Engineers design new synthetic biology circuits that combine memory, logic

MIT engineers have created genetic circuits in bacterial cells that not only perform logic functions, but also remember the results, which are encoded in the cell's DNA and passed on for dozens of generations.

Engineers at MIT have developed genetic circuits in bacterial cells that not only perform logic functions, but also remember the results. Image: Liang Zong and Yan Liang

The circuits, described in the 10 February online edition of Nature Biotechnology, could be used as long-term environmental sensors, efficient controls for biomanufacturing, or to programme stem cells to differentiate into other cell types.

''Almost all of the previous work in synthetic biology that we're aware of has either focused on logic components or on memory modules that just encode memory. We think complex computation will involve combining both logic and memory, and that's why we built this particular framework to do so,'' says Timothy Lu, an MIT assistant professor of electrical engineering and computer science and biological engineering and senior author of the Nature Biotechnology paper.

Lead author of the paper is MIT postdoc Piro Siuti. Undergraduate John Yazbek is also an author.

More than logic
Synthetic biologists use interchangeable genetic parts to design circuits that perform a specific function, such as detecting a chemical in the environment. In that type of circuit, the target chemical would generate a specific response, such as production of green fluorescent protein (GFP). 

Circuits can also be designed for any type of Boolean logic function, such as 'and' gates and 'or' gates. Using those kinds of gates, circuits can detect multiple inputs. In most of the previously engineered cellular logic circuits, the end product is generated only as long as the original stimuli are present: Once they disappear, the circuit shuts off until another stimulus comes along.