Zn solubilizing bacteria (ZSB) mitigate toxicity of silver and Titanium dioxide nanoparticles in Mung bean by increasing photosynthetic pigment content.

Zn-deficiency, a global health challenge affects one-third of the world population. Zn-biofertilizer offer an efficient and cost-effective remedy. As Zn-biofertilizer can improve plant growth and grain's Zn-content ensuring improved dietary Zn-supply. This study sought to understand how silver and TiO₂ nanoparticles in the rhizosphere affect the activity of Zn-solubilization bacteria (ZSB) and plant growth. Two ZSB strains Bacillus sp. D-7 and Pseudomonas sp. D-117 with excellent Zn-solubilization efficiency of 254 and 260%, respectively were isolated and characterized using polyphasic characterization including 16S rRNA gene sequencing to formulate an effective Zn-biofertilizer. The plant growth promoting activity of this biofertilizer in Mung bean was checked in the presence and absence of various doses of TiO₂ and Ag-NPs and was compared with plant grown without biofertilizer. The change in rate of seed germination, vegetative growth (shoot and root length, fresh and dry weight), photosynthetic pigment and Zn-content was checked. Lower doses of nanomaterials (50 and 100 mg kg⁻¹ soil) slightly promoted the plant growth compared to control. While, higher doses (200 and 400 mg kg⁻¹ soil) inhibited the growth. A maximum decrease of shoot length, root length, fresh-weight, and dry-weight of 57.1, 53.9, 53.1, and 10.4% respectively was observed with 400 mg kg⁻¹ of Ag-NPs. However, in the presence of ZSB, the decrease at the same Ag-NP concentration was 41.6, 31.5, 27.4, and 6.6, respectively. These results strongly suggest that Zn-solubilizing bacteria improve resilience to nanoparticles toxicity and helps in Zn fortification in Mung bean even under nanomaterial stress.