Research Complex, Rosalind Franklin, Diamond Light Source and Oxford University collaborate on high-res imaging which reveals organisational behaviour of chlamydia-causing bacteria

A powerful new imaging technique has helped researchers at Research Complex at Harwell, the Rosalind Franklin Institute, Diamond Light Source and Oxford University shed light on an important class of bacteria responsible for a range of diseases in humans and animals.

Best known as the cause of a sexually transmitted infection, Chlamydiae are a diverse group of pathogens whose strains can also lead to pneumonia and blindness.

Chlamydiae form communities inside the cells of their hosts in compartments known as inclusions. During their life cycle they transition between two forms, each responsible for either replication within the cell or infection of other cells.

But little is known about how this system works in practice, or how the nature of these communities influences the individual bacteria within them – knowledge that could open up new treatment avenues for the diseases caused by Chlamydiae pathogens.

Senior author of this new study – which uses cutting-edge Cryo-Soft X-ray Tomography (Cryo-SXT) techniques to investigate the bacteria – is Dr. Maud Dumoux. Dr. Dumoux, Technology Lead for Cryo-imaging at the Rosalind Franklin Institute said:

Chlamydiae are unique bacteria, as they grow only inside cells. Most strains form a specialised compartment in which hundreds – sometimes thousands – of bacteria multiply and differentiate themselves between non-infectious and infectious forms, preparing for release into the wider environment to infect other cells in the body.

How communities of Chlamydiae organise these events, and how each community has an impact on its individual bacteria, are intriguing questions that that have implications beyond this particular pathogen.

In this paper, the research team sought to uncover how communities of Chlamydiae bacteria regulate and organise their space, and how basic factors such as concentration and size of bacteria can impact the life cycle. To do this, the researchers used the cell culture room at Research Complex and Diamond’s Cryo-SXT technology – a combination of X-ray tomography and high-resolution fluorescence microscopy that allows scientists to capture intra-cellular behaviour and interactions quickly and in intricate detail.

Dr. Dumoux explains:

I was based at the Research Complex when most of the work was completed so we used the cell culture room using human pathogen which has been possible thanks to the infrastructure in place at the Research Complex, which included the room, equipment, autoclaving and health and safety.  Our student also had direct access to Diamond Light Source computing thanks to a direct connection. Surprisingly, we found that concentration of bacteria is not correlated with differentiation into the infectious form. In other words, at the time we observed the infected cells, a high concentration did not trigger preparation for exiting the cell and infecting other cells.

However, we did show that higher concentrations lead to smaller individual bacteria, whereas bacteria given space can reach very large volumes – similar to the apocryphal idea that fish will grow to the size of their pond.

This is very interesting because it demonstrates, as is often the case in life science, that things are not black and white. Here, there are shades of grey as the bacteria adapt or respond to their environmental pressures. It also opens up new questions about whether different types of bacteria have different roles within the community.

The researchers conclude that each ‘inclusion’ (specialised compartment of bacteria) operates as an autonomous community that influences the characteristics of individual bacteria within it – and that bacterial concentration is a key factor in determining those characteristics. With Cryo-SXT now established as a useful and rapid technique for studying Chlamydiae, future research will shed light on the evolution of infection and communication between bacterial communities, which could open up new therapeutic opportunities.

To find out more about Research Complex’s cell culture room and Cryo-EM, or to discuss potential applications, please contact Head of Scientific Support: zuzanna.lalanne@rc-harwell.ac.uk

The paper ‘Single Cell Cryo-Soft X-ray Tomography Shows That Each Chlamydia Trachomatis Inclusion Is a Unique Community of Bacteria’ is published in the journal Life.

Description of image:

Observation using cryo-SXT and characterisation of HeLa cells infected by C. trachomatis. HeLa cells infected with C. trachomatis for 24 hpi and observed using cryo-SXT with a 25 nm zone plate (A,B,D) or 40 nm zone plate (E). Mit: mitochondria, N: nucleus, EB: elementary body, RB: reticulate, IM: inclusion membrane, ER: endoplasmic reticulum body, LD: lipid droplets black arrow: inner membrane invagination; (B) corresponds t the box in A and highlights the presence of the pathogen synapse with the T3SS array (white arrow heads); (C): from Dumoux et al. (2012), TEM of the pathogen synapse for reference. D: host cell cytoskeleton. Fig.1, Phillips et al. Life (2021).