Limited information is available that seed biopriming with plant growth-promoting Enterobacter spp. play a prominent role to enhance vegetative growth of plants. Contrary to Enterobacter cloacae, Enterobacter hormaechei is a less-studied counterpart despite its vast potential in plant growth-promotion mainly through the inorganic phosphorus (P) and potassium (K) solubilization abilities. To this end, 18 locally isolated bacterial pure cultures were screened and three strains showed high P-and K-solubilizing capabilities. Light microscopy, biochemical tests and 16S rRNA gene sequencing revealed that strains 15a1 and 40a were closely related to Enterobacter hormaechei while strain 38 was closely related to Enterobacter cloacae (Accession number: MN294583; MN294585; MN294584). All Enterobacter spp. shared common plant growth-promoting traits, namely nitrogen (N 2) fixation, indole-3-acetic acid production and siderophore production. The strains 38 and 40a were able to produce gibberellic acid, while only strain 38 was able to secrete exopolysaccharide on agar. Under in vitro germination assay of okra (Abelmoschus esculentus) seeds, Enterobacter spp. significantly improved overall germination parameters and vigor index (19.6%) of seedlings. The efficacy of root colonization of Enterobacter spp. on the pre-treated seedling root tips was confirmed using Scanning Electron Microscopy (SEM). The pot experiment of bioprimed seeds of okra seedling showed significant improvement of the plant growth (> 28%) which corresponded to the increase of P and K uptakes (> 89%) as compared to the uninoculated control plants. The leaf surface area and the SPAD chlorophyll index of bioprimed plants were increased by up to 29% and 9% respectively. This report revealed that the under-explored species of P-and K-solubilizing Enterobacter hormaechei sp. with multiple plant beneficial traits presents a great potential sustainable approach for enhancement of soil fertility and P and K uptakes of plants.

3 hormaechei sp. improves the early vegetative growth and 4 the P and K uptake of okra (Abelmoschus esculentus) 5 seedling 6 Muhamad Aidilfitri Abstract 23 Limited information is available that seed biopriming by plant growth-promoting bacteria such 24 as those among Enterobacter spp. play a prominent role to enhance vegetative growth of plants.25 Contrary to Enterobacter cloacae, Enterobacter hormaechei is a less-studied counterpart 26 despite its vast potential in plant growth-promotion mainly through the inorganic phosphorus 27 (P) and potassium (K) solubilization abilities. To this end, 18 locally isolated bacterial pure 28 cultures screened and three strains showed high P-and K-solubilizing capabilities. Light 29 microscopy, biochemical tests and 16S rRNA gene sequencing revealed that strains 15a1 and 30 40a were closely related to Enterobacter hormaechei while strain 38 was closely related to 31 Enterobacter cloacae (Accession number: MN294583; MN294585; MN294584). All 32 Enterobacter spp. shared common plant growth-promoting traits, namely N 2 fixators, indole-33 3-acetic acid producers and siderophore producers. Gibberellic acid was only produced by 34 strain 38 and 40a, while exopolysaccharide formation was solely detected on agar containing 35 colonies of strain 38. Under in vitro germination assay of okra (Abelmoschus esculentus) seeds, 36 Enterobacter spp. significantly improved overall germination parameters and vigor index 37 (19.6%) of seedlings. The efficacy of root colonization of Enterobacter spp. on the pre-treated 38 seedling root tips was confirmed using Scanning Electron Microscopy (SEM). The pot 39 experiment of bioprimed seeds of okra seedling showed significant improvement of the plant 40 growth (> 28%) which corresponded to the increase of P and K uptakes (> 89%) as compared 41 to the uninoculated control plants. The leaf surface area and the SPAD chlorophyll index of 42 bioprimed plants were increased up to 29% and 9% respectively. This report revealed that the 43 under-explored species of P-and K-solubilizing Enterobacter hormaechei sp. with multiple 44 plant beneficial traits hold as a good potential sustainable approach for enhancement of soil 45 fertility and P and K uptakes of plants. 3 46