Weird microbial partnership shows how complex life may have evolved

Connecting tubes between bacteria and a kind of microbe called archaea may reflect a symbiotic relationship that led to complex cells more than 2 billion years ago

By Chris Simms

15 August 2025

Stromatolites are rock-like structures formed by bacteria in shallow water

lkonya/Shutterstock

Microbes from a remote bay in Western Australia seem to connect to each other with tiny tubes, forming a relationship that may reflect an early step in the evolution of complex life.

In Shark Bay, or Gathaagudu in the Indigenous Malgana language, microbes form slimy multi-layered communities called microbial mats. It is a harsh environment battered by tides and temperature swings, but these communities of bacteria and another kind of single-celled organism called archaea have survived here for tens of thousands of years. They often live in symbiosis with each other, building up their communities into layered sedimentary formations called stromatolites.

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“The mats form in hyper-saline conditions with high UV levels. They get hit with cyclones. Pretty much everything seems to smash these things but they still seem to hang around,” says Brendan Burns at the University of New South Wales in Sydney.

They are modern analogues of how communities of microbes may have been living together billions of years ago when complex life first evolved, he says. This is theorised to have happened when bacteria and archaea became so mutually dependent on one another that the bacteria ended up living inside the archaea, creating more complex cells known as eukaryotes.

Burns and his colleagues brought some of these microbial mat communities back to their lab and tried growing the organisms in high-salt, low-oxygen conditions.