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Applied and Environmental Microbiology, September 2003, p. 5248-5254, Vol. 69, No. 9
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.9.5248-5254.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Isolation of Strains Belonging to the Cosmopolitan Polynucleobacter necessarius Cluster from Freshwater Habitats Located in Three Climatic Zones

Martin W. Hahn*

Institute for Limnology, Austrian Academy of Sciences, A-5310 Mondsee, Austria

Received 14 April 2003/ Accepted 24 June 2003

More than 40 bacterial strains belonging to the cosmopolitan Polynucleobacter necessarius cluster (Betaproteobacteria) were isolated from a broad spectrum of freshwater habitats located in three climatic zones. Sequences affiliated with the freshwater P. necessarius cluster are among the most frequently detected in studies on bacterial diversity in freshwater ecosystems. Despite this frequent detection with culture-independent techniques and the cosmopolitan occurrence of members affiliated with this cluster, no isolates have been reported thus far. The isolated strains have been obtained from lakes, ponds, and rivers in central Europe, the People's Republic of China, and East Africa by use of the filtration-acclimatization method. The 16S rRNA gene sequences of the isolates are 98.8 to 100% identical to reference sequences obtained by various authors by use of culture-independent methods. The isolates, aerobic heterotrophs, grew on a wide range of standard complex media and formed visible colonies on agar plates. Thus, the previous lack of isolates cannot be explained by a lack of appropriate media. Most of the isolates possess, under a wide range of culture conditions, very small cells (<0.1 µm3), even when grown in medium containing high concentrations of organic substances. Thus, these strains are obligate ultramicrobacteria. The obtained strains have a C-shaped cell morphology which is very similar to that of recently isolated ultramicrobacterial Luna cluster strains (Actinobacteria) and the SAR11 cluster strains (Alphaproteobacteria).

* Mailing address: Institute for Limnology, Austrian Academy of Sciences, Mondseestrasse 9, A-5310 Mondsee, Austria. Phone: 43 6232 3125-29. Fax: 43 6232 3578. E-mail: martin.hahn{at}oeaw.ac.at.

Applied and Environmental Microbiology, September 2003, p. 5248-5254, Vol. 69, No. 9
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.9.5248-5254.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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