True artificial cells are one of the great scientific goals of this age, with the potential to open whole new avenues of synthetic medicine. However, so far there has been a lack of definition about what exactly this means; true artificial cells effectively mimic life, but what constitutes life on a cellular level?

A lack of agreed definition has led to different focuses been taken by different scientists, with most research based on the inherent premise that life is something binary: it either is or isn’t alive.

However, a team of scientists led by Sheref S Mancy at the University of Trento’s Centre for Integrative Biology has proposed that life in this instance should be treated as a series of steps, much in the same way as it evolved.

In research published today in the journal ACS Central Science, they have proposed a “type of imitation game” based on the original Turing test.

In both cases, the test is based on communication: in the original Turing test machines are tested through their ability to use language to trick the judge into thinking they are human, but in the cellular Turing test this artificial cell is being tested on its ability to deceive natural cells into thinking it is one of them.

All cells communicate – it is the mechanism by which they interact and send instructions to one another, and together form processes and systems that make up life. However, this communication also produces measurable changes in gene expression that can be quantified extremely precisely, allowing for a sliding rather than binary scale about what constitutes life.

By breaking this communication down into a number of quantifiable actions, the scientists were able to create a cellular Turing test by which artificial cells can be measured.

To demonstrate their concept, the scientists created nanoscale lipid vesicles – a small fluid sac – that could listen to chemicals that were given off by natural bacteria. These artificial vesicles were designed to respond to the chemicals by turning on genes that made them glow – demonstrating on a sliding scale their ability to sense bacteria – and thus providing part one of the cellular Turing test.

Additional parts of the test are concerned with demonstrating the artificial cell’s ability to synthesise chemicals and send them to a natural cell, provoking a reaction; establish new communication networks between natural cells and ultimately establish two-way communication between artificial and natural cells.

The scientists tested their artificial cell with a number of different bacteria, finding they were able to establish two-way communication with just one strain.

While there is still considerable work to be done to produce a complete artificial cell, the scientists believe their cellular Turing test will help to guide and advance research, by highlighting which processes need greater focus.

“Impressive progress has been made in synthetic genomics, but the resulting living systems still depend on many genes with unknown function and many unidentified factors present in the living cell that receives the synthetic genome. The artificial cells described here suffer from similar complications; extract compositions are not fully known, and it is not currently possible to express in vitro functioning translation machinery,” concluded the scientists.

“Removing these unknowns is necessary to build artificial cells that more fully break from the concept of vivum ex vivo. Building a fully defined artificial cell from scratch would lead to a much deeper understanding of life. A cellular Turing test can help guide progress toward such a goal.”