Fermentative degradation of acetone by an enrichment culture in membrane-separated culture devices and in cell suspensions

Abstract

A mixed culture, WoAct, growing on acetone, consisted of two dominant morphotypes: a rod-shaped acetone-fermenting bacterium producing acetate, and an acetate-utilizing Methanosaeta species. Dense cell suspensions, largely free of the aceticlastic methanogen and supplemented with bromoethanesulfonate, were able to degrade acetone and grow in small volumes in membrane-separated culture devices in which the acetate produced could diffuse into a large volume of medium. Acetone degradation and growth halted when the acetate concentration reached about 10 to 12 mM. Cell suspensions were able to degrade acetone in the absence of active methanogenesis, but the addition of 10 mM acetate inhibited acetone metabolism. Addition of an active culture of Methanosaeta sp. greatly stimulated the rate of acetone degradation. The results show that acetate removal in the mixed culture is not a prerequisite for growth and acetone degradation by the acetone-fermenting bacterium.

Involvement of an ATP-dependent carboxylase in a CO2-dependent pathway of acetone metabolism by Xanthobacter strain Py2

“…Growth of Xanthobacter strain Py2 cultures on nitrogen-limited media supplemented with either natural abundance or 13 C-enriched NaHCO 3 plus CO 2 (7.5 mM) was studied as described previously (19), except that the carbon sources for growth were either isopropanol (32 mM) or acetone (40 mM). The harvesting of cultures, isolation of poly-␤-hydroxybutyrate, and 13 C nuclear magnetic resonance (NMR) analyses were performed as described previously (19).…”

“…For some aerobic bacteria, the metabolism of acetone has been proposed to proceed via an O 2 -and reductant-dependent hydroxylation reaction producing acetol-(1-hydroxyacetone) as the initial product (4,12,21,23). For anaerobic bacteria, the metabolism of acetone has been proposed to proceed via a CO 2 -dependent carboxylation reaction producing acetoacetate as the initial product as shown in the following equation (2,10,11,13,14,(16)(17)(18): CH 3 COCH 3 ϩ CO 2 3CH 3 COCH 2 COO Ϫ . The carboxylation of acetone is the reverse of acetoacetate decarboxylation, a terminal reaction catalyzed by acetoacetate decarboxylases in certain fermentative bacteria of the genus Clostridium (6,26).…”

Untitled

“…Syntrophic oxidation of long chain fatty acids profits as well by efficient removal of the coproduct acetate through the activity of acetotrophic methanogens, and the same appears to be true for all fatty acid degrading systems examined so far. In the exceptional case of isovalerate degradation, acetate transfer is probably even more important than hydrogen transfer, and the case of methanogenic acetone degradation gives an example of interspecies transfer of acetate only (Platen & Schink 1987;Platen et al 1994). One could as well think of interspecies methanol transfer because also this substrate is utilized by methanogens, but there is so far no convincing example of such a cooperation in methanogenic degradation.…”

“…Indications that this process is mediated through a syntrophic cooperation between a methanogen operating in reverse and a sulfate reducer (Hoehler et al 1994) were based on observations that methanogens themselves can oxidize methane simultaneously with methane formation (Zehnder and Brock 1979). On the basis of the reaction energetics it was argued that the small energy gain available in this process ( G • = −18 kJ per mol) could feed only one partner at maximum whereas the second one obviously had to run its activity cometabolically, thus preventing enrichment of both partners by conventional enrichment techniques (Platen et al 1994). Indeed, the concept of a syntrophic cooperation between methanogens and sulfate reducers could be verified recently with the discovery of structured microbial aggregates in marine sediments covering methane gas hydrates (Boetius et al 2000).…”

Metabolic pathways and energetics of the acetone-oxidizing, sulfate-reducing bacterium, Desulfobacterium cetonicum

“…Acetate and butyrate were measured by HPLC (Friedrich and Schink 1993). Acetone was determined colorimetrically (Platen et al 1994). Cell densities in cultures and cell suspensions were determined as an optical density at 440 nm and correlated to total cellular protein and gravimetrically determined dry mass using data obtained from similarly grown 1-1 cultures.…”