Microfluidic chip reveals bacteria swim toward large, complex polymers

Using a new microfluidic chip, ETH researchers led by Professor Roman Stocker and Estelle Clerc have shown that bacteria not only recognize small food molecules, but also swim towards large, complex polymers. Now a startup is using these findings and applying the technology to find microbes in the environment that can break down pollutants.

Scientists have long known that bacteria can move in aqueous solutions thanks to the very fine cilia on their surface. But until now, experts thought microbes were blind to complex polymers. And that they only focus on highly diffusible substances such as simple sugars which are very easily metabolized or ingested.

Conventional Wisdom Disproven

But the findings of Roman Stocker’s research team from the Department of Civil, Environmental and Geomatics Engineering (D-BAUG) at ETH Zurich have refuted conventional wisdom. Using a microfluidic chip co-developed with their collaborators at UTS Sydney, made from a plastic plate the size of a credit card with small chambers inside, the researchers showed during field work in the Norwegian Raunefjord that bacterial communities follow the concentration gradient of laminarin and other complex polysaccharides.

Laminarin is found in many species of microscopic brown algae and other members of marine phytoplankton. Laminarin contains up to a quarter of the carbon bound by photosynthesis in the oceans. “Laminarin is therefore one of the most important food sources for marine bacteria,” explains Estelle Clerc, a postdoctoral researcher in Stocker’s research group and first author of the study recently published in Natural communications.

Well developed sensorium

The fact that marine microbes can actively swim towards complex molecules to break them down has not yet been taken into account in models of global carbon flows. Their new results could therefore play a role in the future calculation of climate scenarios, believes Clerc. But on top of that, the evidence that microbes have a better-developed sensorium than expected gave Clerc the following idea. “Perhaps bacteria also recognize other complex and poorly degradable substances.”

To test the theory, the researchers simply had to equip their instrument with such substances and then release them into the water at different locations (for example in Lake Zurich or in the basin of a sewage treatment plant). Its first results, still preliminary and unpublished, show that there are indeed bacterial communities in the environment attracted by microplastics or pesticide residues, for example.

Solutions in the field of environmental sanitation

“Our instrument works like a bacteria trap,” explains Clerc. “The advantage is that we can use it to isolate bacterial communities with specific metabolic capabilities,” explains Clerc. Some of these bacterial communities appear capable of using these harmful chemicals. “During our first feasibility tests, some bacteria increased their biomass by 20,000 times, even though pollutants were the only food source available to them,” explains Clerc.

Two years ago, Clerc founded a spinoff company, CellX Biosolutions, to use the bacteria trap to specifically search for microorganisms that could be used for environmental remediation. In addition to pesticides and microplastics, the company also focuses on pharmaceuticals and the notorious PFAS, often referred to as “forever chemicals” due to their stability.

The startup’s ultimate goal is to commercialize these bacterial degradants as products that can be used in various industries as an alternative to current unsustainable and costly methods of disposing of toxic chemicals, such as incineration.

CellX recently reached an important milestone in its product development. Clerc is currently planning pilot tests with two major industrial partners, adapted to the specific processing needs of these collaborators. In the next step, Clerc intends to turn to industrial applications.

Together with the technical team at D-BAUG, Clerc also developed a pressure-resistant housing for the microfluidic chip intended for use in the deep sea. A patent application is currently pending. “With this accommodation we can access extreme environments like the eternal darkness of the oceans at 4,000 meters depth,” explains Clerc. “This gives us access to a huge reservoir of bacteria with still largely unexplored metabolic capabilities.”