Soil degradation resulting from intensive agricultural practices, the excessive use of agrochemicals, and climate-induced stresses has significantly impaired soil fertility, disrupted microbial diversity, and reduced crop productivity. Plant growth-promoting bacteria (PGPB) represent a sustainable biological approach to restoring degraded soils by modulating plant physiology and soil function through diverse molecular mechanisms. PGPB synthesizes indole-3-acetic acid (IAA) to stimulate root development and nutrient uptake and produce ACC deaminase, which lowers ethylene accumulation under stress, mitigating growth inhibition. They also enhance nutrient availability by releasing phosphate-solubilizing enzymes and siderophores that improve iron acquisition. In parallel, PGPB activates jasmonate and salicylate pathways, priming a systemic resistance to biotic and abiotic stress. Through quorum sensing, biofilm formation, and biosynthetic gene clusters encoding antibiotics, lipopeptides, and VOCs, PGPB strengthen rhizosphere colonization and suppress pathogens. These interactions contribute to microbial community recovery, an improved soil structure, and enhanced nutrient cycling. This review synthesizes current evidence on the molecular and physiological mechanisms by which PGPB enhance soil restoration in degraded agroecosystems, highlighting their role beyond biofertilization as key agents in ecological rehabilitation. It examines advances in nutrient mobilization, stress mitigation, and signaling pathways, based on the literature retrieved from major scientific databases, focusing on studies published in the last decade.

Modern agriculture faces critical challenges due to increasing soil degradation resulting from overcultivation and excessive chemical use. These factors have led to declining agricultural productivity, reduced soil fertility, and a significant loss of microbial biodiversity. This review examines the role of plant growth-promoting bacteria (PGPB) as symbiotic microorganisms in restoring degraded soils. Key molecular and physiological mechanisms that enhance soil structure, improve water retention, and increase the bioavailability of essential nutrients for plants are explored. Additionally, the capacity of halotolerant bacteria to mitigate salt stress—an urgent issue in soils affected by salinization due to organic matter decomposition and irrigation practices—is analyzed. The role of plant growth regulators (PGRs) in both plant adaptation to adverse conditions and the stimulation of plant growth and development is also highlighted. Finally, current limitations in understanding biotic and abiotic stress resistance mechanisms in plants treated with growth-promoting strains are discussed, emphasizing the need for further research to optimize soil restoration strategies. This work provides a comprehensive overview of microorganism-based approaches for fostering more sustainable and resilient agriculture.