From surface to deep tissues: Co-penetration mechanisms of two Pseudomonas lundensis strains to accelerate the spoilage in fresh pork.

Abstract

This study selected two Pseudomonas lundensis strains (PLA and PLB) with distinct motility phenotypes to systematically evaluate the impact of co-culture on their penetration behavior. In vitro assays indicated that co-culture of PLA and PLB markedly enhanced the diffusion capacity and enlarged the hydrolysis zones on pork agar. Correspondingly, a synergistic penetration effect was shown with the PLA + PLB group infiltrating faster and deeper than either monoculture. Fluorescent labeling combined with confocal laser scanning microscopy further revealed that P. lundensis may migrate inward along muscle fiber gaps and connective tissue channels. At the molecular level, transcriptomic analysis showed that, under co-culture conditions, the two Pseudomonas strains exhibited penetration-associated motility and metabolic responses: genes related to flagellar assembly and chemotaxis in PLA were significantly upregulated, while genes involved in carbohydrate, amino acid and sulfur metabolic pathways, as well as ABC transport systems, were also markedly upregulated in both strains. In accordance with these transcriptional patterns, the co-culture generated higher levels of soluble peptides and ammonia in superficial meat layers, significantly increased the myofibril fragmentation index, and caused severe disruption of muscle microstructure. These results demonstrated that the two P. lundensis strains accelerated the penetration and colonization to increase protein degradation in fresh pork through a synergistic mechanism of "motility combined with nutrient uptake and utilization," making them an important driving force of deep spoilage in fresh pork.