Journal
JOURNAL OF APPLIED PHYCOLOGY
Volume 28, Issue 4, Pages 2123-2138Publisher
SPRINGER
DOI: 10.1007/s10811-015-0746-7
Keywords
Phaeodactylum; Nannochloropsis; Biofuel; Bicarbonate; Nutrients; Microalgae
Funding
- Undergraduate Research Scholars Program at Texas AM University
- Galveston campus
- Welch Foundation [BD 0046]
Ask authors/readers for more resources
Oils, carbohydrates, and fats generated by microalgae are being refined in an effort to produce biofuels. The research presented here examines two marine microalgae, Nannochloropsis salina (green alga) and Phaeodactylum tricornutum (diatom), when grown with 0 (no addition), 0.5, 1.0, 2.0, and 5.0 g L-1 NaHCO3 added to an f/2 medium during the growth phase (GP) and a nutrient induced (nitrate limitation) lipid formation phase (LP). We hypothesize that the addition of NaHCO3 is a sustainable and practical strategy to increase cellular density and concentrations of lipids in microalgae as well as the rate of lipid accumulation. In N. salina, final cell densities were significantly (p< 0.05) higher in the NaHCO3-treated cells than the control while in P. tricornutum the cell densities were higher with >[NaHCO3] during the GP. During the LP, cell densities were generally higher in the NaHCO3-treated cells compared with controls. F-V/F-M (efficiency of photosystem II) patterns paralleled those for cell density with generally higher values with higher concentrations of NaHCO3 and significantly different values between controls and 5.0 g L-1 NaHCO3 at the end of the GP (p< 0.05). F-V/F-M was variable between treatments in P. tricornutum (0.3-0.65) but less so in N. salina for (0.50.7) regardless of [NaHCO3]. The lipid index (measured with Nile red), used as a proxy for triacylglycerides (TAGs), was 10.2+/-6.5 and 4.4+/-2.9 (fluorescence units/OD cells x1000) for N. salina and P. tricornutum, respectively, at the end of the GP. At the end of the LP, the lipid index was eight and four times higher than during the GP in the corresponding 5.0 g L-1 NaHCO3 treatments, revealing that N. salina was accumulating more lipid than P. tricornutum. Dry weights essentially doubled during LP compared with GP for N. salina; this was not the case for P. tricornutum. In general, the percentage of ash in dry weights was significantly higher in the LP relative to the corresponding GP treatments for P. tricornutum; this was not the case for N. salina. During the LP, there was also less soluble protein in N. salina compared to GP; differences were not significant in cells growing with 2.0 or 5.0 g L-1 NaHCO3. In P. tricornutum, faster growing cells had more soluble protein during the GP and LP; differences between treatments were significant. P. tricornutum generally accumulated significantly more crude protein than N. salina at higher [NaHCO3]; there was three times more crude protein in the highest NaHCO3 (5.0 g L-1) treatment compared with the controls. C: N ratios (mol: mol) were similar across treatments during GP: 7.03+/-0.12 and 10.16+/-0.41 for N. salina and P. tricornutum, respectively. Further, C: N ratios increased with increasing [NaHCO3] during LP. Species-specific fatty acid methyl ester (FAMEs) profiles were observed. While C16: 0 was lower in P. tricornutum compared to N. salina, the diatom produced more C16: 1 and C14 but not C18: 3. Monounsaturated fatty acids (MUFA) significantly increased in N. salina in the LP compared to GP and in response to increasing [NaHCO3] (t tests; p< 0.05). Saturated fatty acids (SFA) responded similarly but to a lesser degree. There were more polyunsaturated fatty acids (PUFA) in N. salina than MUFAs or SFAs. In P. tricornutum, there were generally more SFAs, MUFAs and PUFAs in P. tricornutum during LP than GP in the corresponding NaHCO3 treatments. These findings reveal the importance of considering NaHCO3 as a supplemental carbon source in the culturing marine phytoplankton in large-scale production for biofuels.
Authors
I am an author on this paper
Click your name to claim this paper and add it to your profile.
Reviews
Recommended
No Data Available