From fibres to field: biohybrid coating of soybean (Glycine max. L) seeds with PGPB Pseudomonas urmiensis AW4 or Bacillus pumilus SF5 by electrospinning technology

Abstract

The limited viability of plant growth-promoting bacteria (PGPB), particularly non-sporulating strains during storage andapplication, severely compromises biofertiliser efficacy. Nanofibre- based seed coatings represent a promising strategyto overcome this challenge. Herein, we developed a biohybrid coating by electrospinning an aqueous polyvinyl alcohol(PVA) solution containing either Pseudomonas urmiensis AW4 or Bacillus pumilus SF5 directly onto soybean seeds.Scanning electron microscopy (SEM) analysis revealed a homogeneous nanofibre coating, and energy- dispersive X- rayspectroscopy (EDS) confirmed its biohybrid nature. The final deposition of the material onto the seeds ranged from 3.0 to3.7 mg⋅ g− 1 . Encapsulation within the nanofibres extended the viability of the non-sporulating AW4 strain to more thanseven days, a significant improvement over the three days observed with standard inoculation. The spore-forming SF5strain remained viable for over six months, with its integrity uncompromised by the high-voltage electrospinning pro-cess. Furthermore, the biohybrid coatings enhanced soybean germination parameters, including germination percentage,germination index, root length, and relative radical elongation. We propose that the hydrophilic nature of PVA and thehigh surface-area-to-volume ratio of the nanofibrous structure were key to this improved performance. This encapsula-tion approach is not only technically effective but also scalable, representing a promising platform to increase the fieldefficiency of microbial biofertilisers and promote sustainable agricultural systems.