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Applied and Environmental Microbiology, July 2008, p. 4398-4404, Vol. 74, No. 14
0099-2240/08/$08.00+0     doi:10.1128/AEM.02447-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Abundance, Depth Distribution, and Composition of Aerobic Bacteriochlorophyll a-Producing Bacteria in Four Basins of the Central Baltic Sea ^,

Ivette Salka,¹ Vladimíra Moulisová,² Michal Koblíek,^2,3 Günter Jost,¹ Klaus Jürgens,¹ and Matthias Labrenz^1*

IOW-Leibniz Institute for Baltic Sea Research, Seestrasse 15, 18119 Rostock, Germany,¹ Institute of Microbiology AV R, Opatovick mln, 379 81 Tebo, Czech Republic,² Institute of Physical Biology, University of South Bohemia, Zámek 136, 373 33 Nové Hrady, Czech Republic³

Received 30 October 2007/ Accepted 14 May 2008

The abundance, vertical distribution, and diversity of aerobic anoxygenic phototrophic bacteria (AAP) were studied at four basins of the Baltic Sea. AAP were enumerated by infrared epifluorescence microscopy, and their diversity was analyzed by using pufM gene clone libraries. In addition, numbers of CFU containing the pufM gene were determined, and representative strains were isolated. Both approaches indicated that AAP reached maximal abundance in the euphotic zone. Maximal AAP abundance was 2.5 x 10⁵ cells ml^–1 (11% of total prokaryotes) or 1.0 x 10³ CFU ml^–1 (9 to 10% of total CFU). Environmental pufM clone sequences were grouped into 11 operational taxonomic units phylogenetically related to cultivated members of the Alpha-, Beta-, and Gammaproteobacteria. In spite of varying pufM compositions, five clones were present in all libraries. Of these, Jannaschia-related clones were always found in relative abundances representing 25 to 30% of the total AAP clones. The abundances of the other clones varied. Clones potentially affiliated with typical freshwater Betaproteobacteria sequences were present at three Baltic Sea stations, whereas clones grouping with Loktanella represented 40% of the total cell numbers in the Gotland Basin. For three alphaproteobacterial clones, probable pufM phylogenetic relationships were supported by 16S rRNA gene analyses of Baltic AAP isolates, which showed nearly identical pufM sequences. Our data indicate that the studied AAP assemblages represented a mixture of marine and freshwater taxa, thus characterizing the Baltic Sea as a "melting pot" of abundant, polyphyletic aerobic photoheterotrophic bacteria.

Published ahead of print on 23 May 2008.

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