Bradyrhizobium stylosanthis sp. nov., comprising nitrogen-fixing symbionts isolated from nodules of the tropical forage legume Stylosanthes spp.

Abstract

Bradyrhizobium stylosanthis sp. nov., comprising nitrogen-fixing symbionts isolated from nodules of the tropical forage legume Stylosanthes spp. The introduction of legumes and nitrogen-fixing bacteria in tropical areas under pasture is a key factor for improvement of soil fertility. However, there are still very few studies concerning the symbionts of tropical forage legumes. We performed a polyphasic study with three strains representing the genus Bradyrhizobium (BR 446 T , BR 510 and BR 511) isolated from the tropical perennial forage legume of the genus Stylosanthes. On the basis of 16S rRNA gene sequences, the three strains showed highest similarity with B. huanghuaihaiense, and in the analysis of the intergenic transcribed spacer (ITS) they showed less than 93.4 % similarity to all described species of the genus Bradyrhizobium. Multilocus sequence analysis (MLSA) with three, four or five (dnaK, glnII, gyrB, recA and rpoB) housekeeping genes confirmed that the BR strains belong to a distinct clade, with <96.5 % nucleotide identity with other members of the genus Bradyrhizobium. Average nucleotide identity (ANI) of genome sequences between strain BR 446 T and B. huanghuaihaiense was below the threshold for species circumscription (90.7 %). DNA-DNA hybridization resulted in DT m values over 6.7 C with the most closely related species. Similarities among the BR strains and differences from other species were confirmed by rep-PCR analysis. Interestingly, the BR strains were grouped in the analysis of nifH and nodC genes, but showed higher similarity with B. iriomotense and B. manausense than with B. huanghuaihaiense, indicating a different evolutionary history for nitrogen-fixation genes. Morpho-physiological, genotypic and genomic data supported that these BR strains represent a novel species for which the name Bradyrhizobium stylosanthis sp. nov. isAbbreviations: DDH, DNA-DNA hybridization; ITS, intergenic transcribed spacer; MLSA, multilocus sequence analysis.

Bradyrhizobium archetypum sp. nov., Bradyrhizobium australiense sp. nov. and Bradyrhizobium murdochi sp. nov., isolated from nodules of legumes indigenous to Western Australia

“…The 16S rRNA gene phylogeny () split the Bradyrhizobium type strains into the two well-known superclades of Bradyrhizobium japonicum (GI) and Bradyrhizobium elkanii (GII) [2, 8–10, 33]. All strains from our study were clustered in the B.…”

“… Bradyrhizobium is considered as the probable ancestor lineage of all rhizobia and, in the last decade, several studies reported remarkable genetic diversity within the genus, as well as symbiotic associations with an increasing number of legumes [e.g. [1, 2, 6–13]. The environmental and economic applications of Bradyrhizobium and its high diversity reassure the importance of characterization and seeking for strains with biotechnological potential.…”

Phylogeny and Phylogeography of Rhizobial Symbionts Nodulating Legumes of the Tribe Genisteae

“…( Supplementary data Table S1 ). The majority of Clade VII strains originate from North and South America, while some were isolated in south-east Asia (southern China, the Island of Okinawa, Thailand, and the Philippines) [ 143 , 144 , 145 , 146 , 147 ]. Given that Clade VII bradyrhizobia from south-east Asia occupy internal positions relative to the American strains, it can be assumed that this cluster has evolved in the Americas, possibly, in an area of hot and humid tropical climate.…”

Bradyrhizobium centrolobii and Bradyrhizobium macuxiense sp. nov. isolated from Centrolobium paraense grown in soil of Amazonia, Brazil

“…The ANI approach has recently been accepted as an alternative to the traditional DNA: DNA hybridization method (Delamuta et al 2016;Baraúna et al 2016) and similarity values >95-96% are considered as the threshold to determine if two bacterial strains belong to the same species (Richter and Rosselló-Mora 2009).…”