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that AFP activity could have evolved in any location in which freezing stress acted as a
selective pressure for its evolution. However, it is also recognised that the lack of
isolation of Pseudomonas, Halomonas, Psychrobacter or Idiomarina from Ace Lake,
Pendant Lake and Oval Lake does not necessarily mean that they do not exist within
those communities, as culturing bias could have negated their isolation (Amann et al.,
1995). Indeed, characterisation of the remainder of the bacterial isolates cultured from
these lakes during the current study, may indicate the existence of these genera in these
communities. However, the lack of AFP activity within the remainder of the isolates
under the conditions used, suggests the absence of the AFP active species of these genera
from the hypersaline lakes.
DGGE community profiling of the Ace Lake, Pendant Lake and Triple Lake
bacterial communities, demonstrated the distinct difference between saline (Ace Lake &
Pendant Lake) and hypersaline (Triple Lake) Antarctic lake communities. Triple Lake
showed a distinct clustering with two other hypersaline lake communities (Deep Lake
and Club Lake) when the similarity coefficients for the DGGE community profiles were
compared in an UPGMA dendrogram (Fig. 6.5b). Pseudomonas and Halomonas isolates
have been cultured from Deep Lake, Organic Lake and Ekho Lake, which are all
hypersaline lakes from the Vestfold Hills (Bowman et al., 2000b). However, if these
species were cultured from these lakes during the current study (which cannot
be known
as the majority of the 866 environmental isolates were not characterised), then they did
not demonstrate AFP activity under the culturing and AFP assessment conditions.
The AFP activity within these species should provide freeze tolerance which
would allow the bacteria to survive in a niche in which other species are unable to survive
and thus provide a selective advantage. Due to its enhanced freeze-resistance, the AFP
active species would be able to out-compete freeze-intolerant species. In the current
study, the identification, using DGGE, of the Halomonas sp. within the community from
which it was isolated (Triple Lake, 8m), confirmed the presence of that AFP active
species within its community. The DGGE analysis also suggested that the Halonnonas sp.
was the most dominant species in the Triple Lake, 8m community, suggesting AFP
activity may have enabled it to become dominant. The inability to isolate AFP active
species from some lake communities supports the hypothesis that these species have
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