Novel insights into the physiological and molecular responses of Pseudomonas fragi to CO2 for high-oxygen packaged meat preservation

Abstract

The CO₂ in high-oxygen modified atmosphere packaging (HiOx-MAP) could efficiently inhibit the growth of dominant Pseudomonas fragi in meat. However, little detailed information is available about the changes in P. fragi intracellular physiological properties and corresponding proteome and gene regulation in response to CO₂. This study aimed to elucidate the molecular antibacterial mechanism of CO₂ against Pseudomonas fragi held under both HiOx-MAP systems with various CO₂ concentrations (50% O₂/40% CO₂/10% N₂; 50% O₂/50% N₂). P. fragi induced meat spoilage (bacterial counts, pH, and total volatile basic nitrogen), and its physiological characteristics (intracellular pH (pH_i), adenosine triphosphate (ATP) and reactive oxygen species (ROS) levels, and motility), combined with bacterial proteome and targeted gene expression were investigated during chilled storage. Results showed that CO₂ suppressed P. fragi growth and spoilage potential by decreasing ATP contents and motility ability, associated with down-regulated protein and gene expression of glycolysis, flagellar assembly, and chemotaxis (e.g., aldehyde dehydrogenase (aldB), flagellar protein (fliG and motA)). CO₂ also induced oxidative stress via elevated ROS levels at the initial stage, and damaged cell membrane stability and genetic information processing by down-regulating outer membrane porin (oprD) and ribonuclease HI (rnhB) expression. However, CO₂ activated P. fragi citrate cycle to supply energy, and enhanced intracellular redox and pH homeostasis by up-regulating protein and gene expression of glutathione peroxidase, ATPase, and arginine deiminase. These findings underpin a significant advancement in understanding CO₂-bacteriostatic theory for meat packaging preservation.