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

Abstract

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 P26ET 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, P26ET presented similarity values above 98.8% in relation to Paenibacillus azotifigens NF2-4-5T, Paenibacillus graminis RSA19T, Paenibacillus jilunlii Be17T, Paenibacillus salinicaeni LAM0A28T, and Paenibacillus sonchi X19-5T. Phylogenetic reconstructions based on 16S rRNA gene and core proteome data showed that the strains P26ET, 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 P26ET was determined to be 49.4mol%. The major cellular fatty acids are anteiso-C15:0 and iso-C15:0, representing about 58 and 14% of the total fatty acids in P26ET, respectively. Based on different taxonomic genomic metrics, phylogeny, and phenotypic data, we propose that strain P26ET (= DSM 102269 = BR10509) represents a novel species within the genus Paenibacillus, for which the name Paenibacillus helianthi sp. nov. is proposed.