Q and A with Sarah Worsley

Sarah is a PhD student working with Matt Hutchings (School of Biological Sciences, UEA and co-supervised by Colin Murrell, School of Environmental Sciences, UEA). Visit Matt’s website to find out more about this exciting work.

What is the background of your work?

Almost all eukaryotic organisms interact closely with a large number of microorganisms that make up what is known as the organism’s “microbiome”. Many of the microbial members of this microbiome are known to be of benefit to their host. I’m interested in a group of bacteria in the genus Streptomyces that are thought to offer protection to their host by producing a large number of different antibacterial and antifungal compounds. I’m particularly interested in the interaction between Streptomyces and plant roots and aim to increase our understanding of the mechanisms that allow their recruitment to roots. I also study leafcutter ants which use their leaves to farm a fungus for food- they use the antibiotics produced by Streptomyces bacteria (which accumulate and grow on the cuticle of the ant) as weedkillers to prevent the spread of pathogenic infection in their fungal gardens. I am interested in understanding the mechanisms underlying the recruitment of Streptomyces to these two microbiomes because this may help us to enhance their representation in the microbiomes of other species, such as crops or the human microbiome, and thus increase protection against pathogens.

What is the aim of your work? 

I aim to understand how large organisms such as plants and ants recruit beneficial species of microorganism to their microbiome, particularly Streptomyces bacteria which are thought to offer them protection against pathogens. We think that the host organism may provide them with nutrients which are either specifically metabolised by this group of bacteria, or are provided in such large quantities that the bacteria can produce lots of antibiotics and out-compete other organisms during the colonisation of the larger organism. I aim to detect the flow of nutrients from the host to their bacteria by tracking a stable isotope (13C) label from the host to the DNA of the bacteria that metabolise the nutrients.

What have you learnt so far?

Streptomyces that I isolated from plants are capable of inhibiting the growth of many human and plant pathogens. Their genomes also show large biosynthetic potential. They can also be seen to colonise the inside of roots when expressing a green fluorescent protein. My sequencing data also shows Actinobacteria (the phylum to which Streptomyces belong) are abundant in the roots and rhizosphere or Arabidopsis thaliana. Leaf cutter ants recruit a diversity of Streptomyces species that can produce multiple antibiotics to their microbiome.

What do you hope to learn?

By sequencing 13C labelled bacterial DNA associated with the roots of labelled plants I will be able to see if Streptomyces species are capable of eating plant derived resources. I also hope to work out if particular plant defence hormones are specifically being metabolised by this group of bacteria or if their metabolism is more general. I also hope to track 13C from leafcutter ants to their cuticular bacteria to work out if Streptomyces are specifically being fed by the ant. Imaging mass spectrometry may also help us to distinguish the identity of the ant-supplied nutrient and work out if this nutrient regulates antibiotic production.

What does your work prove, why is it important and how is it applicable?

Antibiotic resistance is a problem for human medicine and in agriculture. We need to find new antibiotics. If we can work out how beneficial, protective bacterial species are recruited to microbiomes and how microbiomes are assembled we may be able to develop techniques to enhance the representation of species that we want (such as those that offer protection) over the ones that we don’t want. This could have implications for the health of many organisms including crop plants and humans.

Why did you choose to do a PhD?

I have always had an interest in the problem of antibiotic resistance and the search for alternative treatments to alleviate this problem. I am also fascinated by the complexity of microbiomes. Both the leafcutter ant system and the plant root microbiome are extremely exciting systems to work on and my PhD allows me to combine these two interests. I also love the process of doing science, from formulating the questions to doing the experiments to test them. I can’t think of a more exciting job than being a scientist!

Interview by Emily Kench, ELSA Intern 2017

Earlham institute
Quadram Institute Bioscience
John Innes Centre
The Sainsbury Laboratory
University of East Anglia

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