Two novel Fe(III)-reducing bacteria, Geothrix campi sp. nov. and Geothrix mesophila sp. nov., isolated from paddy soils

In this research, two novel Fe(III)-reducing bacteria, SG10^T and SG198^T of genus Geothrix, were isolated from the rice field of Fujian Agriculture and Forestry University in Fuzhou, Fujian Province, China. Strains SG10^T and SG198^T were strictly anaerobic, rod-shaped and Gram-stain-negative. The two novel strains exhibited iron reduction ability, utilizing various single organic acid as the elector donor and Fe(III) as a terminal electron acceptor. Strains SG10^T and SG198^T showed the highest 16S rRNA sequences similarities to the type strains of Geothrix oryzisoli SG189^T (99.0–99.5%) and Geothrix paludis SG195^T (99.0–99.7%), respectively. The phylogenetic trees based on the 16S rRNA gene and genome 120 conserved core genes showed that strains SG10^T and SG198^T belong to the genus Geothrix. Average nucleotide identity (ANI) and digital DNA–DNA hybridization (dDDH) values between the phylogenetic neighbors and the two isolated strains were 86.1–94.3% and 30.7–59.5%, respectively. The major fatty acids were iso-C_15:0, anteiso-C_15:0, C_16:0 and iso-C_13:0 3OH, and MK-8 was the main respiratory quinone. According to above results, the two strains were assigned to the genus Geothrix with the names Geothrix campi sp. nov. and Geothrix mesophila sp. nov. Type strains are SG10^T (= GDMCC 1.3406 ^T = JCM 39331 ^T) and SG198^T (= GDMCC 62910 ^T = KCTC 25635 ^T), respectively.