Abstract

BackgroundAcetic acid is routinely generated during lignocelluloses degradation, syngas fermentation, dark hydrogen fermentation and other anaerobic bioprocesses. Acetate stream is commonly regarded as a by-product and detrimental to microbial cell growth. Conversion of acetate into lipids by oleaginous yeasts may be a good choice to turn the by-product into treasure.ResultsTen well-known oleaginous yeasts were evaluated for lipid production on acetate under flask culture conditions. It was found that all of those yeasts could use acetate for microbial lipid production. In particular, Cryptococcus curvatus accumulated lipids up to 73.4 % of its dry cell mass weight. When the culture was held in a 3-L stirred-tank bioreactor, cell mass, lipid content, lipid yield and acetate consumption rate were 8.1 g/L, 49.9 %, 0.15 g/g and 0.64 g/L/h, respectively. The fatty acid compositional profiles of the acetate-derived lipids were similar to those of vegetable oil, suggesting their potential for biodiesel production. Continuous cultivation of C. curvatus was conducted under nitrogen-rich condition at a dilution rate of 0.04 h−1, the maximal lipid content and lipid yield were 56.7 % and 0.18 g/g, respectively. The specific lipid formation rate, lipid content and lipid yield were all higher under nitrogen-rich conditions than those obtained under nitrogen-limited conditions at the same dilution rates. Effective lipid production by C. curvatus was observed on corn stover hydrolysates containing 15.9 g/L acetate.ConclusionsAcetate is an effective carbon source for microbial lipid production by oleaginous yeasts. Continuous cultivation of C. curvatus on acetate was promising for lipid production under both nitrogen-rich and nitrogen-limited conditions. These results provide valuable information for developing and designing more efficient acetate-into-lipids bioprocess.

Highlights

  • Acetic acid is routinely generated during lignocelluloses degradation, syngas fermentation, dark hydrogen fermentation and other anaerobic bioprocesses

  • Our results demonstrated that lipid production on acetate by C. curvatus could be operated under nitrogen-rich conditions, providing new opportunity to use acetatecontaining wastes rich in ammonia nitrogen for microbial lipid production [10]

  • The results indicated that C. curvatus favored lipid biosynthesis at lower dilution rates

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Summary

Introduction

Acetic acid is routinely generated during lignocelluloses degradation, syngas fermentation, dark hydrogen fermentation and other anaerobic bioprocesses. Acetate stream is commonly regarded as a by-product and detrimental to microbial cell growth. Conversion of acetate into lipids by oleaginous yeasts may be a good choice to turn the by-product into treasure. When sugars and related materials are used as substrates, Acetate is routinely present in aqueous stream of various biological processes but commonly recognized as a by-product. Acetate is co-produced during syngas fermentation, dark hydrogen fermentation and other anaerobic bioprocesses [8,9,10,11]. Acetate has been known as an inhibitor for cell growth of some oleaginous microorganisms [7, 13, 14]

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