Lipids in benthic diatoms: A new suitable screening procedure

Abstract

The selection of suitable and indigenous microalgae species is a fundamental requirement in developing added-value bioactive compounds recoverable in the food, health, and cosmetics markets. In this work, an integrated screening approach was developed to characterize the lipid rate of 33 diatom species (including 15 species studied for the first time) belonging to 16 genera from the Nantes Culture Collection, with the main objective of discovering bioactive lipid producers. For that purpose, a simple reliable method for establishing growth kinetics of strains and semi-quantitative analysis of lipid rates was developed. Growth kinetics measurements were achieved by daily minimal measurement fluorescence (F0) whereas lipid rate analyses were performed by high-throughput Fourier Transform Infrared spectroscopy on entire cells and lipid extracts. Results indicated that the method could be used directly on entire cells in spite of the presence of silica for the FTIR approach (due to frustule). The total lipid rate was species-dependant and ranged from 3.7% to 30.5% DW. Six strains out of 33 were found to present a higher total lipid rate superior to 15% DW, and 11 showed medium lipid rates ranging from 10% to 15% DW. The results revealed that five diatom species i.e. Amphora sp. NCC169, Nitzschia sp. NCC109, Nitzschia alexandrina NCC33, Opephora sp NCC366 and Staurosira sp. NCC182 presented interesting growth capabilities and should be further investigated as potential sources for their original lipid rate.

Effects of light and nitrogen availability on photosynthetic efficiency and fatty acid content of three original benthic diatom strains

“…Compared with our previous study [6], the three species examined in the current article show lower growth and biomass. However, this difference could be explained by their previously estimated growth under more favorable conditions, in medium using enriched natural seawater and with continuous light.…”

“…During exponential growth phase, the photosynthetic parameters (maximum PSII quantum efficiency, Fv/Fm and light saturation parameter Ek) were estimated using PAM-fluorometry [39]. Thus, culture volumes necessary to harvest 10 7 cells were sampled and centrifuged (10 min at 4500 g ) for biochemical composition determination: pigment composition by spectrophotometry [40] and protein, carbohydrate and lipid composition by HTSXT-FTIR [6]. The total cells in culture were harvested by filtration (0.7 μm) to estimate DW and perform lipid extraction following Bligh and Dyer [41].…”

“…FTIR spectra acquisition was performed according to recommendations of Coat et al (2014) [49] adapted by Cointet et al (2019) [6] for benthic diatom strains. The sample preparation and FTIR device are detailed in Cointet et al FTIR spectra were recorded in transmission mode on 5 μL dried harvested cells (10 7 cells.mL -1 ) allowing to quickly obtain their biochemical signatures expressed in terms of total lipids, total proteins and total carbohydrates.…”

“…To estimate the relative content of lipids, carbohydrates and proteins, their respective integral area was standardized with the total spectrum area and expressed in arbitrary units (a.u.) as recommended by Cointet et al (2019) [6] (Eq 8). Where s = lipids (~1740 cm -1 ) or carbohydrates (~1159 cm -1 ) or amide II (~1540 cm -1 ).…”

“…In this study, three benthic marine diatom species: Entomoneis paludosa NCC18.2, Nitzschia alexandrina NCC33, and Staurosira sp. NCC182, never previously studied except by Cointet et al (2019) [6], were selected for their high growth capacity, high lipid productivity and/or capacity to produce interesting molecular compounds. The purpose of this study was to examine and characterize their photosynthetic capacity and enhance their lipid productivity for potential future applications.…”