Rhizobium flavescens sp. nov., Isolated from a Chlorothalonil-Contaminated Soil

A Gram-negative, facultative anaerobic, non-lagellated and rod-shaped bacterium FML-4^T was isolated from a chlorothalonil-contaminated soil in Nanjing, China. Phylogenetic analyses of 16S rRNA genes revealed that the strain FML-4^T shared the highest sequence similarity of 97.1% with Ciceribacter thiooxidans KCTC 52231^T, followed by Rhizobium rosettiformans CCM 7583^T (97.0%) and R. daejeonense KCTC 12121^T (96.8%). Although the sequence similarities of the housekeeping genes thrC, rceA, glnII, and atpD between strain FML-4^T and C. thiooxidans KCTC 52231^T were 83.8%, 88.7%, 86.2%, and 92.0%, respectively, strain FML-4^T formed a monophyletic clade in the cluster of Rhizobium species. Importantly, the feature gene of the genus Rhizobium, nifH gene (encoding the dinitrogenase reductase), was detected in strain FML-4^T but not in C. thiooxidans KCTC 52231^T. In addition, strain FML-4^T contained the summed feature 8 (C_18:1ω7c and/or C_18:1ω6c), C_19:0 cyclo ω8c and C_16:0 as the major fatty acids. Genome sequencing of strain FML-4^T revealed a genome size of 7.3 Mbp and a G+C content of 63.0 mol%. Based on the results obtained by phylogenetic and chemotaxonomic analyses, phenotypic characterization, average nucleotide identity (ANI, similarity 77.3-75.4%), and digital DNA-DNA hybridization (dDDH, similarity 24.5-22.3%), it was concluded that strain FML-4^T represented a novel species of the genus Rhizobium, for which the name Rhizobium flavescens sp. nov. was proposed (type strain FML-4^T = CCTCC AB 2019354^T = KCTC 62839^T).