The adhesion of Chlamydomonas, a unicellular alga, to surfaces is light-dependent
Sunlight allows green algae to do more than just carry out photosynthesis. Some unicellular algae actually use light to switch the adhesion of their flagella to surfaces on and off - a phenomenon first discovered by physicists at the Göttingen Max Planck Institute for Dynamics and Self-Organization. These findings are particularly relevant to the development of bioreactors in which algae serve as a renewable raw material for producing biofuels.
Green algae can switch their ability to adhere to surfaces on and off by means of light. In light, their two fine hairs, called flagella, stick to a surface, whereas in the dark, the algae swim through the water using a sort of breast-stroke movement.
Credit: Oliver Bäumchen, MPIDS, Göttingen / Thomas Braun, Heidelberg
In everyday life, green algae tend to be bad news. In damp weather, microscopic unicellular algae form a slimy layer on garden furniture and house walls; during warm summers, they form a scum on the surface of garden ponds and water-treatment tanks. But green algae can also be beneficial.
For years now algae have been cultivated in bioreactors, in large facilities comprised of glass tubes, to produce biofuels. However, green algae have a property that makes this process difficult: using small hairs, known as flagella, they adhere to surfaces. In bioreactors, this results in a green biofilm forming on the walls of the glass tubes. As a result, less light penetrates into the reactor. The biofilm reduces the ability of other algae in the reactor to carry out photosynthesis, thus making the bioreactor less efficient.
Chlamydomonas do not stick in red light
A research team led by Oliver Bäumchen, a physicist at the Max Planck Institute for Dynamics and Self-Organization in Göttingen, has now made a discovery that could boost the efficiency of bioreactors. "In experiments with green algae, we found that the algae are sticky and able to adhere to surfaces only under certain light conditions," Oliver Bäumchen says.
The scientist has been focused on the adhesive properties of microorganisms for many years. He is primarily interested in flagella and the mechanisms by which these tiny hair-like structures can exert surprisingly strong adhesive forces. He and his staff devised a precise sensor to measure the forces involved: an ultra-thin glass micropipette that can aspire a single green algal cell. Using the micropipette, they measure the force needed to detach a living cell from a surface.
Chlamydomonas uses various proteins to sense light
Bäumchen's doctoral student, Christian Kreis, found that the adhesion of algae to surfaces can be controlled by light. Experimenting with the green alga Chlamydomonas, he found that it consistently exhibited a strong adhesive force only under white light. Under red light, the cells did not adhere to surfaces at all. It has long been known that many microorganisms orientate themselves to light and, for example, swim towards a light source. However, it was not previously known that the green alga's adhesion mechanism can be switched on and off with light.
Kreis investigated the light response more closely and found that Chlamydomonas exclusively sticks to surfaces when exposed to blue light. The alga uses a number of special light-sensitive proteins to sense the light. "We believe that light-switchable adhesiveness may be a product of evolution," Christian Kreis says. Unlike marine phytoplankton, these related microorganisms usually live in wet soils where they often encounter surfaces. "If those surfaces are exposed to sunlight, this clever mechanism enables the algae to latch on to them and start carrying out photosynthesis," the researcher explains.
Algae with modified blue-light photoreceptors might not form biofilms
This finding does not in itself provide a way to prevent algal deposits from forming on the glass walls of bioreactors. Exposing bioreactors to the red light only to switch off adhesion does not work, because green algae also require blue light for photosynthesis. Oliver Bäumchen and Christian Kreis are therefore taking a different approach. "We've now teamed up with microbiologists who have a great deal of experience with green algae," Bäumchen says. "We plan to study cells in which the various blue-light photoreceptors are blocked to find out which of those photoreceptors is in fact responsible for triggering the adhesive properties." If algae with modified blue-light photoreceptors could be grown in large volumes, we might be able to use them in bioreactors without the annoyance of biofilms forming on the surfaces.
Oliver Bäumchen's research team has focussed on the switchable adhesion of green algae for several reasons: "It is generally interesting to understand the phenomenon of surface adhesion. After all, the adhesion forces are enormous in relation to the cells' size," Bäumchen says. He is also studying flagella because their construction principle is almost identical to that of cilia in the human body, for example in the lungs.
Christian Kreis is also concerned with ways to prevent the formation of algal biofilms. He is currently investigating whether adhesion can be switched on and off by triggers other than light, for example by surfaces carrying weak electrical charges. "Biofilms are troublesome in many applications," the researcher says. "If we could design surfaces in such a way that they prevent microorganisms to stick to them, that would be a boon for many applications in medicine, biotechnology and chemical engineering."
Adhesion of Chlamydomonas microalgae to surfaces is switchable by light
Christian Titus Kreis, Marine Le Blay, Christine Linne, Marcin Michal Makowski and Oliver Bäumchen
Nature Physics, 25 September 2017; doi: 10.1038/nphys4258
Dr. Oliver Bäumchen | EurekAlert!
Rochester scientists discover gene controlling genetic recombination rates
23.04.2018 | University of Rochester
One step closer to reality
20.04.2018 | Max-Planck-Institut für Entwicklungsbiologie
Physicists at the Laboratory for Attosecond Physics, which is jointly run by Ludwig-Maximilians-Universität and the Max Planck Institute of Quantum Optics, have developed a high-power laser system that generates ultrashort pulses of light covering a large share of the mid-infrared spectrum. The researchers envisage a wide range of applications for the technology – in the early diagnosis of cancer, for instance.
Molecules are the building blocks of life. Like all other organisms, we are made of them. They control our biorhythm, and they can also reflect our state of...
University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.
Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.
Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.
Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...
Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.
The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...
Stable joint cartilage can be produced from adult stem cells originating from bone marrow. This is made possible by inducing specific molecular processes occurring during embryonic cartilage formation, as researchers from the University and University Hospital of Basel report in the scientific journal PNAS.
Certain mesenchymal stem/stromal cells from the bone marrow of adults are considered extremely promising for skeletal tissue regeneration. These adult stem...
13.04.2018 | Event News
12.04.2018 | Event News
09.04.2018 | Event News
23.04.2018 | Physics and Astronomy
23.04.2018 | Physics and Astronomy
23.04.2018 | Trade Fair News