Rhizobial Microsymbionts of Kamchatka Species Possess Genes of the Type III and VI Secretion Systems, Which Can Affect the Development of Symbiosis.

A collection of rhizobial strains isolated from root nodules of the narrowly endemic legume species , , , and originating from the Kamchatka Peninsula (Russian Federation) was obtained. Analysis of the 16S ribosomal RNA gene sequence showed a significant diversity of isolates belonging to families (genus ), (genera , ), and (genera , ). A plant nodulation assay showed that only strains belonging to genus could form nitrogen-fixing nodules on plants. The strains 582 and 583, in addition to symbiotic clusters, possessed genes of the type III and type VI secretion systems (T3SS and T6SS, respectively), which can influence the host specificity of strains. These strains formed nodules of two types (elongated and rounded) on roots. We suggest this phenomenon may result from Nod factor-dependent and -independent nodulation strategies. The obtained strains are of interest for further study of the T3SS and T6SS gene function and their role in the development of rhizobium-legume symbiosis. The prospects of using rhizobia having both gene systems related to symbiotic and nonsymbiotic nodulation strategies to enhance the efficiency of plant-microbe interactions by expanding the host specificity and increasing nodulation efficiency are discussed.