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.

Background and Objective: The major storage form of phosphorus in plant-derived feed is presented by phytates and not digested by animals. Phytases are able to hydrolyze phytates and successfully used as feed additives. Nevertheless, nowadays, there is a constant search of new phytases and expression systems for better production of these enzymes. In this study, we describe cloning and expression of gene encoding histidine acid phytase from Pantoea sp. 3.5.1 using methylotrophic yeast Pichia pastoris as the host. Methods: The phytase gene was placed under the control of the methanol-inducible AOX1 promoter and expressed in P. pastoris. Experiments of small-scale phytase expression and activity assays were used to test recombinant colonies. Four different signal peptides were screened for better secretion of phytase by P. pastoris. After 36 h of methanol induction in shake flasks, the maximum extracellular phytase activity (3.2 U/ml) was observed in P. pastoris strain with integrated construct based on pPINK-HC vector and Kluyveromyces maxianus inulinase gene signal sequence. This phytase was isolated and purified using affinity chromatography. Results: Recombinant phytase was a glycosylated protein, had a molecular weight of around 90 kDa and showed maximum activity at pH 4.0 and at 50°C. Recombinant phytase had excellent thermal stability – it retained high residual activity (100% ± 2%) after 1 hour of heat treatment at 70°C. Conclusion: The enhanced thermostability of the recombinant phytase, its expression provided by strong inducible promotor and the effectively designed expression cassette, the simple purification procedure of the secreted enzyme, and the possibility of large-scale expression make the foundation for further production of this bacterial phytase in P. pastoris at an industrial scale.

Смоленцев Сергей Юрьевич, доктор биологических наук, профессор кафедры технологии хранения и переработки продукции растениеводства Марийский государственный университет пл. Ленина,

Bacteria of the Pantoea genus have a positive effect on the growth and development of plants. In the genome of the P. brenneri strain3.5.2 we identified genes and genetic clusters associated with their multiple PGP-properties, previously confirmed by biochemical and microbiological methods. The strains are capable of hydrolyzing soil phytates and are active against inorganic soil phosphates: hydroxyapatite, phosphorite, and tricalcium phosphate. The gcd and pqqE genes responsible for the production of gluconic acid involved in the processes of phosphorus mobilization were identified. When grown on media with various sources of unavailable phosphorus, P. brenneri strains were able to secrete acid and alkaline phosphatases, the activity of which depended on the time of bacterial cultivation and the source of phosphate in the medium.

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