Microbial Allies in Stress Resilience: The Role of Plant Growth-Promoting Bacteria in Crop Rhizosphere, Endosphere, and Phyllosphere

Plants are intimately associated with diverse bacterial communities inhabiting distinct ecological niches, namely the rhizosphere, endosphere, and phyllosphere, all of which contribute to plant health and development. Among these microorganisms, plant growth-promoting bacteria (PGPB) play a pivotal role in enhancing plant growth, resilience, and productivity, particularly under abiotic stress conditions. These bacteria are increasingly being used in sustainable agriculture and phytoremediation strategies because of their ability to modulate plant physiology and improve stress tolerance. PGPB must successfully colonize and persist in plant-associated environments such as the rhizosphere, where they initiate interactions with plant roots before migrating to internal root tissues (endosphere) or aerial plant parts (phyllosphere), where they exert their effects through a variety of mechanisms. This review systematically examines the diversity, ecological distribution, and functional traits of PGPB that associate with the plant rhizosphere, endosphere, and phyllosphere, with a focus on their modes of action, which include phytohormone modulation, nutrient solubilization, and stress alleviation. The current review reveals that the rhizosphere and endosphere have a higher abundance and diversity of beneficial bacterial taxa than the phyllosphere, with genera such as Bacillus sp. and Pseudomonas sp. being particularly common. This review offers a comprehensive overview of the bacterial community and its interactions with plants, focusing on the various microbial types and their roles in the rhizosphere, endosphere, and phyllosphere. This is critical for a better understanding of plant–microbe interactions and choosing the right bacterial taxa and genera to promote plant growth and productivity in the face of environmental stresses and challenges.