The Arsenic Biosensor Collaboration brings together several technologies and combines them in such a way as to create a simple, reliable whole cell biosensor. There are three main areas that are being addressed in the project: Chassis, Detection and Containment.
Simply defined, a chassis is an operational container. In the case of a whole cell biosensor such as the Arsenic Biosensor, the chassis is the bacteria which will conduct the sensing. As we intend to have our sensor used in the field, we need our bacterial chassis to be suitably safe for human handling and it must be proven beyond reasonable doubt that even in the event of unintended release, the GMO will not be capable of affecting the environment or human health.
The first step to creating a safe chassis is to select a bacterium which is already close to meeting the requirements. For this reason we have selected Bacillus subtilis, which holds GRAS (Generally Regarded As Safe) status with the US Food and Drug Administration (FDA) and has been part of the human diet for centuries. Even though wildtype B. subtilis is regarded as safe, we are actually starting with a laboratory strain - B. subtilis 168. This strain has been essentially domesticated and cannot produce all of its own amino acids. Our intention is to further disable this strain, by making it unable to produce even more of its essential nutrients.
Although the GMO we are creating is not unsafe, it is still a GMO and one of our goals is to ensure that even if it is released into the environment it will quickly die out. B. subtilis is a spore forming bacterium and spores are capable of persisting in the environment for extremely long periods of time. One of our objectives is to limit the bacteria’s ability sporulate outside the laboratory in order to reduce the GMO's ability to persist in the environment. Bacteria have evolved to have many mechanisms to deal with the environment in ways to enhance their survivability. This included creating genetic pathways to help them deal with UV radiation, free radicals and other bacteria. We are addressing this issue by making our GMO less capable of dealing with these environmental stresses so that it may not be able to compete in the wild.
Arsenic contamination of water is a widespread enough occurrence that bacteria have developed mechanisms to deal with it. Bacteria are actually capable of determining if the concentration of arsenic in their surroundings is so high as to cause them damage. If it is deemed to be high enough, bacteria then switch on a group of genes tailored to help them survive in this environment.
Our goal is to harness this naturally occurring detection machinery and use it to trigger the production of colour. In keeping with our desire of using genetic material with a long history of safe use, we are using genes that are directly related to one of the most widely used genes in science - that which encodes Green Fluorescent Protein. As with the case of GFP we are using genes found in oceanic fauna. By coupling the genetic switch which is turned on by arsenic to the colour generating gene, we are creating a circuit which will cause bacteria to change in colour if the concentration of arsenic is high enough. Since different species of bacteria naturally sense arsenic at different concentrations, we aim to use this information to build at least two switches, one that will turn on at an arsenic concentration of 10ppb (the WHO guideline for safe levels of arsenic in drinking water) and another at 50ppb (the Nepalese government guideline for safe levels of arsenic in drinking water).
Packaging is an essential aspect of the Arsenic Biosensor proposition. From material selection to construction and assembly, every aspect of containment design directly influences the sensitivity, practicality, cost effectiveness and - most importantly - international regulatory acceptability of our solution. These and other requirements must be satisfied to preserve the sensor integrity, viability and environmental compliance during transportation, long-term storage and deployment in extreme climatic conditions. Cheap, mechanically robust, and biologically inert, our biosensor package is designed to fulfill the most demanding scientific and commercial challenges.