Paralytic
Shellfish
Poisoning
POSSIBLE SYNBIO SOLUTIONS
The problem
Current solutions
Shellfish extract testing and issuance of wide shellfish harvesting bans
◦ --standardized extract, inject into a mouse, time it’s death
Only done in high risk areas with marine labs
Broad ban effects areas only moderately at risk
A future solution?
Detection versus Neutralizing
Saxiphilin in the bullfrog neutralizes STX, but it is expressed broadly and by the time human
symptoms emerge it is hard to block effects by competitive binding
Approaches have used radiolabelled saxiphilin fragments diagnostically
Initial goal was to form a sensor out of saxiphilin fragments to selectively produce a pigment only
when bound, and package this as a paper sensor
Sensor design is hard!
Toehold sensor approach
Not nearly as good as directly testing for the toxin because saxitoxin bioaccumulates
But a proven sensor design method in paper diagnostics that I haven’t used before, will tell me
whether organisms currently producing STX are in a visible bloom
Toehold sensor design
Sequence and design
Do not want to generate an active saxitoxin sequence, obviously
Chose a 90 base region from the middle one of two necessary STX genes as a recognition
sequence
Created two constructs, one with toehold sensor for that sequence followed by GFP, one with the
sequence itself
Test methodology is to grow the toehold sensor on it’s own, lyse, look for GFP
Grow STX sequence. Add lysed STX sequence to toehold lysate. Hopefully see GFP production.
Future work and issues
RNA sensor – will need to lyse microalgae in a bloom and see if enough active RNA is released to
trigger the riboswitch
Direct toxin sensor – will want to continue trying to develop direct sensor based on saxiphilin
binding
Saxitoxin is mucosally absorbed, so direct inactivation in cases of unexpected poisoning seems
difficult. Focus will remain on sensor based approaches.
Aim 1) demonstrate sensors
Aim 2) sensor packaging, storage, and lab testing
Aim 3) field validation
Ethics, Equity, and Biosecurity
Ethics – Positive outcomes could reduce the necessity for routine animal testing
Equity – Climate-related rise of PSP in low resource nations are cause for great concern. We
cannot depend on high expense marine labs in these settings.
Biosecurity – Saxitoxin is a listed agent of concern. In this case, care has been taken not to
synthesize gene fragments that could be assembled into an active toxin. Improved testing
capabilities seem to only benefit any biosecurity considerations.
