STRIVE - Environmental Protection Agency

Molecular Diversity and Dynamics of Toxigenic Blue-green Algae in Irish Lakes
Figure 3.19. Segregation of the denaturant gradient gel electrophoresis (DGGE) bands for both filamentous
(a) and spherical (b) cyanobacteria according to their maximum intensity and frequency of occurrence in the
lakes sampled during summer 2009.
significantly greater when sampling was carried out
under fair weather conditions (Kruskal-Wallis, p < 0.05,
H = 6.28, df = 2).
The occurrence frequency of individual cyanobacterial
bands in the DGGE gels and their peak intensities were
also considered. Figure 3.19 shows the segregation of
bands for both filamentous and spherical cyanobacteria
into four groups: rare bands of low intensity (Gr.A), rare
bands of high intensity (Gr.B), common bands of low
intensity (Gr.C) and frequent bands of high intensity
(Gr.D). No significant pattern was apparent in the
distribution of those groups in space and time for both
filamentous and spherical cyanobacteria (Kruskal-
Wallis, p > 0.10, H < 4.60, df = 2). However, for spherical
cyanobacteria only, the peak heights of bands from
34
Gr.D were significantly lower when rainfall events
coincided with the time of sampling (Kruskal-Wallis,
p < 0.05, H = 7.39, df = 2).
Individual bands from groups B, C and D were
successfully excised from the gels and re-amplified
prior to purification and sequencing. The occurrence
of these indicator bands was assessed in relation
to various environmental descriptors using Fisher’s
exact test (Table 3.7). In particular, bands 64, 78, 80,
83 and bands 55, 66, 72, 78, 79, for spherical and
filamentous cyanobacteria, respectively, showed some
significant correlations with the descriptors pertaining
to cyanobacterial richness, the time of the summer,
temperature, weather conditions and catchment forest
cover.
Table 3.7. Significant correlation (2-tail Fisher’s exact test) between the presence of a selected band within
a gel pattern and a qualitative descriptor.
Band
code
Cyanobacteria
richness
Summer
period
Descriptors
Lake
temperature
Weather
conditions
Catchment
forest cover
16S rDNA identification
(% similarity)
Bd64 - - - 0.000 - Chroococcales
Bd78 - - 0.001 - - Chroococcales
Bd80 - - 0.040 - 0.010 Chroococcales
Bd83 0.020 - 0.050 0.050 Oscillatoriales*
Bd55 - 0.004 - - 0.050 Nostocales
Bd72 0.000 - - - - Nostocales
Bd78 0.001 - - - 0.009 Nostocales
Bd79 0.020 - - - - Nostocales
Bd66 0.018 - - - - Nostocales
* refers to a filamentous cyanobacterial morphotype which is closely related, in the 16S rDNA phylogeny found in Fig. 3.22, to
spherical genotypes.