Isolation and Characterization of Indole Acetic Acid, Gibberellic Acid, and Phosphate Solubilizing Microorganisms from Zingiber officinale Rhizosphere.

Abstract

The rhizosphere, the zone of soil surrounding plant roots, is a hotspot for microbial activity and plays a crucial role in plant health and growth promotion. In this study, we focused on the isolation and characterization of phytohormone-producing microorganisms, including indole acetic acid (IAA) and gibberellic acid (GA) producers, as well as phosphate solubilizing microorganisms (PSMs), from the rhizosphere of Zingiber officinale (ginger). Rhizosphere soil samples were collected from ginger plants grown in agricultural fields, and microbial isolates were obtained using selective media supplemented with tryptophan for IAA production, gibberellic acid for GA production, and Pikovskaya's agar for phosphate solubilization. A total of 57 bacterial and 23 fungal isolates were obtained for IAA production, while 45 bacterial and 19 fungal isolates were obtained for GA production. Additionally, 63 bacterial and 29 fungal isolates were obtained for phosphate solubilization. Molecular characterization based on 16S rRNA gene sequencing for bacteria and internal transcribed spacer (ITS) region sequencing for fungi revealed taxonomic diversity among the isolated microorganisms. The predominant bacterial genera included Pseudomonas, Bacillus, and Enterobacter, while fungal isolates were primarily identified as Aspergillus, Penicillium, and Trichoderma species.Screening assays confirmed the production of IAA and GA by selected bacterial and fungal isolates, as well as their ability to solubilize phosphate. Evaluation of growth-promoting properties demonstrated siderophore production, nitrogen fixation, and biocontrol activity against phytopathogens by the isolated microorganisms. These findings highlight the potential of rhizosphere microorganisms associated with ginger plants in enhancing plant growth and nutrient uptake. Harnessing the beneficial effects of phytohormone-producing bacteria and fungi, as well as phosphate solubilizing microorganisms, could contribute to sustainable agriculture practices by reducing the reliance on chemical fertilizers and promoting soil fertility. Further research on the application of these microbial isolates as biofertilizers and biostimulants in ginger cultivation systems is warranted to optimize their efficacy and environmental sustainability. This study provides valuable insights into the microbial-mediated mechanisms underlying plant-microbe interactions in the rhizosphere of Z. officinale and contributes to the development of microbial-based strategies for crop improvement.