Antiviral Molecules in Bacteria

Bacteria produce not only antibiotics against other bacteria, but also molecules with antiviral effects

9 June 2026

Researchers at Forschungszentrum Jülich, in collaboration with partners from Heinrich Heine University Düsseldorf, as well as from Marburg and Zurich, have shed light on the mechanism of action of the natural compound daunorubicin. The team was able to demonstrate how the molecule prevents the replication of bacteriophages—viruses that infect bacteria. The results have been published in the journal Proceedings of the National Academy of Sciences (PNAS).

Under normal infection conditions, the virus—a bacteriophage—uses the bacterial cell for reproduction. The bacteriophage’s takeover of the host’s metabolism is regulated by toxic, early-stage phage proteins. In the presence of the DNA-intercalating molecule daunorubicin, the infection is incomplete; however, early toxic proteins continue to be produced, which also lead to the death of the host cell. The release of infectious phage particles is thus prevented.

The characteristic smell of a forest floor comes, among other things, from the metabolic products of so-called streptomycetes. These soil bacteria produce a variety of biologically active molecules. More than two-thirds of the natural products used in medicine today are derived from such microorganisms.

The bacteria use these molecules to protect themselves against competing microorganisms. In addition to well-known antibiotics, they also produce substances that protect against bacteriophages.

Daunorubicin stops viral replication

A well-known example is daunorubicin. The molecule has long been used in cancer therapy and also possesses antiviral properties. In the recently published study led by Julia Frunzke from the Jülich Institute of Bio- and Geosciences, the researchers demonstrated that daunorubicin effectively inhibits the successful reproduction of various bacteriophages: During the infection of a bacterium by a bacteriophage, a mutual destruction process is triggered.

“We were able to show that daunorubicin halts or delays the infection cycle at an early stage,” said Frunzke. “As a result, toxic viral proteins—which are normally required in strictly regulated quantities for a successful infection—are produced in increased amounts. They kill the bacterial cell prematurely and thus also prevent viral replication.”

The soil bacterium Streptomyces is a well-known producer of small, bioactive molecules that can possess antibacterial, anticarcinogenic, and antiviral properties.

Enhanced effect of bacterial defense systems

Furthermore, daunorubicin also influences the bacteria’s natural defense mechanisms. “If additional bacterial defense mechanisms are present, the presence of daunorubicin enhances their effectiveness and enables the cell to survive without the viruses being able to reproduce within it,” says Dr. Larissa Ernst, first author of the study and a postdoctoral researcher in Frunzke’s group.

Implications for future phage therapies

The results provide new insights into the interaction of bacterial immune systems. This knowledge could help in the targeted further development of phage therapies. Such therapies are considered a promising approach for treating infections caused by antibiotic-resistant pathogens.

“The past few years have fundamentally changed our understanding of bacterial immune systems. With our research, we are helping to better understand how these different defense systems interact,” says Julia Frunzke. Since phage therapies are often combined with antibiotics, a detailed understanding of bacterial defense mechanisms is crucial for using such approaches even more effectively in the future.

Original publication: Larissa Ernst, Cornelia Gätgens, Bente Rackow, Nadiia Pozhydaieva, Elyès Gaaloul, Aileen Krüger, Johannes Seiffarth, Michelle Bund, Vivien Joisten-Rosenthal, Dietrich Kohlheyer, Björn Usadel, Alexander Harms, Katharina Höfer, Julia Frunzke; DNA-intercalating antiphage molecules trigger abortive infection through ‘mutual destruction’ and synergize with bacterial immunity; PNAS 123 (23) e2602073123, 3. Juni 2026, DOI: 10.1073/pnas.2602073123

Full press release from Heinrich Heine University Düsseldorf (in German)

Contact

Prof. Dr. Julia Frunzke

Head of Bacterial Networks and Interactions

Institute of Bio- and Geosciences (IBG)
Biotechnology (IBG-1)

Building 15.21 /
Room 4028

+49 2461/61-5430

E-Mail

Björn Usadel

Institute of Bio- and Geosciences (IBG)
Bioinformatics (IBG-4)

Building 06.5 /
Room 2002

+49 2461/61-9503

E-Mail

Media Contact

Dr. Regine Panknin

Pressereferentin

Building 15.3 /
Room R 3028

+49 2461/61-9054

E-Mail

Further Information

Institute

Biotechnology (IBG-1)

IBG-1 researchers explore innovative technologies for developing enzymes, production strains, and bioprocesses.

Research Group

Bacterial Networks and Interactions

Prof. Dr. J. Frunzke - We study phage-host interaction to harness viral diversity for metabolic reprogramming and next-generation antimicrobials.

Biotechnology

(in German) 5.8 million euros for a priority program on virus-host interactions

Priority Program SPP 2330, coordinated by Prof. Dr. Julia Frunzke, is conducting research on phage-host interactions. The program will now receive funding from the German Research Foundation (DFG) for another three years.

Announcement

(in German) New Sonderforschungsbereich: Microbial Networks

The DFG is funding a new Collaborative Research Center at HHU: Microbial Networks. The Institute of Biotechnology at Forschungszentrum Jülich is also participating.