Biofertilizer effect of some zinc dissolving bacteria free and encapsulated on Zea mays growth

Crop nutrition depends on zinc for enzymatic, oxidative, and metabolic processes. In the current study 20 different bacteria were isolated from five soil samples collected from different fields in Egypt. Bacterial isolates were screened for their ability to solubilize insoluble zinc oxide and zinc carbonate. The ability of selected isolates to tolerate soluble zinc was determined using different concentrations of (ZnSO₄). Three bacterial isolates were selected with efficiency in solubilizing zinc oxide and zinc carbonate while tolerating high levels of soluble zinc. Molecular identification by 16S rRNA sequencing of the chosen isolates identified them as B3 (Acinetobacter calcoaceticus), B5 (Bacillus proteolyticus) and C6 (Stenotrophomonas pavanii). Sodium alginate beads formulated with the isolated bacteria were tested for stability under different storage conditions for 3 months. A pot experiment was conducted to study and compare the effect of using chosen isolates as an in vivo Zn solubilizer with amended ZnCO₃ either alone or embedded in beads as carrier in the soil and its effect on growth parameters of Zea mays after 2 months. There was an increase in Zn uptake in all treatments compared to the control. However, plants grown in a pot treated with ZnCO₃ and Acinetobacter calcoaceticus showed the highest zinc content and plant dry weight as compared to the control. Finally, selected isolates in both free and encapsulated forms showed improved plant growth parameters and higher zinc content and can be applied as biofertilizers to enhance soil fertility.