# Strain-Specific Phosphate Mobilization in Enterobacter: Organic Acid Production and Genomic Architecture of Solubilization Mechanisms

## TL;DR

This study explores how different Enterobacter strains solubilize phosphate, finding that organic acid production and genetic factors like LuxR mutations affect their efficiency in making phosphorus available for plants.

## Contribution

The study identifies strain-specific phosphate solubilization mechanisms in Enterobacter, linking genomic variations in LuxR to solubilization efficiency and biofilm formation.

## Key findings

- E. soli GMG1156 and E. ludwigii GMG291 showed the highest phosphate solubilization in greenhouse trials.
- Malic acid is the main organic acid secreted, with E. soli producing three times more than E. ludwigii strains.
- LuxR mutations in GMG378 correlate with reduced solubilization, suggesting a role in biofilm-related phosphate mobilization.

## Abstract

Phosphate-solubilizing microorganisms (PSMs) show promise for sustainable agriculture, yet inconsistent field performance limits their application. We investigated phosphate solubilization mechanisms in Enterobacter ludwigii strains GMG278, GMG291, GMG378 and Enterobacter soli GMG1156 through greenhouse wheat experiments, high-performance liquid chromatography (HPLC) organic acid analysis, and comparative genomics. Greenhouse trials demonstrated that bacterial inoculation compensated for phosphorus deficiency, with GMG291, GMG1156, and GMG278 showing superior performance. HPLC identified malic acid as the predominant secreted organic acid, with E. soli producing threefold higher concentrations than E. ludwigii strains. Phosphate solubilization efficiency followed the order FePO4 > AlPO4 > Ca3(PO4)2, with maximal release (95.9–97.7 μg/mL) from iron phosphate despite lower malic acid secretion, suggesting siderophore involvement. An inverse correlation between malic acid levels and soluble phosphate concentrations likely reflects competitive bacterial phosphate uptake and secondary precipitation processes. Comparative genomics revealed missense mutations in the LuxR transcriptional regulator of strain GMG378 (Asp86Asn and Arg97Leu) near predicted DNA-binding domains, correlating with reduced solubilization capacity. Phosphate solubilization in Enterobacter proceeds primarily through metal–malic acid complex formation, with strain-specific efficiency linked to LuxR-regulated biofilm formation genes. These findings suggest PSM screening should incorporate biofilm-related genetic markers alongside acid production measurements.