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Applied and Environmental Microbiology, February 2008, p. 624-632, Vol. 74, No. 3
0099-2240/08/$08.00+0 doi:10.1128/AEM.02137-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.
Subfossil 16S rRNA Gene Sequences of Green Sulfur Bacteria in the Black Sea and Their Implications for Past Photic Zone Anoxia
Ann K. Manske,
Uta Henßge,
Jens Glaeser,
and
Jörg Overmann*
Department Biologie I, Bereich Mikrobiologie, Ludwig-Maximilians-Universität München, Maria-Ward-Str. 1a, D-80638 München, Germany
Received 18 September 2007/ Accepted 13 November 2007
The Black Sea is the largest extant anoxic water body on Earth. Its oxic-anoxic boundary is located at a depth of 100 m and is populated by a single phylotype of marine green sulfur bacteria. This organism, Chlorobium sp. strain BS-1, is extraordinarily low light adapted and can therefore serve as an indicator of deep photic zone anoxia (A. K. Manske, J. Glaeser, M. M. M. Kuypers, and J. Overmann, Appl. Environ. Microbiol. 71:8049-8060, 2005). In the present study, two sediment cores were retrieved from the bottom of the Black Sea at depths of 2,006 and 2,162 m and were analyzed for the presence of subfossil DNA sequences of BS-1 using ancient-DNA methodology. Using optimized cultivation media, viable cells of the BS-1 phylotype were detected only at the sediment surface and not in deeper layers. In contrast, green sulfur bacterial 16S rRNA gene fragments were amplified from all the sediment layers investigated, including turbidites. After separation by denaturing gradient gel electrophoresis and sequencing, 14 different sequence types were distinguished. The sequence of BS-1 represented only a minor fraction of the amplification products and was found in 6 of 22 and 4 of 26 samples from the 2,006- and 2,162-m stations, respectively. Besides the sequences of BS-1, three additional phylotypes of the marine clade of green sulfur bacteria were detected. However, the majority of sequences clustered with groups from freshwater habitats. Our results suggest that a considerable fraction of green sulfur bacterial chemofossils did not originate in a low-light marine chemocline environment and therefore were likely to have an allochthonous origin. Thus, analysis of subfossil DNA sequences permits a more differentiated interpretation and reconstruction of past environmental conditions if specific chemofossils of stenoec species, like Chlorobium sp. strain BS-1, are employed.
* Corresponding author. Mailing address: Department Biologie I, Bereich Mikrobiologie, Ludwig-Maximilians-Universität München, Maria-Ward-Str. 1a, D-80638 München, Germany. Phone: 49 89 2180 6123. Fax: 49 89 2180 6125. E-mail: j.overmann{at}lrz.uni-muenchen.de
Published ahead of print on 26 November 2007.
Present address: Justus-Liebig-Universität Gießen, Institut für Mikro- und Molekularbiologie, Heinrich-Buff-Ring 26-32, 35392 Gießen, Germany.
Applied and Environmental Microbiology, February 2008, p. 624-632, Vol. 74, No. 3
0099-2240/08/$08.00+0 doi:10.1128/AEM.02137-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.
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