title: Haloalkane degradation and assimilation by Rhodococcus rhodochrous NCIMB 13064.
abstract: 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 gamma-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 gamma-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, gamma-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 omega-chlorofatty acid. This is degraded by beta-oxidation to 4-chlorobutyric acid which is chemically lactonized to gamma-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.
authors.affiliation: Questor Centre, Queen's University of Belfast, UK.
authors.forename: H
authors.initials: H
authors.lastname: Curragh
authors.forename: O
authors.initials: O
authors.lastname: Flynn
authors.forename: M J
authors.initials: MJ
authors.lastname: Larkin
authors.forename: T M
authors.initials: TM
authors.lastname: Stafford
authors.forename: J T
authors.initials: JT
authors.lastname: Hamilton
authors.forename: D B
authors.initials: DB
authors.lastname: Harper
mesh_terms: D000473:Alkanes / Q000378:metabolism*; D001673:Biodegradation, Environmental; D002073:Butanes / Q000378:metabolism; D004734:Energy Metabolism; D005227:Fatty Acids / Q000032:analysis; D006843:Hydrocarbons, Chlorinated / Q000378:metabolism; D006846:Hydrocarbons, Halogenated / Q000378:metabolism*; D007220:Industrial Waste; D012240:Rhodococcus / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D012988:Soil Microbiology; D012989:Soil Pollutants / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D000473:Alkanes; D002073:Butanes; D005227:Fatty Acids; D006843:Hydrocarbons, Chlorinated; D006846:Hydrocarbons, Halogenated; D007220:Industrial Waste; D012989:Soil Pollutants; C039858:1-chlorohexadecane; C006854:butyl chloride