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adapt to the extreme environmental conditions prevalent in Antarctica, which are
accompanied by, for example, rapid changes in temperature and light availability
throughout a year (Russell & Hamamoto, 1998). This was substantiated by the current
study in which all but three of the assessed AFP active isolates showed multiple copies of
the 16S rRNA gene.
One genus isolated in the current study, Sphingomonas (isolate 494), an
ultramicrobacterium
((x-Proteobacteria) usually found in oligotrophic marine waters
(Fegatella et al., 1998), has been twice isolated in Antarctica, once in the accreted ice
above the sub-glacial Lake Vostok (Christner et al., 2001) and then in the current study
from the sub-ice, surface water of Pendant Lake. This isolate was shown to have 3 copies
of 16S rRNA operon (Fig 6.1 & 6.2, lanes 7 and 12 respectively). The Sphingomona, s sp.
strain RB2256, which is undoubtedly a different species from that of the current study,
was isolated from cold marine waters in Resurrection Bay, Alaska, and has been shown
to have only 1 copy of the rrn operon (Fegatella et al., 1998). Despite this it has also been
shown to maintain a higher concentration of ribosomes per cell volume than Escherichia
coli, and maintained the ability to show rapid response to nutrient fluctuation within its
substrate (Fegatella et al., 1998). Fegatella et al. (1998) has suggested that this may be a
characteristic of the oligotrophic ultramicrobacteria, but the current study suggests that
this may be inaccurate, unless the multiple-banding pattern shown in figures 6.1 and 6.2
was not accurate. It is possible that two of the bands in the tri-banded profile may be
artefactual (refer to section 6.3.2.4.3).
This possibility was demonstrated in the heterogeneity in the 16S rRNA gene
from the Marinomonas protea strain patterns in the current study (section 6.2.1.1). Where
three of the strains produced a four banded profile, which by further investigation through
sequencing was considered to be only a two banded profile. The fact that three of these
five strains produced a possible two banded profile and the other two strains produced a
single band profile suggests that there was operon copy number heterogeneity within a
single species from the same and similar environments. The presence of two bands within
three of the strains could be due to a mixed culture, however, this was not substantiated
by analysis of cellular and colony morphology which indicated pure cultures. The
production of a second band by erroneous nucleotide insertions introduced during PCR
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