Symbiotic bacteria are a Trojan horse in the fight against pests

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Scientists have developed a cool new technique for getting targeted gene control into insects, which could offer a flexible tool for the biological control of pests as well as disease vectors.

Insects represent major agricultural pests and vectors for many human diseases. One powerful weapon in the control of insects is a technique known as RNA interference (RNAi), which involves introducing molecules of RNA to target the messenger molecules controlling gene expression, preventing particular genes from taking effect. These techniques could have major applications for biological control, but scientists have struggled to apply this well-established laboratory technique to wild species that need to be controlled, such as the kissing bug (Rhodnius prolixus), which spreads the tropical parasitic disease Chagas disease. New research published in Proceedings of the Royal Society B shows that that beneficial bacteria living naturally inside insects can be used as a Trojan horse to deliver RNA interference direct to the pest’s cells.

RNA interference (RNAi) is a natural phenomenon, first discovered in 1998, which biologists have harnessed for experiments – it uses to target specific genes and prevent their expression. mRNA is the messenger molecule of the cell – it carries messages from DNA to the ribosomes where it can be converted into proteins, and it is the proteins that enact the role of the gene, whatever that might be. RNAi in the lab uses specially designed RNA molecules, which target the mRNA of a particular gene and destroy or deactivate it, preventing it ever becoming protein and having any effect. RNAi has been an incredibly useful tool for studying the effect of individual genes – prevent a gene from functioning and you can begin to understand its role based on the symptoms of its loss. But it’s use as a tool to control pests has been limited by the difficulties of getting the RNAi molecules into the organism you want to target. Now, researchers have come up with a possible route in, using bacteria that the pest already trusts as a cellular Trojan horse.

The team of researchers at the Swansea University genetically engineered symbiotic bacteria (Rhodococcus rhodnii) taken from the kissing bug to produce RNA molecules that interfere with the bugs’ fertility genes. They then fed the bugs on blood spiked with these engineered bacteria, allowing them to infect the bug and move to its gut. The technique was extremely effective – the Trojan bacteria caused a 70% reduction in the number of offspring produced by the bug, did not elicit a measurable immune response, and were able to survive inside the gut for more than 250 days. Their longevity gives this technique a major advantage over traditional RNAi – the bacteria keep on pumping the compounds into the host for weeks, even months after treatment.

In the same paper, the authors report using the technique to kill the larvae of an agricultural pest, the western flower thrip (Frankliniella occidentalis), proving that this new method could be applicable to a wide range of problem insects.

Want to Know More?

RNA – Ribonucleic Acid – is a single-stranded version of DNA – Deoxyribonucleic acid. It is used as a messenger molecule (mRNA), as a signalling molecule (tRNA and microRNAs) and plays many other important roles in the cell, which we are only just beginning to understand.

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