Continuous Culture of Auxenochlorella protothecoides on Biodiesel Derived Glycerol under Mixotrophic and Heterotrophic Conditions: Growth Parameters and Biochemical Composition.

Evagelina Korozi,Iordanis Chatzipavlidis,Io Kefalogianni,Vasiliki Tsagou,Dimitris Antonopoulos,Lambis Chakalis,Yannis Kotzamanis,Giorgos Markou

doi:10.3390/microorganisms10030541

Evagelina Korozi, Iordanis Chatzipavlidis + Show 6 more

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https://doi.org/10.3390/microorganisms10030541

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Abstract

As crude glycerol comprises a potential substrate for microalga fermentation and value added products’ biosynthesis, Auxenochlorella protothecoides was grown on it under heterotrophic and mixotrophic conditions and its growth kinetics were evaluated in a continuous system under steady state conditions. Increasing initial glycerol concentration (from 30 to 50 g/L) in the heterotrophic culture led to reduced biomass yield (Yx/S) and productivity (Px), but favored lipid accumulation. Under heterotrophic conditions, the microalga was found to grow better (biomass up to 7.888 g/L) and faster (higher growth rates), the system functioned more effectively (higher Px) and crude glycerol was exploited more efficiently. Heterotrophy also favored proteins synthesis (up to 53%), lipids (up to 9.8%), and carbohydrates (up to 44.6%) accumulation. However, different trophic modes had no significant impact on the consistency of proteins and lipids. Oleic acid was the most abundant fatty acid detected (55–61.2% of the total lipids). The algal biomass contained many essential and non-essential amino acids, especially arginine, glutamic acid, lysine, aspartic acid, leucine, and alanine. In all the experimental trials, the protein contents in the microalgal biomass increased with the increasing dilution rate (D), with a concomitant decrease in the lipids and carbohydrates fractions.

Highlights

Biodiesel as an alternative fuel has attracted increasing attention worldwide in the past few years
The market has been flooded with crude glycerol over recent years and, seeking new ways to dispose of this waste stream seems to be imperative
A red light monochromatic source was chosen on the basis of preliminary trials and the results reported in previous work [14], according to which red light results in high growth rates of A. protothecoides under mixotrophic conditions

Summary

Introduction

Biodiesel as an alternative fuel has attracted increasing attention worldwide in the past few years. During the biodiesel manufacturing process, and, the production of fatty acids esters by the mix of triacylglycerols with alcohol and catalysts, crude glycerol is produced as a primary byproduct. For every liter of biodiesel produced, around 0.08 kg of crude glycerol is generated [1]. Glycerol is prohibitively expensive to be converted and purified into materials that can be used in the food, cosmetic or pharmaceutical industries due to its high concentration of many impurities, such as soap and methanol. The market has been flooded with crude glycerol over recent years and, seeking new ways to dispose of this waste stream seems to be imperative. The microbial fermentation of crude glycerol and its conversion into other useful products (such as polyhydroxyalkanoates, docosahexaenoic acid, lipids, etc.) is of special interest [2]

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