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Background <p>Plant roots are surrounded by communities of microbes that influence plant growth, development, and disease resistance. In soilless culture, microbial diversity in root-associated communities primarily originates from the substrate, irrigation water, and applied microbial inoculants. Phosphate solubilizing bacteria (PSB) capable of mobilizing phosphate from insoluble Ca<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub> were identified from a greenhouse rhizobacteria collection. Plant growth promoting efficacy was investigated at different substrate pH. The influence of the inoculum composition on plant growth responses to the bacteria was also evaluated. Finally, we analyzed the impact of PSB inoculation on microbiome composition and function.</p> Results <p>From 1044 isolates in the rhizobacteria collection, 14 solubilized more than 25% of the phosphorus provided in vitro. Only eight bacterial strains resulted in growth promotion benefits in planta when inoculated as a substrate drench onto marigolds grown in a peat-based substrate (pH 7.0) and fertilized with insoluble Ca<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>. In a follow up experiment, two newly identified (<i>Pantoea</i> sp. C2G6 and <i>Enterobacter soli</i> C4A1) and three previously identified PSB (<i>Pantoea trifolii</i> C2B11, <i>Pantoea formicae</i> C8D10, and <i>Bacillus velezensis</i>) that have demonstrated superior phosphate-mineral solubilization were evaluated. The PSB were tested at a substrate pH of 6.0 and 6.5 using water, 1% glucose, 2% Micromate, or 0.1X Luria-Bertani (LB) broth as inoculant supplements. All five bacteria promoted growth and improved plant health at both pH levels. A greater benefit to marigold growth and health was observed in plants growing at pH 6.5. C2B11, C8D10, C2G6, and <i>B. velezensis</i> treatment resulted in a significant increase in shoot P content. Microbiome diversity and community structure exhibited no significant alterations in response to PSB treatment. Genes enriched in PSB treated rhizospheres were mostly related to colonization, competition, and biofertilization traits.</p> Conclusions <p>PSB isolated from the rhizosphere of floriculture crops grown in soilless substrates promoted growth and enhanced health of marigolds grown under P limitation. They also enhanced growth under optimal or slightly basic pH, but their efficacy was not improved by the inoculant supplements evaluated in this experiment. The native microbial community in peat-based soilless substrate was resilient to PSB inoculation.</p>

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Calcium phosphate-solubilizing bacteria promote growth and alleviate phosphorus deficiency in French marigold with minimal impact on the rhizosphere microbiome

  • 期刊论文

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  • 发表日期：

    2026年1月13日

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  • Juan Quijia-Pillajo,
  • Sachin Naik,
  • Laura J. Chapin,
  • James S. Owen Jr.,
  • Michelle L. Jones

摘要

Background

Plant roots are surrounded by communities of microbes that influence plant growth, development, and disease resistance. In soilless culture, microbial diversity in root-associated communities primarily originates from the substrate, irrigation water, and applied microbial inoculants. Phosphate solubilizing bacteria (PSB) capable of mobilizing phosphate from insoluble Ca3(PO4)2 were identified from a greenhouse rhizobacteria collection. Plant growth promoting efficacy was investigated at different substrate pH. The influence of the inoculum composition on plant growth responses to the bacteria was also evaluated. Finally, we analyzed the impact of PSB inoculation on microbiome composition and function.

Results

From 1044 isolates in the rhizobacteria collection, 14 solubilized more than 25% of the phosphorus provided in vitro. Only eight bacterial strains resulted in growth promotion benefits in planta when inoculated as a substrate drench onto marigolds grown in a peat-based substrate (pH 7.0) and fertilized with insoluble Ca3(PO4)2. In a follow up experiment, two newly identified (Pantoea sp. C2G6 and Enterobacter soli C4A1) and three previously identified PSB (Pantoea trifolii C2B11, Pantoea formicae C8D10, and Bacillus velezensis) that have demonstrated superior phosphate-mineral solubilization were evaluated. The PSB were tested at a substrate pH of 6.0 and 6.5 using water, 1% glucose, 2% Micromate, or 0.1X Luria-Bertani (LB) broth as inoculant supplements. All five bacteria promoted growth and improved plant health at both pH levels. A greater benefit to marigold growth and health was observed in plants growing at pH 6.5. C2B11, C8D10, C2G6, and B. velezensis treatment resulted in a significant increase in shoot P content. Microbiome diversity and community structure exhibited no significant alterations in response to PSB treatment. Genes enriched in PSB treated rhizospheres were mostly related to colonization, competition, and biofertilization traits.

Conclusions

PSB isolated from the rhizosphere of floriculture crops grown in soilless substrates promoted growth and enhanced health of marigolds grown under P limitation. They also enhanced growth under optimal or slightly basic pH, but their efficacy was not improved by the inoculant supplements evaluated in this experiment. The native microbial community in peat-based soilless substrate was resilient to PSB inoculation.