f Haloalkane degradation and assimilation by Rhodococcus rhodochrous NCIMB 13064
- Authors: Helen Curragh, Orla Flynn, Michael J. Larkin*, Thomas M. Stafford, John T. G Hamilton, David B. Harper
- *Author for correspondence: Michael Larkin. Tel: +44 232 245133 ext. 2288/4390 (QUESTOR +44 252 335577). Fax: +44 232 236505 (QUESTOR +44 232 661462).
- Microbiology, June 1994 140: 1433-1442, doi: 10.1099/00221287-140-6-1433
- Subject: Biochemistry
- Published Online:
The bacterium Rhodococcus rhodochrous NCIMB 13064, isolated from an industrial site, could use a wide range of 1-haloalkanes as sole carbon source but apparently utilized several different mechanisms simultaneously for assimilation of substrate. Catabolism of 1-chlorobutane occurred mainly by attack at the C-1 atom by a hydrolytic dehalogenase with the formation of butanol which was metabolized via butyric acid. The detection of small amounts of γ-butyrolactone in the medium suggested that some oxygenase attack at C-4 also occurred, leading to the formation of 4-chlorobutyric acid which subsequently lactonized chemically to γ-butyrolactone. Although 1-chlorobutane-grown cells exhibited little dehalogenase activity on 1-chloroalkanes with chain lengths above C10, the organism utilized such compounds as growth substrates with the release of chloride. Concomitantly, γ-butyrolactone accumulated to 1 mM in the culture medium with 1-chlorohexadecane as substrate. Traces of 4-hydroxybutyric acid were also detected. It is suggested that attack on the long-chain chloroalkane is initiated by an oxygenase at the non-halogenated end of the molecule leading to the formation of an Ω-chlorofatty acid. This is degraded by β-oxidation to 4-chlorobutyric acid which is chemically lactonized to γ-butyrolactone which is only slowly further catabolized via 4-hydroxybutyric acid and succinic acid. However, release of chloride into the medium during growth on long-chain chloroalkanes was insufficient to account for all the halogen present in the substrate. Analysis of the fatty acid composition of 1-chlorohexadecane-grown cells indicated that chlorofatty acids comprised 75% of the total fatty acid content with C14:0' C16:0' C16:1 and C18:1 acids predominating. Thus the incorporation of 16-chlorohexadecanoic acid, the product of oxygenase attack directly into cellular lipid represents a third route of chloroalkane assimilation. This pathway accounts at least in part for the incomplete mineralization of long-chain chloroalkane substrates. This is the first report of the coexistence of a dehalogenase and the ability to incorporate long-chain haloalkanes into the lipid fraction within a single organism and raises important questions regarding the biological treatment of haloalkane containing effluents.
© Society for General Microbiology 1994 | Published by the Microbiology Society
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