Microbial Toxins in Agro-ecosystems: Rhizosphere Interactions, Ecological Functions and Cry Protein Implications

The soil-plant interphase rhizosphere is a dynamic zone where intricate biochemical interactions occur among plants, soil, and microorganisms. Microbial toxins produced by bacteria, fungi, and actinomycetes including phytotoxins, mycotoxins, antibiotics, siderophores, and other secondary metabolites play crucial yet often overlooked roles in regulating plant health and soil functioning. These compounds influence root architecture, nutrient acquisition, hormonal balance, and defense signaling pathways, thereby affecting plant performance under biotic and abiotic stresses. While some toxins function as virulence factors that cause plant diseases, others act at sub-lethal concentrations as signaling molecules that enhance plant-microbe communication and induce systemic resistance. Generally, microbial toxins also shape microbial community dynamics through antagonistic interactions, contributing to pathogen suppression and soil suppressiveness. Their production and persistence are strongly influenced by soil pH, organic matter, moisture, and nutrient status. Understanding toxin-mediated interactions is essential for harnessing beneficial microbes and developing sustainable soil and crop management strategies.