Safety

When we decided to engineer a biological system able to produce ethylene, we looked at all the existing natural pathways. We firstly checked the plants ethylene producing pathway.

An unwanted byproduct is produced in the last step of ethylene synthesis: hidrogen cyanide, an highly toxic gas that inhibits the cytochrome C oxydase enzyme. At very low concentration (around 300ppm) it can kill a human within 10 minutes. Plants however have a detoxyfication mechanism that gets rid of this hazardous acid.That's why we don't die when we eat a fruit!

This pathway would have been the easiest choice for us to produce ethylene because it already contains SAM synthetase that could have been exploited even for methyl salycilate production. Although we went for another pathway for several reasons: first it would have been lethal for us, second we have had to insert the detossification system in the complete circuit, for it is also toxic for the poor bacteria; last but not least we are not sure that the detossification enzyme would have worked. In fact plants enzymes often have glycosilisation pattern that our chassis (e. coli and b. subtilis) can not reproduce. In order to avoid these problems, we quitted this path and focused on a more interesting one. Pseudomonas Syrigae pv., a plant pathogen bacteria, is able to produce ethylene explointing only one enzyme. 2-Oxoglutarate Oxygenase/Decarboxylase enzyme takes 2-Oxoglutarate as substrate and transforms it into ethylene + water + carbon-dioxyde. Goto M. Plant and Cell Physiology (2012) 26, 141-150.