Acetoin Metabolism in Bacteria

Abstract

Acetoin is an important physiological metabolite excreted by many microorganisms. The excretion of acetoin, which can be diagnosed by the Voges Proskauer test and serves as a microbial classification marker, has its vital physiological meanings to these microbes mainly including avoiding acification, participating in the regulation of NAD/NADH ratio, and storaging carbon. The well-known anabolism of acetoin involves alpha-acetolactat synthase and alpha-acetolactate decarboxylase; yet its catabolism still contains some differing views, although much attention has been focused on it and great advances have been achieved. Current findings in catabolite control protein A (CcpA) mediated carbon catabolite repression may provide a fuller understanding of the control mechanism in bacteria. In this review, we first examine the acetoin synthesis pathways and its physiological meanings and relevancies; then we discuss the relationship between the two conflicting acetoin cleavage pathways, the enzymes of the acetoin dehydrogenase enzyme system, major genes involved in acetoin degradation, and the CcpA mediated acetoin catabolite repression pathway; in the end we discuss the genetic engineering progresses concerning applications. To date, this is the first integrated review on acetoin metabolism in bacteria, especially with regard to catabolic aspects. The apperception of the generation and dissimilation of acetoin in bacteria will help provide a better understanding of microbial strategies in the struggle for resources, which will consequently better serve the utilization of these microbes.

The Metabolic Regulation of Sporulation and Parasporal Crystal Formation in Bacillus thuringiensis Revealed by Transcriptomics and Proteomics

“…Acetoin Metabolism-Acetoin (3-hydroxy-2-butanone) is produced and excreted by a number of fermentive bacteria during the exponential growth phase to prevent over-acidification of the cytoplasm and surrounding environment, and also acts as an extracellular carbon and energy store (43). Our RNA-seq data showed that the acetoin biosynthesis-associated genes alsS (␣-acetolactate synthase) and alsD (␣-acetolactate decarboxylase) (44) were expressed at high levels at 7 h, but were down-regulated by about threefold at 9 h, and were finally undetectable at 13 h. At the translational level, AlsS was decreased by 3.2-and 3.1-fold at 9 h and 13 h, respectively, while AlsD was detected by iTRAQ but could not be quantified.…”

Disruption of the alsSD operon of Enterococcus faecalis impairs growth on pyruvate at low pH

“…Excretion of C4 compounds, which can be determined by the VP test, has vital implications for the physiology of different micro-organisms because, as described elsewhere, it is used to avoid acidification, participates in the regulation of the NAD : NADH ratio and functions as a carbon-storing strategy (Xiao & Xu, 2007). Although production of these compounds in Ent.…”

“…faecalis as being involved in pyruvate metabolism is a-acetolactate synthase (ALS), which catalyses the thyamine pyrophosphate (TPP)-dependent condensation of two moles of pyruvate to give one mole of a-acetolactate (AL). ALS constitutes the first enzyme of the C4 biosynthetic pathway (Xiao & Xu, 2007). The apparent K m for pyruvate of ALS in cell-free extracts of Ent.…”

Discovery of a putative acetoin dehydrogenase complex in the hyperthermophilic archaeon Sulfolobus solfataricus

“…This acetoin dehydrogenase complex also has multiple copies of E1, E2 and E3 and operates via the same lipoic acid mediated mechanism, although acetaldehyde, and not CO 2 , is released by the action of E1 [2].…”