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Effects of overexpression of a bHLH transcription factor on biomass and lipid production in Nannochloropsis salina.

Kang NK, Jeon S, Kwon S, Koh HG, Shin SE, Lee B, Choi GG, Yang JW, Jeong BR, Chang YK - Biotechnol Biofuels (2015)

Bottom Line: These enhanced growth and nutrient uptake resulted in increased productivities of biomass and FAME.Conclusively, the improved growth in the transformants can be associated with the enhanced nutrient uptake.We are currently assessing their potential for scale-up cultivation with positive outcomes.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical and Biomolecular Engineering, KAIST, 291 Daehak-ro, Yuseong-gu, Daejeon, 305-701 Republic of Korea.

ABSTRACT

Background: Microalgae are considered promising alternative energy sources because they consume CO2 and accumulate large amounts of lipids that can be used as biofuel. Nannochloropsis is a particularly promising microalga due to its high growth rate and lipid content, and the availability of genomic information. Transcription factors (TFs) are global regulators of biological pathways by up- or down-regulation of related genes. Among these, basic helix-loop-helix (bHLH) TFs regulate growth, development, and stress responses in plants and animals, and have been identified in microalgae. We identified two bHLH TFs in the genome of N. salina CCMP1776, NsbHLH1, and NsbHLH2, and characterized functions of NsbHLH2 that may be involved in growth and nutrient uptake.

Results: We obtained NsbHLH2 overexpressing transformants of N. salina CCMP1776 by particle bombardment and confirmed that these were stable transformants. Quantitative real-time polymerase chain reaction (qRT-PCR) and Western blotting using antibodies against the FLAG tag that was attached at the end of the coding sequence confirmed the expression of the NsbHLH2 protein under various culture conditions. The qRT-PCR results also indicated that the endogenous and transgenic expression of NsbHLH2 was reduced under stressed conditions. Overexpression of NsbHLH2 led to increased growth rate in the early growth period, and concomitantly higher nutrient uptake, than wild type (WT). These enhanced growth and nutrient uptake resulted in increased productivities of biomass and FAME. For example, one of the transformants, NsbHLH2 3-6, showed increased biomass productivity by 36 % under the normal condition, and FAME productivity by 33 % under nitrogen limitation condition. Conclusively, the improved growth in the transformants can be associated with the enhanced nutrient uptake. We are currently assessing their potential for scale-up cultivation with positive outcomes.

Conclusion: Overexpression of NsbHLH2 led to enhanced growth rate and nutrient uptake during the early growth phase, and increased biomass and FAME productivity, especially in the later period under normal and stressed conditions. Based on these results, we postulate that NsbHLH2 can be employed for the industrial production of biodiesel from N. salina.

No MeSH data available.


Related in: MedlinePlus

DCW and FAME productivity of NsbHLH2 transformants under various culture conditions. The biomass for DCW (a) and FAME productivity (b) was obtained at day 8. Cells were cultivated at 25 °C, 120 rpm, 120 µmol photons/m2/s of fluorescent light, and 0.5 vvm of 2 % CO2. The data points represent the average of samples and error bars indicate standard error (n = 4). Significant differences, as determined by Student’s t test, are indicated by asterisks (*P < 0.05, **P < 0.01, ***P < 0.001)
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Fig4: DCW and FAME productivity of NsbHLH2 transformants under various culture conditions. The biomass for DCW (a) and FAME productivity (b) was obtained at day 8. Cells were cultivated at 25 °C, 120 rpm, 120 µmol photons/m2/s of fluorescent light, and 0.5 vvm of 2 % CO2. The data points represent the average of samples and error bars indicate standard error (n = 4). Significant differences, as determined by Student’s t test, are indicated by asterisks (*P < 0.05, **P < 0.01, ***P < 0.001)

Mentions: The high growth rate at early growth phase of the transformants was also associated with a greater dry cell weight (DCW) and biomass productivity at day 8 (Fig. 4; Table 2). Under the normal condition, DCW of the NsbHLH2 3–6 transformant at 8th day was increased by 36 % (Fig. 4a). Under N limitation and osmotic stress, the DCW of the transformants at 8th day was more than 20 % greater than WT (Fig. 4a). However, biomass productivity of all strains was similar at day 12 under normal conditions and under osmotic stress (Table 2).Fig. 4


Effects of overexpression of a bHLH transcription factor on biomass and lipid production in Nannochloropsis salina.

