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Microbiology 142 (1996), 2213-2221; DOI  10.1099/13500872-142-8-2213
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Oxygen-dependent low-temperature {delta}12 (n6)-desaturase induction and alteration of fatty acid composition in Acanthamoeba castellanii

Simon V. Avery1,{dagger},3, Andrew J. Rutter2, John L. Harwood2 and David Lloyd1

Microbiology Group, School of Pure and Applied Biology, University of Wales College of Cardiff, PO Box 915, Cardiff CF1 3TL, UK
School of Molecular and Medical Biosciences, University of Wales College of Cardiff, PO Box 915, Cardiff CF1 3TL, UK

3Author for correspondence: Simon V. Avery. Tel: +44 1865 484192. Fax: +44 1865 483242. e-mail: SVAvery@Brookes.ac.uk

ABSTRACT

The influence of dissolved oxygen on the synthesis and activity of {delta}12-desaturase in Acanthamoeba castellanii was investigated. A decline in oxygen concentration during batch growth at 30° was correlated with a decline in the degree of cellular fatty acid unsaturation. Chilling of early-stationary-phase cultures to 15° led to increased dissolved oxygen levels (from < 1 µM to 305 µM) and increased fatty acid unsaturation, which has been shown previously [Avery, S. V., Harwood, J. L. & Lloyd, D. (1994) Microbiology 140, 2423-2431] to be due mainly to {delta}12-desaturase induction. In contrast, chilling of mid-exponential-phase cultures, where the dissolved oxygen concentration prior to chilling was high (> 160 µM), gave no change in cellular fatty acid unsaturation. Measurement of [1-14C]acetate incorporation by oxygen-limited A. castellanii revealed that labelling of the {delta}12-desaturase product, linoleate (18:2), increased with oxygen concentration. Microsomal levels of the {delta}12-desaturase enzyme were found to increase by up to 10-fold during aeration of A. castellanii cultures; a transient elevation in oxygen was sufficient to induce {delta}12-desaturase synthesis that was still fully detectable 1 h later. In addition, the activity of pre-existing {delta}12-desaturase, measured in isolated microsomal membranes, increased by up to fivefold with increases in the oxygen concentration of assay mixtures. These results demonstrate for the first time that (i) oxygen availability alone can regulate de novo {delta}12-desaturase synthesis in A. castellanii, and that (ii) oxygen can limit the activity of pre-existing {delta}12-desaturase. These responses can occur independently of temperature changes.

Keywords: {delta}12-desaturase, low-temperature adaptation, dissolved oxygen concentration, Acanthamoeba castellanii, fatty acid composition

{dagger} Present address: School of Biological and Molecular Sciences, Oxford Brookes University, Headlington, Oxford OX3 0BP, UK.






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