Aggressive predatory behavior discovered in tiny single-celled organisms

Archaea, a unique group of single-celled microorganisms, thrive in the most unexpected places, including a remarkable aquatic ecosystem in the heart of Antarctica – Deep Lake.

Despite temperatures plunging to -20°C, Deep Lake remains unfrozen throughout the year, thanks to its high salt content.

This icy oasis is far from barren; it teems with life, particularly archaea, whose diverse and intriguing characteristics have captivated microbiologists.

Among these ancient life forms, DPANN archaea stand out, revealing a fascinating glimpse into the evolution of life on Earth and the potential for life beyond our planet.

Unraveling the mysteries of archaea

This noble group of organisms – neither bacteria nor nucleus-bearing eukaryotes – has been under intense study by a dedicated team of microbiologists, including Dr. Yan Liao and Professor Iain Duggin from the University of Technology Sydney (UTS).

“Archaea is one of three lineages of life, alongside Bacteria and Eukarya (organisms whose cells have a membrane-bound nucleus, including plants and animals). They are widespread and play a crucial role in supporting Earth’s ecosystems,” explained Dr. Leo.

The team discovered that archaea are not only widespread across various extreme environments but also instrumental in maintaining Earth’s ecosystems through processes such as nutrient cycling and methane production.

An unexpected discovery

In collaboration with Dr. Joshua Hamm from the Royal Netherlands Institute for Sea Research, Dr. Liao has discovered that some archaea exhibit previously unseen predatory behaviors.

“This is the first time such aggressive behavior has been observed in archaea. In many ways, the activity is similar to some viruses,” said Dr. Hamm.

The study shows that DPANN archaea, a group with very small genomes and limited metabolic capabilities, behave like parasitic predators that rapidly kill their hosts, leading to the swift demise of the host cells.

Living in extreme conditions

Archaea are known to thrive in extreme environments, such as boiling hot springs with high acidity levels, undersea hydrothermal vents with temperatures soaring above 100°C, supersaline waters akin to the Dead Sea, and the icy expanses of Antarctica.

“They have been found thriving in very acidic boiling hot springs, deep-sea hydrothermal vents at temperatures well over 100°C, in hypersaline waters like the Dead Sea, as well as in Antarctica,” Dr. Liao noted.

Understanding this unique biochemistry opens promising avenues in biotechnology and bioremediation.

A study in host-parasite interaction

The DPANN archaea were sampled from the frosty hypersaline environs of Antarctica’s Deep Lake, along with other sites like Australian pink salt lakes.

In order to study their host-parasite interaction, innovative techniques were used, including unique sample staining, live fluorescence microscopy, and electron microscopy.

Dr. Liao stained the host, an archaeon called Halorubrum lacusprofundi, and the parasitic DPANN archaeon 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. We saw DPANN parasites attach, and then appear to move into the host cell, leading to the host cell’s lysis or bursting open,” explained Dr. Liao.

Ecosystem impact of predatory parasites

The impact of these predatory parasites on ecosystems can’t be understated. When DPANN archaea kill their hosts, they not only feed themselves but also enable other organisms to feast on the host remains.

“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 Professor Duggin.

This leads to a more dynamic ecosystem, preventing the hoarding of nutrients by a single host organism.

The DPANN archaea appear to play a much more significant role in ecosystems than previously realized, with their parasitic or infection-like lifestyle possibly being more common than initially thought.

Broader implications of the research

The researchers believe that understanding the lifestyles of archaea could have broad implications. While no disease-causing archaea have been discovered, future findings could impact human well-being.

Dr. Liao emphasized that archaea’s unique biochemistry holds promising applications in biotechnology and bioremediation.

Furthermore, given that archaea are primarily responsible for livestock methane emissions, a more profound understanding of their lifestyles could aid in combating climate change.

The study is published in the journal Nature Communications.

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