Abstract/Summary

2,3-Butanediol (2,3-BD) is an important platform chemical of industrial interest due to its extensive applications and high market value. Global warming, environmental impact and limitation of fossil fuel reserves are driving the development of eco-friendly and sustainable bio-based 2,3-BD. A global market of 2,3-BD is anticipated to reach 300 million US dollars in 2030. 2,3-BD stereoisomers are linked to specific industrial applications, with pure chiral 2,3-BD isomers being highly sought after from a commercial point of view. The present study focused on the production of highly pure 2,3-BD stereoisomers by non-pathogenic wild-type bacterial strains and the development of efficient downstream processing. The first task was the screening for non-pathogenic wild-type bacterial strains capable of producing 2,3-BD from sucrose-based media. Among the strains tested, Bacillus subtilis and Serratia plymuthica showed promising characteristics of producing notable concentrations of 2,3-BD in batch-flask cultures. Corn steep liquor (CSL) was proven as an alternative low-cost nitrogen source to costly nitrogen sources for 2,3-BD production. Furthermore, the impact of dissolved oxygen concentrations on 2,3-BD production was assessed in batch bioreactor process. Limited dissolved oxygen conditions suppressed butanediol dehydrogenase activity and supported maximum (R, R)-2,3-BD production at high purity (100%) in B. subtilis, whereas high dissolved oxygen conditions promoted bacterial growth and acetoin formation. S. plymuthica was reported for the first time as capable producer of highly pure (95%) meso-2,3-BD. A fed-batch fermentation with optimum DO conditions and a constant residual sucrose feeding regime improved 2,3-BD production in both strains, reaching 42.31 g/L of 2,3-BD with a production yield of 0.52 g/g sucrose in B. subtilis, v and 26.23 g/L of 2,3-BD with a production yield of 0.34 g/g sucrose in S. plymuthica fermentation. With regards to downstream processing, the yellowish-brown colour of two different fermentation broths (S. plymuthica and B. subtilis) were successfully reduced through treatment with activated charcoal. Subsequently, the ionic liquid (IL), 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([C2mim][CF3SO3]) was investigated with inorganic salts for 2,3-BD separation. In the case of S. plymuthica broth, 95.6% of 2,3-BD was successfully recovered from the fermentation broth with a partition coefficient of 24.6 by using a system composed of 30%[C2mim][CF3SO3] - 35%K2HPO4 (w/w). In addition, 35%[C2mim][CF3SO3] - 30%K2HPO4 provided a high yield for recovering 2,3-BD (97.3%) from B. subtilis fermentation broth, thus verifying the effectiveness of this separation method. Additionally, the study showed that IL could be effectively recovered (90% to 98%). Hence, non-pathogenic wild-type B. subtilis and S. plymuthica could be potentially employed as promising strains for high chiral purity of 2,3-BD stereoisomer production. Also, IL-based salting out method enables the development of a novel separation process for efficient recovery of 2,3-BD from diverse fermentation broths.