Pantoea phytostimulans sp. nov., a novel strain with plant growth-promoting properties

A phosphate-solubilizing bacterial strain, designated C3^T, was isolated from the rhizosphere of sorghum. The taxonomic classification of this novel isolate was investigated by using a polyphasic approach. Cells of this strain were Gram-stain-negative, facultatively anaerobic and motile short rods with a polar flagellum. Phylogenetic analyses based on the 16S rRNA gene indicated that strain C3^T showed high similarity (98.66%) to certain <i>Pantoea</i> species, indicating that the isolate belongs to this genus. The genome of strain C3^T was 5.05 Mb in size with a G+C content of 51.1 mol%. Whole-genome analysis revealed that the novel strain shared 21.60-27.10% digital DNA-DNA hybridization values and 78.35-83.87% average nucleotide identity with closely related <i>Pantoea</i> species; both values below the accepted thresholds for defining a novel species. The predominant cellular fatty acids of strain C3^T were C_16:0, summed feature 3 (C_16:1 ω6c and/or C_{16 :1} ω7c), summed feature 8 (C_{18: 1} ω7c and/or C_18:1 ω6c), summed feature 2 (C_{12: 0} aldehyde and/or C_14:0 3OH and/or C_16:1 iso I and/or an unidentified fatty acid of 10.9525 chain length) and C_17:0 cyclo. Apart from the ability to solubilize phosphates, stain C3^T exhibited other <i>in vitro</i> plant growth-promoting activities such as K, Ca and Si solubilization, and the production of indole-3-acetic acid (IAA) and siderophores. Several genes related to phosphate solubilization, siderophore biogenesis and IAA, cytokinin and gamma-aminobutyric acid production were identified in the C3^T genome. Summarizing, based on phylogenetic, genomic, phenotypic and chemotaxonomic criteria, the isolate represents a novel species of the genus <i>Pantoea,</i> for which the name <i>Pantoea phytostimulans</i> sp. nov. is proposed. The type strain is C3^T (=CECT 31163^T=NCIMB 15596^T).