Research to 'save the most valuable silk moth in the world'

Researchers from the University are developing a technique known as phage therapeutics to target harmful bacterial infections in Muga silkworms in order to protect them from disease.

Muga silk yarn is golden in colour and is produced only in Assam, India, by Muga caterpillars to form their cocoons. As one of the rarest and most valuable silks in the world, it remains an integral part of the tradition and culture there.

However, crops of Muga silkworms have been in decline over the last few years due to the growing presence of bacterial disease called Flacherie caused by the silkworm larvae eating infected leaves.

In an attempt to save the Assam silk industry, Dr Mahananda Chutia, a Visiting Post-Doctoral Fellow from Assam, has been working with Professor Martha Clokie in the University of Leicester's Department of Infection, Immunity and Inflammation to identify bacteriophages to treat the disease and to establish how, and when it is best to deploy them to the caterpillars.

Professor Martha Clokie has been investigating an alternative approach to antibiotics, which utilises naturally occurring viruses called bacteriophages, meaning 'eaters of bacteria', for nearly a decade at Leicester.

Dr Chutia, who is employed by the Indian Government's Central Silk Board as a Scientist, has been working on scientific developments within the field silk production, and advises farmers on improved methods, said: "In our model system at Leicester, we have found that the consumption of phages by caterpillars is a very effective method of preventing bacterial diseases.

"As well as its silk trade, Assam is known for its tea and farmers often spray pesticides to protect the tea leaves -- these sprays are thought to have reached the silkworms and have weakened them.

"Flacherie is the biggest killer of Muga caterpillars, and we have been trying to find out successful treatment options. I was aware of the work carried out at the University of Leicester looking at bacteriophages as an alternative to antibiotics and am so happy to be able to collaborate with the team to find out more. I am also thankful to the Department of Biotechnology, Government of India for their support."

The team at Leicester has been working with common white waxworms available in the UK, which are the caterpillar larvae of wax moths, because the Muga worm is only able to survive in the wild conditions found in Assam.

Professor Clokie said: "Dr Chutia began by learning techniques to isolate bacteria and phages and how to study the genetic sequences of the virus's genome to ensure viruses are suitable for development.

"He then applied his knowledge to a caterpillar model here in the lab, where he investigated what the best timings and dosages were in order to reduce infection in caterpillars. He has learned how to select appropriate viruses that can be used as therapeutics and he has successfully shown that he can prevent infection in caterpillars.

"It's a really good model because the caterpillars are small and white and it is really easy to tell when they are ill because they turn brown, and then black, before dying.

"Normally the phages would be injected into the caterpillar but we have managed to do it by putting these into their oral cavity. Ideally we would look to put the viruses onto the leaves that the caterpillar consumes, which would protect them from disease."

This model will inform the way in which he uses phages in Muga caterpillars and Dr Chutia is planning to apply the knowledge he has learned at Leicester when he returns to Assam to identify appropriate phages for the main causative agents of disease. If it is successful, this approach is expected to be used by the thousands of Muga growers where it could dramatically reduce the amount of caterpillars that are lost during production.

Dr Chutia added: "What we need to establish now is the cost-effectiveness of applying phages as a preventative measure to all Muga caterpillars, or just to those we know are infected.

"I will continue to collaborate with the University of Leicester when I return to Assam to identify and characterise phages and establish the most effective ways of using them in order to save the caterpillars from bacterial infection."