Zinc solubilizing bacteria for sustainable biofortification: Mechanisms, rhizospheric interactions, and emerging biotechnological approaches

Nutritional depletion of agricultural soils has resulted in widespread zinc (Zn²⁺) deficiency or “hidden hunger,” which is a major global public health challenge. Traditional agronomic and genetic bio fortification methods have sustainability and economic limitations, but microbial bio fortification using Zinc Solubilizing Bacteria (ZSB) offers an eco-friendly, sustainable option. This review discusses the mechanisms of ZSB for converting insoluble zinc complexes in soil to bioavailable Zn²⁺ through rhizosphere acidification by low-molecular-weight organic acids (LMWOAs), proton extrusion, siderophore chelation, and biofilm formation. We discuss the symbiotic dynamics of ZSB in the microbiome including partnerships with diazotrophs, phosphate solubilizers and mycorrhizae and the microbial regulation of the host plant ZIP transporters. The recent molecular advances are also reviewed such as the application of CRISPR-Cas9 genome editing targeting the glucose dehydrogenase (gcd) gene to re-route the metabolic flux toward hyper-solubilization, and the combination of ZSB with Nano biotechnology by means of bio-nanofertilizer. Despite field challenges related to rhizospheric persistence and formulation shelf-life, the inclusion of engineered climate resilient ZSB strains into sustainable agriculture represents a paradigm shift towards global nutritional security.