ý.,,: V. ý ýý . - Nottingham eTheses - University of Nottingham

Russell, 1984). The most important low temperature active thermo-regulation enzyme in
this pathway is ß-ketoacyl-ACP synthetase II, which elongates palmitoleate to cis-
vaccenate. As the temperature falls, more carbon flows down the unsaturated arm relative
to the saturated arm of the split pathway (Russell & Hamamoto, 1998). This increases
unsaturated fatty acids and consequently diunsaturated phospholipids, causing the
transition temperature of the membrane to fall (de Mendoza & Cronan, 1983). The
pathway divergence occurs within seconds of any temperature reduction. However, once
fatty acid synthetase products have been produced, they must be incorporated into the
membrane lipids and this takes much longer (due to cellular growth and membrane
formation) (Russell & Hamamoto, 1998).
Desaturases (aerobic pathway) can introduce double bonds into fatty acids much
faster than the anaerobic pathway. They have been shown to use intact acyl lipids as their
substrate for double bond insertion in bacteria and algae (Foot et al., 1983). Therefore,
because the fatty acids do not have to be made de novo the system is more rapid. The
desaturase is activated by a decrease in membrane fluidity which is rapidly restored as
exisiting fatty acids are desaturated (Russell & Hamamoto, 1998).
Other mechanisms for transition temperature reduction (i. e. changes in fatty acyl
chain length and the amount or type (anteiso/iso) of methyl branching) must be
introduced by the production of new fatty acids, because methyl branching is reliant upon
the primer molecule and the chain length is governed by the termination mechanism
(Harwood & Russell, 1984). The mechanism of temperature regulation of
activity/specificity of fatty acid synthetase is not well understood (Kaneda, 1991),
however for a review of current theories refer to Russell & Hamamoto (1998) and Russell
& Nichols (1999).
1.6 -
Biodiversity and biogeography of bacteria
There have been numerous extensive studies on microbial diversity and ecology within
Antarctic ecosystems (Hand, 1980; Hand & Burton, 1981; Wright & Burton, 1981; Burke
& Burton, 1988; Franzmann et al., 1990; Mancuso et al., 1990; Franzmann & Rohde,
1991,1992; Laybourn-Parry & Marchant, 1992b; James et al., 1994. Ellis-Evans, 1985a:
Laybourn-Parry et al., 1996; Laybourn-Parry, 1997; Ellis-Evans et al., 1998; Murray et
al., 1998. Nichols et al., 1999, Bowman et al., 2000a and b; Waters et al., 2000; Brown
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