Many animals have symbiotic relationships with bacteria, with some bacteria even living inside the cells of their hosts. However, only a few are able to infiltrate cell organelles, such as the nucleus. A remarkable group of bacteria, known as intranuclear parasites, have mastered the ability to colonize the nuclei of their hosts, which is impressive considering the nucleus is the control center of the cell. Despite this feat, little is known about the molecular and cellular processes that these bacteria use to infect and reproduce within animal hosts.
In a groundbreaking study published in Nature Microbiology, scientists from the Max Planck Institute for Marine Microbiology in Bremen, Germany, conducted the first in-depth analysis of an intranuclear parasite of animals. The parasite, Candidatus Endonucleobacter, infects the nuclei of deep-sea mussels from hydrothermal vents and cold seeps worldwide. This bacterium has the unique ability to penetrate the host nucleus and reproduce to over 80,000 cells, causing the nucleus to swell to 50 times its original size. The researchers aimed to understand how the bacterium infects and reproduces inside nuclei, as well as how it acquires the necessary nutrients for replication while keeping the host cells alive.
Through a combination of molecular and imaging techniques, the scientists discovered that Ca. Endonucleobacter feeds on sugars, lipids, and other cell components from its host, rather than digesting host nucleic acids like many other intranuclear bacteria. This feeding strategy ensures that the host cell continues to function long enough to provide the necessary nutrients for the bacterium to reproduce in vast numbers. Additionally, the bacterium produces inhibitors of apoptosis (IAPs) to suppress the host cell’s suicide program, allowing the bacteria to multiply without triggering cell death.
The discovery of IAPs in Ca. Endonucleobacter was a surprising finding, as these proteins are typically only found in animals and a few viruses, not bacteria. The researchers determined that the parasite likely acquired these genes through horizontal gene transfer (HGT) from its host, a rare occurrence where genetic material is transferred from a eukaryote to a bacterium. This finding expands our understanding of host-microbe interactions and sheds light on the complex strategies parasites have evolved to thrive within their hosts.
The implications of this study extend beyond understanding the interactions between parasites and hosts, as it may also provide valuable insights into parasitic infections and immune evasion strategies in other organisms. Furthermore, the research offers new perspectives on microbial evolution and pathogenesis, as well as apoptosis regulation, which has relevance for cancer research and cell biology. By unraveling the mechanisms used by intranuclear parasites like Ca. Endonucleobacter to thrive within host cells, scientists can gain a deeper understanding of the intricate relationships between pathogens and their hosts.
