What is a Virus?

A virus is a type of microorganism, or microbe. Unlike bacteria (another microbe), a virus is not a cell and is in fact more like a particle. This means they can't really do anything at all until they infect a living cell. Because of this, a virus isn’t considered ‘alive’ in a conventional sense as it cannot move or produce energy on its own. The only way a virus can survive and reproduce is by essentially hijacking a living animal or plant cell, taking over the cell’s internal machinery, and making a ‘virus factory’ to replicate its genetic code and produce more viruses.

Viruses are the most abundant lifeform on Earth – if you were to try to count them all, you would find about 5x10³¹ viruses (that means a number 5 followed by 31 zero's)! There are also over 100 million different types!

Viruses are also incredibly tiny, much smaller than bacteria. Typical viruses are only 20-300 nanometres in diameter (1 nanometre is only 0.000000001 metres). To put this into context, this is about 10 million times smaller than us as humans. If you do some quick calculations, you can find that between 500-1000 million common cold viruses (rhinoviruses) could fit on the head of a pin, or about 100 million coronavirus particles!

A virus consists primarily of its genetic material, either DNA or RNA, surrounded by a protein coat, called a capsid. This capsid protects the virus’ genetic material, and is sometimes surrounded by a second protective layer known as the envelope. These can come in many different shapes.

Viruses can infect animals and plants too, as well as humans. They can also be found in the ocean and can survive in the harshest of conditions, including polar ice caps, thermal vents, and even acid lakes!

The Project

What are we researching?

Our research group focuses on two main areas: first, we use data from 3D images to answer interesting biological questions; and second, we work on developing new software to make it easier to analyse the 3D image data we are interested in. Most of our team is from Diamond Light Source, the UK's national synchrotron (a synchrotron is a type of particle accelerator). As our research involves lots of different areas of science, the background of our team is split between biology, imaging, and computer science.

We work with many different types of 3D imaging data. Right now, we're working with data from a technique called Cryo Electron Tomography to answer questions about how cells change during a virus infection. You can find out more about this type of imaging in the Education tab at the top of the page.

Aerial view of Diamond Light Source on the Harwell Science and Innovation Campus in South Oxfordshire, UK.

What virus are we studying?

The virus we're working with here is a Reovirus. Reoviruses belong to a large family of viruses that infect a wide range of animals and plants. Some members of the family cause widespread disease, notably Rotaviruses, which are responsible for serious gastroenteritis (otherwise known as a "tummy bug"). In contrast, reoviruses themselves, whilst they do infect humans, do not typically produce any symptoms. Because of this, they are being trialled as possible anti-cancer agents, since they specifically replicate in many cancer cells activated for division. They are therefore a good starting point to try to understand the life-cycle of this family of viruses.

What is a virus factory, and why are we studying them?

In order to reproduce, a virus first needs to enter the body, which it can do through the nose, eyes, throat, and any open wounds for example. Once inside the body, a virus will bind to the surface of a host cell. However, a virus can’t necessarily gain access to every type of cell – it has to have a certain protein that ‘unlocks’ a specific type of cell. These proteins are called spike proteins and they sit on the outside of the virus envelope.

Once inside the host cell, the virus injects its genetic material into the cell. The presence of the virus DNA essentially tricks the cell into thinking that it is a part of the cell’s own DNA. It is through this that the virus hijacks the host cell’s inner workings, meaning that the cell replicates the virus genetic material instead of its own, creating this ‘Virus Factory’. This newly created virus DNA can then assemble itself into new virus particles.

By virus standards Reoviruses are quite large. They are made up of several layers that self-assemble in these factory-like structures that appear in an infected cell just a few hours after infection. These layers capture and protect the genetic material of the virus in the process.

As time goes on, particles are released from the cell in increasing numbers as triple-layered particles. The particles themselves have been well studied - they have been able to be isolated and their detailed structure has been determined. However the intermediate steps as the virus particles self-assemble inside the cells have not been imaged.

What we are doing now is using cryo-electron tomography to visualise virus particles in very thin slices cut from infected cells that have been frozen. Our aim is, ultimately, to understand the full life cycle: how the virus gets into the cell, replicates, assembles more copies of itself, and finally leaves the cell. In the 3D pictures here we have taken a snapshot 12 hours after infection. We are aiming to visualise the intermediate steps in the assembly process which have not been visible before, and to then work out how virus assembly is organised in time and space within the cell. Within this snapshot, there will be multiple stages of the virus.

Here are some example cartoons and reference images of each of the stages:

• The earliest stage is the star-like structure (leftmost in image above). This is the newly formed, empty shell of the virus.
• The next stage is the circular, but still empty structure (2nd from the left in image above). This is the expanded form ready to be filled with the RNA genome (the genetic material) of the virus.
• Next is the same circular, but now filled structure (3rd from the left in image above). This is the virus filled with its RNA genome.
• Last, is the circular, filled virus with a membrane around it (rightmost in image above). This is the fully packaged, enveloped virus.