Opportunities and challenges with microbial synthesis of selenium nanoparticles and its applications in agriculture

Selenium (Se) is an essential trace element known for its physiological importance in plants and its broad applicability across human health, agriculture, and industry. Selenium nanoparticles (SeNPs), owing to their superior bioavailability, reduced toxicity, and enhanced biocompatibility, have emerged as promising candidates in various biological and environmental domains. Among the available synthesis approaches, microbial biosynthesis offers an eco-friendly, cost-effective, and sustainable alternative to conventional chemical and physical methods, which are often energy-intensive and environmentally hazardous. Microorganisms such as bacteria, fungi, and yeasts act as bio-factories that reduce Se salts into stable SeNPs, aided by enzymatic processes and protein-mediated stabilization. These biogenic SeNPs exhibit high structural uniformity and colloidal stability, making them suitable for diverse agricultural applications, including stress alleviation, improved nutrient uptake, and enhanced crop productivity. This review highlights recent advances in microbial synthesis of SeNPs with efficient applications in agriculture. We emphasize critical challenges such as low yields, polydispersity, incomplete understanding of microbial pathways, and limited field validation. This review focuses on how genomics, microbial engineering, and bioprocess optimization can overcome these barriers and pave the way for the safe and efficient use of SeNPs in sustainable agriculture. • Microbial selenium nanoparticles are green alternative to chemical synthesis. • SeNPs enhance crop growth, stress tolerance, and soil health sustainably. • Reductase enzymes drive SeNPs biosynthesis in bacteria and fungi. • TEM and FTIR confirm small, stable, protein-capped SeNP structures. • Challenges like yield and size variability can be overcome via bioengineering.