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Applied and Environmental Microbiology, January 2002, p. 365-371, Vol. 68, No. 1
0099-2240/02/$04.00+0     DOI: 10.1128/AEM.68.1.365-371.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Identification of a Gene Essential for Sheathed Structure Formation in Sphaerotilus natans, a Filamentous Sheathed Bacterium

Toshihiko Suzuki, Takahiro Kanagawa, and Yoichi Kamagata*

Research Institute of Biological Resources, National Institute of Advanced Industrial Science and Technology (AIST), Central 6, 1-1-1 Higashi, Tsukuba 305-8566, Japan

Received 4 June 2001/ Accepted 28 September 2001

Sphaerotilus natans, a filamentous bacterium that causes bulking in activated sludge processes, can assume two distinct morphologies, depending on the substrate concentration for growth; in substrate-rich media it grows as single rod-shaped cells, whereas in substrate-limited media it grows as filaments. To identify genes responsible for sheath formation, we carried out transposon Tn5 mutagenesis. Of the approximately 20,000 mutants obtained, 7 did not form sheathed structures. Sequencing of the Tn5-flanking regions showed that five of the seven Tn5 insertions converged at the same open reading frame, designated sthA. The deduced amino acids encoded by sthA were found to be homologous to glycosyltransferase, which is known to be involved in linking sugars to lipid carriers during bacterial exopolysaccharide biosynthesis. Disruption of the gene of the wild-type strain by inserting a kanamycin resistance gene cassette also resulted in sheathless growth under either type of nutrient condition. These findings indicate that sthA is a crucial component responsible for sheath formation.

* Corresponding author. Mailing address: Research Institute of Biological Resources, National Institute of Advanced Industrial Science and Technology (AIST), Central 6, 1-1-1 Higashi, Tsukuba 305-8566, Japan. Phone: 81-298-61-6591. Fax: 81-298-61-6587. E-mail: y.kamagata{at}aist.go.jp.

Applied and Environmental Microbiology, January 2002, p. 365-371, Vol. 68, No. 1
0099-2240/02/$04.00+0     DOI: 10.1128/AEM.68.1.365-371.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.





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