Around 1452 the first operational printing press was created, followed in 1799 by lithographic printing. Now, these inventions are reflected in the world’s first bacterial printing press.

The press will print live bacteria onto solid surfaces in precise patterns, a technique that may help explain how bacteria influence each other spatially. Understanding these relationships will help find ways of thwarting their attacks and using them to clean up pollutants.

For instance, bacteria sometimes form biofilms, unique communities of sticky, sugary plaques which cling to surfaces (New Scientist, 20 November 2004, p 34). In this state bacteria are better at resisting antibiotics and more efficient at processing waste. But we do not know which conditions prompt bacteria to form these biofilms and why they are more resilient when they do. “One thing we want to study is the distance dependence for signalling between two adjacent bacteria on a surface,” says Doug Weibel, a member of the Harvard University team that built the printing press.

Biologists already have crude techniques for patterning bacteria, including dipping an array of evenly spaced pins into a bacterial solution and letting the drops fall onto a fresh surface. But the liquid spreads out, making it impossible to create delicate, reproducible patterns.

To create intricate patterns of many different types of bacteria, Weibel borrowed a technique from the computer chip industry called photolithography. Conventionally, this involves coating a silicon wafer with a thin layer of light-sensitive polymer, shining UV light onto it through a template, and then dissolving the affected areas to create a pattern.

Weibel uses this patterned chip as a mould, into which he pours a liquid polymer. This cools, sets and is popped out, forming a stamp. This is then coated with agarose, a nutrient gel that bacteria will grow on. He pipettes solutions of bacteria onto the agarose, which sucks out the water, leaving a solid layer of bacteria.

To print the bacteria, this stamp is simply pressed into a clean nutrient gel, producing a living replica of the original pattern, with features as small as 1 micrometre across, the size of one bacterium. As some bacteria remain on the stamp, it is “re-inked” by warming until the bacteria multiply to form a fresh carpet over its surface.

Weibel has used his stamp to form patterns of different types of bacteria, and of the same bacteria on surfaces with different chemical compositions, as well as to grow biofilms. He will publish the results in an upcoming issue of the journal Langmuir.

By Celeste Biever

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