Caulobacter crescentus CB15 Pathway: acetoin degradation
Inferred by computational analysis

Pathway diagram: acetoin degradation

If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.

Locations of Mapped Genes:

Schematic showing all replicons, marked with selected genes

Superclasses: Degradation/Utilization/AssimilationCarbohydrates Degradation

Pathway Summary from MetaCyc:
Acetoin, along with diacetyl, is one of the compounds that give butter its characteristic flavor. It is natuarally found in many plants, including apples, asparagus, black currants, blackberry, wheat, broccoli, brussels sprouts, and cantaloupe.

Many bacteria can grow on acetoin. Both aerobic bacteria, such as Bacillus subtilis [Huang99], Ralstonia eutropha H16 [Priefert91] and Pseudomonas putida [Huang94a], as well as anaerobes, such as Clostridium magnum [Kruger94] and Pelobacter carbinolicus DSM 2380 [Oppermann94], were shown to degrade acetoin by a direct cleavage to acetaldehyde and acetyl-CoA, catalyzed by EC, acetoin dehydrogenase.

The products, acetaldehyde and acetyl-CoA, can be channeled to either respiration or fermentation, depending on the organism and conditions.

The substrate range for growth of the strict anaerobe Pelobacter carbinolicus DSM 2380 is restricted to acetoin, methylacetoin, 2,3-butanediol, and ethylene glycol [Oppermann88]. During fermentation, acetoin is degraded to equimolar amounts of acetate and ethanol [Schink84]. The key enzyme in this degradation pathway is the acetoin dehydrogenase complex, a large enzyme complex that belongs to the 2-oxo acid dehydrogenase complex family, which also includes pyruvate dehydrogenase (PDHC), 2-oxoglutarate dehydrogenase complex, branched-chain α-keto acid dehydrogenase complex and glycine cleavage (GDHC).

The formation of the acetoin dehydrogenase complex is induced during growth on acetoin, and the induction was demonstrated in several related species, including Pelobacter venetianus, Pelobacter acetylenicus, Pelobacter propionicus, Acetobacterium carbinolicum, and Clostridium magnum [Oppermann94].

Pathway Evidence Glyph:

Pathway evidence glyph

This organism is in the expected taxonomic range for this pathway.

Key to pathway glyph edge colors:

  An enzyme catalyzing this reaction is present in this organism
  An enzyme catalyzing this reaction was identified in this organism by the Pathway Hole Filler
  The reaction is unique to this pathway in MetaCyc

Created 04-Sep-2008 by SRI International


Blomqvist93: Blomqvist K, Nikkola M, Lehtovaara P, Suihko ML, Airaksinen U, Straby KB, Knowles JK, Penttila ME (1993). "Characterization of the genes of the 2,3-butanediol operons from Klebsiella terrigena and Enterobacter aerogenes." J Bacteriol 175(5);1392-404. PMID: 8444801

Booth83: Booth IR, Kroll RG (1983). "Regulation of cytoplasmic pH (pH1) in bacteria and its relationship to metabolism." Biochem Soc Trans 11(1);70-2. PMID: 6298028

Huang94a: Huang M, Oppermann FB, Steinbuchel A (1994). "Molecular characterization of the Pseudomonas putida 2,3-butanediol catabolic pathway." FEMS Microbiol Lett 124(2);141-50. PMID: 7813883

Huang99: Huang M, Oppermann-Sanio FB, Steinbuchel A (1999). "Biochemical and molecular characterization of the Bacillus subtilis acetoin catabolic pathway." J Bacteriol 181(12);3837-41. PMID: 10368162

Kruger94: Kruger N, Oppermann FB, Lorenzl H, Steinbuchel A (1994). "Biochemical and molecular characterization of the Clostridium magnum acetoin dehydrogenase enzyme system." J Bacteriol 176(12);3614-30. PMID: 8206840

Magee87: Magee, R.J., Kosaric, N. (1987). "The microbial production of 2,3-butanediol." Adv. Appl. Microbiol. 32: 89-161.

Oppermann88: Oppermann, F. B., Steinbuchel, A., Schlegel, H. G. (1988). "Utilization of methylacetoin by the strict anaerobe Pelobacter carbinolicus and consequences for the catabolism of acetoin." FEMS Microbiol. Lett. 55:47-52.

Oppermann94: Oppermann FB, Steinbuchel A (1994). "Identification and molecular characterization of the aco genes encoding the Pelobacter carbinolicus acetoin dehydrogenase enzyme system." J Bacteriol 176(2);469-85. PMID: 8110297

Priefert91: Priefert H, Hein S, Kruger N, Zeh K, Schmidt B, Steinbuchel A (1991). "Identification and molecular characterization of the Alcaligenes eutrophus H16 aco operon genes involved in acetoin catabolism." J Bacteriol 173(13);4056-71. PMID: 2061286

Schink84: Schink, B. (1984). "Fermentation of 2,3-butanediol by Pelobacter carbinolicus sp. nov. and Pelobacter propionicus sp. nov., and evidence for propionate formation from C2 compounds." Arch. Microbiol. 137:33-41.

Syu01: Syu MJ (2001). "Biological production of 2,3-butanediol." Appl Microbiol Biotechnol 55(1);10-8. PMID: 11234948

Wardwell01: Wardwell SA, Yang YT, Chang HY, San KY, Rudolph FB, Bennett GN (2001). "Expression of the Klebsiella pneumoniae CG21 acetoin reductase gene in Clostridium acetobutylicum ATCC 824." J Ind Microbiol Biotechnol 27(4);220-7. PMID: 11687934

Other References Related to Enzymes, Genes, Subpathways, and Substrates of this Pathway

Forsythe97: Forsythe RG, Karp PD, Mavrovouniotis ML "Estimation of Equilibrium Constants Using Automated Group Contribution Methods." CABIOS 13(5):537-543 1997.

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