Discovery of microbes with mixed membranes sheds new light on early
evolution of life

Date:
September 17, 2020
Source:
Royal Netherlands Institute for Sea Research
Summary:
Current research suggests that more complex life-forms, including
humans, evolved from a symbiosis event between bacteria and another
single-celled organism known as archaea. However, evidence of a
transition period in which the two organisms mixed where nowhere to
be found. That is, until now. In the deep waters of the Black Sea,
a team of scientists found microbes that can make membrane lipids
of unexpected origin.



FULL STORY ========================================================================== Current research suggests that more complex life-forms, including humans, evolved from a symbiosis event between bacteria and another single-celled organism known as archaea. However, evidence of a transition period
in which the two organisms mixed where nowhere to be found. That is,
until now. In the deep waters of the Black Sea, a team of scientists
found microbes that can make membrane lipids of unexpected origin.


========================================================================== Cells are surrounded by a layer of membrane lipids that protect them from changes in their environment such as temperature, much in the same way
that our skin changes when we are cold or exposed to the sun. Lead author
and NIOZ senior scientist Laura Villanueva explains why they make such interesting biomarkers. 'When a cell dies, these lipids preserve like
fossils and hold ancient-old information on Earths' early environmental conditions.' Our tree of life includes small and simple cells (Bacteria
and Archaea) and more complex cells (Eukaryotes), including animals and
humans. Bacteria and Eukaryotes share a similar lipid membrane. Looking
at Archaea, their 'skin' or membrane looks very different and is
primarily designed to help these microorganisms to survive in extreme environments. Villanueva: 'This "lipid divide," or difference in membranes between Bacteria and Eukaryotes on the one hand and Archaea on the other,
is believed to have happened after the emergence of Bacteria and Archaea
from the last universal cellular ancestor (LUCA).' Missing piece hidden
in the deep Black Sea The leading theory is that Eukaryotes evolved from
a symbiosis event between archaeal and bacterial cells in which the
archaeal cell was the host. But how does this work when their 'skins'
are so different and share no sign of common ancestry? Villanueva: 'To
explain the creation of more complex life-forms, the archaeal membrane
must have made a switch to a bacterial type membrane. Such a switch
likely needed a transition period in which the two membrane types were
mixed.' However, mixed lipid membranes had never been found in microbes
until the team of Villanueva made an unexpected discovery in de deep
waters of the Black Sea.

Villanueva: 'We found a possible missing piece of this puzzle in the
Black Sea.

Here, an abundant group of bacteria thrive in the deep-sea, absent of
oxygen and with high sulfide concentration. We discovered that the
genetic material of this group did not only carry pathway genes for
bacterial lipids but archaeal ones as well.' The peculiarity was also
found in the genetic material of other, closely related Bacteria and
supports the idea that this ability to create 'mixed' membranes is more widespread than previously thought. This discovery sheds new light on the evolution of all cellular life forms and may have important consequences
for the interpretation of archaeal lipid fossils in the geological record
and paleoclimate reconstructions.


========================================================================== Story Source: Materials provided by Royal_Netherlands_Institute_for_Sea_Research. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Laura Villanueva, F. A. Bastiaan von Meijenfeldt, Alexander
B. Westbye,
Subhash Yadav, Ellen C. Hopmans, Bas E. Dutilh, Jaap S. Sinninghe
Damst�. Bridging the membrane lipid divide:
bacteria of the FCB group superphylum have the potential to
synthesize archaeal ether lipids. The ISME Journal, 2020; DOI:
10.1038/s41396-020-00772-2 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200917105322.htm

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