Enhanced acetoin production by Bacillus amyloliquefaciens through improved acetoin tolerance

Acetoin production by Bacillus amyloliquefaciens was used as a model of product feedback to develop a strategy to enhance the production of acetoin. To enhance the resistance of B. amyloliquefaciens to acetoin, an acetoin-tolerant mutant E-11 was screened by using adaptive evolution with acetoin stress as the selection pressure. When compared with the parent FMME044, the mutant E-11 exhibited superior fermentation performance as follows: (1) the mutant E-11 exhibited increased tolerance to high concentration of acetoin, and the specific growth rate was 265.2% higher than that of the parent FMME044 in medium containing 80 g/L acetoin; (2) acetoin production by the mutant E-11 reached 71.5 g/L at 44 h when cultured in a 7-L fermentor with 173 g/L glucose, and the acetoin concentration and productivity of the mutant E-11 were 39.6% and 14.4% higher than those of the parent FMME044, respectively; (3) the unsaturated fatty acid contents in the mutant E-11 were 64.8%, 37.8%, and 18.4% higher than those in the parent FMME044 when cultured in 0, 40, and 60 g/L acetoin, whereas the saturated fatty acid contents in the mutant E-11 were 9.5%, 13.9%, and 14.1% lower than those in the parent FMME044, respectively.     

乙偶姻生物合成代谢调控及其应用

许多微生物在糖酵解过程中能够将糖类转化为乙偶姻来避免过度酸化。乙偶姻能够调节NAD＋/NADH的比率并存储碳源。此外,乙偶姻作为一种具有特殊奶油香气的食用香料,广泛应用于食品,烟草、酒类和化妆品行业。近些年研究发现许多植物根际促生菌能够通过产生乙偶姻激活植物对外界环境压力的抗性,激活植物系统抗性,抵御病原菌的侵袭。乙偶姻还可以促进植物生长,提高产量。另外,乙偶姻还是调节根际促生菌与宿主植物相互作用的信号分子。简述乙偶姻的生物合成路径及其调控,并介绍乙偶姻在食品、医药、化工、化妆品、植物保护、生物燃料等方面的应用。     

Formation of acetoin by Actinomyces olivaceus cultures]

Actinomyces olivaceus and some other actinomycetes accumulate acetoin and 2,3-butanediol in the cultural broth. Addition of cobalt to the medium favours the accumulation of acetoin.     

Metabolism of poly-beta-hydroxybutyrate and acetoin in Bacillus cereus

Kominek, Leo A. (University of Illinois, Urbana), and H. Orin Halvorson. Metabolism of poly-beta-hydroxybutyrate and acetoin in Bacillus cereus. J. Bacteriol. 90:1251-1259. 1965.-The synthesis of poly-beta-hydroxybutyrate (PHB) in Bacillus cereus strain T begins after the cessation of logarithmic growth. Its accumulation is preceded by the formation of acetoacetyl coenzyme A reductase, an enzyme used for its biosynthesis. Exogenous acetic acid present in the medium owing to incomplete glucose oxidation serves as the carbon source for polymer formation during the initial stages of its synthesis. Pyruvic acid is converted to acetoin by an enzyme system that is formed during vegetative growth. The formation of this enzyme system is dependent on a low pH in the medium. As the cells enter the sporulating stage, they lose the ability to form acetoin. The acetoin that accumulates is utilized via the 2,3-butanediol cycle which begins to function late in the sporulation stage. This cycle generates acetic acid which is used for PHB synthesis and is also oxidized to carbon dioxide. PHB accumulation reaches a maximum just prior to the formation of spores, and it is degraded during the process of sporulation. The effect of sporulation inhibitors and pH on PHB and acetoin metabolism are discussed.     

The rebalanced pathway significantly enhances acetoin production by disruption of acetoin reductase gene and moderate-expression of a new water-forming NADH oxidase in Bacillus subtilis

Bacillus subtilis produces acetoin as a major extracellular product. However, the by-products of 2,3-butanediol, lactic acid and ethanol were accompanied in the NADH-dependent pathways. In this work, metabolic engineering strategies were proposed to redistribute the carbon flux to acetoin by manipulation the NADH levels. We first knocked out the acetoin reductase gene bdhA to block the main flux from acetoin to 2,3-butanediol. Then, among four putative candidates, we successfully screened an active water-forming NADH oxidase, YODC. Moderate-expression of YODC in the bdhA disrupted B. subtilis weakened the NADH-linked pathways to by-product pools of acetoin. Through these strategies, acetoin production was improved to 56.7 g/l with an increase of 35.3%, while the production of 2,3-butanediol, lactic acid and ethanol were decreased by 92.3%, 70.1% and 75.0%, respectively, simultaneously the fermentation duration was decreased 1.7-fold. Acetoin productivity by B. subtilis was improved to 0.639 g/(l h).     

Fermentative production of chiral acetoin by wild-type Bacillus strains

Abstract

In recent years, there have been many studies on producing acetoin by microbial fermentation, while only a few studies have focused on chiral acetoin biosynthesis. The weight assignment method was first applied to balance the chiral purity (expressed as the enantiomeric excess value) and the titer of acetoin. Bacillus sp. H-18W, a thermophile, was selected from seven Bacillus strains for chiral acetoin production. To lower the cost of the fermentation medium, soybean meal was used as a feedstock. Four kinds of frequently used commercial proteinases with different active sites were tested for the hydrolyzation of the soybean meal, and the combination of the acidic proteinase and the neutral proteinase showed the best results. In a fermentation medium containing 100?g L^?1 glucose and 200?g L^?1 hydrolysate, Bacillus sp. H-18W produced 21.84?g L^?1 acetoin with an ee value of 96.25% at 60?h. This is the first report of using a thermophilic strain to produce chiral acetoin by microbial fermentation. Thermophilic fermentation can reduce the risk of bacterial contamination and can save cooling water. Using soybean meal hydrolysate and glucose as feedstocks, this work provides an economical and alternative method for the production of chiral pure acetoin.