Three alkalitolerant bacterial strains were isolated from the surface of decomposing rhizomes of reed [Phragmites australia (Cav.) Trin. et Steudel] in Lake Fertö (Hungary). Cells of the novel isolates were Gram-negative, motile rods and formed star-shaped aggregates. They were facultatively anaerobic and chemo-organotrophic. Bacteriochlorophyll a was not synthesized under aerobic conditions. The strains were catalase and oxidase positive, produced acid from D-glucose under aerobic and anaerobic conditions and reduced nitrate to nitrogen. They tolerated pH values from 7.0 to 11.0 and grew in the absence of NaCl as well as in up to 5% (w/v) NaCl. The G + C content of the DNA was 64.6 mol% and the major isoprenoid quinone was Q-10. The dominant cellular fatty acid was C18 : 1omega7c. The cell membrane contained phosphatidyl glycerol, diphosphatidyl glycerol, phosphatidyl ethanolamine, phosphatidyl serine and one unknown phospholipid as polar lipids. Polyphasic taxonomic characterization revealed that strain C6/19T is most closely related to the Stappia-Roseibium cluster in the alpha-subclass of the Proteobacteria (showing 95.8-93.6% 16S rDNA sequence similarity). According to the phylogenetic and phenotypic evidence presented, a new genus and species is proposed, Pannonibacter phragmitetus gen. nov., sp. nov. The type strain is C6/19T (=DSM 14782T =NCAIM B02025T).