Triggering and focusing bacterial quorum sensing signal by nano-magnetic assembly

Q. Wang, Y. Guan, W. Bentley, G. Payne, C-Y Tsao, D.N. Quan, Y. Li, B. Zhang, L. Mei
University of Maryland,
United States

Keywords: quorum sensing, target and reporter cell, magnetic assembly, bacteria


Quorum sensing (QS) widely exists in bacteria system, which has function of adjusting cell behaviors as the bacterial population reaches a critical density. Autoinducer-2 (AI-2) has been found as an inducer molecule facilitating bacterial communication. In the present study, we fabricated a nano-level amine group coated superparamagnetic assembly (~5 nm) with positive surface charge of 5.8 mV at pH 7.1 to collect negatively charged bioengineered Escherichia coli (E. coli) CT104 (pCT6+pET200-dSRed) (reporter cells, not producing AI-2, but accepting AI-2 and turning on) and BL21 (pCT5+pET200-GFP) (target cells, releasing AI-2) to generate a higher local cell concentration from a lower cell density. Adsorption and desorption efficiencies results suggested that the capturing efficiencies of MNP with E. coli cells was 71.8-72.9% as the reporter : target cells = 1:0, 1:0.01, 1:0.1 and 1:1 (OD600 of reporter cells = 0.4). Further addition of 100mM sodium sulfate can significantly desorb E. coli cells from MNP, with desorption efficiencies of 81.4-87.6%. The nano-level magnetic assembly of mixed reporter and target cells in a small space significantly focused bacterial quorum signal comparing with that in cell suspensions at reporter : target cell ratios of 1:0.1 and 1:1. The percent of population fluorescing of reporter cells was 22 and 40% after collecting the mixed E. coli cells at reporter : target cell ratios of 1:0.1 and 1:1, vs less than 10-% triggered reporter cells in suspension. Capturing reporter cells only cannot trigger the quorum signal, while, respective capturing reporter and target cells with subsequent mixing generated same-level quorum signal (40%) comparing with that of capturing mixed reporter-target E. coli cells. Insignificant difference on percent of population fluorescing of reporter cells was found after concentrating target cells from OD600 = 0.3 and 0.01, indicating that the evaluated quorum signal focusing method can be used in a relatively low cell density. Theoretically, the marked bacterial quorum signal focused by nano-level magnetic assembly was likely due to the shortened cell-cell distance caused by a higher local cell density. This study is important to facilitate cell gene expression, change intercellular information communication, and detect pathogen population in pathogenic bacteria system.