Microbiology and Biotechnology Research: An Overview Vol. 10

Rhizobacteria are central participants in the biological regulation of plant nutrition, development, stress tolerance and defence. Their capacity to fix or conserve nitrogen, mobilise phosphorus and micronutrients, alter phytohormone balance, lower stress ethylene, release volatile signals and suppress pathogens has made plant growth-promoting rhizobacteria prominent candidates for reducing dependence on mineral fertilisers and pesticides. Yet the literature is marked by a persistent disparity between mechanistic promise under controlled conditions and variable performance in field soils. This critical narrative review evaluates rhizobacteria as components of plant growth promotion by integrating evidence on rhizosphere assembly, colonisation, direct and indirect mechanisms, abiotic-stress mitigation, inoculant formulation, field efficacy, microbiome interactions and biosafety. Literature available from 1978 to 31 May 2026 was selected through transparent searches of accessible scholarly indexes and bibliographic registries, with emphasis on verified peer-reviewed evidence and claim-level appraisal. The strongest conclusions concern the mechanistic plausibility of nutrient mobilisation, 1-aminocyclopropane-1-carboxylate deaminase activity, auxin-mediated root remodelling and induced systemic resistance. Confidence is lower when these traits are used alone to predict agronomic benefit, because expression depends on plant genotype, soil chemistry, resident microbiota, climate, formulation and management. Meta-analytical evidence indicates overall positive effects of microbial inoculation, but also shows inflation under sterile, short-duration and pot-based experiments. Reliable translation therefore requires a shift from trait-positive strain selection towards context-matched ecological design, verified root competence, durable formulations, multi-environment trials and monitoring of persistence and non-target effects. Rhizobacteria should not be regarded as universal substitutes for conventional inputs. Their defensible role is as biologically active, management-dependent components of integrated nutrient, stress and disease management systems.