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METHYL KETONE METABOLISM in HYDROCARBON-UTILIZING MYCOBACTERIA Cane-I-C'4. Aliphatic Alkane-Utilizing Mycobac

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METHYL KETONE METABOLISM in HYDROCARBON-UTILIZING MYCOBACTERIA Cane-I-C'4. Aliphatic Alkane-Utilizing Mycobac METHYL KETONE METABOLISM IN HYDROCARBON-UTILIZING MYCOBACTERIA H. B. LUKINS' AND J. W. FOSTER Department of Microbiology, The University of Texas, Austin, Texas Received for publication 15 December 1962 ABSTRACT which micro- LUKINS, H. B. (University of Texas, Austin) The most common means by in organisms utilize aliphatic, saturated hydrocar- AND J. W. FOSTER. Methyl ketone metabolism bons is an oxidative attack at a terminal methyl hydrocarbon-utilizing mycobacteria. J. Bacteriol. group (for literature see Fuhs, 1961; Foster, 1962a, 85: 1074-1087. 1963.-Speciesof Mycobacterium especially M. smegmatis 422, produced the homol- b). The usual first, stable product is the homol- ketones the oxidation of ogous primary alcohol which is further converted ogous methyl during to this in turn propane, n-butane, n-pentane, or n-hexane. A the corresponding fatty acid; carrier-trapping experiment demonstrated the undergoes beta-degradation of the carbon chain. formation of 2-undecanone, as well as 1,11-un- As early as 1932, methyl ketones were sus- the oxidation of unde- pected of being involved in paraffin oxidation; decanedioic acid, during Aspergillus versicolor, which grew at the expense cane-i-C'4. Aliphatic alkane-utilizing mycobac- of was teria were able to at the of several long-chain paraffins, also able to grow at grow expense the expense of related methyl ketones (Hopkins aliphatic methyl ketones as sole sources of carbon. and Other ketones which did not support growth Chibnall, 1932). Recently, Pseudomonas were oxidized by resting bacterial suspensions. M. methanica was discovered to produce methyl smegmatis 422 cells grown on propane or acetone ketones, along with alcohols and fatty acids, were simultaneously adapted to oxidize both during the oxidation of gaseous alkanes (Lead- substrates, as well as n-propanol. n-Propanol better and Foster, 1959a, 1960). cells were unadapted to propane or acetone. Methyl ketone formation is well known in Acetone produced from propane in a medium mammals (Fruton and Simmonds, 1958), in in contained a bacteria (Johnson, Peterson, and Fred, 1933), and enriched D20 negligible quantity in fungi (Stiirkle, 1924; Franke and Heinen, of D, presumably eliminating propylene as an intermediate in the oxidation. Cells grown at the 1958). In these cases, the ketone is formed by expense of alkanes or methyl ketones in the decarboxylation of a p-keto acid and has, there- presence of O?18 had a higher content of 018 than fore, one less carbon atom than the precursor. did cells grown on terminally oxidized com- On the other hand, bacterial formation of methyl pounds, e.g., primary alcohols or fatty acids. An ketones from alkanes is a unique alpha-oxidation, oxygenase reaction is postulated for the attack with no change in the carbon skeleton. Methyl on methyl ketones. Acetol was isolated and char- ketones are also formed by bacterial dehydrogena- acterized as an oxidation product of acetone by tion of secondary alcohols (Miiller, 1931), a M. smegmatis 422. Acetol-grown cells had a higher reaction which appears to be part of the alkane 018 content than did n-propanol cells, and its oxidation sequence (Leadbetter and Foster, utilization appears to involve at least one oxy- 1960). genase reaction. Acetol produced from acetone The formation of methyl ketones in the oxida- in the presence of 0218 was not enriched in the tion of gaseous alkanes implies that they are isotope, indicating the occurrence of exchange intermediates. Their metabolism thus automati- reactions or of oxygenation reactions at a later cally becomes a legitimate aspect of hydrocarbon stage in the assimilation of acetone and acetol. metabolism, especially of alkyl groups. Ladd's (1956) soil diptheroid oxidized 2-undecanone at a 1 Present address: Department of Biochemistry, rate better than n-decylaldehyde, and the possi- University of Sydney, Sydney, Australia. bility of an oxidation at a nonterminal carbon was 1074 VOL. 85, 1963 METHYL KETONE METABOLISM IN MYCOBACTERIA 1075 pointed out. In an abstract, Klausmeier et al. Propane or butane was used in a 50% gas-50% (1958) reported that a propane-utilizing myco- air mixture, and liquid alkanes were added at bacterium was simultaneously adapted to the 0.2% (v/v). The hydrocarbons were at least oxidation of isopropanol and propylene, which 99 moles % pure. were postulated as intermediates. Chemical. Ketones were estimated photometri- Subterminal oxidation of alkyl groups is best cally by means of the colorimetric reaction with established in the rabbit, when fed short-chain salicylaldehyde, acetone in alkaline solution monoalkylbenzenes. For example, ethylbenzene (Neish, 1952), and the longer chain ketones in is converted to methylphenylcarbinol (Smith, acidic solution (Mukherjee, 1951). Acetone and Smithies, and Williams, 1954), and n-propyl- and 2-butanone were distilled from the culture n-butylbenzene are oxidized at two different liquids into a solution of reagent for preparation subterminal carbons (El Masry, Smith, and of derivatives according to Vogel (1951). Longer Williams, 1955). chain ketones were extracted with three changes This paper is concerned with the role of methyl of ether. Acetol was assayed by periodate titra- ketones in the oxidation of the gaseous alkanes by tion (Neish, 1952). Infrared-absorption spectra species of Mycobacterium. Hydrocarbon utiliza- were obtained with a Baird instrument, and tion seems to be an intrinsic capability of myco- melting points with a Fisher block. bacteria (Lukins andFoster, Z. Allgem. Mikrobiol., Isotope experiments. 