Physiological and metabolic effects of a transposon-mediated mutation in the glutamate synthase gene, gltB, of plant-beneficial, cytokinin-producing Pseudomonas hormoni G20-18T

Pseudomonas species are well-studied Gram-negative bacteria involved in plant-microbe interactions, particularly in the rhizosphere and phyllosphere, where they enhance plant growth and resilience under stress. A key trait of these bacteria is the production of plant hormones, which help plants resist biotic and abiotic stresses. Pseudomonas hormoni G20-18 T (previously denoted P. fluorescens G20-18) is a beneficial bacterium that produces cytokinins (CKs), improving plant resistance to pathogens and drought. A mutant strain, CNT1, shows reduced CK levels, but the mechanisms behind this reduction and its effects on plant interactions are not fully understood. Genome sequencing of the mutant revealed insertion of a transposon in the glutamate synthase, large subunit gene ( glt B). This mutation led to reduced growth, survival, and biofilm formation at 25°C and pH 5.0. The carbon substrate utilization pattern also differed from the wild type, and applying exogenous CKs failed to restore the wild type effects, suggesting a broader impact on metabolism. Untargeted metabolomics confirmed the global influence of the glt B mutation, also affecting CK and auxin expression. These findings highlight the significant role of the glt B gene in regulating bacterial physiology and plant-beneficial interactions.