Microalgae are diverse microorganis

Microalgae are diverse microorganisms, whichincludeboth prokaryotic and eukaryotic photosynthetic microorganisms,that can grow rapidly and are able to biosynthesize a variety of value-added substances (1). Of the manymicroalgal species, Euglena gracilishas attracted increasedacademic and industrial interest due to its promising potentialas a commercialsource of value-added products(2). E. gracilisis a single-celled flagellate protist found in freshwater. It canaccumulate a wide variety of metabolites,such as α-tocopherol, paramylon,and wax ester,inside its body (3, 4). E. gracilis can be cultured heterotrophically, photoautotrophically, or photoheterotrophically, which allows the biosynthesis of diverse metabolites to different extentsdepending on the different culture conditions (5). For example, heterotrophicallycultivated E. gracilisare able to accumulate high amount of paramylon, predominantly consisting ofβ-1,3-glucan (6).The β-glucans compriseheterogeneous and naturally occurring polysaccharides that consist of glucose monomers linked by a β-glycosidicbond (7). Several studies suggested the functional benefits ofthe dietary intake ofβ-glucans on the immune system(8, 9).Arecent report suggested the benefit of paramylon on diverse diseases,including cardiovascular diseases,due to the lowered levels of low density lipoproteincholesterol (10). The importance of β-glucanshas spurred various explorations of their natural sources. The β-glucans are intrinsic component of cereal grains and fungal and yeast cell walls, and are typically extracted from baker’s yeast (Saccharomyces cerevisiae) (11). However, the production yields from conventional yeast or cereal grainsourcesare significantly lower than the yield from E. gracilis. This reflects the ability ofE. gracilisto accumulate paramylon(β-glucans) to levels that are more than 60% of the dry cell weight. The development of E. gracilis as a bio-resource of β-glucans and the formulation of a strategy to enhance the production and collection of β-glucanshave become important goals.