“This is a very, very important part of the food chain, as a disturbance in nitrogen levels can decimate larger species starting with their food source.” - Arijit Bose

ARIJIT BOSE Distinguished Engineering Professor

Photo by Jason Jaacks

To test if cyanobacteria recognize microplastics in their environment, Bose recreated an ocean water environment in the lab with polystyrene and polyethylene particles and bacteria in a plastic suspension, and then imaged their interaction using electron microscopy, which can observe a much finer scale than a traditional microscope. The findings surprised even Bose. Upon encounter with the microplastics, the bacteria excreted a sticky biofilm that allowed it to bind to the particle, the same way a barnacle binds to the hull of a ship. “They need to attack this thing they don’t know,” Bose said. After the biofilm formed, the bacteria sent out a signal to summon other bacteria to the foreign object. But contrary to the labs’ hypothesis that the bacteria may die upon encounter, instead the bacteria began to change biologically in order to better attack and degrade the plastic. Tripathi and Bose began to sequence the bacteria’s DNA. A little more than a week after exposure to the stressor, the scientists began to see modifications. The bacteria’s DNA was changing to overexpress a gene that codes for an enzyme that degrades the plastic. “Fish eat plastic and may die, but the bacteria

respond to the plastic in an active way where they convert themselves and secrete an enzyme that degrades the plastic,” Bose said. “There’s a little bit of good news in the face of this very bad problem. We may be finding that the plastic is actually degrading — at least the stuff that is making its way into the water column — which is a good thing.” Though the time scale of this degradation may be too long to be useful to humans, these initial findings have excited Bose to dive in deeper, as there may be ways to harness this bacterial action as an effective new tool to tackle this problem. In his initial tests, he looked at spherical plastic particles, but wonders how the shape and size of microplastics could affect bacteria. In the coming months he also plans to test the interaction between different types of bacteria and different plastics including those made from renewable sources. His lab has added two undergraduate students to help expand his research. “I love doing research,” Bose said. “For me, research is the best way to tackle problems that are crucially important to society. “We are asking questions that no one knows the answers to. We struggle a little bit, we a take a few wrong turns and learn from them, and then we make some progress. For me that’s the most exciting thing that happens at a research university.”

URI Initiative Plastics: Land to Sea SPRING | 2021 Page 33

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