Coproduction of bio-microbicide and silver nano-microbicide mediated by endospore-forming Bacillus and their synergetic control of plant disease

Background One-pot synthesis of metal nanoparticles under ambient temperature and pressure using reducing and stabilizing materials from microbes is energy-effective and ecofriendly, but upstream extraction of biological raw materials and downstream purification of nanoparticles from bioreactors are laborious and expensive. To simplify the productive process for using metal nanoparticles as microbicides to control plant pathogens, we use an endospore-forming Bacillus biocontrol agent to produce the nano-microbicide and use the bacterial raw materials as bio-microbicides together with the nano-microbicide. Results Bacillus cells at the stationary phase form endospores and tolerate Ag + and Ag nanoparticles (AgNPs), while the cell-free culture supernatant (CFCS) mediates the synthesis of AgNPs. AgNPs produced from the Bacillus culture and CFCS show similar physical, chemical, and electrical characteristics, and bactericidal and anti-biofilm activities. Moreover, the diluted products effectively protect the kiwifruit leaves from the infection of the pathogen Pseudomonas syringae pv. actinidiae . Conclusions This coproduction of bio-microbicide and nano-microbicide is a totally green one-pot synthesis process without extraction and purification and without production of waste and can be easily scaled up using the existing fermentation processing of Bacillus biocontrol agents. The application of the synergistic bio-microbicide and nano-microbicide can effectively control the bacterial canker disease of kiwifruit plants. Graphical Abstract Highlights Endospore-forming Bacillus cells can tolerate metal and metal nanoparticles. Bacillus biocontrol agents can be used as bio-microbicides and to produce nano-microbicides. Coproduction of bio-microbicides and nano-microbicides is a solution of large-scale production of nano-microbicides. Screening biocontrol Bacillus agents producing metal nanoparticle in bacterial culture is a key of this solution. Cooperation of bio-microbicides and nano-microbicides can effectively control the bacterial canker disease of kiwifruit.