Isolation of Zinc Solubilizing Bacteria and its Application in Improving Soil Fertility

Zinc (Zn) is an important micronutrient for the growth and development of plants and animals. It is essential for various physiological functions as it acts as a cofactor for multiple enzymes. The present study aimed to isolate Zinc Solubilizing Bacteria (ZSB) from diverse soil samples and organic substrates, and evaluate their potential as bio-inoculants for stimulating plant growth. A total of 25 bacterial isolates were obtained from vermicompost, paddy field soils, and rhizospheres of various fruit and vegetable trees. Among these, the most potential isolate was identified as Acinetobacter baumannii and Acinetobacter calcoaceticus based on 16S rRNA sequencing. The consortium of A. baumannii and A. calcoaceticus demonstrated significantly enhanced Zn solubilization, reaching 1058 mg/L within 24 h, which was notably higher than the solubilization potential observed for individual isolates (797 mg/L and 784 mg/L Zn solubilization, respectively in 7 days). Zn tolerance assays demonstrated tolerance of A. baumannii and A. calcoaceticus up to 1200 ppm and 800ppm of Zn. Apart from Zn solubilization, the isolates showed diverse plant growth promoting properties, including phosphate solubilization, Indole-3-acetic acid production, nitrogen fixation, ammonia synthesis and hydrolytic enzyme activity. The activity of bacterial consortium significantly enhanced stem height, root length, and leaf length and width of Macrotyloma uniflorum (horse gram). Overall, the study indicates good potential of the constructed consortium to be used as a bio-inoculant in agriculture.