Phosphorus is an important macronutrient, but its availability in soil is limited. Many soil microorganisms improve the bioavailability of phosphate by releasing it from various organic compounds, including phytate. To investigate the diversity of phytate-hydrolyzing bacteria in soil, we sampled soils of various ecological habitats, including forest, private homesteads, large agricultural complexes, and urban landscapes. Bacterial isolate Pantoea sp. strain 3.5.1 with the highest level of phytase activity was isolated from forest soil and investigated further. The Pantoea sp. 3.5.1 agpP gene encoding a novel glucose-1-phosphatase with high phytase activity was identified, and the corresponding protein was purified to apparent homogeneity, sequenced by mass spectroscopy, and biochemically characterized. The AgpP enzyme exhibits maximum activity and stability at pH 4.5 and at 37°C. The enzyme belongs to a group of histidine acid phosphatases and has the lowest K _m values toward phytate, glucose-6-phosphate, and glucose-1-phosphate. Unexpectedly, stimulation of enzymatic activity by several divalent metal ions was observed for the AgpP enzyme. High-performance liquid chromatography (HPLC) and high-performance ion chromatography (HPIC) analyses of phytate hydrolysis products identify dl - myo -inositol 1,2,4,5,6-pentakisphosphate as the final product of the reaction, indicating that the Pantoea sp. AgpP glucose-1-phosphatase can be classified as a 3-phytase. The identification of the Pantoea sp. AgpP phytase and its unusual regulation by metal ions highlight the remarkable diversity of phosphorus metabolism regulation in soil bacteria. Furthermore, our data indicate that natural forest soils harbor rich reservoirs of novel phytate-hydrolyzing enzymes with unique biochemical features.

Phosphate solubilizing microorganisms (PSMs) in soil have been shown to reduce mineral phosphate fertilizer supplementation and promote plant growth. Nevertheless, only several P-solubilizing microorganisms capable of solubilizing both organic and mineral sources of soil phosphorus have been identified up to now. The aim of this study was to evaluate the inorganic soil phosphate solubilizing activity of phytate-hydrolyzing Pantoea brenneri soil isolates. We showed that the strains efficiently solubilize a variety of inorganic phosphates. We optimized the media composition and culturing conditions to improve the solubilization efficiency of the strains and investigated the mechanisms of their phosphate solubilization. Through HPLC analysis, it was determined that P. brenneri produce oxalic, malic, formic, malonic, lactic, maleic, acetic, and citric acids as well as acid and alkaline phosphatases while growing on insoluble phosphate sources. Finally, we analyzed the influence of P. brenneri strains with multiple PGP-treats on plant growth in greenhouse experiments and showed their ability to promote growth of potato.

Bacillus subtilis is traditionally classified as a PGPR that colonizes plant roots through biofilm formation. The current study focused on investigating the influence of various factors on bacilli biofilm formation. In the course of the study, the levels of biofilm formation by the model strain B. subtilis WT 168 and on its basis created regulatory mutants, as well as strains of bacilli with deleted extracellular proteases under conditions of changes in temperature, pH, salt and oxidative stress and presence of divalent metals ions. B. subtilis 168 forms halotolerant and oxidative stress-resistant biofilms at a temperature range of 22 °C–45 °C and a pH range of 6–8.5. The presence of Ca²⁺, Mn²⁺ and Mg²⁺ upsurges the biofilm development while an inhibition with Zn²⁺. Biofilm formation level was higher in protease-deficient strains. Relative to the wild-type strain, degU mutants showed a decrease in biofilm formation, abrB mutants formed biofilms more efficiently. spo0A mutants showed a plummeted film formation for the first 36 h, followed by a surge after. The effect of metal ions and NaCl on the mutant biofilms formation is described. Confocal microscopy indicated that B. subtilis mutants and protease-deficient strains differ in matrix structure. The highest content of amyloid-like proteins in mutant biofilms was registered for degU-mutants and protease-deficient strains.

Accurate strain identification within the Pantoea genus is difficult due to homologous recombination, which may affect the species boundaries. An integrated approach is presently the most effective one in determining the species of bacteria. Biochemical identification using the API20E system, phylogenetic analysis of the 16S rRNA gene sequences, and MLSA analysis based on partial sequences of the fusA, pyrG, leuS, gyrB, and rpoB genes showed that the soil phytate-hydrolyzing isolates belonged to the genus Pantoea, specifically to the species Pantoea brenneri. It was also established that phytate-hydrolyzing activity of the strains was accompanied by their ability to fix atmospheric nitrogen.

Iron is a ubiquitous element on Earth, but despite its abundance in the environment, it remains unavailable to many organisms. An antagonistic bacterium P. brenneri 3.5.1 was screened for the production of siderophores—iron-binding compounds on CAS agar and showed halo zones around the colonies. Bacteria secrete catechol-type siderophores at the concentration of 104 μM after 24 h of cultivation. The production of hydroxamate-type siderophores by P. brenneri 3.5.1 was not detected. The siderophore-containing metabolite fraction of P. brenneri 3.5.1 was extracted and purified. In an antagonistic plate assay, it inhibited the growth of Fusarium oxysporum mycelia in the absence of FeCl₃. A complete cluster, containing 17 open reading frames, responsible for the production and export of an enterobactin-like siderophore, is present in the genome of P. brenneri 3.5.1. No other siderophore production genes or their homologues were found in the P. brenneri 3.5.1 genome. Therefore, taking together multiple PGP properties of P. brenneri 3.5.1 and after careful assessment of the biosafety of the strain, it could be considered as a biofungicide against Fusarium oxysporum.