Enhanced Lipid Production of Chlorella sp. HS2 Using Serial Optimization and Heat Shock

Abstract

Chlorella sp. HS2, which previously showed excellent performance in phototrophic cultivation and has tolerance for wide ranges of salinity, pH, and temperature, was cultivated heterotrophically. However, this conventional medium has been newly optimized based on a composition analysis using elemental analysis and ICP-OES. In addition, in order to maintain a favorable dissolved oxygen level, stepwise elevation of revolutions per minute was adopted. These optimizations led to 40 and 13% increases in the biomass and lipid productivity, respectively (7.0 and 2.25 g l-1 d-1). On this basis, heat shock was successfully adopted in novel Chlorella sp. HS2 cultivation as a lipid inducer for the first time. Considering its fast and cost-effective characteristics, heat shock will enhance the overall microalgal biofuel production process.

Molecular analysis of sugar transporters and glycolysis pathways in Ettlia sp. under heterotrophy using fructose and glucose

“…Multisugar medium (FG‐72) contained 72 g L –1 total sugars with a 3.8:1 fructose and glucose ratio, which represents a portion of hydrolyzed H. tuberosus (North American sunchoke). [ 11,7 ] Glucose medium (G‐72) contained 72 g L –1 glucose instead of fructose. Glucose medium (G‐15) contained 15 g L –1 glucose as a carbon source without any fructose.…”

“…The productivity of microalgal biorefineries is highly dependent on cultivation strategy; accordingly, heterotrophic cultivation strategies have attracted increasing attention due to their higher biomass productivity relative to photoautotrophic or mixotrophic strategies. [ 5,6 ] However, the heterotrophic strategy requires higher amounts of carbon sources, which is highly associated with the renewability and economic feasibility of bioprocesses [ 7 ] ; thus, the C source should be chosen carefully. However, most algae cultivated under heterotrophy favor glucose, [ 8–10 ] which is expensive and favored by humans.…”

“…The most representative case would be Helianthus tuberosus , [ 11,12 ] which generates approximately 3.8:1 fructose and glucose when hydrolyzed. [ 7,13 ] Sugar beet molasses, [ 14 ] sweet sorghum juice, [ 15 ] and winery wastewater [ 16 ] are also promising candidates as alternative carbon sources, and they contain both glucose and fructose. Therefore, to utilize fructose from those sources efficiently, fructophily is a necessary condition.…”

“…[ 8 ] Moreover, in a follow‐up study, the same species was successfully cultivated with hydrolyzed H. tuberosus , which mostly consists of fructose. [ 7 ] Strategies using fructose or H. tuberosus were possible because Ettlia sp. could take up fructose effectively.…”

“…which is a promising microalga producing high‐quality lipids, carotenoids, and lutein. [ 7 ] The fructophilic behavior of Ettlia sp. was validated by measuring cellular growth and sugar consumption for the first step.…”