Identification of the Carotenoid Pigment Canthaxanthin from Photosynthetic Bradyrhizobium Strains

Canthaxanthin (4,4(prm1)-diketo-(beta)-carotene) is produced as the major carotenoid pigment by orange- and dark-pink-pigmented bacteriochlorophyll-containing Bradyrhizobium strains isolated from stem nodules of Aeschynomene species. These two new pigmentation groups differ from the well-studied strain BTAi1, which accumulates spirilloxanthin as the sole carotenoid

Characterization of tropical tree rhizobia and description of Mesorhizobium plurifarium sp. nov.

A collection of strains isolated from root nodules of #Acacia species in Senegal was analysed previously by electrophoresis of total cell protein, auxanographic tests, rRNA-DNA hybridization, 16S rRNA gene sequencing, DNA base composition and DNA-DNA hybridization. Strains from #Acacia were shown to belong to two groups, #Sinorhizobium terangae and a so-called gel electrophoretic cluster U, which also included some reference strains from Brazil. Further taxonomic characterization of this group using the same techniques plus repetitive extragenic palindromic-PCR and nodulation tests is presented in this paper. Reference strains from Sudan and a number of new rhizobia isolated from nodules of #Acacia senegal, #Acacia tortilis subsp. #raddiana and #Prosopis juliflora in Senegal were included. As a result of this polyphasic approach, the creation of a new species, #Mesorhizobium plurifarium, is proposed for a genotypically and phenotypically distinct group corresponding to the former cluster U and containing strains isolated from #Acacia, #Leucaena, #Prosopis and #Chamaecrista in West Africa (Senegal), East Africa (Sudan) and South America (Brazil). The type strain of #Mesorhizobium plurifarium$ ORS 1032 has been deposited in the LMG collection as LMG 11892. (Résumé d'auteur

Rhizobium-legume symbiosis in the absence of Nod factors: two possible scenarios with or without the T3SS

International audienceThe occurrence of alternative Nod factor (NF)-independent symbiosis between legumes and rhizobia was first demonstrated in some Aeschynomene species that are nodulated by photosynthetic bradyrhizobia lacking the canonical nodABC genes. In this study, we revealed that a large diversity of non-photosynthetic bradyrhizobia, including B. elkanii, was also able to induce nodules on the NF-independent Aeschynomene species, A. indica. Using cytological analysis of the nodules and the nitrogenase enzyme activity as markers, a gradient in the symbiotic interaction between bradyrhizobial strains and A. indica could be distinguished. This ranged from strains that induced nodules that were only infected intercellularly to rhizobial strains that formed nodules in which the host cells were invaded intracellularly and that displayed a weak nitrogenase activity. In all non-photosynthetic bradyrhizobia, the type III secretion system (T3SS) appears required to trigger nodule organogenesis. In contrast, genome sequence analysis revealed that apart from a few exceptions, like the Bradyrhizobium ORS285 strain, photosynthetic bradyrhizobia strains lack a T3SS. Furthermore, analysis of the symbiotic properties of an ORS285 T3SS mutant revealed that the T3SS could have a positive or negative role for the interaction with NF-dependent Aeschynomene species, but that it is dispensable for the interaction with all NF-independent Aeschynomene species tested. Taken together, these data indicate that two NF-independent symbiotic processes are possible between legumes and rhizobia: one dependent on a T3SS and one using a so far unknown mechanism