Artificial citrate operon confers mineral phosphate solubilization ability to diverse fluorescent pseudomonads

PLoS One. 2014 Sep 26;9(9):e107554. doi: 10.1371/journal.pone.0107554. eCollection 2014.

Abstract

Citric acid is a strong acid with good cation chelating ability and can be very efficient in solubilizing mineral phosphates. Only a few phosphate solubilizing bacteria and fungi are known to secrete citric acids. In this work, we incorporated artificial citrate operon containing NADH insensitive citrate synthase (gltA1) and citrate transporter (citC) genes into the genome of six-plant growth promoting P. fluorescens strains viz., PfO-1, Pf5, CHAO1, P109, ATCC13525 and Fp315 using MiniTn7 transposon gene delivery system. Comprehensive biochemical characterization of the genomic integrants and their comparison with plasmid transformants of the same operon in M9 minimal medium reveals the highest amount of ∼7.6±0.41 mM citric and 29.95±2.8 mM gluconic acid secretion along with ∼43.2±3.24 mM intracellular citrate without affecting the growth of these P. fluorescens strains. All genomic integrants showed enhanced citric and gluconic acid secretion on Tris-Cl rock phosphate (TRP) buffered medium, which was sufficient to release 200-1000 µM Pi in TRP medium. This study demonstrates that MPS ability could be achieved in natural fluorescent pseudomonads by incorporation of artificial citrate operon not only as plasmid but also by genomic integration.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism
  • Citrate (si)-Synthase / genetics
  • Citrate (si)-Synthase / metabolism
  • Citric Acid / metabolism*
  • Gene Expression
  • Gene Order
  • Glucose / metabolism
  • Minerals / metabolism*
  • Operon*
  • Phosphates / metabolism*
  • Plasmids / genetics
  • Pseudomonas fluorescens / genetics*
  • Pseudomonas fluorescens / growth & development
  • Pseudomonas fluorescens / metabolism*

Substances

  • Carrier Proteins
  • Minerals
  • Phosphates
  • citrate-binding transport protein
  • Citric Acid
  • Citrate (si)-Synthase
  • Glucose

Grants and funding

This research was funded by Department of Biotechnology, Government of India as a research grant to GNK and GA. The funders had no role in study design, data collection and anlaysis, decision to publish or preparation of the manuscript.