Quorum Sensing and iGEM

As an electrical engineer, I’m used to being able to wire components together to get essentially interference free communication. In biological systems, this capability isn’t available. Cells communicate with each other mainly using proteins and other small molecules that diffuse through cell membranes. This means that all neighbors of a cell may sense whatever it’s transmitting, along the lines of wireless networks. Unlike wireless networks, cells don’t have IP addresses and their state is very stochastic. This makes effective cellular communication very difficult and inaccurate.

Quorum sensing seems to be the method most used by cells to communicate. In nature it’s just used to sense local concentrations of cells. This can be used by engineers to accomplish a variety of different tasks that require cells to work together.

Many iGEM projects this year deal with new ways of using quorum sensing. Many of the projects use quorum sensing to differentiate cells, while others use quorum sensing for environmental detection or generalized communication mechanisms.

Grenoble: Mercury Detection using E-coli

The Grenoble team created e-coli that switch from one state to another in the presence of mercury. If mercury is present, the cells become “sender cells” that produce a quorum sensing molecule. Cells where IPTG is dominant over mercury become “receiver cells”. These cells produce RFP if the concentration of the quorum sensing molecule is high enough. The layout of the cells causes only the receiver cells closest to the sender cells to turn red. This creates a visible indicator of the concentration of mercury in the sample.

USTC: Infection targeting anti-bacterials

The USTC-China team developed a genetic circuit that allows for differentiation of cells. Cells become either “sleeper” cells or “attacker” cells, and AHL quorum sensing causes a suitable percentage of the undifferentiated cells to become attackers. The attacker cells move towards a bacterial infection (of AIIS) through chemotaxis. When the concentration of the molecule produced by the AIIS infection becomes high enough, the attacker cells create pyosin, which causes them to die. Excess pyosin is released that kills the bacterial infection.

Monterey: Code interpretation through quorum sensing

The Monterey, Mexico team developed three different strains of e-coli. Each strain responds to a different wavelength of light by releasing a different quorum sensing molecule. The strains can communicate among each other through these quorum sensing molecules to determine which color light has been shone on them. By using bistable switches, it is possible to record the order of the light that was received.

Peking: Chemical wire toolbox

As part of their chemical wire toolbox, the Peking team developed a set of quorum sensing molecules that can be used to send signals between cells. Their goal was to create a number of orthogonal signal mechanisms to allow cells to communicate with each other without interfering with other routes of communications (basically creating the non-interfering wires I take for granted in EE).

Sevilla: Ubbit communication standard

The Sevilla team created a standard for information exchange among cells. Like the wire toolbox from Peking, the Sevilla Ubbit is a standardized communication mechanism among cells. The Ubbit is meant to be a synthetic quorum sensing molecule.