Environmental Engineering Reference
In-Depth Information
phaeobacteroides
and
Chl. phaeovibrioides
. Pigment concentrations reached
940 ng BChl
e
l
−
1
at a depth of 74 m in the central western basin [60].
From water samples obtained during the same U.S.-Turkish expedition on
the RV
Knorr
, the first successful enrichment of green sulfur bacteria could
be established in 1989 (strain MN1; [54]). The inoculum was retrieved in the
central western basin from a water depth of 80 m where oxygen and hydrogen
sulfide concentrations were below detection limit. A very similar green sulfur
bacterial strain (BS-1) was isolated again from chemocline water samples
recovered in 2001 from a depth of 95 m in the central western basin [45].
In a recent survey of 16S rRNA genes of chemocline bacteria, no green
sulfur bacteria-like sequences could be detected [75] despite the presence of the
specific pigment biomarkers. This discrepancy may be attributed to the clonal
bias in the
E. coli
library used for 16S rRNA gene analyses and, together with
the very low concentrations of green sulfur bacterial pigments, indicates that
specific detection methods need to be employed for a molecular identification
of the green sulfur bacteria present in the Black Sea. Primers specific for 16S
rRNA gene sequences of green sulfur bacteria have become available [55] and
permit a highly selective PCR amplification of 550 bp-gene fragments from
as little as 100 cells [19]. Employing these specific primers and separation of
the PCR products by denaturing gradient gel electrophoresis yielded a single
and novel type of 16S rRNA gene sequence from the 2001 chemocline water
samples, phylogenetically clustering with the other marine strains of green
sulfur bacteria (Fig. 1). This sequence was identical to that from strains MN1
and BS-1, indicating that the
in situ
population exclusively consists of this
type of green sulfur bacterium which persisted at least over a time period
of 13 years. The successful isolation of the green sulfur bacterium permits
detailed laboratory investigations of the physiological adaptations to the specific
environmental conditions in the Black Sea chemocline.
3. ENVIRONMENTAL CONDITIONS IN THE BLACK
SEA CHEMOCLINE
Within the chemocline of the Black Sea, salinity values of 20 - 21 ‰ and
temperatures of8-9
◦
C have been measured. Chemical analysis of samples
from 70 to 100 m showed suboxic concentrations of molecular oxygen (0 - 3.8
µM), concentrations of nitrate of up to 8 µM, of nitrite
<
0.3 µM, of ammonia
between 0.2 and 8.8 µM, and of phosphate between 1 and 7 µM. Sulfide
concentrations reach 15 µM and elemental sulfur 0.2 µM in the chemocline
[12, 32, 33, 49, 60].
Whereas the above environmental factors correspond to those in other oxic-
/anoxic habitats, the Black Sea chemocline is characterized by a very extreme
light climate. The chemocline is positioned much deeper in the water column
than in other environments of phototrophic sulfur bacteria described so far.
