POLY-Γ-GLUTAMIC ACID (Γ-PGA): AN EMERGING GREEN BIOSTIMULANT FOR SUSTAINABLE CROP PRODUCTION

Abstract

Poly-γ-glutamic acid (γ-PGA) is a biodegradable, water-soluble biopolymer increasingly recognized for its diverse applications in sustainable agriculture. Synthesized predominantly by Bacillus species through microbial fermentation, and it possesses distinctive characteristics including exceptional water retention, strong ion-chelating ability, biodegradability, and environmental safety. At soil level, γ-PGA improves soil quality by enhancing aggregation, porosity, and water-holding capacity, while reducing nutrient depletion. At physiological level, it stimulates the Ca²⁺/calmodulin (CaM) signalling pathway, accelerating nitrogen assimilation through enhanced activity of nitrate reductase and glutamine synthetase, thereby promoting chlorophyll biosynthesis, photosynthetic efficiency and root development. These combined effects improve fertilizer efficiency and reduce dependence on chemical inputs. Empirical research from cereals, vegetables, legumes, and horticultural crops demonstrates a continuous improvement in biomass accumulation, nutrient efficiency, and yield; for example, γ-PGA application increased rapeseed fresh weight by 7.6-9.3% and grain yield by 6.5-11.0% and has been reported to enhance nitrogen use efficiency and chlorophyll content in several species. γ-PGA also mitigates abiotic stresses including drought, salinity and heavy metal toxicity, supporting its value for climate-resilient cropping systems. Despite the positive results, challenges persist regarding production costs, field unpredictability, and the absence of long-term studies. Overall, γ-PGA represents a promising eco-friendly biostimulant for sustainable and climate-resilient agriculture.