IGEM:Imperial/2010/Detection of contaminants and pathogens

Introduction
At the moment we plan to couple our "rapid response" system to a detection system for water contaminants or pathogens, especially parasites. For this we have been doing a literature research for bacteria that are able to sense and/or interact with common parasites of humans.

Salmonella and Schistosoma
A number of papers (Link) from around 1970-1985 point out the association of Salmonella with Schistosoma parasites in patients. There is evidence that special type 1 pili are involved in this interaction that is thought to help Salmonella reproduce by providing a multiplication focus and evade the host immune system. So far we have not been able to learn about the exact molecular mechanism behind this interaction so we have still to demonstrate that exploiting this system for parasite detection is feasible. This paper gives loads of information about the expression of fimbriae proteins and how fimbriae are assembled. It also hints about the downstream pathways, but not in much detail...

Parker et al. (2006) - fimbriae synthesis controlled by two-component system using a sigma 54 dependent pathway.

Book discribing fimbriae biosynthesis (2005) - in E.coli and other bacteria, fimbriae biosynthesis appears to be regulated by detection of extracellular signals via two-component systems, often via sigma 54.

Ruiz et al (2005) - Cpx two component system e.coli senses envelope stresses, e.g. damage due to extracellular proteases. If pathogens excrete theses, indirect detection could be possible. Also a possible option for a logic AND gate approach in the input module.

Schistosoma sensoring via Cercarial proteases
The cercarial stage of the schistosoma life-cycle represents the infective form for humans. Living in open or closed water systems, upon detection of skin-lipids the excretion of various proteases from primary secretory glands is triggered by thermal and chemical signals associated with skin lipids. Two major classes of proteases have been identified: a chemotrypsin like protease with specifity for large hydrophobic side chains and a trypsin like with preference for positively charged side chains ((Salter et al 2000). A highly potent option is cercarial elastase (reference).

These proteases could be used to cleave membrane associated Fret-pairs, or release other response mediators from a membrane-scaffhold. This would e.g. produce a color response in the sample.

Three key problems exist here:


 * Artificial triggering of protease secretion of potential circaria in the sample. This can be achieved by using linoleic acid residues which can mimic skin lipids.
 * Targeting of the response carrier protein to the extracellular membrane.
 * Releasing a sufficiently strong signal to be detected by simple means. As e.g. spores can be stored easily and used in desired quantities, an additional way exists in which we can increase total concentration of e.g. color-response molecules to be released, in addition to high-level expression mechanisms.

Wolbachia and Mansonella
Also the parasite Mansonella perstans needs an endosymbiont - a Wolbachia species - to survive and be virulent (Paper 1Paper 2). Unfortunately no information about the molecular mechanism of this interaction is given. Wolbachia bacteria are frequently found in insects, where they act as intracellular parasites, however they often have a symbiotic relationship. Wolbachia is an obligate intracellular endosymbiont without which the worm cannot survive in the host (targetting the bacteria with antibiotics is an effective treatment for Mansonella infections). The promlem seems to be that no extracelluar interactions are required between the worm and the bacteria as they are passed down horizontally to the offspring and thus never have to enter the worm cells in the first place.

Cryptosporidium parvum
This section has yet to be writen.

Vibrio cholerae
This is a major cause of diarrhea in areas of bad sanitation. So it would be great if we could detect it! We could use the autoinducers produced and detect them by expressing the receptors (for example CqsS) in our cell. For more information, read this paper, which tells you about the actual mechanisms of quorum sensing used by V. cholerae. However, we're concerned that in water, the cell density might be really low, so would autoinducers be produced at all?

Toluene, benzene, xylene rings
Contaminants of water - let's detect them!