On 12/04/2024 06:10, Pro Plyd wrote:
https://www.uri.edu/news/2024/04/evolution-in-action-new-study-finds-possibility-of-nitrogen-fixing-organelles/
Nitrogen is a nutrient essential for all life
on Earth. Although nitrogen gas (N2) is
plentiful, it is largely unavailable to most
organisms without a process known as nitrogen
fixation, which converts dinitrogen to
ammonium — a major inorganic nitrogen source.
While there are bacteria that are able to
reduce dinitrogen to ammonium, researchers at
the University of Rhode Island, Institut de
Ciències del Mar in Barcelona, University of
California at Santa Cruz and the Massachusetts
Institute of Technology have discovered
nitrogen-fixing symbiotic organisms exhibiting
behaviors similar to organelles. In fact,
researchers posit these symbiotic organisms –
UCYN-A, a species of cyanobacteria – may be
evolving organelle-like characteristics.
...
paper here
https://www.sciencedirect.com/science/article/pii/S009286742400182X
Metabolic trade-offs constrain the cell size
ratio in a nitrogen-fixing symbiosis
Very interesting !
I don't think they're super-clear about the line between endosymbiont
and organelle. At the end they discuss "protein trafficking and/or gene migration" between the symbiotic partners as something that would
demonstrate it is indeed an organelle, and the potential instability of
the symbiosis.
I also thought this bit was very interesting:
"One might question why an N2-fixing organelle-like entity has not yet
evolved or is evolving so slowly compared with mitochondria and
plastids. Although we cannot answer this question, we could speculate
that at least the evolution of the B. bigelowii/UCYN-A symbiosis is
based on recent events in a geological timescale. For example, ocean
conditions on Earth during the mid to late Cretaceous, such as a warm
tropical surface ocean and global anoxia,40 together with the dominance
of diazotrophic cyanobacteria41 and B. bigelowii species turning into a
more phagotrophic strategy to survive and recover from the
end-Cretaceous darkness period caused after the bolide impact on
Earth,32 might have favored the encounter of N2-fixers and eukaryotes. Accordingly, not only did the B. bigelowii/UCYN-A symbiosis originate
ca. 91 mya,42 i.e., in the late Cretaceous, but also the origin of other
marine (e.g., marine planktonic diatom diazotroph associations43) and non-marine (e.g., plants with specialized root organs [nodules] where
N2-fixing bacteria are hosted44) N2-fixing symbioses have been dated to
the Cretaceous period."
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