Utilization of High-Salinity Crude Glycerol Byproduct from Biodiesel Production for Biosynthesis of γ-Aminobutyric Acid in Engineered Halomonas elongata

Abstract

As the development of renewable energy has become imperative, biodiesel fuel (BDF) has been used as renewable biofuel with the advantage of having lower levels of greenhouse gas emissions. However, the transesterification reaction that produces BDF generates a high-salinity crude glycerol (CG) byproduct, which is difficult to recycle. Halomonas elongata is a moderately halophilic bacterium being used as a cell factory due to its ability to assimilate varieties of substrates for growth in high-salinity conditions. Previously, we engineered a recombinant H. elongata GOP-Gad to biosynthesize and accumulate γ-aminobutyric acid (GABA) as a high-value product. Here, we tested the ability of H. elongata GOP-Gad to use CG as a substrate for cell growth and GABA production. The CG byproduct was obtained from a BDF facility in Unzen City, Nagasaki, Japan, where geothermal energy catalyzed BDF production from waste cooking oil and biomethanol. Prior to use as the sole carbon (C) source in culture media, the CG byproduct was partially purified to remove soap substances and other impurities. Finally, we showed that H. elongata GOP-Gad could grow and accumulate GABA up to 28 μmol/g cell fresh weight in a minimal M63 medium containing 7% w/v NaCl with 4% w/v glycerol from the partially purified CG as a C source and 15 mM (NH4)2SO4 as a nitrogen (N) source. This result demonstrates a new circulatory bioprocess of C and N, in which H. elongata GOP-Gad can use partially purified CG and (NH4)2SO4 as the sole C and N sources for growth and GABA production.

Keywords

• halomonas elongata
• crude glycerol
• biodiesel byproduct
• salting out
• γ-aminobutyric acid
• h. elongatacell factory