Lipid extraction from microbial biomass

Abstract

Archaeal lipids are needed and investigated for its potential application in stable liposome formulation. It is believed that these liposomes can withstand the gastrointestinal tract and therefore make it possible to deliver active pharmaceutical ingredients, currently administered via injection, by an oral treatment. The aim of this work was the development and improvement of extraction and purification processes for archaeal lipids from the microorganism Sulfolobus acidocaldarius. The main focus was directed to the isolation and purification of dialkyl glycerol diether and glycerol dialkyl glycerol tetraether specifically. For this purpose the whole downstream process was evaluated, critical process steps were identified and systematically improved. Methods for each process step were evaluated based on gravimetric yields and the composition of the lipid pattern measured via liquid chromatography - mass spectrometry analysis. As initial downstream step, the drying of biomass from continuous cultivations of S. acidocaldarius was investigated. Both drying methods, spray drying and lyophilization, were shown to yield equal results regarding yield and lipid pattern. Also, a homogenization method with an ionic liquid was investigated, which resulted in an incrased extraction yield. Subsequently lipids were extracted using soxhlet method as well as an approach based on acidified extraction. This work shows the latter to be impractical, as under acidified conditions the entire organism is partly decomposed, which makes isolation and purification of specific lipid classes impossible. Inspired by this acidified approach, the effect of acidic and basic reaction conditions were investigated further on crude lipid extracts to reduce the amount of polar head groups. Additionally, the impact of two organic solvents, under a solid-liquid extraction from a sample of dried lipids was investigated, with acetic acid ethyl ester showing high potential in a purification prcess.These systemcatic investigations of separate downstream operations yieldedin an improved downstream process for lipid extraction starting from a frozen archael biomass pellet until enriched dialkyl glycerol diether and glycerol di- alkyl glycerol tetraether.