Transcriptomic analysis of mature biofilm and planktonic cells of Listeria monocytogenes under nutritional stress

Abstract

Listeria monocytogenes can adhere to various surfaces and form biofilms under environments with reduced nutrients, resulting in persistent contamination of products. In the present study, RNA sequencing was utilized to establish complete transcriptome profiles of L. monocytogenes in both the planktonic state (TF) and the biofilm state (TB), cultured in TSB-YE, as well as in the planktonic (dTF) and biofilm (dTB) states, cultured in a 10-fold dilution of TSB-YE (dTSB-YE). In our lab, MRL300083 (Lm83) was identified as the strain with the highest biofilm formation in dTSB-YE. There were 1, 6, and 3 significantly enriched pathways in TF vs. dTF, TB vs. dTB, TF vs. TB, respectively (p_adj < 0.05), indicating that these pathways or genes might be critical for bacterial survival. However, no significantly enriched pathway was found in dTF vs dTB. Interestingly, in both planktonic and biofilm states, the differentially expressed genes (DEGs) involved in flagellar assembly were exclusively up-regulated (p_adj < 0.05), indicating that flagellar synthesis was increased under nutritional stress. In biofilm-associated cells cultured in dTSB-YE, the DEGs involved in pathways including flagellar assembly, bacterial chemotaxis, fructose and mannose metabolism, and the phosphotransferase system (PTS) were significantly up-regulated (p_adj < 0.05). Compared to the planktonic state, bacteria in the biofilm state can mobilize various programs to resist adverse environments. RNA-Seq results were confirmed by RT-qPCR. This study has initially explored the underlying mechanisms of enhanced biofilm formation and environmental resistance of L. monocytogenes in biofilms under nutrient stress, which may help reveal or resolve L. monocytogenes persistence in food processing environments.