Genomic and physiological characterization of Pseudomonas fluorescens RHBA17 reveals density-dependent growth...

Pseudomonas fluorescens plays a vital role in plant root ecosystems. Earlier observations indicated its varying effects on potato growth under different population density, yet the biological basis remained uncertain. In the present study, a bacterial strain exhibiting plant growth-promoting potential was isolated from the roots of Codonopsis pilosula. This strain was subsequently identified as Pseudomonas fluorescens RHBA17, contrasting its properties with the established P. fluorescens ATCC 13525 strain. Whole-genome sequencing of P. fluorescens RHBA17 revealed a genome size of 6,462,390 bp with a GC content of 60.10 %, harboring 5935 predicted protein-coding sequences. Genomic analysis of P. fluorescens RHBA17 revealed a diverse array of genes linked to induced systemic resistance (ISR) and plant growth-promoting (PGP) traits, encompassing phytohormone production, nitrogen assimilation and reduction, siderophore biosynthesis, phosphate solubilization, biofilm formation and synthesis of PGP-related amino acids. Co-culture experiments found that the high population density of P. fluorescens RHBA17 inhibited the potato growth. Elevated bacterial loads triggered measurable physiological shifts, including heightened photosynthetic output (19.38 μmol CO₂/m²/s), activated antioxidant systems (SOD:153.56 U/g) and redirected carbon utilization. Gene expression patterns further linked high-density inoculation to weakened auxin signaling (71 % baseline) and enhanced starch breakdown (51 % β-amylase elevation). Collectively, the work establishes that over-proliferation of this bacterium impairs redox-hormone coordination, induces metabolic imbalance, and negatively impacts potato development. The genomic basis of strain-specific ecological niche adaptation (pstB/ugpC vs. pchC) was deciphered, and a viable metric for the safe deployment of microbial inoculants was established. These steps advanced strategies to utilize inter-root endophytes without compromising crop productivity.