Bochum researcher Dr. Janka Schmidt in front of a cryo-electron microscope of the cooperation partners at the Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons at Forschungszentrum Jülich.
The four project leaders of the Research Training Group “Microbial Substrate Conversion” (MiCon), with the decoded protein structure: Professor Julia Bandow, Professor Franz Narberhaus, Professor Eckhard Hofmann and Professor Lars Leichert (from left to right)
Microbiology Bacterium Uses Double Protection Against Plant Defenses
Plants know how to defend themselves against pathogenic microorganisms. In turn, pathogens have sensors to detect such defense mechanisms. What happens when plant and pathogen are locked in that duel.
A team from Ruhr University Bochum and Forschungszentrum Jülich in Germany has studied how plant-pathogenic bacteria protect themselves against their host’s defense mechanisms. The researchers focused on Agrobacterium tumefaciens, a common plant pathogen that uses two sensors to detect reactive oxygen species – toxic molecules plants release to damage the DNA, lipids, and proteins of invading microbes. One of these bacterial sensors, known as OxyR, had already been characterized in detail. In the current study, the team identified the structure and function of the second sensor, i.e. LsrB. The findings were published online in the journal Nucleic Acids Research on April 7, 2025.
“In the long term, insights into bacterial stress responses could facilitate targeted intervention of regulatory networks – both to combat infections and to optimize beneficial bacteria in biotechnology,” says Dr. Janka Schmidt, lead author of the study.
Two transcription factors act as sensors
Reactive oxygen species such as hydrogen peroxide, which is a common household bleach and disinfectant, impose oxidative stress on organisms: They trigger chemical reactions that can cause damage to DNA, lipids and proteins. To mount an effective defense, cells must first detect the presence of reactive oxygen species. This is achieved through redox sensors: molecules capable of undergoing reversible oxidation (donation of electrons) or reduction (gain of electrons). These sensors rely on specific cysteine side chains that can cycle between oxidized and reduced states without being damaged. In Agrobacterium tumefaciens, both identified sensors – OxyR and LsrB – are transcription factors, regulating the expression of genes involved in oxidative stress response.
Bacteria without redox sensors more susceptible to plant defenses
The researchers engineered Agrobacterium tumefaciens strains without the redox sensors OxyR and/or LsrB. These modified bacteria were susceptible to reactive oxygen species and were less able to infect plants – which highlights how important the two sensors are.
In order to understand the structure and function of LsrB, microbiologists, biochemists and structural biologists from Bochum and Jülich joined forces under the leadership of Dr. Janka Schmidt and Professor Franz Narberhaus. Using high-resolution cryo-electron microscopy images, they showed that LsrB contains four cysteine residues, which are perfectly positioned to form two redox-active pairs. Complementary biochemical analyses further confirmed that LsrB functions as a redox sensor.
Unlike OxyR, which responds specifically to reactive oxygen species, LsrB appears to play a broader regulatory role in coordinating both oxidative stress responses and virulence. The interdisciplinary team from Bochum and Jülich now aims to decipher this role in more detail in future.