The nitrogen-fixing strains of Enterobacter cloacae isolated from mung bean (Vigna radiata L.) enhance mung bean nodulation and growth

Abstract

The mung bean hosts endophytic microorganisms that improve soil fertility, particularly in degraded soils. This study aimed to isolate, characterize and evaluate nitrogen-fixing Enterobacter strains derived from mung bean samples collected from four districts in Ethiopia. Thirteen of 20 isolates were identified morphologically, physiologically, and biochemically, with five efficient strains further characterized by partial 16S rRNA sequencing. These strains were tested for nitrogen fixation, mineral solubilization and ammonia, indole-3-acetic acid (IAA) and siderophore production. The strains, identified as Enterobacter cloacae, demonstrated tolerance to pH 4–5, temperatures of 24–40 °C, and salt concentrations of 0.5 to 3.5%. All strains used citrate as a carbon source and produced ammonia, siderophores, and IAA with varying efficiencies. The solubilization indices of phosphorus, potassium, magnesium, zinc, and silicates ranged from 2.27 to 4.74. The MRS8 and MRS4 strains significantly enhanced mung bean growth, increasing the dry mass and nodulation by 88% and 100%, respectively. These findings suggest that E. cloacae strains are effective bioinoculants after evaluating pathogenicity tests, promoting Vigna radiata growth, and offering potential as environmentally sustainable solutions to improve productivity in other crops.