Butanol production in Lactic acid bacteria

Abstract: Butanol as an alternative liquid fuel has many advantages compared to ethanol, the number one biofuel used nowadays. This 4-carbon alcohol has higher energy content, lower enthalpy of vaporization, lower water adsorption, better blending characteristics, it is less corrosive, and it can be used in conventional engines without any modification.

The aim of this project was to understand and characterize proteins involved in the 2-butanol production in Lactobacillus brevis strains: diol dehydratase dependent oncoenzyme B12 and alcohol dehydrogenase.

Strains of L. brevis (SE20 and SE31) originally isolated from SEKAB ETechnology biorreactors (Örnskoldsvik, Sweden), were studied with respect to their ability to reduce 2,3-butanediol to 2-butanol. Later, enzyme activity in these strains was determinated.

Diol dehydratase was studied using the MBTH method based on the ability of ketones and aldehydes to react with it, forming azine derivatives which can be determined spectrophotometrically at 305 nm. The presence of substrate in the medium, has a positive control effect in enzyme activation, as the activity values increased abouttwice. Due to a limit project time, this enzyme wasn’t characterized in terms of Km and Vmax.

Alcohol dehydrogenase activity was determined by measuring the reduction of NAD⁺ to NADH at 340 nm. The parameters, maximum velocity and Michaelis constant were determined graphically by three linear methods (Lineweaver-Burk, Eadie Hofstee and Hanes-Woolf), for forward and reverse butanol reaction, showing that both reaction directions were active.