New research shows that Candidatus Nanohaloarchaeum antarcticus, a DPANN archaeon from an Antarctic hypersaline lake called Deep Lake, behaves like a parasitic predator that rapidly kills its host, Halorubrum lacusprofundi.
Electron microscopy showing Candidatus Nanohaloarchaeum antarcticus attached to its host, Halorubrum lacusprofundi. Image credit: Joshua N. Hamm.
“Archaea is one of three lineages of life, alongside Bacteria and Eukarya (organisms whose cells have a membrane-bound nucleus, including plants and animals),” said Dr. Yan Liao, a microbiologist at the University of Technology Sydney.
“They are widespread and play a crucial role in supporting Earth’s ecosystems.”
“They are less studied and understood than the other lineages. However, archaea provide clues about the evolution of life on Earth, as well as how life might exist on other planets.”
“Their unique biochemistry also holds promising applications in biotechnology and bioremediation.”
“They have been found thriving in very acidic boiling hot springs, deep-sea hydrothermal vents at temperatures well over 100 degrees Celsius, in hypersaline waters like the Dead Sea, as well as in Antarctica.”
Candidatus Nanohaloarchaeum antarcticus was collected from the cold and hypersaline Deep Lake in Antarctica by University of New South Wales Professor Ricardo Cavicchioli.
This species is a member of a group called DPANN archaea, which are much smaller than other archaea, with very small genomes and limited metabolic capabilities.
The study reveals it depends on host microbes, particularly other archaea, to survive.
“This is the first time such aggressive behavior has been observed in archaea,” said Dr. Joshua Hamm, a microbiologist at the Royal Netherlands Institute for Sea Research.
“In many ways, the activity is similar to some viruses. It leads us to re-evaluate their ecological role in the Antarctic environment.”
Very few DPANN archaea have been cultivated in the lab, and the authors developed new techniques, including unique sample staining, live fluorescence microscopy, and electron microscopy, to visualise the internal parts of the host cells and track interactions between DPANN archaea and their hosts.
They stained the host, an archaeon called Halorubrum lacusprofundi, and Candidatus Nanohaloarchaeum antarcticus, with non-cytotoxic dyes that glow with different colors when exposed to laser light.
“This allowed us to observe the organisms together over extended periods and identify the cells by color,” Dr. Liao said.
“We saw DPANN parasites attach, and then appear to move into the host cell, leading to the host cell’s lysis or bursting open.”
“Predators are important players in ecosystems because when they kill their hosts, they not only feed themselves but also make the remains of the host cells available for other organisms to feed on,” said Dr. Iain Duggin, a microbiologist at the University of Technology Sydney.
“This allows other microbes to grow and prevents the host organism from hoarding nutrients.”
“The DPANN archaea we investigated appear to play a much more significant role in ecosystems than realised.”
“A parasitic or infection-like lifestyle of these archaea may be common.”
The results appear in the journal Nature Communications.
_____
J.N. Hamm et al. 2024. The parasitic lifestyle of an archaeal symbiont. Nat Commun 15, 6449; doi: 10.1038/s41467-024-49962-y