018-incorporation experi- in press), but practically nothing is known about ments were conducted in 500-ml growth cultures the mechanisms they employ. in 4-liter suction flasks incubated with continuous shaking. The atmosphere consisted of N2 con- MATERIALS AND METHODS taining 10% 02 labeled with 018 prepared by Organisms. M. smegmatis 422, which grows at electrolysis of water (5.5 to 6.5% H2018). Im- the expense of several gaseous and liquid alkanes mediately after gassing the culture vessel, a (Lukins and Foster, in press), was used for most of sample of the gas was taken for isotopic analysis. this work. When grown with continuous shaking At maximal growth, the cells were harvested by on propane-mineral salts medium, it produces a centrifugation, washed with water, lyophilized, copious, uniform suspension suitable for physio- and pyrolyzed to CO2 (Rittenberg and Ponti- logical experiments. M. rhodochrous 382 and the corvo, 1956). Analysis of the masses 44, 45, and yellow, glistening Mycobacterium sp. "tap-water" 46 in the mass spectrometer permitted calculation also were extensively employed. These cultures of the 018 content as follows: were kindly furnished by Ruth Gordon, Institute %018 = 100 X I48 of Microbiology, Rutgers University, New Bruns- 2(I44 + I45 + 146) wick, N. J. A number of other organisms were isolated from soils and muds, using 2-butanone or where I46 equals intensity of mass 46, etc. Like- 2-undecanone as selective substrates. wise, the 018 content of the 02 in the gas phase was The mineral salts medium contained, per liter calculated from the intensities of masses 32, 33, of deionized water: (NH4)2SO4, 1.0 g; Na2CO3, and 34. 0.1 g; KH2PO4, 0.5 g; MgSO477H20, 0.2 g; CaCl2, 10 mg; FeSO4-7H20, 5 mg; MnSO4, 2 mg; RESULTS AND DISCUSSION Cu, 50 Mg (as CuSO4.5H20); B, 10 Ag (as H3BO3); Production of methyl ketones from n-alkanes. P. Zn, 70 ,ug (as ZnSO4.7H20); Mo, 10 MAg (as methanica growing on methane co-oxidizes pro- MoO3); pH 7.0. Water-washed agar was added pane and butane to acetone and 2-butanone, when solid media were desired. Ordinarily, the respectively (Leadbetter and Foster, 1959a). liquid growth cultures were prepared in "pre- This organism cannot utilize propane or butane scription" bottles or suction flasks. Procedures for growth, and it is desirable to determine for cultivation in gaseous substrates are given whether organisms that can utilize them for elsewhere (Lukins and Foster, in press; Kester growth are likewise able to produce the ketones. and Foster, 1963). Washed cellular suspensions Acetone from n-propane. Washed cells of M. were prepared from liquid cultures, using 0.067 M smegmatis 422 from 3 liters of a 3-day culture phosphate buffer (pH 7) as the suspension fluid. were resuspended in mineral salts solution with 1076 LUKINS AND FOSTER J. BACTERIOL. TABLE 1. Melting points of hydrazones prepared hr. A salicyaldehyde estimation indicated there from products of the oxidation of short-chain were 83 ,g of 2-pentanone per ml of the super- n-alkanes by Mycobacterium smegmatis 422 natant culture liquid. The diethyl ether extract of 2,4-Dinitro- p-Nitro- the supernatant liquid was concentrated almost Product source phenyl- phenyl hydrazone hydrazone to dryness, and then taken up in 1 ml of ethanol. This solution gave a crystalline 2,4-dinitro- C C phenylhydrazone which was identified by melt- Propane growth culture... 123-124 ing-point determinations (Table 1) and by a Propane replacement cul- comparison of the infrared-absorption spectra of ture .................... 124 149 the bacterial and authentic 2-pentanone deriva- Authentic acetone ........ 124 147 tives. Mixed sample from re- placement culture and 2-Hexanone from n-hexane. Propane-grown authentic acetone....... 124 147 cells of III. smegmatis 422 were furnished with 2 n-Butane growth culture.. 108-109 122-123 ml of n-hexane, and after 20 hr of incubation the Authentic 2-butanone..... 110 123 concentrated ether extract was analyzed in a Mixture of two above..... 109-110 123 Perkin-Elmer gas chromatograph with a 2-m Pentane growth culture... 138 column of didecylphthalate, at 120 C. Two peaks, Authentic 2-pentanone.... 140 with retention times of 6 and 7 min, were ob- Mixture of two above..... 138-139 served. They were shown to have the same reten- tion times as authentic 2-hexanone and 2-hexanol, respectively. They could not be differentiated the (NH4)2SO4 omitted, and exposed to 30 % from the authentic specimens by cochromatog- propane-70 % air for 15 hr.
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