A microscale approach for simple and rapid monitoring of cell growth and lipid accumulation in Neochloris oleoabundans

Abstract

Due to the increasing environmental problems caused by the use of fossil fuels, microalgae have been spotlighted as renewable resources to produce biomass and biofuels. Therefore, the investigation of the optimum culture conditions of microalgae in a short time is one of the important factors for improving growth and lipid productivity. Herein, we developed a PDMS-based high-throughput screening system to rapidly and easily determine the optimum conditions for high-density culture and lipid accumulation of Neochloris oleoabundans. Using the microreactor, we were able to find the optimal culture conditions of N. oleoabundans within 5 days by rapid and parallel monitoring growth and lipid induction under diverse conditions of light intensity, pH, CO2 and nitrate concentration. We found that the maximum growth rate (µ max = 2.13 day(-1)) achieved in the microreactor was 1.58-fold higher than that in a flask (µ max = 1.34 day(-1)) at the light intensity of 40 µmol photons m(-2) s(-1), 5 % CO2 (v/v), pH 7.5 and 7 mM nitrate. In addition, we observed that the accumulation of lipid in the microreactor was 1.5-fold faster than in a flask under optimum culture condition. These results show that the microscale approach has the great potential for improving growth and lipid productivity by high-throughput screening of diverse optimum conditions.

Outdoor cultivation of microalgae in a coal-fired power plant for conversion of flue gas CO2 into microalgal direct combustion fuels

“…The conversion of CO 2 into biomass by microalgae is faster than that by food crops [10][11][12]. Under nitrogendepleted conditions, microalgae can accumulate a considerable amount of lipids in the intracellular region [13][14][15][16]. As reported by Choi et al, high-lipid content microalgae biomass has a high calorific value and can be used in the combustion process as a solid fuel [17].…”

Microfluidic techniques for enhancing biofuel and biorefinery industry based on microalgae

“…This can lengthen the duration before stationary phase and is undesirable when investigating the induction of lipid accumulation. Therefore, outlet microchannels having size (2 μm) smaller than microalgae cells [42, 43] and microfilter composed of micropillars [41, 45, 46] are applied to retain microalgae cells in the column. These features also enable in situ extraction of lipids for further analysis as addressed in a later section.…”

“…A previous review article [4] provides detailed information for the design and fabrication of the microfluidic photobioreactor. The simplest method of applying different lighting conditions to microfluidic devices is placing the whole device into a light-controlled environment [42, 43]. Since most of the microfluidic devices for microalgae culture are made of transparent materials (PDMS and glass slides), the light intensity inside the microfluidic compartment should be nearly identical to the imposed intensity.…”

“…Additionally, the optimal lighting conditions change when different metabolites are desired. For example, the production of lipids in Neochloris oleoabundans [42] and astaxanthin in Haematococcus pluvialis [43] requires significantly different lighting intensities in the same microfluidic bioreactor.…”

“…grown in traps [17, 18] and microchambers [48] showed similar final cell density or biomass productivity, but much higher growth rate compared to those in flasks. Growth rates of other microalgae strains in traps [18, 22] and microchambers [42, 48] were also higher than in the flask, while those from the droplet [25] were similar with the bulk culture. The differences in the growth rate and the final cell density in different microscale cultures are likely due to the dissimilar quantification methods for cell amounts.…”