In humans, dietary polyunsaturated fatty acids (PUFAs) are involved in therapeutic processes such as prevention and treatment of cardiovascular diseases, neuropsychiatric disorders, and dementia. We examined the physiology, PUFA accumulation and glycerol lipid biosynthesis in the marine microalga Nannochloropsis salina in response to constant suboptimal temperature (<20 °C). As expected, N. salina exhibited significantly reduced growth rate and photosynthetic activity compared to optimal cultivation temperature. Total fatty acid contents were not significantly elevated at reduced temperatures. Cultures grown at 5 °C had the highest quantity of eicosapentanoic acid (EPA) (C20:5n3) and the lowest growth rate. Additionally, we monitored broadband lipid composition to model the occurrence of metabolic alteration and remodeling for various lipid pools. We focused on triacylglycerol (TAG) with elevated PUFA content. TAGs with EPA at all three acyl positions were higher at a cultivation temperature of 15 °C. Furthermore, monogalactosyldiacylglycerol and digalactosyldiacylglycerol, which are polar lipids associated with chloroplast membranes, decreased with reduced cultivation temperatures. Moreover, gene expression analysis of key genes involved in Kennedy pathway for de novo TAG biosynthesis revealed bimodal variations in transcript level amongst the temperature treatments. Collectively, these results show that Nannochloropsis salina is a promising source of PUFA containing lipids.
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Enhancing oil production and harvest by combining the marine alga Nannochloropsis oceanica and the oleaginous fungus Mortierella elongata
Background: Although microalgal biofuels have potential advantages over conventional
fossil fuels, high production costs limit their application in the market. We developed
bio-flocculation and incubation methods for the marine alga Nannochloropsis oceanica
CCMP1779 and the oleaginous fungus Mortierella elongata AG77 resulting in
increased oil productivity.
Results: Grown separately and then combining the cells the M. elongata mycelium
could efficiently capture N. oceanica due to an intricate cellular interaction between the
two species leading to bio-flocculation. Use of a high-salt culture medium induced
accumulation of triacylglycerol (TAG) and enhanced the content of polyunsaturated
fatty acids (PUFAs) including arachidonic acid (ARA) and docosahexaenoic acid (DHA)
in M. elongata. To increase TAG productivity in the alga, we developed an effective
reduced nitrogen supply regime based on ammonium in environmental
photobioreactors (ePBRs). Under optimized conditions, N. oceanica produced high
levels of TAG that could be indirectly monitored by following chlorophyll content.
Combining N. oceanica and M. elongata to initiate bio-flocculation yielded high levels
of TAG and total fatty acids, ~15% and 22% of total dry weight (DW), respectively, as
well as high levels of PUFAs. Genetic engineering N. oceanica for higher TAG content
in nutrient-replete medium was accomplished by overexpressing DGTT5, a gene
encoding the type II acyl-CoA:diacylglycerol acyltransferase 5. Combined with bioflocculation
this approach led to increased production of TAG under nutrient replete
conditions (~10% of DW) compared to the wild type (~6% of DW).
Conclusions: The combined use of M. elongata and N. oceanica with available
genomes and genetic engineering tools for both species opens up new avenues to
improve bio-fuel productivity and allows the engineering of polyunsaturated fatty acids.
Keywords: Microalgae, Filamentous fungi, Flocculation, Cell wall interaction, Biofuel,
Nitrogen starvation, Polyunsaturated fatty acid, Triacylglycerol
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- Award ID(s):
- 1737898
- NSF-PAR ID:
- 10060878
- Date Published:
- Journal Name:
- Biotechnology for biofuels
- ISSN:
- 1754-6834
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Microalgae cultivation on wastewater offers the dual benefit of lowering costs for feedstock production with simultaneous wastewater remediation. This study utilized biochemical and quantitative label-free proteomic approaches to evaluate the growth and proteomic response for diatom
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The unique attributes of very-long-chain polyunsaturated fatty acids (VLC-PUFAs), their long carbon chains (n > 24) and high degree of unsaturation, impart unique chemical and physical properties to this class of fatty acids. The changes imparted by VLC-PUFA 32:6 n-3 on lipid packing and the compression moduli of model membranes were evaluated from π-A isotherms of VLC-PUFA in 1,2-distearoyl-sn-3-glycero-phosphocholine (DSPC) lipid monolayers. To compare the attractive or repulsive forces between VLC-PUFA and DSPC lipid monolayers, the measured mean molecular areas (MMAs) were compared with the calculated MMAs of an ideal mixture of VLC-PUFA and DSPC. The presence of 0.1, 1, and 10 mol % VLC-PUFA shifted the π-A isotherm to higher MMAs of the lipids comprising the membrane and the observed positive deviations from ideal behavior of the mixed VLC-PUFA:DSPC monolayers correspond to repulsive forces between VLC-PUFAs and DSPC. The MMA of the VLC-PUFA component was estimated using the measured MMAs of DSPC of 47.1 ± 0.7 Å2/molecule, to be 15,000, 1100, and 91 Å2/molecule at 0.1, 1, and 10 mol % VLC-PUFA:DSPC mixtures, respectively. The large MMAs of VLC-PUFA suggest that the docosahexaenoic acid tail reinserts into the membrane and adopts a nonlinear structure in the membrane, which is most pronounced at 0.1 mol % VLC-PUFA. The presence of 0.1 mol % VLC-PUFA:DSPC also significantly increased the compression modulus of the membrane by 28 mN/m compared with a pure DSPC membrane. The influence of VLC-PUFA on lipid “flip-flop” was investigated by sum-frequency vibrational spectroscopy. The incorporation of 0.1 mol % VLC-PUFA increased the DSPC flip-flop rate fourfold. The fact that VLC-PUFA promotes lipid translocation is noteworthy as retinal membranes require a high influx of retinoids which may be facilitated by lipid flip-flop.more » « less
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Accepted Manuscript1.0
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