Effect of γ‐polyglutamic Acid Produced by Drought Tolerant Bacillus subtilis FSO3 on Soil Moisture Retention

ABSTRACTDrought stress poses significant risks to agricultural productivity by reducing soil moisture availability. Bacterial polymers, such as γ‐polyglutamic acid (γ‐PGA), have effectively enhanced soil moisture retention and promoted agricultural resilience. This study aimed to investigate the effects of drought stress on Bacillus subtilis FSO3, a glutamate‐independent γ‐polyglutamic acid (γ‐PGA) producer, and to evaluate the potential of its γ‐PGA‐rich fermentation medium for soil moisture retention. The strain produced up to 2.24 g/L γ‐PGA without external glutamate supplementation. Under polyethylene glycol‐6000 (PEG‐6000)‐induced water‐deficit conditions, B. subtilis FSO3 demonstrated moderate drought tolerance, with a 50% reduction in maximum biomass at 20% PEG‐6000. Interestingly, γ‐PGA yield increased from 1.6 g/L at 5% PEG‐6000 to 2.3 g/L at 20%. The γ‐PGA‐rich fermentation medium, applied at 100 mg γ‐PGA/kg of soil sustained soil moisture levels above 60% for approximately 33% longer than the control. These findings highlight the potential of the γ‐PGA‐rich fermentation medium produced by B. subtilis FSO3 as a promising and cost‐effective solution for enhancing soil water retention under drought conditions.