What is Synthetic biology?

Figure 1: A plasmid (A) with an antibiotics resistance gene (in green) can be cut by restriction enzymes (dark red) (B). A new piece of DNA (bright red) can be insterted into the gap (C). The insertion is 'glued' into place by ligases (D). We then have our product to insert into bacteria (E).

Synthetic biology is the science of constructing biological systems and devices through application of biological knowledge and synthetic chemistry. In the case of the iGEM competition, the basic idea is to make relatively simple genetic constructs and apply those constructs to a task through bacteria. We go through a simplified example here. The reality has a lot more steps but the broad strokes remain the same.

Bacteria have their own tools with which they can read genetic code, and translate that code into proteins; the molecules that perform nearly all functions within a living cell. We can use these tools when we insert custom-made DNA sequences into the bacteria in the form of plasmids. Plasmids are 'rings' of DNA, which bacteria can pick up and use. In nature, bacteria share plasmids to gain new functions.

Before we have our plasmid with the desired DNA sequence, we will have to design it. Usually, one starts with a 'backbone' plasmid, and the desired piece of DNA. Such plasmids are often isolated from bacteria found in nature and contain a DNA sequence with an ability that makes the bacteria able to survive conditions that other bacteria cannot. The most common are antibiotic resistance genes.

If we have a backbone, we can insert a sequence of DNA into the plasmid by cutting it with restriction enzymes, and pasting in the DNA sequence with DNA ligases. Restriction enzymes are molecules that can recognize very specific parts of DNA, called restriction sites, and cut them (see figure 1: A, B). DNA ligases are molecules that can 'glue' together two large molecules, such as two ends of DNA.

Restriction enzymes can be used to cut a desired piece of DNA from another bacteria, to transplant into our backbone. Then the backbone is cut, the desired seqeunce is inserted and our plasmid is ready to be inserted into a bacteria (see figure 1: C, D, E).

When we insert our plasmid, the bacteria will read the DNA, and produce the product. We can abuse the bacteria's own system to make bacteria produce molecules like DspB, a molecule which is already used in nature by bacteria that make biofilms, a kind of 'reef' of bacteria. They use this molecule to cut themselves loose. When we flood the area with DspB, the bacteria will not be able to make the biofilm, because they will be cut loose as soon as they try to attach themselves.