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DGGE band for the sediment layers of Unit III, but the band was no longer
detected in sediment layers which were deposited shortly after marine waters
first entered Ace Lake (Unit II, Fig. 6). Sequence analysis of the two unique
DGGE bands revealed that sequence 1 (phylotype AL-GSB 1) recovered from
the extant anoxic water column as well as from Unit I and II sediments was
related to anoxygenic photolithotrophic species of the family Chlorobiaceae
with Chlorobium phaeovibrioides DSMZ 269 T as the closest relative (99.6%
sequence similarity, Fig. 7). Sequence 2 (phylotype AL-GSB 2) was affiliated
with uncultivated, unclassified green sulfur bacteria which form a cluster sepa-
rated from the anoxygenic photosynthetic members of the Chlorobiaceae (Fig.
7).
Figure 6. DGGE analysis of PCR-amplified partial 16S rDNA of green sulfur bacteria obtained
from the water column as well as the Holocene sediments of Ace Lake. No amplicons were
recovered from the oxygenated mixolimnion or the deepest analyzed water column sample.
DGGE bands that were sliced from the gel and subsequently sequenced are indicated with
numbers.
The amount of rDNA of GSB was quantified by means of real time PCR. No
rDNA of GSB was detected within the oxygenated mixolimnion. The highest
concentration of GSB DNA was found in the chemocline of the lake (600
ng.L 1 filtered water) and its concentration declined sharply in the deeper and
dark monimolimnion (Fig. 3b). The ratio between rDNA and chlorobactene of
GSB was 2 orders of magnitude lower at 18 m depth compared to the euxinic
chemocline (Fig. 3c). GSB rDNA comprised up to 30% of the total rDNA
content within the chemocline, but only 0.1% at a depth of 18 m (Fig. 3d).
Within the Holocene sediment core, rDNA concentrations of AL-GSB 1
were up to 3 µg per gram of total organic carbon (TOC) within the upper 50
cm, but increased significantly up to 23 µg.g 1 TOC in older Unit II deposits
(Fig. 5e). The phylotype Al-GSB 1 was not detected from the Unit III sediment
layers. Instead, up to 0.08µg.g 1
Unit III sediments and this phylotype was below the detection limit from sedi-
ment
T OC of rDNA of AL-GSB 2
was
detected
from
layers above 121 cm (Fig. 5e). The ratio between DNA and chlorobactene
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