Three symbiotic nitrogen-fixing bacteria (BD68(T), BD66 and BD73) isolated from root nodules of Lotus tenuis in lowland soils of the Flooding Pampa (Argentina), previously classified as members of the Mesorhizobium genus, were characterized in this study. Phylogenetic analysis of their 16S rRNA gene sequences showed a close relationship to M. japonicum MAFF 303099(T), M. erdmanii USDA 3471(T), M. carmichaelinearum ICMP 18942(T), M. opportunistum WSM 2975(T) and M. jarvisii ATCC 33699(T), with sequence identities of 99.72%-100%. Multilocus sequence analysis of other housekeeping genes revealed that the three isolates belonged to a phylogenetically distinct clade within the genus Mesorhizobium. Strain BD68(T) was designated as the group representative and its genome was fully sequenced. The average nucleotide identity and in silico DNA-DNA hybridization comparisons between BD68(T) and the most related type strains showed values below the accepted threshold for species discrimination. Phenotypic and chemotaxonomic features were also studied.

Based on these results, BD68(T), BD66 and BD73 could be considered to represent a novel species of the genus Mesorhizobium, for which the name Mesorhizobium intechi sp. nov. is hereby proposed. The type strain of this species is BD68(T) (=CECT 9304(T) = LMG 30179(T)). (C) 2019 Elsevier GmbH. All rights reserved.