Ferrigenium kumadai gen. nov., sp. nov., a microaerophilic iron-oxidizing bacterium isolated from a paddy field soil

An iron-oxidizing bacterium, designated strain An22^T, which was isolated from a paddy field soil in Anjo, Japan, was described taxonomically. Strain An22^T was motile by a single polar flagellum, curved-rod, Gram-negative bacterium that was able to grow at 12-37 °C (optimally at 25-30 °C) and at pH 5.2-6.8 (pH 5.9-6.1). The strain grew microaerobically and autotrophically by oxidizing ferrous iron, but did not form stalks, a unique structure of iron oxides. The major cellular fatty acids were C16 : 0 and C16 : 1ω7c/C16 : 1ω6c. The major respiratory quinones were UQ-10 and UQ-8. The strain possessed ribulose-1,5-bisphosphate carboxylase/oxygenase indicating an autotrophic nature via the Calvin-Benson-Bassham cycle. The total DNA G+C content was 61.4 mol%. 16S rRNA gene sequence analysis revealed that strain An22^T was affiliated with the class Betaproteobacteria and clustered with iron-oxidizing bacteria, Gallionella ferrugineaJohan (94.8 % similarity) and Ferriphaselus amnicola OYT1^T (94.4 %) in the family Gallionellaceae. Based on the low 16S rRNA gene sequence similarity to the phylogenetically closest genera and the combination of unique morphological, physiological and biochemical characteristics, strain An22^T represents a novel genus and species within the family Gallionellaceae, for which the name Ferrigenium kumadai gen. nov., sp. nov. is proposed. The type strain is An22^T (=JCM 30584^T=NBRC 112974^T=ATCC TSD-51^T).