Home Medizin Genetischer Mechanismus schützt Bakteriengemeinschaften vor viralen Bedrohungen

Genetischer Mechanismus schützt Bakteriengemeinschaften vor viralen Bedrohungen

von NFI Redaktion

Just as humans struggle to survive the COVID-19 pandemic, bacterial cells need social distancing to ward off viruses. But in some situations, such as elevators or within the candy-colored bacterial structures known as „pink berries,“ it is simply not possible to remain separated from each other.

The communal, multicellular pink berries look like spilled Nerds or Pop Rocks and are found on the submerged surface of salt marshes in and around Woods Hole. New research conducted at the Marine Biological Laboratory (MBL) provides evidence that a genetic mechanism might help the berry-forming bacteria – and others like them – protect against diseases. The study, published this week in the Proceedings of the National Academy of Sciences, also has implications for understanding the development of single-celled organisms like bacteria into complex multicellular organisms, including humans.

„It tells us about the challenges we faced when we were still little balls of cells. When you form multicellular structures, you have to develop some pretty fancy immune defense systems to stay alive.“

Lizzy Wilbanks, MBL Whitman Fellow and microbiologist at the University of California, Santa Barbara

Mysterious, Mutation-Inducing Systems

Wilbanks first encountered the pink berries as a graduate student in the MBL course „Microbial Diversity.“ These spherical aggregates are among the structures that bacteria form when genetically similar individuals sit closely together and coordinate their activities. The pink berries are colonized by a bacterium species called Thiohalocapsa PSB1, which feeds on sulfur and light, as well as a relatively small number of other symbiotic bacteria. Through cooperation, these cells create oxygen-free pockets that could poison them and reach the necessary mass to settle safely in their ideal habitat.

Like all organisms, these cooperative microbes are at risk of being infected with viruses from their environment. Pink berries and other multicellular bacteria have an increased need for protection, as they consist of genetically similar cells packed closely together, allowing no social distancing.

„It’s a perfect cocktail for an epidemic that wipes everything out,“ says Wilbanks.

Through her colleague Blair Paul, a research assistant at MBL, Wilbanks learned about an unusual genetic mechanism that was abundant in Thiohalocapsa. This system, known as Diversity Generating Retroelements (DGRs), contains DNA segments that are transcribed into RNA and then back into DNA through a error-prone process, leading to mutation in a target gene.

In this way, DGRs introduce many new genetic variations, the raw material for adaptation, at specific locations in the genome. While scientists have found these systems in viruses, bacteria, and other microbes called archaea, they do not fully understand how the microbes use them.

Wilbanks and Hugo Doré, a postdoctoral researcher in her lab and the first author of the study, began to discuss what DGRs could do for Thiohalocapsa. Through their research, they learned that the target genes of DGRs contain components related to those found in the immune system of multicellular organisms, including humans, plants, and even some fungi. The similarity to parts of the immune system of other organisms led the researchers to believe that DGRs could diversify sensor proteins in Thiohalocapsa for defense against pathogens, similar to the antibodies of our own immune system.

All living organisms need to recognize threats they have never encountered before. Humans and other vertebrates solve this problem by shuffling and mutating genes for their sensor proteins (antibodies) to produce a diverse army of guardians. While recent research has shown that many components of our innate immune system have evolved from bacterial ancestors, scientists have never before seen anything like our hyperdiverse antibodies in bacteria.

A Widely Shared Immunological Connection

The team first comprehensively investigated DGRs in bacteria and archaea, focusing on the gene responsible for the reversion of RNA to DNA. This method divided the DGRs of bacteria and archaea into two groups. Within the group to which Thiohalocapsa belongs, they found that 82 percent of the DGRs belonged to microbes forming multicellular, cooperative structures, similar to pink berries. Although they were related to remotely related microbes, the changes in the DGRs tend to affect the same genes of the immune system as in Thiohalocapsa.

When examining hundreds of individual pink berries, they found that DGRs had diversified 14 out of the total 15 target genes in active Thiohalocapsa. However, the extent of variation found for these genes varied depending on the location where the pink berries were collected. The viruses in pools in the same marsh area may vary – perhaps the reason for the differences observed by the team.

„The next frontier is to see what Thiohalocapsa is actually doing with its DGRs in the environment,“ says Wilbanks.

This research not only provides insights into the evolution of life but also has practical implications. Wastewater treatment plants use multicellular bacteria to remove nutrients that can harm local ecosystems, and researchers at federal and industrial levels are exploring a variety of other applications for artificially produced microbial clumps. These microbial structures face the same challenge – virus epidemics – as pink berries. In developing these microbial systems, it makes sense, according to Wilbanks, to mimic the DGR-based immunity of wild community bacteria.

Quelle:

Meeresbiologisches Labor

Zeitschriftenreferenz:

H. Doré, H., et al. (2024). Gezielte Hypermutation mutmaßlicher Antigensensoren in mehrzelligen Bakterien. Verfahren der Nationalen Akademie der Wissenschaften. doi.org/10.1073/pnas.2316469121.

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