Novel Acetone Metabolism in a Propane-Utilizing Bacterium,Gordoniasp. Strain TY-5

Abstract

In the propane-utilizing bacterium Gordonia sp. strain TY-5, propane was shown to be oxidized to 2-propanol and then further oxidized to acetone. In this study, the subsequent metabolism of acetone was studied. Acetone-induced proteins were found in extracts of cells induced by acetone, and a gene cluster designated acmAB was cloned on the basis of the N-terminal amino acid sequences of acetone-induced proteins. The acmA and acmB genes encode a Baeyer-Villiger monooxygenase (BVMO) and esterase, respectively. The BVMO encoded by acmA was purified from acetone-induced cells of Gordonia sp. strain TY-5 and characterized. The BVMO exhibited NADPH-dependent oxidation activity for linear ketones (C 3 to C 10 ) and cyclic ketones (C 4 to C 8 ). Escherichia coli expressing the acmA gene oxidized acetone to methyl acetate, and E. coli expressing the acmB gene hydrolyzed methyl acetate. Northern blot analyses revealed that polycistronic transcription of the acmAB gene cluster was induced by propane, 2-propanol, and acetone. These results indicate that the acmAB gene products play an important role in the metabolism of acetone derived from propane oxidation and clarify the propane metabolism pathway of strain TY-5 (propane 3 2-propanol 3 acetone 3 methyl acetate 3 acetic acid ؉ methanol). This paper provides the first evidence for BVMO-dependent acetone metabolism.Gordonia sp. strain TY-5 is an actinomycete that is capable of aerobic growth on gaseous propane as a carbon and energy source. Our previous study showed that propane is oxidized to 2-propanol by monooxygenase-mediated subterminal oxidation and then 2-propanol is further metabolized to acetone by three distinct NAD ϩ -dependent secondary alcohol dehydrogenases (27). Although n-alkanes can be metabolized to the corresponding ketones through subterminal oxidation in some bacteria, microbial metabolism of the downstream ketone is poorly understood (1,2,22,36,46,47). A variety of bacteria, including Gordonia sp. strain TY-5, are able to utilize acetone as a source of carbon and energy. Previous studies on bacterial acetone metabolism both in vivo and in vitro suggested that acetone can be metabolized in two ways. In most aerobic bacteria, acetone was hydroxylated by an O 2 -dependent reaction producing acetol (hydroxyacetone), although the corresponding enzyme system is not known (13,29,42,45). For most anaerobes (and some aerobes), acetone undergoes CO 2 -dependent carboxylation, yielding acetoacetate. Recently, the enzyme responsible for the latter reaction, acetone carboxylase (EC 6.4.1.6), has been purified and characterized (3,12,15,(39)(40)(41).This study was conducted to characterize acetone metabolism in propane-utilizing Gordonia sp. strain TY-5 at the enzymatic and gene levels. We first identified two acetone-induced proteins and cloned their corresponding genes, acmA and acmB. Subsequently, we showed that acetone is oxidized to methyl acetate by a novel Baeyer-Villiger monooxygenase (BVMO) (acmA gene product) and that the methyl acetate produced was hydrol...

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Acetone and Butanone Metabolism of the Denitrifying Bacterium "Aromatoleum aromaticum" Demonstrates Novel Biochemical Properties of an ATP-Dependent Aliphatic Ketone Carboxylase

“…The first pathway involves an initial hydroxylation of the methyl group of acetone (and probably also butanone) by a cytochrome P450-type monooxygenase to acetol (1-hydroxyacetone) in mammals (11,12). The second known pathway is initiated by an FADH 2 -and NADPH-dependent monooxygenase in a Gordonia sp., which catalyzes a Bayer-Villiger rearrangement to yield methyl acetic ester (methylacetate) as the first intermediate (13). Finally, the third known pathway is initiated by carboxylating acetone to acetoacetate by a novel type of ATP-dependent carboxylase (see Fig.…”

Monooxygenases involved in the n-alkanes metabolism by Rhodococcus sp. BCP1: molecular characterization and expression of alkB gene

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“…Sub-terminal oxidation of n-alkanes has also been described ( Fig. 1.1) [58][59][60]. A secondary alcohol is produced that is converted to the corresponding ketone, and then oxidized by a Baeyer-Villiger monooxygenase to form an ester.…”