Algal mixotrophic metabolism for the production of lipids

Abstract

The challenges associated with the use of conventional sources of crude oil increase the demand for alternative fuel sources. Biofuels offer the chance of replacing the depleting fossil fuels. However, the food versus fuel conflict that exists with the use of crops as source of biofuels means that algal biomass may be the only potentially viable biofuel source that ensures high production without trading off food production. Algal biomass may also ensure year-round production and uses minimal space. I confirm the known observation that the addition of glucose (0.2% w/v) to otherwise autotrophically grown algae (Auxenochlorella pyrenoidosa and isolate W7) increase lipid accumulation (based on chlorophyll content) 12-fold and 20-fold, respectively. More realistically, on per culture basis, lipid production increased 3-fold and 5-fold, respectively. Recently, cellulose was shown to be hydrolysed by algae and I provide preliminary evidence for the existence of extracellular cellulase produced by both algae used in my study. I show that on per culture basis, A. pyrenoidosa and isolate W7 supplemented with complex carbohydrates such as carboxymethyl cellulose, crystalline cellulose or paper mill sludge will increase their lipid content (up to triple for W7 supplemented with paper mill sludge). However, these carbohydrates as well as pure glucose depressed chlorophyll content of both algae, resulting in inflated apparent increase in lipid content based on chlorophyll concentration. This study adds important new information for the future potential commercialization of the mixotrophic production of algal lipid using cheap organic substrate in the form of pulp mill waste.