Microvirga tunisiensis sp. nov., a root nodule symbiotic bacterium 1 isolated from Lupinus 2 micranthus and L. luteus grown in Northern Tunisia

Abstract

Three bacterial strains, LmiM8T, LmiE10 and LluTb3, isolated from nitrogen-fixing nodules 20 of Lupinus micranthus (Lmi strains) and L. luteus (Llu strain) growing in Northern Tunisia 21 were analysed using genetic, phenotypic and symbiotic approaches. Phylogenetic analyses 22 based on rrs and concatenated gyrB and dnaK genes suggested that these Lupinus strains 23 constitute a new Microvirga species with identities ranging from 95 to 83% to its closest 24 relatives Microvirga makkahensis, M. vignae, M. zambiensis, M. ossetica, and M. 25 lotononidis. The genome sequences of strains LmiM8T and LmiE10 exhibited pairwise 26 Average Nucleotide Identities (ANIb) above 99.5%, significantly distant (73-89% pairwise 27 ANIb) from other Microvirga species sequenced (M. zambiensis and M. ossetica). A 28 phylogenetic analysis based on the symbiosis-related gene nodA placed the sequences of the 29 new species in a divergent clade close to Mesorhizobium, Microvirga and Bradyrhizobium 30 strains, suggesting that the M. tunisiensis strains represent a new symbiovar different from 31 the Bradyrhizobium symbiovars defined to date. In contrast, the phylogeny derived from 32 another symbiosis-related gene, nifH, reproduced the housekeeping genes phylogenies. The 33 study of morphological, phenotypical and physiological features, including cellular fatty acid 34 composition of the novel isolates demonstrated their unique profile regarding close reference 35 Microvirga strains. Strains LmiM8T, LmiE10 and LluTb3 were able to nodulate several 36 Lupinus spp. Based on genetic, genomic and phenotypic data presented in this study, these 37 strains should be grouped within a new species for which the name Microvirga tunisiensis sp. 38 nov. is proposed (type strain LmiM8T = CECT 9163T, LMG 29689T).