How bacteria recognise and respond to surface contact

Bacterial biofilms can cause medical problems and issues in technical systems. While a large body of knowledge exists on the phenotypes of planktonic and of sessile cells in mature biofilms, our understanding of what happens when bacteria change from the planktonic to the sessile state is still very incomplete. Fundamental questions are unanswered: for instance, how do bacteria sense that they are in contact with a surface, and what are the very initial cellular responses to surface contact. Here, we review the current knowledge on the signals that bacteria could perceive once they attach to a surface, the signal transduction systems that could be involved in sensing the surface contact and the cellular responses that are triggered as a consequence to surface contact ultimately leading to biofilm formation. Finally, as the main obstacle in investigating the initial responses to surface contact has been the difficulty to experimentally study the dynamic response of single cells upon surface attachment, we also review recent experimental approaches that could be employed to study bacterial surface sensing, which ultimately could lead to an improved understanding of how biofilm formation could be prevented

Reassessing the role of the Escherichia coli CpxAR system in sensing surface contact

For proper biofilm formation, bacteria must have mechanisms in place to sense adhesion to surfaces. In Escherichia coli, the CpxAR and RcsCDB systems have been reported to sense surfaces. The CpxAR system is widely considered to be responsible for sensing attachment, specifically to hydrophobic surfaces. Here, using both single-cell and population-level analyses, we confirm RcsCDB activation upon surface contact, but find that the CpxAR system is not activated, in contrast to what had earlier been reported. Thus, the role of CpxAR in surface sensing and initiation of biofilm formation should be reconsidered

Manipulating rod-shaped bacteria with optical tweezers

Optical tweezers have great potential in microbiology for holding and manipulating single cells under a microscope. However, the methodology to use optical tweezers for live cell studies is still at its infancy. In this work, we determined suitable parameters for stable trapping of single Escherichia coli bacteria, and identified the upper limits of IR-exposure that can be applied without affecting viability. We found that the maximum tolerable IR-exposure is 2.5-fold higher when employing oscillating instead of stationary optical trapping (20 J and 8 J, respectively). We found that good stability of cells in an oscillating trap is achieved when the effective trap length is 20% larger than the cell length, the oscillation frequency higher than 100 Hz and the trap oriented perpendicular to the medium flow direction. Further, we show, using an IR power just sufficient for stable holding, that bacteria remain viable during at least 30 min of holding in an oscillating trap. In this work, we established a method for long-term stable handling of single E. coli cells using optical tweezers. This work will pave the way for future use of optical tweezers in microbiology

MONOLAYERS AND LANGMUIR-BLODGETT MULTILAYER FILMS OF A CONJUGATED AZO POLYMER

A black pi-conjugated azo polymer was synthesized by oxidative coupling of 3,5-diamino-1-octadecylbenzoate. The polymer, with a number average molecular weight of about 16 000, was soluble in chloroform. Monolayer formation was studied by transmission electron microscopy and the structure of the deposited Langmuir-Blodgett multilayer film was investigated with small angle X-ray diffraction and Fourier transform IR spectroscopy. A smooth monolayer was obtained when, after spreading, the material was allowed to disintegrate without any applied surface pressure for 18 h at 20-degrees-C and 1 h at 40-degrees-C. Monolayers could be transferred successfully onto different substrates at high temperature (40-degrees-C) and high pressure (30 mN m-1). The deposition was of the Y type with transfer ratios of 1 on both the downstroke and the upstroke. It was concluded that the aliphatic side chains are not able to crystallize and therefore form amorphous layers

Method for manufacturing a film of arylalkyl-modified polyacetylene, said polyacetylene obtained, and the use thereof

The present invention relates to a method of manufacturing a film of arylalkyl-modified polyacetylene, wherein a layer of an arylalkyldiacetylene compound with the formula (I): X(N)-L-CC-CC-L-(N)X wherein X(N) represents a nitrogen-containing planar aromatic group L represents a linear aliphatic group -(CH2)n- with

Oxidative Coupling Polymerization in a Langmuir Monolayer of Octadecyl 3,5-Diaminobenzoate

In a Langmuir monolayer of the surface active monomer octadecyl 3,5-diaminobenzoate (ODDB), stabilized at a surface pressure of 10 mN/m and a temperature of 23.7 °C at the air-water interface, oxidative coupling polymerization occurs when copper(II) chloride was added or already was present in the subphase. Even in the absence of the catalyst this reaction takes place. Deposition of the polymerized monolayer onto glass, zinc sulfide, or gold substrates, using the vertical dipping method, gave transfer ratios between 0 and 0.4 on the downstroke and 1 on the upstroke. The multilayer films on zinc sulfide and gold substrates were characterized by means of Fourier transform IR spectroscopy, and multilayer films on quartz were characterized by means of UV/vis spectroscopy. Collected monolayers were characterized by means of size exclusion chromatography and again Fourier transform IR and UV/vis spectroscopy. During the stabilization of the monolayer without addition of copper(II) chloride to the subphase, the area per molecule decreased very slowly. Addition of copper(II) chloride enhanced this effect. The reduction of the area per molecule is probably caused by the polymerization itself accompanied by a reorientation of the molecules in the monolayer at the air-water interface. After stabilization the area per molecule was found to be about 27 Å2 and electron micrographs showed the formation of a smooth monolayer. From this it has been concluded that a closely packed monolayer was formed. Fourier transform IR and UV/vis spectra of polymerized multilayer materials are analogous to the spectra of the azo polymer of ODDB prepared in bulk solution. Size exclusion chromatography revealed that the molecular weight and the molecular weight distribution of the coupling product with and without copper(II) chloride in the subphase were the same. The average molecular weight was somewhat lower than the high-molecular-weight part of the corresponding material prepared in bulk solution.

A RARE CASE OF AZEOTROPIC COPOLYMERIZATION

Copolymerizations with both reactivity ratios equal to one are rare. Therefore, we report here on the radical copolymerization of styrene and p-tert-butoxy-carbonyl-oxy-styrene in toluene with AIBN as initiator. We found it to be an azeotropic copolymerization for all compositions, i.e. f1 = F1 and r1 = r2 = 1. This is so because the electron density on the beta carbon of the substituted styrene is the same as on the beta carbon of the styrene