In our attempt to understand the cold shock response of Bacillus subtilis,
we report on the role of the B. subtilis fatty acid desaturase (FA-D) Des d
uring membrane adaptation to low temperatures and demonstrate its importanc
e during cold shock. A des null mutant was constructed and analysed in comp
arison with its parental strain. Growth studies and large-scale comparative
fatty acid (FA) analysis revealed a severe cold-sensitive phenotype of the
des deletion mutant during the absence of isoleucine and showed that four
unsaturated fatty acid (UFA) species differing in length, branching pattern
and position of the double bond are synthesized in B. subtilis JH642 but n
ot in the des null mutant. Apart from the lack of UFA synthesis, the FA-D d
eletion strain showed a dramatically altered saturated fatty acid (SFA) pro
file at the onset of the stationary growth phase in the presence of exogeno
us isoleucine sources. Expression of des integrated in trans at the amyE lo
cus of the des deletion strain not only cured the cold-sensitive phenotype
observed for the des mutant but allowed much better growth than in strain J
H642 after a shift from 37 degreesC to 15 degreesC. These results show that
, during cold shock adaptation, des expression can completely replace the i
soleucine-dependent, long-term, FA branching adaptation mechanism. We concl
ude that the crucial aspect in cold adaptation of the cytoplasmic membrane
is not its specific molecular composition but rather its physical status in
terms of its fluidity.