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6.2.2 -
Temporal and spatial variation in microbial communities
Community samples were taken for each lake at 2m depth intervals on two
different dates and then analysed by computer assessment of the DGGE profiles for the
eubacterial communities of each sample (Fig 6.4a & b). Both images show complex
microbial communities. However, there is some distinct change between the profiles in
each lane. The original profile images were analysed using the Image Master ID elite
V3.01 gel analysis software (Amersham Pharmacia Biotech & Non-Linear Dynamics) to
demark lanes within the profiles and then analyse the similarity between the profiles by
matching the Rf values of each band (Fig 6.4c, Gel 1 and Fig 6.4d, Gel 2). Similarity
matrices were based on the Dice coefficient which weights positives matches (refer to
section 2.9.4).
Inter-lane comparison of the two gels was undertaken by standardisation of two
replicates present in both gels, the V3 community fingerprint for Ace Lake I Om during
September (Fig 6.4a Lane 8; Fig 6.4b Lane 4) and Pendant Lake 4m during September
(Fig 6.4a, Lane 13; Fig 6.4b, Lane 5) were standardised using Rf (retardation factor)
values so that the two gels could be compared. This inter-gel comparison was performed
using ImageMaster 1D database V2.12 (Amersham Pharmacia Biotech). A similarity
matrix was produced (Fig 6.5a) using the Dice coefficient and a dendrogram was derived
(Fig. 6.5b).
For the following descriptions of temporal and spatial variation of similarity
values between communities refer to figure 6.5a. Ace Lake showed a similarity between
communities throughout its mixolimnion during September, 2000, ranging from 0.72
between 4m and 8m, to 0.9 between Om and 2m. The only exception was 8m to l Om
which was only 0.61 which correlated with the introduction of the bacterial community
associated with the chemocline. The temporal variation between depths. however.
showed a low similarity indicating a change in the community between September and
November, 2000. During November, 2000 the similarity between communities at
different depths throughout the mixolimnion
in Ace Lake was very low compared with
September, suggesting that the communities had undergone zonation due to an increase
in the salinity gradient and temperature gradient caused by changing environmental
conditions with the start of the austral summer.
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