Emended description of the genus Phyllobacterium and description of four novel species associated with plant roots: Phyllobacterium bourgognense sp. nov., Phyllobacterium ifriqiyense sp. nov., Phyllobacterium leguminum sp. nov. and Phyllobacterium brassicacearum sp. nov.

Abstract

Gram-negative bacteria were isolated from the rhizoplane of Brassica napus in France and from root nodules of Argyrolobium uniflorum, Astragalus algerianus and Lathyrus numidicus growing in the infra-arid zone of southern Tunisia. Based on phylogenetic analysis of the 16S rRNA gene sequences, the seven isolates belong to the Alphaproteobacteria and are related to Phyllobacterium myrsinacearum strains. The isolates formed three clusters; clusters A and C consist of Tunisian strains, whereas cluster B consists of two strains from Brassica napus from France. Phylogenetic reconstruction based on the atpD gene strongly supports their affiliation to the genus Phyllobacterium. DNA–DNA hybridizations revealed that (i) none of the isolates belong to the species P. myrsinacearum, (ii) clusters A and C represent two distinct genomospecies and (iii) the two strains of cluster B represent two separate genomospecies. Distinctive phenotypic features were deduced from numerical analysis of phenotypic data. Based on this polyphasic approach, four novel species are proposed: Phyllobacterium leguminum sp. nov. (type strain ORS 1419T=CFBP 6745T=LMG 22833T), Phyllobacterium ifriqiyense sp. nov. (type strain STM 370T=CFBP 6742T=LMG 22831T), Phyllobacterium brassicacearum sp. nov. (type strain STM 196T=CFBP 5551T=LMG 22836T) and Phyllobacterium bourgognense sp. nov. (type strain STM 201T=CFBP 5553T=LMG 22837T). The description of the genus Phyllobacterium is emended accordingly.