LONG-CHAIN HALOALKANES ARE INCORPORATED INTO FATTY-ACIDS BY RHODOCOCCUS-RHODOCHROUS NCIMB-13064

The fatty acid composition of the cellular lipids of Rhodococcus rhodo chrous NCIMB 13064 grown on various long-chain haloalkanes has been in vestigated and the influence of halogen substituents, carbon chain len gth and the position of halogen substitution in the growth substrate e xplored. Of the total fatty acids present in cells grown on 1-chloro-, 1-bromo- and 1-iodohexadecane, 75, 90 and 81%, respectively, were sub stituted in the omega-position by the corresponding halogen but only 1 % of the fatty acids present after growth on 1-fluorotetradecane were fluorinated in this position. The extent of the halofatty acid incorpo ration with different halogen substituents in the growth substrate app ears to reflect the degree to which oxygenase attack is restricted to the non-halogenated end of the haloalkane. Studies of the fatty acid c omposition of cells after growth on a series of 1-chloroalkanes contai ning an even number of carbon atoms between C-10 and C-18 indicated ch lorofatty acid incorporation from C-12 to C-18 substrates at levels ra nging from 21% with C-12 to 75% with C-16. The chlorofatty acids forme d by initial oxidation of the chloroalkane were chain-lengthened or ch ain-shortened by from two to eight carbon atoms, with accompanying des aturation in some instances. Substantial quantities of a methyl-branch ed C-19:0 chlorofatty acid were also present with several chloroalkane substrates, When the fatty acid composition of cells after growth on 1-bromoalkanes containing an odd number of carbon atoms between C-11 a nd C-17 was examined, the incorporation of bromofatty acids was observ ed with C-13, C-15 and C-17 substrates; a maximum of 76% was recorded for the C-15 bromoalkane. As with even chain-length chloroalkanes, bot h chain-lengthening and -shortening occurred predominantly via two-car bon units so that most bromoacids present possessed an odd number of c arbon atoms, When 1-bromododecane or 2-bromododecane were substrates, overall incorporations of bromofatty acids into the lipid fraction wer e very similar, demonstrating that the position of halogen substitutio n in the haloalkane was not critical in determining the extent of inco rporation of the haloacids into cellular lipids. The results of the st udy indicate a mechanism by which degradation products of chlorinated paraffins could enter the biological food chain.