Organic acid production in vitro and plant growth promotion in maize under controlled environment by phosphate-solubilizing fluorescent Pseudomonas

Pratibha Vyas,Arvind Gulati

doi:10.1186/1471-2180-9-174

Pratibha Vyas, Arvind Gulati

Open Access

https://doi.org/10.1186/1471-2180-9-174

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Abstract

BackgroundPhosphorus deficiency is a major constraint to crop production due to rapid binding of the applied phosphorus into fixed forms not available to the plants. Microbial solubilization of inorganic phosphates has been attributed mainly to the production of organic acids. Phosphate-solubilizing microorganisms enhance plant growth under conditions of poor phosphorus availability by solubilizing insoluble phosphates in the soil. This paper describes the production of organic acids during inorganic phosphate solubilization and influence on plant growth as a function of phosphate solubilization by fluorescent Pseudomonas.ResultsNineteen phosphate-solubilizing fluorescent Pseudomonas strains of P. fluorescens, P. poae, P. trivialis, and Pseudomonas spp. produced gluconic acid, oxalic acid, 2-ketogluconic acid, lactic acid, succinic acid, formic acid, citric acid and malic acid in the culture filtrates during the solubilization of tricalcium phosphate, Mussoorie rock phosphate, Udaipur rock phosphate and North Carolina rock phosphate. The strains differed quantitatively and qualitatively in the production of organic acids during solubilization of phosphate substrates. Cluster analysis based on organic acid profiling revealed inter-species and intra-species variation in organic acids produced by Pseudomonas strains. The phosphate-solubilizing bacterial treatments P. trivialis BIHB 745, P. trivialis BIHB 747, Pseudomonas sp. BIHB 756 and P. poae BIHB 808 resulted in significantly higher or statistically at par growth and total N, P and K content over single super phosphate treatment in maize. These treatments also significantly affected pH, organic matter, and N, P, and K content of the soil.ConclusionThe results implied that organic acid production by Pseudomonas strains is independent of their genetic relatedness and each strain has its own ability of producing organic acids during the solubilization of inorganic phosphates. Significant difference in plant growth promotion by efficient phosphate-solubilizing Pseudomonas strains point at the need for selecting potential strains in plant growth promotion experiments in conjunction with various phosphate substrates for their targeted application as bioinoculants.

Highlights

Phosphorus deficiency is a major constraint to crop production due to rapid binding of the applied phosphorus into fixed forms not available to the plants
Production of organic acids during phosphate solubilization The bacterial strains grown in triplicate in 10 ml NBRIP broth supplemented with 0.5% tricalcium phosphate (TCP), Mussoorie rock phosphate (MRP), Udaipur rock phosphate (URP) and North Carolina rock phosphate (NCRP) at 28°C for 5 days at 180 rpm in a refrigerated incubator shaker (Innova Model 4230, New Brunswick Scientific, USA) were centrifuged at 10,000 rpm for 10 min. and passed through 0.22 μm nylon filter
Production of organic acids High Performance Liquid Chromatogram (HPLC) analysis of the culture filtrates was done to identify and quantity the organic acids produced during the solubilization of TCP, MRP, URP and NCRP by Pseudomonas fluorescens strain, three Pseudomonas poae strains, ten Pseudomonas trivialis strains, and five Pseudomonas spp. strains (Fig. 1)

Summary

Introduction

Phosphorus deficiency is a major constraint to crop production due to rapid binding of the applied phosphorus into fixed forms not available to the plants. Microbial solubilization of inorganic phosphates has been attributed mainly to the production of organic acids. Improving soil fertility by releasing bound phosphorus by microbial inoculants is an important aspect for increasing crop yield. Phosphorus release from insoluble phosphates reported for several soil microorganisms has been attributed mainly to the production of organic acids and their chelation capacity [1,2,3]. Increased solubilization of fixed soil phosphates and applied phosphates ensuring higher crop yields has been reported on inoculation of phosphate-solubilizing bacteria including Pseudomonas, Bacillus, Rhizobium, Micrococcus, Flavobacterium, Burkholderia, Achromobacter, Erwinia, and Agrobacterium [5,6]. Several Pseudomonas species have been reported among the most efficient phosphate-solublizing bacteria and as important bio-inoculants due to their multiple biofertilizing activities of improving soil nutrient status, secretion of plant growth regulators, and suppression of soil-borne pathogens [5,7,8,9]

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