Mechanism of 10-HDA inhibiting Escherichia coli
10-Hydroxy-2-decenoic acid (10-HDA), an unique and prominent fatty acid found in royal jelly, has been reported to exhibit inhibitory effects against various bacteria including both Gram-positive and Gram-negative strains. Studies have shown that 10-HDA is able to induce cellular stresses which may disrupt bacterial cell surface structures and interfere with essential cellular processes, leading to cell death or the inhibition of cell growth. However, the specific mechanisms of action are not fully understood. It is worth noting that bacterial small RNAs (sRNAs) play essential roles in various cellular processes, especially stress responses. But there is limited information on the influence of 10-HDA on bacerial sRNAs. In this study, bacterial model organism MG1655 strain was challenged with 10-HDA, and the transcriptomic changes including the overall changes in both sRNAs and mRNAs were investigated. Our results of the whole-transcriptomic analysis revealed that 10-HDA altered the expression of the sRNA involved in biofilm formation, iron uptake and antibiotic resistance. It was found that 10-HDA inhibited biofilm by up-regulating the sRNAs OmrA, OmrB and MicF, as demonstrated by congo red staining assay, crystal violet staining assay and determination of extracellular polymeric substances (EPS) contents. In addition, it was observed that 10-HDA also suppressed iron uptake by up-regulating OmrA and OmrB, as revealed by determination of intracellular iron ion levels. Furthermore, 10-HDA made bacterial cells more sensitive to antibiotics by interfering with the expression of sgrS and gcvB, as established by the results of titration survival assay. The above results were further confirmed by the knockout and over-expression of the encoding genes of the relative sRNAs. In summary, our results indicate that 10-HDA can inhibit biofilm formation, iron uptake, and antibiotic resistance in E.coli by altering the expression of sRNA.