Under stressful conditions, Escherichia coli forms biofilm for survival by sensing a variety of environmental conditions. CsgD, the master regulator of biofilm formation, controls cell aggregation by directly regulating the synthesis of Curli fimbriae. In agreement of its regulatory role, as many as 14 transcription factors (TFs) have so far been identified to participate in regulation of the csgD promoter, each monitoring a specific environmental condition or factor. In order to identify the whole set of TFs involved in this typical multi-factor promoter, we performed in this study ‘promoter-specific transcription-factor’ (PS-TF) screening in vitro using a set of 198 purified TFs (145 TFs with known functions and 53 hitherto uncharacterized TFs). A total of 48 TFs with strong binding to the csgD promoter probe were identified, including 35 known TFs and 13 uncharacterized TFs, referred to as Y-TFs. As an attempt to search for novel regulators, in this study we first analysed a total of seven Y-TFs, including YbiH, YdcI, YhjC, YiaJ, YiaU, YjgJ and YjiR. After analysis of curli fimbriae formation, LacZ-reporter assay, Northern-blot analysis and biofilm formation assay, we identified at least two novel regulators, repressor YiaJ (renamed PlaR) and activator YhjC (renamed RcdB), of the csgD promoter.
Oleyl-phosphate-modified TiO nanoparticles (OP_TiO) were prepared via phase transfer from an aqueous phase containing dispersed TiO nanoparticles to a toluene phase containing oleyl phosphate (OP, a mixture of monoester and diester), and employed for the preparation of OP_TiO/cyclo-olefin polymer (COP) hybrid films with high-refractive indices. The modification of TiO by OP was essentially completed by reaction at room temperature for 8 h, and essentially all the TiO nanoparticles in the aqueous phase were transferred to the toluene phase. The infrared and solid-state C cross-polarization and magic-angle spinning (CP/MAS) NMR spectrum of OP_TiO showed the presence of oleyl groups originating from oleyl phosphate. The solid-state P MAS NMR spectrum of OP_TiO exhibited new signals at -1.4, 2.1, and 4.8 ppm, indicating the formation of Ti-O-P bonds. CHN and inductively coupled plasma analyses revealed that the major species bound to the TiO surface was tridentate CH(CH)CH═CH(CH)P(OTi). These results clearly indicate that the surfaces of the TiO nanoparticles were modified by OP moieties via phase transfer. OP_TiO/COP hybrid films exhibited excellent optical transparency up to 19.1 vol % TiO loading, and the light transmittance of the hybrid films with 19.1 vol % TiO loading was 99.8% at 633 nm. The refractive index of these hybrid films rose to 1.83.
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