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Applied and Environmental Microbiology, January 2004, p. 332-339, Vol. 70, No. 1
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.1.332-339.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Successful Predation of Filamentous Bacteria by a Nanoflagellate Challenges Current Models of Flagellate Bacterivory

Qinglong L. Wu,1,2* Jens Boenigk,1 and Martin W. Hahn1

Institute for Limnology, Austrian Academy of Sciences, A-5310 Mondsee, Austria,1 Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, People's Republic of China2

Received 14 July 2003/ Accepted 1 October 2003

Current models suggest that (i) filamentous bacteria are protected against predation by nanoflagellates, (ii) prey size is positively correlated with prey-predator contact probability, and (iii) contact probability is mainly responsible for size-selective predation by interception-feeding flagellates. We used five strains of filamentous bacteria and one bacterivorous nanoflagellate, Ochromonas sp. strain DS, to test these assumptions. The five strains, including one spirochete and four Betaproteobacteria strains, were isolated by the filtration-acclimatization method. All five strains possess flexible cells, but they differ in average cell length, which ranged from 4.5 to 13.7 µm. High-resolution video microscopy was used to measure contact, capture, and ingestion rates, as well as selectivity of the flagellate feeding. Growth and feeding experiments with satiating and nonsatiating food conditions, as well as experiments including alternative well-edible prey, were performed. In contrast to predictions by current models, the flagellate successfully consumed all the tested filamentous strains. The ingestion rate was negatively correlated with bacterial length. On the other hand, the lengths of the filamentous bacteria were not positively correlated to the contact rate and capture rate but were negatively correlated to ingestion efficiency. In experiments including alternative nonfilamentous prey, the flagellates showed negative selection for filamentous bacteria, which was independent of food concentration and is interpreted as a passive selection. Our observations indicate that (i) size alone is not sufficient to define a refuge for filamentous bacteria from nanoflagellate predation and (ii) for the investigated filamentous bacteria, prey-predator contact probability could be more influenced by factors other than the prey size.

* Corresponding author. Mailing address: Institute for Limnology, Austrian Academy of Sciences, Mondseestrasse 9, A-5310 Mondsee, Austria. Phone: 43 6232 3125-45. Fax: 43 6232 3578. E-mail: qinglong.wu{at}assoc.oeaw.ac.at.

Applied and Environmental Microbiology, January 2004, p. 332-339, Vol. 70, No. 1
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.1.332-339.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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