Decipher the role of late lytic genes activator, a key determinant of active lysogeny in Listeria monocytogenes

Project Information

BacPro

Grant agreement ID: 101107942

DOI

10.3030/101107942

Project closed

EC signature date 26 June 2023

Start date 1 October 2023

End date 30 September 2025

Funded under

• Marie Skłodowska-Curie Actions (MSCA)

Total cost

No data

EU contribution

€ 200 538,24

Coordinated by

TEL AVIV UNIVERSITY
Israel

Periodic Reporting for period 1 - BacPro (Decipher the role of late lytic genes activator, a key determinant of active lysogeny in Listeria monocytogenes)

Reporting period: 2023-10-01 to 2025-09-30

Summary of the context and overall objectives of the project

Foodborne infections caused by Listeria monocytogenes remain a major public-health concern worldwide. This bacterium can survive in many environments, including food-processing facilities and the human body, making it difficult to control. Surprisingly, Listeria also carries viruses called prophages, which live quietly inside the bacterial genome without killing their host. Although these prophages lead to bacterial killing under stress, they seem to have evolved to support bacterial survival in the mammalian environment.

The BacPro project set out to understand how these prophages influence the behaviour and survival of Listeria, especially when the bacterium infects a mammalian host. The focus was on a phage protein called LlgA, which normally activates phage genes involved in viral reproduction. Interestingly, these genes remain off when Listeria is inside a host, and the reasons for this were unknown before the project.

The project’s overall objective was to uncover how the bacterium controls these viral genes and how this silent cooperation between bacteria and their resident prophages supports infection. By identifying the molecular signals that switch phage genes on or off, the project contributes to a better understanding of Listeria survival strategies as a pathogen.

These insights have broader importance: understanding how prophages shape bacterial virulence can support efforts to design new antimicrobial tools, phage-based therapies, and food-safety strategies. The results of the project help address key public health needs by improving our understanding of how dangerous bacteria remain resilient in the environment and within the human body.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

During the project, I conducted a series of experiments to understand how the phage regulator LlgA functions under stress and during Listeria infection of mammalian cells, seeking the mechanism that controls its activity in the mammalian environment. The work combined molecular biology, genetics, protein analyses, and infection models.

One of the major achievements was the discovery that LlgA is produced by the phage, but becomes unstable and quickly broken down at body temperature. This finding helps explain why the phage genes controlled by LlgA remain silent during infection. By comparing conditions similar to the outside environment (30°C) with those found inside the human body (37°C), the project showed that Listeria uses temperature as a signal to control this phage regulator.

The project also examined how bacterial regulatory proteins compete with the phage regulator. Early results showed that certain bacterial factors can bind to the same DNA regions as LlgA, acting as natural “blockers” that prevent the virus from activating its genes. This revealed a new way in which the bacterium keeps the virus under control and maintains a stable relationship during infection.

Finally, the project identified bacterial proteases- enzymes that break down proteins-that may be responsible for degrading LlgA at higher temperatures. This opens new scientific questions about how bacteria use their own machinery to fine-tune viral activity.

Together, these findings provide new insights into how Listeria and its resident prophages interact. They help explain why phage genes remain inactive inside the host and reveal several molecular players involved in maintaining this delicate balance.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The BacPro project produced several results that advance our understanding of how bacteria and their resident prophages cooperate during infection. Before this project, little was known about how Listeria maintains viral genes in an inactive state while benefiting from the presence of prophages. The findings go beyond the current scientific knowledge in several important ways.

First, the project uncovered that temperature-dependent protein instability is a key mechanism used by Listeria to control the viral regulator LlgA. This suggests that the bacterium uses environmental cues- such as the shift from room temperature to body temperature- to decide when viral genes should remain silent. This type of thermoregulation in phage control has not been described before and offers a new concept in host–virus interactions.

Second, the project showed that bacterial regulatory proteins directly compete with a viral regulator for control of the same genes. This finding reveals a previously unknown layer of interaction in which the bacterium actively suppresses viral activity through its own transcription factors. This type of competitive regulation highlights a sophisticated cooperation between bacteria and prophages.

Third, the identification of specific bacterial proteases that contribute to the degradation of LlgA provides a new direction for future research. Understanding which enzymes break down viral proteins could help identify potential targets for antimicrobial development, especially for pathogens where prophages play an important role in virulence.

These results pave the way for several future opportunities:
• Further research is needed to fully map the bacterial and viral proteins involved.
• Potential applications in phage therapy, where controlling phage activation is crucial.
• Possibilities for developing new strategies in food safety and public health monitoring.

Overall, the project provides new scientific ideas and tools that microbiologists, phage researchers, and biotechnology developers can further develop.

Images attached separately illustrate the project background, scientific approach, and key concepts.