Bacillus as Premier Biocontrol Agents: Mechanistic Insights, Strategic Application, and Future Regulatory Landscapes in Sustainable Agriculture

Agricultural productivity currently faces challenges such as soil fertility issues, climatic instability, pests and diseases, and anthropization. This drives a shift towards sustainable agricultural practices, including biopreparations—products derived from living organisms or their metabolites that serve as biofertilizers, biopesticides, biostimulants, or biodegradation agents. Among these, the genus Bacillus is a primary candidate for sustainable agriculture; however, this review primarily covers rhizosphere-isolated organisms referred to as plant growth-promoting rhizobacteria. Bacillus strains possess a suite of direct and indirect mechanisms to promote plant development and biocontrol, as well as to tolerate various abiotic stresses. This review aims to describe all the mechanisms attributed to strains of this genus and their impact on different crops to promote plant growth, hormonal regulation (indole-3-acetic acid (IAA), abscisic acid (ABA), and ethylene), tolerance to abiotic stresses such as drought, heavy metals, salinity and heat stress, as well as resistance to pests and diseases. Furthermore, this work analyzes quantitative data regarding yield improvements and the environmental variables that influence the consistency of Bacillus performance in the field. Finally, to provide a balanced perspective, the review incorporates future directions in research on biosafety and risk assessment frameworks.