Isolation and characterization of a β-propeller gene containing phosphobacterium Bacillus subtilis strain KPS-11 for growth promotion of potato (Solanum tuberosum L.).

Muhammad Kashif Hanif,Jan D. Van Elsas,Asma Imran,Tahir Naqqash,Sohail Hameed,Muhammad Shahid

doi:10.3389/fmicb.2015.00583

Abstract

Phosphate-solubilizing and phytate-mineralizing bacteria collectively termed as phosphobacteria provide a sustainable approach for managing P-deficiency in agricultural soils by supplying inexpensive phosphate to plants. A phosphobacterium Bacillus subtilis strain KPS-11 (Genbank accession no. KP006655) was isolated from potato (Solanum tuberosum L.) rhizosphere and characterized for potato plant growth promoting potential. The strain utilized both Ca-phosphate and Na-phytate in vitro and produced 6.48 μg mL-1 indole-3-acetic acid in tryptophan supplemented medium. P-solubilization after 240 h was 66.4 μg mL-1 alongwith the production of 19.3 μg mL-1 gluconic acid and 5.3 μg mL-1 malic acid. The extracellular phytase activity was higher (4.3 × 10-10 kat mg-1 protein) than the cell-associated phytase activity (1.6 × 10-10 kat mg-1 protein). B. subtilis strain KPS-11 utilized 40 carbon sources and showed resistance against 20 chemicals in GENIII micro-plate system demonstrating its metabolic potential. Phytase-encoding gene β-propeller (BPP) showed 92% amino acid similarity to BPP from B. subtilis (accession no.WP_014114128.1) and 83% structural similarity to BPP from B. subtilis (accession no 3AMR_A). Potato inoculation with B. subtilis strain KPS-11 increased the root/shoot length and root/shoot weight of potato as compared to non-inoculated control plants. Moreover, rifampicin-resistant derivative of KPS-11 were able to survive in the rhizosphere and on the roots of potato up to 60 days showing its colonization potential. The study indicates that B. subtilis strain KPS-11 can be a potential candidate for development of potato inoculum in P-deficient soils.

Highlights

Phosphorous (P) ranks second among essential plant nutrients and a major component of vital molecules such as nucleic acid, ATP and phospholipids
Identification and Metabolic Characterization of Bacterial Strain KPS-11 The bacterial strain KPS-11 isolated from potato rhizosphere was a Gram positive, motile bacterium having rod shaped cell morphology
On the bases of these sequence similarity results, the strain KPS-11 was named as B. subtilis and 16S rRNA gene sequence was deposited to NCBI Genbank under accession number KP006655

Summary

Introduction

Phosphorous (P) ranks second among essential plant nutrients and a major component of vital molecules such as nucleic acid, ATP and phospholipids It is involved in regulating cell metabolic activity by controlling key enzymatic reactions Plant rhizosphere harbors a variety of microorganisms that can significantly change the soil P dynamics These microorganisms collectively called as phosphobacteria are involved either in solubilizing the inorganic forms of phosphates by producing organic acid e.g., gluconic, 2-ketogluconic acid, malic, lactic, acetic, citric, and succinic acid (Rodríguez et al, 2006; Bianco and Defez, 2010; Shahid et al, 2012) or in mineralization of organic forms of phosphates by enzymatic degradation (Jorquera et al, 2008b). PQQ biosynthesis involves several enzymes encoded by these genes including the pqqE that encodes a regulatory enzyme named as PQQ synthase (Goldstein et al, 2003)

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