Combination of bicarbonate and low temperature stress induces the biosynthesis of both arachidonic and docosahexaenoic acids in alkaliphilic microalgae Dunaliella salina HTBS

Abstract

High bicarbonate levels and low temperature may have an impact on microalgae cultivation. However, changes in cellular composition in response to the combination of the above stresses are still poorly understood. In this study, the combined effects of bicarbonate and low temperature on biochemical changes in alkaliphilic microalgae Dunaliella salina HTBS were investigated. Comparing to the control condition of 25°C without bicarbonate, the cell density was increased from 0.69 to 1.18 in the treatment condition of 0.15 M bicarbonate and low temperature (16 °C) while the lipid\protein\carbohydrate contents were increased from 34.71% to 43.94%, 22.44% to 26.03%, 22.62% to 29.18%, respectively. Meanwhile, the PUFAs, arachidonic acid (AA) and docosahexaenoic acid (DHA) contents reached to 3.52% and 4.73% with the combination of low temperature and bicarbonate, respectively, whereas they were not detected when the cells were treated with single condition. Moreover, both the chlorophyll and carotenoid contents were also detected with increased profiles in the combined treatments. As a result, the maximum photochemical efficiency but not reduced non-photochemical quenching was strengthened, which enhanced the photosynthetic performance. Additionally, our results indicated that D. salina HTBS could acclimate to the combined stress by up-regulating the activity of SOD\CAT and reducing MDA content. These findings demonstrated that the addition of a certain bicarbonate under low temperature could effectively enhance the biomass production and accumulation of AA and DHA, which would benefit the development of the microalgae industry in value-added products.

A novel system integrating electrolysis and ionic membranes (EIMs) enables artificial carbon concentration and alleviation of metal cation stress in microalgae cultivation

“…TIC was measured using a total organic carbon analyser (Multi N/C 2100S, Analytik Jena AG). 44 Five milliliters of culture was collected by centrifugation at 12 000 rpm for 10 min, and the supernatant was used for detection.…”

“…The contents of fatty acid methyl ester (FAME) were obtained with the slightly modified Folch method using a GC system (GC2010, Shimadzu; SP-2560, 100 m × 0.25 mm × 0.2 μm, Supelco, USA), as described previously. 44 To detect the chlorophyll fluorescence parameters, algal cells were sampled on the 13 th day and then dark-adapted for 20 min and determined with MAXI IMAGING-PAM (WALZ, Germany).…”