Algae with light switch

September 29, 2017

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.

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."
Original publication

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


Related Photosynthesis Articles from Brightsurf:

During COVID, scientists turn to computers to understand C4 photosynthesis
When COVID closed down their lab, a team from the University of Essex turned to computational approaches to understand what makes some plants better adapted to transform light and carbon dioxide into yield through photosynthesis.

E. coli bacteria offer path to improving photosynthesis
Cornell University scientists have engineered a key plant enzyme and introduced it in Escherichia coli bacteria in order to create an optimal experimental environment for studying how to speed up photosynthesis, a holy grail for improving crop yields.

Showtime for photosynthesis
Using a unique combination of nanoscale imaging and chemical analysis, an international team of researchers has revealed a key step in the molecular mechanism behind the water splitting reaction of photosynthesis, a finding that could help inform the design of renewable energy technology.

Photosynthesis in a droplet
Researchers develop an artificial chloroplast.

Even bacteria need their space: Squished cells may shut down photosynthesis
Introverts take heart: When cells, like some people, get too squished, they can go into defense mode, even shutting down photosynthesis.

Marine cyanobacteria do not survive solely on photosynthesis
The University of Cordoba published a study in a journal from the Nature group that supports the idea that marine cyanobacteria also incorporate organic compounds from the environment.

Photosynthesis -- living laboratories
Ludwig-Maximilians-Universitaet (LMU) in Munich biologists Marcel Dann and Dario Leister have demonstrated for the first time that cyanobacteria and plants employ similar mechanisms and key proteins to regulate cyclic electron flow during photosynthesis.

Photosynthesis seen in a new light by rapid X-ray pulses
In a new study, led by Petra Fromme and Nadia Zatsepin at the Biodesign Center for Applied Structural Discovery, the School of Molecular Sciences and the Department of Physics at ASU, researchers investigated the structure of Photosystem I (PSI) with ultrashort X-ray pulses at the European X-ray Free Electron Laser (EuXFEL), located in Hamburg, Germany.

Photosynthesis olympics: can the best wheat varieties be even better?
Scientists have put elite wheat varieties through a sort of 'Photosynthesis Olympics' to find which varieties have the best performing photosynthesis.

Strange bacteria hint at ancient origin of photosynthesis
Structures inside rare bacteria are similar to those that power photosynthesis in plants today, suggesting the process is older than assumed.

Read More: Photosynthesis News and Photosynthesis Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to