Ultrahigh‐cell‐density heterotrophic cultivation of the unicellular green microalga <i>Scenedesmus acuminatus</i> and application of the cells to photoautotrophic culture enhance biomass and lipid production

Front. Bioeng. Biotechnol.

Chen

et al. 2021

Self Cite

Microalgal heterotrophic cultivation is an emerging technology that can enable producing high cell-density algal cell cultures, which can be coupled with photoautotrophic cultivation for valuable chemicals such as lipids manufacturing. However, how the heterotrophically grown algal cells respond to the lipid-inducing conditions has not been fully elucidated so far. In this study, when the heterotrophically grown Scenedesmus acuminatus cells were subjected to the high light (HL) and nitrogen-limited (NL) conditions, both the biomass and lipid productivity were enhanced as compared to that of the photoautotrophically grown counterparts. The chlorophyll a fluorometry analysis showed that the Fv/Fm and Y(II) of the heterotrophically grown cells subjected to the HL and NL conditions was recovered to the maximum value of 0.75 and 0.43, respectively, much higher than those of the photoautotrophically grown cells under the same stress conditions. Transcriptomic analysis revealed that heterotrophically grown cells fully expressed the genes coding for the photosystems proteins, including the key photoprotective proteins D1, PsbS, light-harvesting-complex (LHC) I and LHC II. Meanwhile, downregulation of the carotenoid biosynthesis and upregulation of the glycolysis/gluconeogenesis, tricarboxylic acid (TCA) cycle and oxidative phosphorylation pathways were observed when the heterotrophically grown cells were subjected to the HL and N-limited conditions for lipid production. It was deduced that regulation of these pathways not only enhanced the light utilization but also provided the reducing power and ATP by which the biomass accumulation was significantly elevated. Besides, upregulation of the acetyl-CoA carboxylase/biotin carboxylase, digalactosyl diacylglycerol synthase and diacylglycerol acyltransferase 2 encoding genes may be attributable to the enhanced lipid production. Understanding the cellular responses during the trophic transition process could guide improvement of the strength of trophic transition enhancing microalgal biomass and lipid production.

Section: Introductionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Trophic Transition Enhanced Biomass and Lipid Production of the Unicellular Green Alga Scenedesmus acuminatus

Front. Bioeng. Biotechnol.

Chen

et al. 2021

Self Cite

“…Microalgae are of particular interest as the most promising source for sustainable energy which has the potential to meet the increasing global demand for transport fuels by displacing non-renewable fuels. Although biodiesel production extracted from microalgae is proved to be technically practicable, a scalable and commercially viable are far from competitive fossil fuels' prices (Jin et al, 2020). Thus, new methods must be developed to increase yield and decrease the cost of the production.…”

Section: Introductionmentioning

confidence: 99%

An integrated digital microfluidic bioreactor for fully automatic screening of microalgal growth and stress-induced lipid accumulation

Wang

Liu

et al. 2020

Preprint

Algae are promising feedstock of biofuel. The screening of competent species and proper fertilizer supply are of the most important tasks. To accelerate this rather slow and laborious step, we developed an integrated high-throughput digital microfluidic (DMF) system that uses discrete droplet to serve as micro-bioreactor, encapsulating microalgal cells. Based on the fundamental understanding of various droplet hydrodynamics induced by the existence of different sorts of ions and biological species, an incorporation of capacitance-based position estimator, electrode-saving-based compensation and deterministic splitting approach was performed to optimize the DMF bioreactor. Thus, it enables all processes (e.g. nutrient gradient generation, algae culturing and analyzing of growth and lipid accumulation) occurring automatically on-chip especially in a high-fidelity way. The ability of the system to compare different micro algal strains on chip was investigated. Also, the Chlorella sp. were stressed by various conditions and then growth and oil accumulation were analyzed and compared, which demonstrated its potential as a powerful tool to investigate microalgal lipid accumulation at significantly lower laborites and reduced time.

“…Microalgae are of particular interest as the most promising source for sustainable energy which has the potential to meet the increasing global demand for transport fuels by displacing nonrenewable fuels. Although biodiesel production extracted from microalgae is proved to be technically practicable, a scalable and commercially viable are far from competitive fossil fuels’ prices (Jin et al, 2020). Thus, new methods must be developed to increase the yield and decrease the cost of production.…”

Section: Introductionmentioning

confidence: 99%

An integrated digital microfluidic bioreactor for fully automatic screening of microalgal growth and stress‐induced lipid accumulation

Wang

Biotech & Bioengineering

Liu

et al. 2020

Algae are the promising feedstock of biofuel. The screening of competent species and proper fertilizer supply is of the most important tasks. To accelerate this rather slow and laborious step, we developed an integrated high-throughput digital microfluidic (DMF) system that uses a discrete droplet to serve as a microbioreactor, encapsulating microalgal cells. On the basis of fundamental understanding of various droplet hydrodynamics induced by the existence of different sorts of ions and biological species, incorporation of capacitance-based position estimator, electrodesaving-based compensation, and deterministic splitting approach, was performed to optimize the DMF bioreactor. Thus, it enables all processes (e.g., nutrient gradient generation, algae culturing, and analyzing of growth and lipid accumulation) occurring automatically on-chip especially in a high-fidelity way. The ability of the system to compare different microalgal strains on-chip was investigated. Also, the Chlorella sp. were stressed by various conditions and then growth and oil accumulation were analyzed and compared, which demonstrated its potential as a powerful tool to investigate microalgal lipid accumulation at significantly lower laborites and reduced time.