Rhizobial isolates in active layer samples of permafrost soil of Spitsbergen, Arctic

Abstract

Twenty-nine strains were isolated from two samples of the permafrost active layer of the Spitsbergen archipelago. The estimated number of bacteria ranged from 4.0⋅104 to 1.7⋅107 CFU∙g-1. As a result of sequencing of the 16S rRNA (rrs) genes, the isolates were assigned to 13 genera belonging to the phyla Actinobacteria, Proteobacteria (classes α, β, and γ), Bacteroidetes, and Firmicutes. Six isolates belonged to the rhizobial genus Mesorhizobium (order Rhizobiales). A plant nodulation assay with seedlings of legume plants Astragalus norvegicus, A. frigidus, A. subpolaris and Oxytropis sordida, originated from Khibiny (Murmansk region, Russia) and inoculated with Mesorhizobium isolates, showed the inability of these strains to form nodules on plant roots. Symbiotic (sym) genes nodC and nodD were not detected in Mesorhizobium strains either.