Not just a human pursuit (Image: Nick Cunard/Rex Features)

The appeal of sudoku has spread to the prokaryotic world. A strain of Escherichia coli bacteria can now solve the logic puzzles – with some help from a group of students at the University of Tokyo, Japan.

“Because sudoku has simple rules, we felt that maybe bacteria could solve it for us, as long as we designed a circuit for them to follow,” says team leader Ryo Taniuchi.

The team begin with 16 types of E. coli, each colony assigned a distinct genetic identity depending on which square it occupied within a four-by-four sudoku grid. The bacteria can also express one of four colours to represent the numerical value of their square. As with any sudoku puzzle, a small number of the grid squares are given a value from the beginning by encouraging the bacteria in these squares to differentiate and take on one of the four colours.


These bacteria then use RNA recombinases packaged in viruses to send information about their location in the grid – and their colour value – to the undifferentiated bacteria in “unsolved” grid squares. The E. coli are “programmed” to accept RNA only from cells in the same row, column or block as themselves. The genetic information stored in the viral messages forbids the receiving bacteria from differentiating into the same colour as the transmitting bacteria, so by a process of elimination the undifferentiated cells establish which colour to adopt to “solve” the grid.

By expanding these principles, 81 types of bacteria could solve a full nine-by-nine grid, says Taniuchi.

Spread the load

Programming bacteria is not new, but there’s a limit to how much DNA you can insert into their genome. Spreading the code across many cells allows for more complex programs by creating a distributed network. “By this parallel calculating, bacteria can fill in all the sudoku cells simultaneously, which is impossible for human beings,” Taniuchi says.

Martyn Amos at Manchester Metropolitan University, UK, is a member of Bactocom, a project funded by the European Union to develop a biochemical computing device. “If you consider an ant colony, an individual ant isn’t very useful,” he told New Scientist. “But if you put millions of ants together they’re suddenly capable of very rich, very complex population-level behaviour. That’s what we’re trying to harness.”

The Tokyo team’s sudoku-solving bacteria competed in the International Genetically Engineered Machine competition at the Massachusetts Institute of Technology last week.