Chassis

Bacillus subtilis is a gram-positive bacteria, 5-10uM in length. We chose it as our chassis primarily for its complex metal-ion homeostasis system as well as its ease of genetic manipulation. Some heavy metals, such as manganese, iron and zinc, are essential to micro-organisms as trace nutrients, in contrast to others such as cadmium and lead, which have no known beneficial roles. However, all heavy metals are toxic at high (micro- or millimolar) concentrations. Yet it is widely known that certain bacteria are capable of growing in metal contaminated areas. These bacteria are usually adapted to the presence of toxic metals by genetically encoded resistance mechanisms, whose expression is precisely regulated. Specifically, these resistance mechanisms towards many toxic metals work by excretion of the metal by an energy-dependent pump in the cell membrane. This system serves as the basis of our biosensor.