Kang NK, Jeon S, Kwon S, Koh HG, Shin SE, Lee B, Choi GG, Yang JW, Jeong BR, Chang YK - Biotechnol Biofuels (2015)

DCW and FAME productivity of NsbHLH2 transformants under various culture conditions. The biomass for DCW (a) and FAME productivity (b) was obtained at day 8. Cells were cultivated at 25 °C, 120 rpm, 120 µmol photons/m2/s of fluorescent light, and 0.5 vvm of 2 % CO2. The data points represent the average of samples and error bars indicate standard error (n = 4). Significant differences, as determined by Student’s t test, are indicated by asterisks (*P < 0.05, **P < 0.01, ***P < 0.001)
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4666162&req=5

Fig4: DCW and FAME productivity of NsbHLH2 transformants under various culture conditions. The biomass for DCW (a) and FAME productivity (b) was obtained at day 8. Cells were cultivated at 25 °C, 120 rpm, 120 µmol photons/m2/s of fluorescent light, and 0.5 vvm of 2 % CO2. The data points represent the average of samples and error bars indicate standard error (n = 4). Significant differences, as determined by Student’s t test, are indicated by asterisks (*P < 0.05, **P < 0.01, ***P < 0.001)
Mentions: The high growth rate at early growth phase of the transformants was also associated with a greater dry cell weight (DCW) and biomass productivity at day 8 (Fig. 4; Table 2). Under the normal condition, DCW of the NsbHLH2 3–6 transformant at 8th day was increased by 36 % (Fig. 4a). Under N limitation and osmotic stress, the DCW of the transformants at 8th day was more than 20 % greater than WT (Fig. 4a). However, biomass productivity of all strains was similar at day 12 under normal conditions and under osmotic stress (Table 2).Fig. 4

Bottom Line: These enhanced growth and nutrient uptake resulted in increased productivities of biomass and FAME.Conclusively, the improved growth in the transformants can be associated with the enhanced nutrient uptake.We are currently assessing their potential for scale-up cultivation with positive outcomes.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical and Biomolecular Engineering, KAIST, 291 Daehak-ro, Yuseong-gu, Daejeon, 305-701 Republic of Korea.

ABSTRACT

Background: Microalgae are considered promising alternative energy sources because they consume CO2 and accumulate large amounts of lipids that can be used as biofuel. Nannochloropsis is a particularly promising microalga due to its high growth rate and lipid content, and the availability of genomic information. Transcription factors (TFs) are global regulators of biological pathways by up- or down-regulation of related genes. Among these, basic helix-loop-helix (bHLH) TFs regulate growth, development, and stress responses in plants and animals, and have been identified in microalgae. We identified two bHLH TFs in the genome of N. salina CCMP1776, NsbHLH1, and NsbHLH2, and characterized functions of NsbHLH2 that may be involved in growth and nutrient uptake.

Results: We obtained NsbHLH2 overexpressing transformants of N. salina CCMP1776 by particle bombardment and confirmed that these were stable transformants. Quantitative real-time polymerase chain reaction (qRT-PCR) and Western blotting using antibodies against the FLAG tag that was attached at the end of the coding sequence confirmed the expression of the NsbHLH2 protein under various culture conditions. The qRT-PCR results also indicated that the endogenous and transgenic expression of NsbHLH2 was reduced under stressed conditions. Overexpression of NsbHLH2 led to increased growth rate in the early growth period, and concomitantly higher nutrient uptake, than wild type (WT). These enhanced growth and nutrient uptake resulted in increased productivities of biomass and FAME. For example, one of the transformants, NsbHLH2 3-6, showed increased biomass productivity by 36 % under the normal condition, and FAME productivity by 33 % under nitrogen limitation condition. Conclusively, the improved growth in the transformants can be associated with the enhanced nutrient uptake. We are currently assessing their potential for scale-up cultivation with positive outcomes.

Conclusion: Overexpression of NsbHLH2 led to enhanced growth rate and nutrient uptake during the early growth phase, and increased biomass and FAME productivity, especially in the later period under normal and stressed conditions. Based on these results, we postulate that NsbHLH2 can be employed for the industrial production of biodiesel from N. salina.

No MeSH data available.


Related in: MedlinePlus