Jtg. Hamilton et al., LONG-CHAIN HALOALKANES ARE INCORPORATED INTO FATTY-ACIDS BY RHODOCOCCUS-RHODOCHROUS NCIMB-13064, Microbiology, 141, 1995, pp. 2611-2617
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.