A moderately thermophilic aerobic bacterium, strain 25-4(T), was isolated from a hot spring at Baekdoo Mountain in Korea. The cells were Gram-negative, motile rods each having a polar flagellum. Analysis of the 16S rRNA gene sequence indicated that the strain represented a new lineage within the family 'Xanthomonadaceae' of the 'Gammaproteobacteria', being most closely related to the genera Thermomonas, Xanthomonas, Luteimonas, Pseudoxanthomonas, Stenotrophomonas and Xylella and having 16S rRNA gene sequence similarities to the most related species of the genera of between 92.9 and 94.4%. The strain contained Q-8 as the major isoprenoid quinone and had a fatty acid profile with predominant iso-branched fatty acids. Growth occurred at pH 6.0-10, with an optimum at pH 9.0, and at 25-53 degreesC, witch an optimum at 47 degreesC. The G+C content of the genomic DNA was 50.7 mol%. On the basis of phylogenetic analyses and its phenotypic characteristics, strain 25-4T belongs to a new genus, Silanimonas gen, nov., within the 'Gammaproteobacteria'. The sole species of this genus is Silanimonas lenta sp. nov. (type strain, 25-4(T) = DSM 16282(T) = KCTC 12236(T)).