Peter W. Trudgill

The Microbial Metabolism of Acetone

Four Gram-positive bacteria have been isolated from separate soil samples by enrichment culture with acetone as sole source of carbon. Whole cells of all strains grown on acetone rapidly oxidized acetone, acetol and methylglyoxal, and three of the four also oxidized isopropanol. The patterns of induced enzymes in cell extracts are compatible with the oxidation sequence: isopropanol → acetone → acetol → methylglyoxal → pyruvate. Although an enzyme system capable of converting acetone into acetol has not been detected, the inclusion of acetol in the pathway is supported by the results of studies with whole cells and [14C]acetone. The proposed pathway of acetone metabolism is contrasted with evidence for an alternative, but not fully understood, pathway used by Mycobacterium vaccae JOB5.

Evidence of two pathways for the metabolism of phenol by Aspergillus fumigatus

Aspergillus fumigatus (ATCC 28282), a thermotolerant fungus, has been shown to be capable of growth on phenol as the sole carbon and energy source. During growth of the organism on phenol, catechol and hydroquinone accumulated transiently in the medium; cells grown on phenol oxidised these compounds without a lag period. Two different routes operating simultaneously, leading to different ring-fission substrates, are proposed for the metabolism of phenol. In one route, phenol undergoes ortho-hydroxylation to give catechol, which is then cleaved by an intradiol mechanism leading to 3-oxoadipate. In the other route, phenol is hydroxylated in the para-position to produce hydroquinone, which is then converted into 1,2,4-trihydroxybenzene for ring fission by ortho-cleavage to give maleylacetate. Cell-free extracts of phenol-grown mycelia were found to contain enzymic activities for the proposed steps. Two ring-fission dioxygenases, one active towards 1,2,4-trihydroxybenzene, but not catechol, and one active towards both ring-fission substrates, were separated by FPLC. Succinate-grown mycelia did not oxidise any of the intermediates until a clear lag period had elapsed and did not contain any of the enzymic activities for phenol metabolism.

The Degradation of n-Alkylcycloalkanes by a Mixed Bacterial Culture

Mycobacterium rhodochrous strain 7EIC grows with dodecylcyclohexane at the expense of acetyl fragments released by β-oxidation of the side-chain. Cyclohexaneacetic acid, which is not amenable to β-oxidation and is not oxidized by this organism, accumulates in significant yield. In combination with Arthrobacter strain CA1, which degrades cyclohexaneacetic acid by a novel pathway, a stable mixed culture is established that is capable of the complete degradation of dodecylcyclohexane and related hydrocarbons.

Purification and Properties of E-Caprolactone Hydrolases from Acinetobacter NCIB 9871 and Nocardia globerula CL1

SUMMARY: The E-caprolactone hydrolases (EC 3.1.1-) induced by growth of Acinetobacter NCIB 9871 and Nocardia globerula CL1 with cyclohexanol were purified to homogeneity. Both enzymes constituted approximately 1% of the soluble protein of the bacteria. Each was formed from two electrophoretically indistinguishable subunits and each had a closely similar M r value (⋍60000). Both enzymes had high turnover numbers typical of carboxyesterases, broad pH-activity spectra and very restricted substrate specificities. In contrast to other bacterial lactone hydrolases they catalysed irreversible lactone hydrolysis and were not inhibited by thiol-reactive compounds. Their sensitivity to Paraoxon (diethyl p-nitrophenylphosphate) suggested that they, in common with mammalian acetylcholinesterase and carboxyesterases, have a functional catalytic centre serine.