Plant Growth Promoting Rhizobacteria (PGPR) for Sustainability: Bioremediation and Biofertilization: A Mini-Review

Soil, the uppermost layer of the Earth, serves as a habitat for a vast diversity of living organisms and supports complex ecological processes. It provides a dynamic ecosystem essential for sustaining biodiversity. However, since the Industrial Revolution, intensified mining activities and the prolonged use of industrial and agricultural chemicals, including pesticides and herbicides, have significantly contributed to soil pollution, fertility loss, and structural degradation [1]. Degraded soils exhibit reduced porosity, increased hydrophobicity, and diminished water retention capacity [2]. These changes adversely affect primary producers, thereby disrupting entire ecosystems. Additionally, organic matter depletion accelerates in degraded soils, further compromising soil quality. Environmental pollutants such as industrial effluents, heavy metals, and plastic waste represent major global threats, negatively impacting biodiversity, food security, and human health [3]. Under natural conditions, soil maintains a balance of water and nutrients through microbial activity, which also preserves soil structure and porosity. Bioremediation strategies mimic these natural processes by employing microorganisms capable of restoring soil health. Among these, plant growth-promoting rhizobacteria (PGPR) have emerged as highly effective agents due to their multifunctional roles in soil restoration and plant growth enhancement.

PGPR play a vital role in the bioremediation of heavy metalcontaminated soils through several mechanisms. One important process involves the production of metal-chelating compounds that bind toxic metal ions in the rhizosphere, thereby reducing their mobility and bioavailability [4]. Additionally, PGPR form biofilms that act as protective barriers, limiting heavy metal exposure to plant roots [5]. Certain microorganisms can also transform highly toxic metals into less toxic forms via enzymatic activity and biosorption [6]. In hydrophobic soils, bioaugmentation improves soil hydraulic properties by enhancing porosity and water-holding capacity. Beyond heavy metal contamination, nutrient depletion and recurrent drought further exacerbate soil degradation, resulting in reduced crop productivity and disruption of biogeochemical cycles. PGPR promote plant growth by improving root architecture and increasing water absorption efficiency. They also produce phytohormones such as abscisic acid (ABA), which regulates stomatal closure and enhances plant water-use efficiency under stress conditions for essential vital activities [7].

PGPR effectively colonize the rhizosphere and enhance nutrient availability and plant growth. Nitrogen-fixing genera such as Azotobacter, Azospirillum, and Rhizobium convert atmospheric nitrogen into bioavailable forms, thereby improving soil fertility in nutrient-deficient conditions [8]. Additionally, several species of Bacillus, Pseudomonas, and Enterobacter are capable of solubilizing phosphorus and other essential nutrients [9], and increase its uptake by plants. PGPR also synthesize plant growth regulators, including indole-3-acetic acid, gibberellins, and cytokinins, which further enhance plant development [10,11]. Plants growing in degraded soils are often more susceptible to diseases and environmental stresses. PGPR-mediated bioaugmentation enhances plant resilience by improving overall plant vigor and enabling the production of osmoprotectants, stress-related enzymes, and phytohormones [12] (Figure 1).

Despite the well-documented benefits of plant growthpromoting rhizobacteria (PGPR) in soil restoration and plant growth enhancement, several limitations and challenges remain. The effectiveness of PGPR under field conditions often shows significant variability compared to controlled laboratory studies, largely due to differences in soil type, climate, and native microbial communities [13]. Additionally, the survival and colonization efficiency of introduced PGPR strains can be inconsistent, limiting their long-term impact [14]. While many studies report positive outcomes, discrepancies exist regarding the extent of their effectiveness under stress conditions, indicating the need for more standardized and large-scale field trials. Furthermore, the interaction between PGPR and plants is highly complex and influenced by multiple biotic and abiotic factors, which are not yet fully understood. Economic feasibility and scalability of PGPR-based bioformulations also require further evaluation for widespread agricultural application [15]. Therefore, future research should focus on improving strain stability, understanding plant–microbe interactions at the molecular level, and developing efficient delivery systems to maximize their practical utility in sustainable agriculture [16].

This review highlights the significant potential of PGPR as a sustainable solution for improving soil health, enhancing plant growth, and increasing agricultural productivity. PGPR also contribute to soil detoxification by removing or immobilizing toxic substances. Degraded soils, characterized by disruptions in essential biogeochemical cycles, are generally unsuitable for optimal plant growth; however, PGPR effectively mitigate these adverse effects and promote plant development [17]. Furthermore, PGPR-inoculated plants exhibit distinct gene expression patterns under environmental stress compared to non-inoculated plants, indicating enhanced stress tolerance mechanisms [18]. The multifunctional nature of PGPR makes them a powerful tool for soil remediation and sustainable agriculture. Their application reduces dependence on chemical inputs, thereby supporting environmentally friendly practices and contributing to long-term food security.

None.

No conflict of Interest.

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