Two strains of aluminium-tolerant bacteria, SA33(T) and 7A078, were isolated from Chinese water chestnut (Eleocharis dulcis) growing in highly acidic swamps (pH 2-4) in actual acid sulfate soil areas of Vietnam (SA33(T)) and Thailand (7A078). The strains were Gram-negative, aerobic, non-spore-forming rods, 0.6-0.7 mum wide and 1.3-1.7 mum long. These strains showed good growth at pH 3.0-8.0 and 17-37 degrees C. The organisms contained ubiquinone Q-8 as the predominant isoprenoid quinone and C(16 : 0), C(18 : 1) ω 7c and C(17 : 0) cyclo as the major fatty acids. Their fatty acid profiles were similar to those reported for other Burkholderia species. The DNA G+C content of these strains was 64 mol%. On the basis of 16S rRNA gene sequence similarity, the strains were shown to belong to the genus Burkholderia. Although the 16S rRNA gene sequence similarity values calculated for strain SA33(T) to 7A078 and the type strains of Burkholderia kururiensis, B. sacchari and B. tuberum were 100, 97.3, 97.1 and 97.0 %, respectively, strains SA33(T) and 7A078 formed a group that was distinct in the phylogenetic trees; the DNA-DNA relatedness of strain SA33(T) to 7A078 and these three type strains were respectively 90, 47, 46 and 45 %. The results of physiological and biochemical tests, including whole-cell protein pattern analysis, allowed phenotypic differentiation of these strains from described Burkholderia species. Therefore, strains SA33(T) and 7A078 represent a novel species, for which the name Burkholderia acidipaludis sp. nov. is proposed. The type strain is SA33(T) (=NBRC 101816(T) =VTCC-D6-6(T)). Strain 7A078 (=NBRC 103872 =BCC 36999) is a reference strain.