Pantoea phosphatilytica sp. nov. and Pantoea phyllosphaerae sp. nov., two phosphate-solubilizing and siderophore-producing bacteria isolated from citrus phyllosphere.

Abstract

Two yellow-pigmented, Gram-stain-negative, aerobic, motile and rod-shaped bacterial strains, designated RHCKP32^T and RRHST58^T, were isolated from the citrus leaves in Renhua County, a famous planting area located in Guangdong Province, China. Phylogenomic analysis showed that they belonged to the genus Pantoea, and strain RHCKP32^T was most closely related to Pantoea deleyi LMG 24200^T, while strain RRHST58^T showed the closest relationship to Pantoea septica LMG 5345^T. The overall genomic relatedness analysis showed that strains RHCKP32^T and RRHST58^T shared 84.3‒94.6 and 89.5‒94.5% average nucleotide identity and 32.0‒58.0 and 38.5‒58.2% digital DNA-DNA hybridization with their closely related type strains, respectively, which were all below the suggested threshold values for novel species delimitation. They both took ubiquinone 8 (Q-8) as the predominant respiratory quinone and C_16:0, C_17:0 cyclo, summed feature 2 (C_14:0 3-OH and/or iso-C_16:1 I), summed feature 3 (C_16:1  ω7c and/or C_16:1  ω6c) and summed feature 8 (C_18:1  ω7c and/or C_18:1  ω6c) as their major fatty acids. The genomic DNA G+C contents of strains RHCKP32^T and RRHST58^T were 57.33 and 58.77 mol%, respectively. Based on the phenotypic, phylogenetic and chemotaxonomic analyses, they should be considered as two novel species of the genus Pantoea, for which the names Pantoea phosphatilytica sp. nov. and Pantoea phyllosphaerae sp. nov. are proposed with RHCKP32^T (=GDMCC 1.2672^T=JCM 34793^T) and RRHST58^T (=GDMCC 1.2673^T=JCM 34797^T) as the type strains, respectively. In addition, they showed the ability to solubilize inorganic phosphates and produce siderophores, for which the maximum soluble phosphorus concentrations could reach 510.03±7.11 and 506.47±3.08 mg l^-1 for strains RHCKP32^T and RRHST58^T after 5 days of inoculation in liquid National Botanical Research Institute's (NBRIP) medium, respectively, and the corresponding relative siderophore production was 21.25±2.23 and 10.20±0.15 percent siderophore unit after 2 days of inoculation in nutrient broth, implicating they might have potential application in promoting plant growth.