Derxia lacustris sp. nov., a nitrogen-fixing bacterium isolated from a freshwater lake

A novel nitrogen-fixing strain, designated HL-12(T), was isolated from a freshwater lake in Taiwan. Cells of strain HL-12(T) were aerobic, Gram-negative, motile rods that were surrounded by a thick capsule, contained poly-β-hydroxybutyrate granules, and formed light-yellow to brownish-red colonies. Growth occurred at 15-40 °C (optimum 25-35 °C), at pH 6.0-7.0 (optimum pH 6.0) and with 0-4 % NaCl (optimum 0-1 %). Phylogenetic analysis based on 16S rRNA gene sequences showed that strain HL-12(T) belonged to the genus Derxia and exhibited 99.1 and 98.8 % 16S rRNA gene sequence similarity, respectively, with Derxia gummosa IAM 14990 and D. gummosa IAM 13946(T). The major fatty acids (>10 %) of strain HL-12(T) were summed feature 3 (comprising C16 : 1ω7c and/or C16 : 1ω6c), C16 : 0 and C18 : 1ω7c. The cellular hydroxy fatty acids were C12 : 0 3-OH, C14 : 0 2-OH and C14 : 0 3-OH. The isoprenoid quinone was Q-8 and the DNA G+C content was 72.0 mol%. The polar lipid profile contained phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol and several unknown aminophospholipids and phospholipids. DNA-DNA relatedness between strain HL-12(T) and http://dx.doi.org/10.1601/nm.1758 LMG 3975 and http://dx.doi.org/10.1601/nm.1758 LMG 3977(T) was <70 %. On the basis of the genotypic and phenotypic data, strain HL-12(T) represents a novel species in the genus Derxia, for which the name Derxia lacustris sp. nov. is proposed. The type strain is HL-12(T) ( = BCRC 80208(T)  = KCTC 23311(T)).