Environmental Engineering Reference
In-Depth Information
ANOXYGENIC PHOTOTROPHIC BACTERIA IN
THE BLACK SEA CHEMOCLINE
J org Overmann and Ann K. Manske
University of Munich, Institute for Genetics and Microbiology, Department Biology I, Maria-
Ward-Str. 1a, Munich, Germany
Abstract
Currently, the Black Sea is the largest anoxic water body on the planet and
represents the closest contemporary analogue to past sulfidic oceans. For the
understanding of such oxic/anoxic environments, green sulfur bacteria are sig-
nificant, since they [1] can substantially alter the carbon and sulfur cycles and
[2] may be used as indicator organisms for the reconstruction of past photic
zone anoxia. In the chemocline of the Black Sea, brown-colored green sulfur
bacteria form an extremely dilute, but detectable population. Based on analysis
of their 16S rRNA gene sequences, these bacteria represent a single and novel
phylotype. Measurements of light intensities in the chemocline and experiments
with laboratory cultures revealed that the strain from the Black Sea is extraordi-
narily low-light adapted and grows with doubling times of several years. Fossil
16S rRNA gene sequences of the chemocline green sulfur bacterium have been
detected in different sediment layers, indicating past photic zone anoxia dur-
ing which the chemocline must have been positioned at a depth of up to 150 m.
Although not significant in the carbon and sulfur cycles of the Black Sea, the par-
ticular type of green sulfur bacterium present in the chemocline thus represents
a valuable indicator organism for the reconstruction of the paleoenvironmental
conditions of the Black Sea.
Keywords:
Chemocline, green sulfur bacteria, 16S rRNA, low-light adaptation, primary
productivity, photic zone, paleomicrobiology
1.
INTRODUCTION
In the present day ocean, anoxic sediments cover
∼
0.3% of the seafloor [44],
corresponding to
0.22% of the surface of the earth. An even smaller area of
the planet is covered by sulfidic water bodies like the Black Sea (0.083%), the
Cariaco Basin as the second largest basin (
∼
0.0022%) [62], the Gotland Basin
of the Baltic Sea, some smaller anoxic fjords, and numerous coastal lagoons
[8]. Since 87-92% of the water body of the Black Sea is permanently anoxic
[11, 38, 69], the latter currently contains the largest volume of anoxic water on
the planet.
∼
523
