Paenibacillus helianthi sp. nov., a nitrogen fixing species isolated from the rhizosphere of Helianthus annuus L.

Three facultatively anaerobic endospore-forming bacteria were isolated from the rhizosphere of sunflowers grown in fields of Rio Grande do Sul State, Brazil. The designated type strain P26E(T) was previously identified as a sunflower growth promoting bacterium and is able to fix nitrogen and to excrete ammonia. According to analyses of 16S rRNA gene sequences, P26E(T) presented similarity values above 98.8% in relation to Paenibacillus azotifigens NF2-4-5(T), Paenibacillus graminis RSA19(T), Paenibacillus jilunlii Be17(T), Paenibacillus salinicaeni LAM0A28(T), and Paenibacillus sonchi X19-5(T). Phylogenetic reconstructions based on 16S rRNA gene and core proteome data showed that the strains P26E(T), P3E and P32E form a distinct clade, which did not include any type strain of the currently described Paenibacillus species. Also, genomic comparisons using average nucleotide identity (ANI), Orthologous ANI and in silico DNA-DNA hybridization revealed similarity ranges below the recommended thresholds when the three isolates from sunflower were compared to their close relatives. The DNA G+C content of strain P26E(T) was determined to be 49.4mol%. The major cellular fatty acids are anteiso-C-15:0 and iso-C-15:0, representing about 58 and 14% of the total fatty acids in P26E(T), respectively. Based on different taxonomic genomic metrics, phylogeny, and phenotypic data, we propose that strain P26E(T) (=DSM 102269=BR10509) represents a novel species within the genus Paenibacillus, for which the name Paenibacillus helianthi sp. nov. is proposed.