Archaea are microorganisms that were only discovered in the 1970s, and scientists still have a lot to learn about them. One challenge is that archaea are difficult to raise in the laboratory. As of 2020, only six of the 27 proposed archaeal phyla had been grown in the lab. But scientists are starting to learn more about these mysterious microbes.
In a new study in Science Advances, researchers have outlined the structure and function of a kind of molecular dagger used by haloarchaea. These contractile infection systems can have a significant influence on the microbial community or microbiome that certain archaea reside in.
Microbes have been competing for space and resources in a kind of microbial arms race for many years. In this study, the investigators wanted to shed light on how haloarchaea, which love to live in extremely salty places and carry contractile injection systems (CISs), behave in microbiomes.
This research assessed the antagonistic behavior of these archaea, which can kill or infect other cells. This study focused on the relationship between a haloarchaeon called Halogeometricum borinquense, which carries a CIS, and another haloarchaeon called Haloferax volcanii. The scientists showed that H. borinquense attacks H. volcanii, which then breaks open or stops growing. But this behavior only happens when the two cells are actually in physical contact, so a CIS is also required for this interaction.
Cryo-electron tomography was used to visualize the H. borinquense CIS as it attached to the cell envelope of H. volcanii. The effort revealed that there are structural and evolutionary similarities to another CIS called type six secretion systems (T6SSs) that are found in some Gram-negative bacteria.
The researchers also studied gene and protein expression, which revealed several toxin-immunity pairs. These allow an attacking cell to kill other cells while avoiding doing any damage to themselves in the process.
Other haloarchaeal species were found to carry gene clusters that point to the presence of other CIS mechanisms. The researchers suggested that this CIS is a conserved process that has been retained in multiple types of archaea.
Archaea also seem to have the potential to affect the compositions of microbiomes and the interactions among microbes, especially in environments that are rich in salty water.
Sources: ETH Zurich, Science Advances