TITLE:
Evaluation of Carbon and Electron Flow in Lactobacillus brevis as a Potential Host for Heterologous 1-Butanol Biosynthesis
AUTHORS:
Oksana V. Berezina, German Jurgens, Natalia V. Zakharova, Rustem S. Shakulov, Sergey V. Yarotsky, Tom B. Granström
KEYWORDS:
Lactobacillus brevis; Metabolism; Carbon and Electron Flow; Heterologous Butanol Synthesis; SO2-Ethanol-Water Hydrolysate
JOURNAL NAME:
Advances in Microbiology,
Vol.3 No.5,
September
11,
2013
ABSTRACT: Heterofermentative lactic acid bacterium Lactobacillus brevis may be considered
as a promising host for heterologous butanol synthesis because of tolerance to
butanol and ability to ferment pentose and hexose sugars from wood hydrolysates
that are cheap and renewable carbohydrate source. Carbon and electron flow was
evaluated in two L. brevis strains in
order to assess metabolic potential of these bacteria for heterologous butanol
synthesis. Conditions required for generation of acetyl-CoA and NADH which are
necessary for butanol biosynthesis have been determined. Key enzymes
controlling direction of metabolic fluxes in L. brevis in various redox conditions were defined. In
anaerobic glucose fermentation, the carbon flow through acetyl-CoA is regulated
by aldehyde dehydrogenase ALDH possessing low affinity to NADH and activity (KmNADH= 200 μM, Vmax= 0.03 U/mg of total cell
protein). Aerobically, the NADH-oxidase NOX (KmNADH= 25 μM, Vmax = 1.7 U/mg) efficiently
competes with ALDH for NADH that results in formation of acetate instead of
acetyl-CoA. In general, external electron acceptors (oxygen, fructose) and
pentoses decrease NADH availability for native ethanol and recombinant butanol
enzymes and therefore reduce carbon flux through acetyl-CoA. Pyruvate
metabolism was studied in order to reveal redirection possibilities of
competitive carbon fluxes towards butanol synthesis. The study provides a basis
for the rational development of L. brevis strains producing butanol from wood hydrolysate.