HALOALKANE DEGRADATION AND ASSIMILATION BY RHODOCOCCUS-RHODOCHROUS NCIMB-13064

The bacterium Rhodococcus rhodochrous NCIMB 13064, isolated from an in dustrial site, could use a wide range of 1-haloalkanes as sole carbon source but apparently utilized several different mechanisms simultaneo usly for assimilation of substrate. Catabolism of 1-chlorobutane occur red 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 sugges ted that some oxygenase attack at C-4 also occurred, leading to the fo rmation of 4-chlorobutyric acid which subsequently lactonized chemical ly to gamma-butyrolactone. Although 1-chlorobutane-grown cells exhibit ed little dehalogenase activity on 1-chloroalkanes with chain lengths above C-10, the organism utilized such compounds as growth substrates with the release of chloride. Concomitantly, gamma-butyrolactone accum ulated to 1 mM in the culture medium with 1-chlorohexadecane as substr ate. Traces of 4-hydroxybutyric acid were also detected. It is suggest ed that attack on the long-chain chloroalkane is initiated by an oxyge nase at the non-halogenated end of the molecule leading to the formati on of an omega-chlorofatty acid. This is degraded by beta-oxidation to 4-chlorobutyric acid which is chemically lactonized to gamma-butyrola ctone which is only slowly further catabolized via 4-hydroxybutyric ac id and succinic acid. However, release of chloride into the medium dur ing 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 chlorofat ty acids comprised 75% of the total fatty acid content with C-14:0, C- 16:0, C-16:1, and C-18:1 acids predominating. Thus the incorporation o f 16-chlorohexadecanoic acid, the product of oxygenase attack directly into cellular lipid represents a third route of chloroalkane assimila tion. This pathway accounts at least in part for the incomplete minera lization of long-chain chloroalkane substrates. This is the first repo rt of the coexistence of a dehalogenase and the ability to incorporate long-chain haloalkanes into the lipid fraction within a single organi sm and raises important questions regarding the biological treatment o f haloalkane containing effluents.