracted following the method described by Gao et al. (2015) with some modifications. In order to determine the content of neutral lipids (NL), glycolipids (GL) and phospholipids (PL) the total lipid obtained was fractionated. Fractionation was performed in a silica column prepared with chloroform, through which the lipid fractions of the extract were eluted using a sequence of solutions with increasing polarity (Christie & Han 2012). Each fraction (NL, GL, PL) obtained was dried and weight. Growth estimated by DW and cell counting increased from day 10 to day 30 in all strains. The values of DW ranged between 0.04 - 0.38 g/L in 10 days of cultivation and 0.20 - 0.78 g/L in 30 days of cultivation. The highest value obtained (0.78 g/L) was in Eustigmatos ACOI 3411 and the lowest (0.04 g/L) in Tetraplekton ACOI 3414. Growth results obtained for all strains are within the range of values known for microalgae (Chun-Yen et al. 2011). Regarding the cell counting results, the highest value obtained was for Nannochloropsis CCMP 1775 with 4.81 x 108 cell/mL in 30 days of cultivation and the lowest for Tetraplekton ACOI 3414 with 1.73 x 104 cell/mL. Total lipid (TL) estimations revealed a decrease from day 10 to day 30 for most of the studied strains. This was unexpected since several reports indicate accumulation of lipids in older cultures (Baoyan et al. 2015). The highest values of TL were obtained after 10 days of cultivation in Nannochloropsis CCMP 1775 (32.53% DW), Characiopsis ACOI 2424 (29.04% DW), Nannochloropsis SAG 38.85 (22.07% DW) and Dioxys ACOI 2029 (21.11% DW). Lipid production of the Nannochloropsis strains had already been estimated previously and the strains considered a good source of lipids (Baoyan et al. 2015), reason why they were selected in this study for comparison of results. The values obtained for these strains of Nannochloropsis are within the values reported by other authors (Bongiovani 2014). In all the strains the largest fraction obtained from TL was neutral lipids, followed by glycolipids and phospholipids. It is expected that TAGs compose most of the NL fraction, however carotenoids may be an important portion of this fraction, since they are also produced in large amounts by eustigmatophytes (Baoyan et al. 2015). This is the first survey of growth and lipid profiles covering five new eustigmatophyte genera from a total of nine studied. Results were obtained under non optimized culture conditions, reinforcing the position of eustigmatophytes as a very promising biotechnological class of microalgae.

Acknowledgements

Special thanks to the members of the ACOI team for all the support throughout this work.

References

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Keywords: Microalgae, Eustigmatophyceae, Growth, Lipids, lipid fractions

Conference: IMMR'18 | International Meeting on Marine Research 2018, Peniche, Portugal, 5 Jul - 6 Jul, 2018.

Presentation Type: Poster Presentation

Topic: Blue Biotech

Citation: Lima T, Assunção M and Santos L (2019). Survey of growth and lipid profiles in eustigmatophytes. Front. Mar. Sci. Conference Abstract: IMMR'18 | International Meeting on Marine Research 2018. doi: 10.3389/conf.FMARS.2018.06.00092

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Received: 23 Apr 2018; Published Online: 07 Jan 2019.

* Correspondence: Mr. Tiago S. Lima, Algoteca de Coimbra (ACOI), Departamento de Ciências da Vida, Universidade de Coimbra, Coimbra, Coimbra, 3000-451, Portugal, btiago_al@hotmail.com