Microscopic and Transcriptomic Characterization of Listeria Monocytogenes Aggregation and Biofilm Formation in Cantaloupe Juice

Plant exudate is likely the major nutrient source supporting the survival and biofilm formation of microorganisms in fresh produce processing environments. This study compared the impact of cantaloupe juice on the physiology and gene expression of Listeria monocytogenes (Lm) using microscopic and transcriptomic tools. Lm showed a strong autoaggregation and formed significantly more biofilms on stainless steel (SS) coupons when grown in cantaloupe juice in comparison to in TSB. SEM images revealed a different attachment profile of Lm on SS coupons. In TSB, Lm cells were mainly found in scratches and grooves of the metal surface, whereas, in cantaloupe juice they attached to the smooth surface as well. Lm planktonic and biofilm cells in cantaloupe juice exhibited stress-induced phenotypes, including strong cell elongation and increased proportion of cells with membrane permeability.Lm growth in cantaloupe juice resulted in distinct transcriptional profiles of both biofilm and planktonic cells in comparison to that in TSB. Functional annotation indicated that the significantly differentially expressed genes mainly participated in metabolism, signaling and stress response. Notably, certain pathways downregulated for planktonic cells were significantly upregulated for biofilm cells in cantaloupe juice compared to TSB, including ABC transporters, two-component system, quorum sensing, chemotaxis, and flagellar assembly.