Phormidium, a genus of filamentous cyanobacteria, forms endosymbiotic associations with seedling roots that accelerate the growth of the vegetable seedlings. Understanding the gliding mechanism of Phormidium will facilitate improved formation of this association and increased vegetable production. To observe the gliding movements, we fabricated various microfluidic chips termed nanoaquariums using a femtosecond (fs) laser. Direct fs laser writing, followed by annealing and successive wet etching in dilute hydrofluoric acid solution, can easily produce three-dimensional (3D) microfluidics with different structures embedded in a photostructurable glass. Using the fs laser, optical waveguides and filters were integrated with the microfluidic structures in the microchips, allowing the gliding mechanism to be more easily clarified. Using this apparatus, we found that CO(2) secreted from the seedling root attracts Phormidium in the presence of light, and determined the light intensity and specific wavelength necessary for gliding.
Summary. The existence of two photoreceptors regulating chloroplast orientation was found in the centric diatom Pleurosira laevis. Chloroplasts migrate through the transvacuolar cytoplasmic strands according to the light conditions. Weak white light of less than 46 ~tmol/m 2 9 s (10 W/m 2) induces chloroplast movement to the cortical cytoplasm, which is located next to the plasma membrane (dispersion), while intense white light of more than 92 ~tmol]m 2. s (20 W/m 2) induces chloroplast movement towards the nucleus, which is situated in the center of the cell (assemblage). Chloroplast dispersion was maintained as long as the ceils were irradiated with weak white light. Conversely, chloroplast assemblage under intense white light was transient and the chloroplasts were released from assemblage after 15 rain. Action spectra determined with the Okazaki Large Spectrograph revealed that the weak white light receptor and the intense white light receptor are characterized by 540 nm and 450 nm optima, respectively.
In this paper, we propose a novel, magnetically driven microrobot equipped with a frame structure to measure the effects of stimulating aquatic microorganisms. The design and fabrication of the force-sensing structure with a displacement magnification mechanism based on beam deformation are described. The microrobot is composed of a Si-Ni hybrid structure constructed using micro-electro-mechanical system (MEMS) technologies. The microrobots with 5 μm-wide force sensors are actuated in a microfluidic chip by permanent magnets so that they can locally stimulate the microorganisms with the desired force within the stable environment of the closed microchip. They afford centimetre-order mobility (untethered drive) and millinewton-order forces (high power) as well as force-sensing. Finally, we apply the developed microrobots for the quantitative evaluation of the stimuation of Pleurosira laevis (P. laevis) and determine the relationship between the applied force and the response of a single cell.
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