Two-Stage pH Control Strategy Based on the pH Preference of Acetoin Reductase Regulates Acetoin and 2,3-Butanediol Distribution in Bacillus subtilis

Abstract

Acetoin reductase/2,3-butanediol dehydrogenase (AR/BDH), which catalyzes the interconversion between acetoin and 2,3-butanediol, plays an important role in distribution of the products pools. This work characterized the Bacillus subtilis AR/BDH for the first time. The enzyme showed very different pH preferences of pH 6.5 for reduction and pH 8.5 for oxidation. Based on these above results, a two-stage pH control strategy was optimized for acetoin production, in which the pH was controlled at 6.5 for quickly converting glucose to acetoin and 2,3-butanediol, and then 8.0 for reversely transforming 2,3-butanediol to acetoin. By over-expression of AR/BDH in the wild-type B. subtilis JNA 3-10 and applying fed-batch fermentation based on the two-stage pH control strategy, acetoin yield of B. subtilis was improved to a new record of 73.6 g/l, with the productivity of 0.77 g/(l·h). The molar yield of acetoin was improved from 57.5% to 83.5% and the ratio of acetoin/2,3-butanediol was switched from 2.7∶1 to 18.0∶1.

Acetoin production via unbalanced fermentation in Shewanella oneidensis

“…Many bacterial strains like Enterobacter aerogenes, Serratia marcescens, Paenibacillus polymyxa, or Bacillus subtilis can produce acetoin (Xiao and Lu, 2014). Using Bacillus, Zhang et al (2014Zhang et al ( , 2016 reported yields of 68.5%-83.5% depending on the substrate and the genetic background of the strains. Bacillus subtilis is by the Food and Drug Administration listed as a "generally regarded as safe" strain (Xiao and Lu, 2014).…”

High acetoin production by a newly isolated marine Bacillus subtilis strain with low requirement of oxygen supply

“…Most of the commercial acetoin is a racemic mixture which is mainly produced by chemical way, while the biological product is highly enantioselective. Therefore, acetoin fermentation has attracted much attention in recent years, and many exciting results through strain screening and enhancement, fermentation strategies on pH control and aeration control have been achieved to increase acetoin production [1,2], and the highest acetoin concentration reached 73.6 g/l by an engineered Bacillus subtilis strain when glucose was used as carbon source [3]. Direct production of acetoin from 2,3-butanediol was also an efficient way and the acetoin concentration reached 89.2 g/l by Gluconobacter oxydans DSM 2003 [4].…”

“…The acetoin concentration was generally around 40 g/l obtained by the wild type of Bacillus strains [7][8][9] and the highest could reach 51.2 g/l by a native strain of B. amyloliquefaciens FMME044 [10]. After mutagenesis the concentration of acetoin was increased to more than 50 g/l [3,[11][12][13][14]. The production ability and culture conditions of strains which were generally recognized as safe (GRAS) were compared ( Table 1).…”

Genome Structure ofBacillus cereustsu1 and Genes Involved in Cellulose Degradation and Poly-3-Hydroxybutyrate Synthesis

“…These results confirmed the extracellular cellulase activity of the bacterial strain. [61]. RCS was estimated to have 8.98 g/L crude proteins, and it also contained all the essential amino acids for bacterial growth, and some -and -amino-butyric acid (AIB, GABA) (see Figure S3 in Supplementary Material).…”