Magnetic Fields Disperse Escherichia coli from Biofilm via CsrA and RpoE Regulation

The biofilm formation of pathogenic bacteria improves their infectivity, virulence, and stress tolerance. Therefore, inhibition of biofilm is beneficial for antibiosis. Magnetic fields (MFs) have been found to suppress the adhesion of Escherichia coli, but their underlying molecular mechanisms remain unclear. This study aims to explore the effects of different MFs on E. coli biofilm and the detailed molecular mechanism. The quantitative results of crystal violet staining showed that the biofilm significantly decreased by 20.5% (±6.3%) with 2.5 T pulse MF (PMF) treatment, 24.7% (±13.2%) with 15 mT rotating MF (RMF) treatment, and 14.9% (±8.8%) with 100 mT static MF (SMF) treatment. No obvious cell death or change in cellular metabolism was observed after 1 h RMF treatment, while the number of planktonic cells increased, indicating that 1 h RMF treatment dispersed biofilm without killing cells. Transcriptome profiling of PMF-treated E. coli revealed significant downregulation of core genes associated with biofilm formation, such as pgaA and csgD. This was associated with the upregulation of the gene csrA and the activation of transcription factor RpoE, which inhibits the translation of pgaA and csgD, respectively. qRT-PCR analysis and promoter activity assay verified these molecular changes in biofilm-forming cells under PMF and RMF. The essential roles of CsrA and RpoE in RMF-mediated biofilm inhibition were further supported by gene overexpression, knockout, or silencing. Additionally, it was demonstrated that RMF exerted consistent anti-biofilm effects in E. coli O157:H7 and Bacillus subtilis WB800N. Thus, the findings of this study provide evidence for the molecular mechanism of MF on E. coli biofilm inhibition.