Printing press spells out bugs' behaviour
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.
据《新科学家》杂志网站2005年5月30日消息，1452年第一台印刷机诞生，随后在1799年人们发明了平版印刷技术。现在，这些旧日的发明都在世界上第一台细菌印刷机上得到了体现。
这种设备能够以精细的图案将活细菌印刷到固体表面，它将有助于研究细菌之间怎样相互作用。如果能够了解它们之间的关系，科学家们就能够找出方法来抵挡细菌的进攻，或者利用细菌来分解污染物。
例如，细菌有时能构成生物被膜，这种独特的细菌群落具有粘性、富含糖分，而且可以粘附在物体的表面。这种状态下的细菌具有更强的能力来抵抗抗生素，同时在处理废物的时候效率也会变高。但是我们还不知道在什么情况下细菌会形成这样的生物被膜，以及为什么在形成被膜后细菌的复原能力也会增强。“我们目前计划研究在同一物体表面上相邻两个细菌的细菌信号的依赖距离，”来自哈佛大学的Doug Weibel说，他所在的研究小组研制了那种可以印刷细菌的印刷机。
生物学家已经能够利用简单的办法来排列细菌，其中包括将排列整齐间距相等的一组针头浸入细菌溶液中，然后将液体滴到干净的物体表面。但是液体有时会扩散，这样一来就无法制造既精细又能够繁殖细菌的图案。
为了精细地制造各种不同的细菌排列，Weibel借用了计算机芯片制造中的微影技术。和传统方法一样，先给硅片薄薄地涂上一层对光线十分敏感的聚合物，再隔着一个模板用紫外线照射硅片，然后溶解那些受到影响的区域，这样就制成了一个图案。
Weibel把已经被照射过的硅片作为模具，然后将一种聚合液体到入其中。随后取出冷却固定后看起来像印章的聚合液体。在印章上图一层琼脂糖，细菌就能够在这种营养凝胶体上生长。然后他用吸液管将细菌溶液滴到琼脂糖上，在琼脂糖吸干了溶液中的水分后，印章表面就会形成一层固体细菌。
印刷细菌时，只需简单地将这个印章放入干净的营养凝胶中就能够制造出一个和原有图案相同的，活的复制品，而且这种图案的细节能够精确到一微米，犹如单个细菌的大小。如果在印章上仍然有细菌存在，可以利用加热的方法来给印章“重新加墨”，在其表面繁殖新的一层细菌。
Weibel已经使用这种印章制作了多种不同细菌的图案，并且还将相同的细菌放到由不同化学物质成分的表面来培养生物被膜。他将在下一期的《Langmuir》上发表其研究结果。
