Fatty acid remodeling and flagellar motility orchestrate Pseudomonas fluorescens biofilm formation during chilled meat distribution

The formidable biofilm-forming ability of Pseudomonas fluorescens enables its persistent contamination under distribution conditions (0 - 4℃) of chilled meat, yet the mechanisms governing its biofilm formation remain inadequately explored. In this study, with 25℃ serving as the control, P. fluorescens developed more substantial and architecturally coherent biofilms at 4℃ during 96 h-incubation, accompanied by increased extracellular polymeric substances synthesis. This response phenotype enhanced cell adhesion to facilitate persistence and increased the cross-contamination after multiple cell transfers. Transcriptomic analysis revealed that 514 differentially expressed genes (DEGs) were up-regulated and 327 DEGs were down-regulated, which were involved in fatty acid degradation, flagellar assembly, lysine degradation, pyruvate metabolism, etc. Notably, as primary regulatory pathways, flagellar assembly and fatty acid metabolism suggested they could facilitate microbial accumulation and the efficient conversion of fatty acids, respectively. Correspondingly, changes in flagellar assembly-related genes and fatty acid degradation-related genes were consistent with transcriptome results. In view of these, the apparent reduction in motility and the increase in unsaturated fatty acid content, along with the enhancement of cell surface hydrophobicity and auto-aggregation, further verified the above-mentioned pathways. This study provided insights into formation mechanism of P. fluorescens biofilm and the development of control strategies.