2024-10-01 06:50:20
Bacteria that colonize warm-blooded mammals, including pathogens like Escherichia coli, are constantly exposed to brutal variations in their environment, whether it be changes in temperature or fluctuations in pH. To survive, they employ sophisticated molecular mechanisms to adjust gene expression according to external conditions. One of these mechanisms is Rho-dependent transcription termination (TTRD), which utilizes the Rho protein to regulate the transcription of messenger RNAs. Two recent studies, conducted by chemists and biologists from CNRS and Vanderbilt University, shed light on the essential role of this mechanism in bacterial response to thermal stress and starvation.
The first study, published in Molecular Cell, focuses on the temperature variations that bacteria frequently experience. When they leave their host and its “warm” environment (37°C) for a cold medium, they undergo a “cold shock.” This shock slows down the production of proteins, which are crucial for bacterial survival. The team of scientists demonstrates how the Rho protein is involved in this process by regulating the production of essential messenger RNAs for the synthesis of proteins that help the bacteria withstand the cold. At high temperature (37°C), Rho interacts with these RNAs to halt their production, but at low temperature (15°C), this interaction is blocked, allowing the bacteria to produce the necessary proteins. Once acclimated, production is again slowed to conserve energy, ensuring a finely tuned and effective adaptive response.
The second study, published in PNAS, focuses on bacterial adaptation to pH fluctuations associated with cycles of famine and abundance. Indeed, during periods of nutrient abundance, such as easily degradable carbohydrates, bacterial metabolism releases rather acidic by-products that tend to lower the pH of the medium they are in. Conversely, during famine periods, bacteria feed on more complex nutrients whose degradation raises the pH. Bacteria must adapt to these pH fluctuations to maintain their internal balance and continue to function effectively. The team of scientists shows that a mutation in the Rho protein, Rho(R109H), makes its activity sensitive to pH variations, enabling bacteria to adjust their metabolic response according to the external environment and thereby optimize their survival in extreme conditions (famine or abundance). This mutation affects Rho’s ability to bind to RNAs and stop their transcription. In environments where the pH is often high, such as during famine periods, this mutation seems to help bacteria better regulate their metabolism by optimizing the use of available resources and facilitating the management of organic waste.
These results provide a new perspective on how bacteria that colonize humans and warm-blooded animals, including most pathogenic bacteria, utilize adaptive genetic strategies to survive and thrive in changing environments. This work reveals the importance of the Rho-dependent mechanism in this rapid adaptation and could have implications in the fight against bacterial infections.