Papers by Author: Norihiro Kato

Abstract: Bacterial quorum sensing (QS) is one of the cell-to-cell communication systems. N-Acyl-homoserine lactones (AHLs) are the most common QS signals and responsible for biofilm formation in gram-negative bacteria. Inactivation of QS, also referred to as quorum quenching, has been regarded as a popular strategy to control membrane bioreactor (MBR) operations because biofouling in MBR wastewater treatment systems is often caused by biofilm formation. In the present study, 24 bacterial strains were isolated from the secondary effluent of a wastewater treatment plant and AHL productivity and biofilm formation were evaluated on 8 out of 24 isolates. The isolated 8 strains can produce AHLs that only possess a long (C8-C14) acyl side chain. The representative 3 strains were selected from these isolates based on the higher activity of biofilm formation. The AHL separation analysis with a thin layer chromatography clearly showed that N-octanoyl-L-homoserine lactone (C8-HSL) and N-hexanoyl-L-homoserine lactone (C6-HSL) existed in the secondary effluent sample, while no C6-HSL producing strain was isolated. C8-HSL was identified as the product of isolate No. 6. These results suggest that the secondary effluent probably contains various cell-to-cell signaling molecules derived not only from the inhabitants but also from the other microorganisms involved in the activated sludge for the biological pre-treatment. In this secondary effluent, AHL trapping techniques can be proposed as one of the acceptable strategies for the control of the QS systems because the remaining AHLs have relatively long acyl side chain and low concentrations.

Abstract: An assembly of diacetylene molecules is necessary to progress a topochemical reaction as UV-irradiated polymerization. In this study, we attempt to regularly assemble 10, 12- pentacosadiynoic acid (PCDA) by freezing the solution, followed by lyophilization. Dried PCDA assembly was easily dispersed in aqueous solution by sonication. Irradiation of UV light can promote polymerization reaction of PCDA judging from a color change of the solution into blue. A color transition of the polyPCDA-dispersed solution from blue to red was observed at approximately 56°C due to distortion of its π-conjugated system. A color transition temperature could be controlled by hybridization with thermosensitive hydroxypropyl cellulose, of which lower critical solution temperature appears around 38-39°C. By synchronizing to coli-globule transition of HPC in aqueous media, blue-red transition response of water-dispersed polyPCDA could be induced by changing conformation of surrounded polymer.

Abstract: Some gram-negative bacteria possess N-acylhomoserine lactone (AHL)-mediated quorum sensing (QS) as one of the cell-to-cell communication systems for regulation of various cell functions. Increase in the AHL concentration above its threshold leads to simultaneous activation of target gene expression in each cell. The AHL can diffuse in and out of the cells through the cell membrane. Artificial reduction of the AHL concentration can inhibit the AHL complex formation with its receptor inside the cell. In this study, the AHL that diffused out into the culture broth was captured on α-cyclodextrin (CD), which possesses a hydrophobic cavity and a hydrophilic shell. The α-CD-immobilized calcium alginate gel beads, which were prepared using a non-contact jet dispenser, were immersed in the culture medium during the cell growth of Serratia marcescens AS-1, which was used as the model opportunistic human pathogen. The trapping of AHLs on immobilized α-CDs due to hydrophobic interaction of the AHL acyl-chain led to an effective inhibition of AHL-mediated prodigiosin production to approximately 2% in the presence of 27 wt% gel beads in the culture broth. The results of our study suggest that CD has high potential to regulate QS involved in matter production, biofilm formation, and virulence factor expression.

Abstract: Bacterial cell-to-cell communication system quorum sensing (QS) could be effectively controlled with polymer gel sheets which possess affinity to QS signals. Cyclic oligosaccharide cyclodextrin (CD) was successfully immobilized onto 2-hydroxypropyl cellulose gel sheets to trap the QS signals produced in one of the opportunistic pathogen Serratia marcescens. In gram-negative bacteria including S. marcescens, N-acylhomoserine lactones (AHL) with different length of acyl-chains were produced as the QS signal autoinducer. The inclusion complex formation between AHL and CD is responsible for the artificial decrease of the AHL concentration inside and outside of cells. Because the QS system is the AHL-concentration dependent mechanism that activates the specific gene transcription, the AHL trapping method was simple and greatly effective to intercept the QS system. By using the 2-hydroxypropyl-β-CD immobilized gel sheets, the prodigiosin of which production was regulated by the AHL-mediated QS system could be reduced to approximately 20%.

Abstract: To control the microstructure and the responsive rates of hydrogels, a temperature-induced phase separation (TIPS) method applied to an organic-inorganic hybrid hydrogel. A copolymer between thermosensitive poly(N-isopropylacrylamide), polyNIPA, and a vinyl monomer possessing a trimethoxysilyl group was synthesized by radical reaction. Its cross-linking could be carried out by hydrolytic polycondensation of trimethoxysilyl groups. During both reactions, the pre-gel solution was separated into two phases by heating above a lower critical solution temperature of the elongating polyNIPA copolymer. The responsive rates of the microporous gel could be controlled by characteristic diffusion path length as the thickness of micropore wall, instead of the macroscopic sample size. Therefore, the shrinking rates of the hydrogel could be successfully maximized by fixing the phase-separated, microporous polymer network. Besides the interconnectivity of generated pores, the thermally triggered shrinking kinetics was investigated.

Abstract: To control and maximize the shrinking rates of thermo-sensitive organic-inorganic (O-I) hybrid gels, microporous structure of gels could be controlled by ice-templating. Water-swollen gels easily became porous after freezing. Applying the freezing method effectively accelerate the shrinking rates of the poly(N-isopropylacrylamide), polyNIPA-based O-I hybrid gels by two different ways. One is the interpenetrating network with polyNIPA and polysiloxane. The other is the copolymer network of NIPA and a vinyl monomer possessing the trimethoxysilane, of which crosslinking was carried out by sol-gel reaction. Their thermally-triggered shrinking kinetics was investigated by measuring the weight change of gels. Shrinking coefficients (D) were determined by fitting the shrinking data with the Fick’s model. The coefficients after applying the freezing method increased to approximately 10-3 cm2s-1 while those before freezing were on the order of 10-5 - 10-6 cm2s-1.