Acetone is activated by aerobic and nitrate-reducing bacteria via an ATP-dependent carboxylation reaction to form acetoacetate as the first reaction product. In the activation of acetone by sulfate-reducing bacteria, acetoacetate has not been found to be an intermediate. Here, we present evidence of a carbonylation reaction as the initial step in the activation of acetone by the strictly anaerobic sulfate reducer Desulfococcus biacutus. In cell suspension experiments, CO was found to be a far better cosubstrate for acetone activation than CO 2 . The hypothetical reaction product, acetoacetaldehyde, is extremely reactive and could not be identified as a free intermediate. However, acetoacetaldehyde dinitrophenylhydrazone was detected by mass spectrometry in cell extract experiments as a reaction product of acetone, CO, and dinitrophenylhydrazine. In a similar assay, 2-amino-4-methylpyrimidine was formed as the product of a reaction between acetoacetaldehyde and guanidine. The reaction depended on ATP as a cosubstrate. Moreover, the specific activity of aldehyde dehydrogenase (coenzyme A [CoA] acylating) tested with the putative physiological substrate was found to be 153 ؎ 36 mU mg ؊1 protein, and its activity was specifically induced in extracts of acetone-grown cells. Moreover, acetoacetyl-CoA was detected (by mass spectrometry) after the carbonylation reaction as the subsequent intermediate after acetoacetaldehyde was formed. These results together provide evidence that acetoacetaldehyde is an intermediate in the activation of acetone by sulfate-reducing bacteria.A cetone is produced by bacterial fermentations, for example, by several Clostridium species (1). It is also produced in chemistry as a solvent and as an intermediate in the synthetic chemical industry. Aerobic degradation of methyl ketones was first observed with hydrocarbon-utilizing bacteria (2). Acetone is degraded by some aerobic bacteria (3) and mammalian liver cells via oxygenase-dependent hydroxylation to acetol (4). Carboxylation of acetone to acetoacetate as a means of acetone activation was first proposed for a methanogenic enrichment culture (5). The requirement of CO 2 as a cosubstrate for acetone degradation was also observed with the nitrate reducer Thiosphaera pantotropha (6) and with Rhodobacter capsulatus and other phototrophs (7). The reaction was studied with the nitrate-reducing strain Bun N under anoxic conditions, and it was concluded that acetoacetate was formed by the ATP-dependent carboxylation of acetone (8, 9).Attempts to measure an in vitro carboxylation of acetone at that time were unsuccessful. However, exchange of radioactively labeled CO 2 with the carboxyl group of acetoacetate was catalyzed by cell extracts of strain Bun N (10). A similar CO 2 -and ATPdependent activation reaction was observed with the aerobic bacterium Xanthobacter autotrophicus strain Py2 (11). A comparison between the acetone carboxylase of strain Py2 and the carboxylase of the phototrophic bacterium Rhodobacter capsulatus showed that they are ide...
BackgroundThe sulfate-reducing bacterium Desulfococcus biacutus is able to utilize acetone for growth by an inducible degradation pathway that involves a novel activation reaction for acetone with CO as a co-substrate. The mechanism, enzyme(s) and gene(s) involved in this acetone activation reaction are of great interest because they represent a novel and yet undefined type of activation reaction under strictly anoxic conditions.ResultsIn this study, a draft genome sequence of D. biacutus was established. Sequencing, assembly and annotation resulted in 159 contigs with 5,242,029 base pairs and 4773 predicted genes; 4708 were predicted protein-encoding genes, and 3520 of these had a functional prediction. Proteins and genes were identified that are specifically induced during growth with acetone. A thiamine diphosphate-requiring enzyme appeared to be highly induced during growth with acetone and is probably involved in the activation reaction. Moreover, a coenzyme B12- dependent enzyme and proteins that are involved in redox reactions were also induced during growth with acetone.ConclusionsWe present for the first time the genome of a sulfate reducer that is able to grow with acetone. The genome information of this organism represents an important tool for the elucidation of a novel reaction mechanism that is employed by a sulfate reducer in acetone activation.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-584) contains supplementary material, which is available to authorized users.
Acetone can be degraded by aerobic and anaerobic microorganisms. Studies with the strictly anaerobic sulfate-reducing bacterium Desulfococcus biacutus indicate that acetone degradation by these bacteria starts with an ATP-dependent carbonylation reaction leading to acetoacetaldehyde as the first reaction product. The reaction represents the second example of a carbonylation reaction in the biochemistry of strictly anaerobic bacteria, but the exact mechanism and dependence on cofactors are still unclear. Here, we use a novel fluorogenic ATP analogue to investigate its mechanism. We find that thiamine pyrophosphate is a cofactor of this ATP-dependent reaction. The products of ATP cleavage are AMP and pyrophosphate, providing first insights into the reaction mechanism by indicating that the reaction proceeds without intermediate formation of acetone enol phosphate.
The effect of the addition of two different polyamines into a foamed polymeric matrix with embedded natural fiber, to synthesize biocomposites, was studied during the degradation of toluene in batch experiments. The synthesized biocomposites were able to adsorb and facilitate the degradation of toluene by micro-organisms attached in the biocomposite matrix, at a high extent (80%), in a very short period of time (1 day). The adsorption and biodegradation processes were simultaneous. The molecular weight of polyamine had a slight effect on toluene adsorption, with the lower-molecular-weight polyamine being more favorable for the adsorption process. However, the biocomposites, with polyamines, were not able to carry out the complete biodegradation of toluene during the term of experiment (26 days). The absence of polyamine in the biocomposite had a dramatic effect on adsorption and biodegradation of toluene, improving both processes and showing a CO2 production that is 730% higher than biocomposites synthesized with polyamine, because of a toxic and/or barrier effect of polyamine. This biocomposite, synthesized without polyamine, was able to carry out the complete biodegradation during the first 5 days, and it had adequate cyclic performance.
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