Insect repellents can help prevent serious diseases such as malaria, as well as nuisance bites. DEET is the most widely used mosquito repellent worldwide and is often still the most effective. However, some mosquito populations are evolving resistance to DEET, so alternatives are needed.
Many studies have shown that nepetalactone is an effective insect repellent, with some even finding it more effective than DEET. Yet while catnip in various forms has long been used as a repellent, mass production of a cheap version isn’t feasible using the plant.
Instead, Vincent Martin and his colleagues at Concordia University in Canada added eight extra genes to a strain of yeast, including some key enzymes from catnip, to create a chemical pathway for nepetalactone production.
“We still need to do some work to boost levels,” says Martin. “I don’t believe it will be a huge hurdle.”
The main obstacle is that the process also produces a substance toxic to the yeast. However, other groups engineering yeasts to produce various chemicals have had the same problem, and have solved it, Martin says.
The researchers are now in discussion with companies about getting the investment needed to develop the yeast further and commercialise the process.
They will also need to look at whether nepetalactone acts as a cat attractant as well as an insect repellent. “If you are walking around with this molecule on you, will there be no mosquitoes, but all the neighbourhood cats chasing you around? To be honest, I don’t know,” says Martin. “That’s certainly something we’re going to have to investigate.”
DEET has disadvantages, too, however, including the fact that it dissolves some plastics and can damage synthetic clothing and devices such as watches and glasses.
A growing number of chemicals that once could only be obtained from plants can now be brewed in vats by genetically engineered organisms. One of the first was the antimalarial drug artemisinin.
Proponents say this approach is more environmentally friendly than growing a lot of plants just to extract one rare chemical. “If we are going to use land to grow things, let’s grow valuable foods rather than these molecules,” says Martin.
Reference: bioRxiv, DOI: 10.1101/2021.08.30.458239
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