Research Paper Efficiency of plant growth-promoting P-solubilizing Bacillus circulans CB7 for enhancement of tomato growth under net house conditions Preeti Mehta 1 , Abhishek Walia 2 , Saurabh Kulshrestha 3 , Anjali Chauhan 2 and Chand Karan Shirkot 2 1 Department of Advance Bioenergy Research, Research and Development Centre, Indian Oil Corporation Limited, Government of India, Faridabad, New Delhi, India 2 Department of Basic Sciences (Microbiology Section), Dr. Y. S. Parmar University of Horticulture and Forestry, Nauni, Solan, Himachal Pradesh, India 3 School of Biotechnology, Shoolini University of Biotechnology and Management Sciences, Solan, Himachal Pradesh, India P-solubilizing bacterial isolate CB7 isolated from apple rhizosphere soil of Himachal Pradesh, India was identified as Bacillus circulans on the basis of phenotypic characteristics, biochemical tests, fatty acid methyl esters analysis, and 16S rRNA gene sequence. The isolate exhibited plant growth- promoting traits of P-solubilization, auxin, 1-aminocyclopropane-1-carboxylate deaminase activity, siderophore, nitrogenase activity, and antagonistic activity against Dematophora necatrix. In vitro studies revealed that P-solubilization and other plant growth-promoting traits were dependent on the presence of glucose in PVK medium and removal of yeast extract had no significant effect on plant growth-promoting traits. Plant growth-promoting traits of isolate CB7 were repressed in the presence of KH 2 PO 4 . P-solubilization activity was associated with the release of organic acids and a drop in the pH of the Pikovskaya’s medium. HPLC analysis detected gluconic and citric acid as major organic acids in the course of P-solubilization. Remarkable increase was observed in seed germination (22.32%), shoot length (15.91%), root length (25.10%), shoot dry weight (52.92%) and root dry weight (31.4%), nitrogen (18.75%), potassium (57.69%), and phosphorus (22.22%) content of shoot biomass over control. These results demonstrate that isolate CB7 has the promising PGPR attributes to be developed as a biofertilizer to enhance soil fertility and promote plant growth. Keywords: PGPR / P-solubilization / Siderophore / ACC deaminase / Tomato Received: July 12, 2013; accepted: November 16, 2013 DOI 10.1002/jobm.201300562 Introduction Phosphorus is one of the major essential macronutrients for biological growth and development. On average, soil contains 0.02–0.5% of total phosphorus [1]. It is added to the soil in the form of P- fertilizers, a part of which (1%) is utilized by plants and the rest is rapidly converted into insoluble complexes. Phosphate anions (H 2 PO 4  , HPO 4 2 ) are extremely reactive and form metal complexes with Ca in calcareous soils and Fe 3þ and Al 3þ in acidic soils. These metal ion complexes precipitated the 80% of added P-fertilizer [2]. This leads to the need of frequent application of P-fertilizers, but its use on a regular basis has become a costly affair and environmentally undesir- able. Therefore, the necessity to develop economical and eco-friendly technologies is steadily increasing. The use of plant growth-promoting rhizobacteria (PGPR) including phosphate solubilizing bacteria as biofertilizers was suggested as a sustainable solution for the improvement of nutrient availability, plant growth, and yields [3]. The mechanism by which PGPR promote plant growth are not fully understood, but are thought to include: (a) the ability to produce plant hormones, such as auxins, cytokinins, gibberellins, (b) asymbiotic N 2 fixation, (c) solubilization of Correspondence: Prof. C. K. Shirkot, Department of Basic Sciences, Dr. Y. S. Parmar University of Horticulture and Forestry, Nauni, Solan 173230, Himachal Pradesh, India E-mail: profckshirkot@gmail.com Phone: þ91 9418117399 Fax: þ91 1792252354 Environment  Health  Techniques Efficiency of plant growth-promoting P-solubilizing B. circulans 1 ß 2014 WILEY-VCH Verlag GmbH & Co. KGaA,Weinheim www.jbm-journal.com J. Basic Microbiol. 2014, 53,1–12