Finding a new niche: mining for antibiotics in the nest of leafcutter ants

© Matt Hutchings

Tetraponera penzigi ants on their host Acacia trees. The swellings at the base of the thorns are the domatia which the plants have evolved to house the ants and their larvae.

The Microbiology Society is undertaking a project entitled A Sustainable Future as part of our 75th Anniversary, which aims to highlight the Sustainable Development Goals (SDGs) to our members and empower them to use their research to evidence and impact the goals. Earlier this year, we put a call out to our members to submit case studies in the following three areas: antimicrobial resistance, soil health and the circular economy.

This case study is written by Professor Matt Hutchings, who is a Professor of Molecular Microbiology at the University of East Anglia and a member of the Microbiology Society. It focuses on antimicrobial resistance; a naturally occurring process, whereby micro-organisms (bacteria, viruses, fungi and parasites) can change and adapt over time, either by modifying the target of the antimicrobial, or by developing and exchanging resistance genes.

Introduction the project

When it comes to antibiotics, it is said that resistance is inevitable and this certainly seems to be true when we look at all the antibiotics developed during the Golden age of discovery, which peaked in the mid-1950s. There are few, if any, clinically used antibiotics discovered during this time which are still effective and most of these, including penicillin, have had to be chemically modified or used in combination with other drugs to bypass resistance in disease-causing bacteria. The majority of the antibiotics used in medicine were first discovered from Streptomyces species, a genus of bacteria which can be isolated from soil anywhere in the world. More than 600 Streptomyces species have been discovered in soil over the last 80 years, but now we just rediscover the same species making the same antibiotics. This is called the rediscovery problem.

What are the challenges that this research/initiative addresses?

The challenge is to find new species of Streptomyces to make new antibiotics, which will ideally have a high barrier to resistance. That is, it will be hard for disease-causing bacteria, such as MRSA to become resistant. Given that soil has been well sampled, we decided to look in more unusual places. We knew that some insects form mutually beneficial symbioses with Streptomyces bacteria which they feed and house, in return for protection against disease. We decided to look for symbiotic Streptomyces bacteria to try and find new species that make unusual and potentially useful antibiotics.

What findings and solutions were provided by this research?

We searched the nests of the Kenyan plant-ant Tetraponera penzigi. These ants live inside hollow swellings called domatia which their host plants have evolved to house the ants. In return the ants protect the plants against large herbivores, including elephants. We reasoned that because these ants rarely contact the soil, we may be able to find new species of Streptomyces; and in fact we identified a very promising new strain and named it Streptomyces formicae (because formicae is Latin for ants). This strain makes antibiotics called the formicamycins, which are powerful against MRSA and other superbugs. Most importantly MRSA never becomes resistant to formicamycins under laboratory conditions, even when we grow them with very low, non-lethal concentrations of the antibiotics.

Why does this research matter?

It matters for a number of reasons. Firstly, we have shown that by searching in new ecological niches it is possible to discover new species of bacteria making new antibiotics which may eventually be used in the clinic. Secondly, it shows that we have a lot to learn about the ecology of these bacteria and the reasons why they make all these potent antibiotics, so there is a lot of interesting microbiology to be done. Thirdly, it was a great collaboration between several research groups from around the world, including the natural products chemists Professor Barrie Wilkinson and Dr Zhiwei Qin at the John Innes Centre, myself and Dr Rebecca Devine doing the microbiology at the University of East Anglia (UEA), Professor Naomi Pierce who is an ecologist at Harvard University, and Dr Dino Martins who is Executive Director of the Mpala Research Centre in Kenya. This shows that interdisciplinary science and international collaborations could provide solutions to some of the biggest problems faced by humans in the 21st century.

About the author

Professor Matt Hutchings is a Professor of Molecular Microbiology at the University of East Anglia. and a member of the Microbiology Society. More information about his work is available here.