Diazotrophic Plant Growth Promoting Bacteria: A Reliable Tool for Sustainable Agriculture

Growing global pressures on food production have intensified efforts to identify sustainable strategies for improving nitrogen availability in agricultural systems. While synthetic nitrogen fertilizers remain widely used due to their effectiveness in boosting crop yields, their prolonged application is associated with soil nutrient imbalances, environmental contamination, and declining long-term sustainability. Biological nitrogen fixation (BNF), performed by diazotrophic microorganisms, provides a viable and environmentally responsible alternative by converting atmospheric nitrogen into forms that plants can readily assimilate. A substantial proportion of diazotrophs also express diverse plant growth-promoting traits, classifying them as plant growth-promoting diazotrophs (PGPDs). These microorganisms contribute to plant development and productivity through multiple mechanisms, including phosphate solubilization, siderophore production, phytohormone biosynthesis, and ACC deaminase activity. They also suppress phytopathogens by generating antimicrobial compounds and eliciting induced systemic resistance. Beyond these functions, PGPDs enhance plant tolerance to abiotic stresses such as drought, salinity, and nutrient limitation, thereby supporting crop performance under suboptimal environmental conditions. This chapter provides an in-depth examination of the taxonomic diversity, biochemical capabilities, and ecological relevance of diazotrophic plant growth-promoting bacteria. It discusses their modes of interaction with host plants, their potential to decrease dependence on chemically synthesized fertilizers, and their contributions to sustainable intensification of agricultural systems. Recent advances in elucidating the molecular, physiological, and ecological dimensions of PGPD activity are highlighted, along with the principal challenges and emerging opportunities associated with their field application. By integrating current research findings, this chapter underscores the central role of diazotrophic microorganisms in driving the transition toward environmentally sustainable and resilient agriculture.