title: Selective fermentation of carbohydrate and protein fractions of Scenedesmus, and biohydrogenation of its lipid fraction for enhanced recovery of saturated fatty acids.
abstract: Biofuels derived from microalgae have promise as carbon-neutral replacements for petroleum. However, difficulty extracting microalgae-derived lipids and the co-extraction of non-lipid components add major costs that detract from the benefits of microalgae-based biofuel. Selective fermentation could alleviate these problems by managing microbial degradation so that carbohydrates and proteins are hydrolyzed and fermented, but lipids remain intact. We evaluated selective fermentation of Scenedesmus biomass in batch experiments buffered at pH 5.5, 7, or 9. Carbohydrates were fermented up to 45% within the first 6 days, protein fermentation followed after about 20 days, and lipids (measured as fatty acid methyl esters, FAME) were conserved. Fermentation of the non-lipid components generated volatile fatty acids, with acetate, butyrate, and propionate being the dominant products. Selective fermentation of Scenedesmus biomass increased the amount of extractable FAME and the ratio of FAME to crude lipids. It also led to biohydrogenation of unsaturated FAME to more desirable saturated FAME (especially to C16:0 and C18:0), and the degree of saturation was inversely related to the accumulation of hydrogen gas after fermentation. Moreover, the microbial communities after selective fermentation were enriched in bacteria from families known to perform biohydrogenation, i.e., Porphyromonadaceae and Ruminococcaceae. Thus, this study provides proof-of-concept that selective fermentation can improve the quantity and quality of lipids that can be extracted from Scenedesmus.
authors.affiliation: Swette Center for Environmental Biotechnology, The Biodesign Institute at Arizona State University, P.O. Box 875701, Tempe, Arizona, 85287-5701.
authors.forename: YenJung Sean
authors.initials: YS
authors.lastname: Lai
authors.affiliation: Swette Center for Environmental Biotechnology, The Biodesign Institute at Arizona State University, P.O. Box 875701, Tempe, Arizona, 85287-5701. prathap@asu.edu.
authors.forename: Prathap
authors.initials: P
authors.lastname: Parameswaran
authors.affiliation: State Key Laboratory of Urban Water Resource and Environment, School of Municipal and Environmental Engineering, Harbin Institute of Technology, Harbin, People's Republic of China.
authors.forename: Ang
authors.initials: A
authors.lastname: Li
authors.affiliation: Swette Center for Environmental Biotechnology, The Biodesign Institute at Arizona State University, P.O. Box 875701, Tempe, Arizona, 85287-5701.
authors.forename: Alyssa
authors.initials: A
authors.lastname: Aguinaga
authors.affiliation: Swette Center for Environmental Biotechnology, The Biodesign Institute at Arizona State University, P.O. Box 875701, Tempe, Arizona, 85287-5701.
authors.forename: Bruce E
authors.initials: BE
authors.lastname: Rittmann
mesh_terms: D050260:Carbohydrate Metabolism; D002241:Carbohydrates / Q000302:isolation & purification*; D005227:Fatty Acids / Q000302:isolation & purification*; D005285:Fermentation; D006863:Hydrogen-Ion Concentration; D011506:Proteins / Q000302:isolation & purification* / Q000378:metabolism*; D044444:Scenedesmus / Q000737:chemistry* / Q000378:metabolism; D013997:Time Factors
chemical_list: D002241:Carbohydrates; D005227:Fatty Acids; D011506:Proteins
keywords: Scenedesmus; fermentation; lipids; microbial community