OT? The first nitrogen-fixing eukaryote

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A little biology background…

Eukaryotes are cells that have membrane-enclosed nuclei which contain DNA. They include all plants and animals, as well as more primitive life forms such as algae.

Prokaryotes have their DNA scattered in the cell interior without a nuclear membrane to enclose it. They include bacteria and archaea.

Life depends upon proteins and nucleic acids which contain nitrogen. Although the atmosphere is 78% nitrogen gas (N2) it can’t be used by living organisms unless it is converted into a form that can be reacted with carbon, hydrogen and oxygen. This is done by nitrogen-fixing bacteria but not by any known eukaryotes.

Nitrogen-fixing bacteria can live symbiotically on the roots of legumes (such as peas, etc.). The legumes cannot fix nitrogen but can absorb the nitrogen-containing compounds created by the bacteria. But staple grains (wheat, corn, rice, etc.) do not support the growth of nitrogen-fixing bacteria. To grow these grains, nitrogen-containing fertilizer must be added to soil.

Until now, no eukaryote has been known to fix nitrogen. In a truly stunning advance, a eukaryotic algae has been discovered with an organelle which can fix nitrogen.

An organelle is a specific structure in a cell such as chloroplast or mitochondrion. These organelles are thought to be the descendants of free-floating organisms that were absorbed into larger eukaryotic cells and remained symbiotically. In a similar way, according to genetic analysis from a previous study, ancestors of the algae and nitrogen-fixing bacteria entered a symbiotic relationship around 100 million years ago. Eventually, this gave rise to the nitroplast organelle, now seen in B. bigelowii.

https://www.nature.com/articles/d41586-024-01046-z?utm_medium=Social&utm_campaign=nature&utm_source=Facebook&fbclid=IwAR2LK3igY7HxSzA3t73LKiITMLFMGdBG4qysd6Botz4xtP-q3BDwdyvp5yc#Echobox=1712912186-1

Scientists discover first algae that can fix nitrogen — thanks to a tiny cell structure

A newly discovered ‘organelle’ that converts nitrogen gas into a useful form could pave the way for engineered plants that require less fertilizer.

By Carissa Wong, Nature.com, 11 April 2024

Researchers have discovered a type of organelle, a fundamental cellular structure, that can turn nitrogen gas into a form that is useful for cell growth.

The discovery of the structure, called a nitroplast, in algae could bolster efforts to genetically engineer plants to convert, or ‘fix’, their own nitrogen, which could boost crop yields and reduce the need for fertilizers. The work was published in Science on 11 April… [end quote]

This may be on-topic because genetically-engineered grains that fix their own nitrogen could have world-wide impact on the food supply.

Wendy

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Or soils rotated.

The Captain

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That will work if a green or animal manure is provided and plowed into the soil. However, low-cost food depends on large-scale factory farming which uses chemical fertilizers because rotating soils reduces profitability. Unfortunately, that eventually destroys the soil tilth and ruins the soil permanently in dry regions where there isn’t enough rainfall to leach away salts.

Wendy

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Good topic and thanks for the biology refresher.

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That discovery is probably one of the major finds of this century.

See my thread about to be posted on a related topic. I had to find a bit of research on the bacteria.

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I don’t know the biochemistry of this eukaryotic nitrogen-fixation trait but I would guess based on the well-studied prokaryote pathways that it will be genetically complex and so difficult to engineer into other plants. Furthermore, because nitrogen gas is stable and nonreactive, breaking it down to make organic material is very energy intensive. This means that if one were able to genetically modify corn to fix nitrogen, it would probably end up being slower growing with lower yields.

So there is certainly potential, but I wouldn’t be overly optimistic. In other words, I wouldn’t bet my retirement savings that this will be commercially successful (based on the little I know).

A more practical approach IMO is to genetically modify plants to be more accommodating of nitrogen-fixing bacteria.

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You make an interesting point. The N2 molecule is one of the most stable in nature since there is a triple bond between the two nitrogen atoms.

That being said, tearing covalent bonds by force majeure (as in the Haber-Bosch process) is a far cry from the delicate touch of enzymes. After all, nitrogen-fixing bacteria live humbly underground. Their energy source is the glucose they derive from their legume symbionts.

Incredible things happen in organelles. Complex multi-step reactions such as the Krebs Cycle in mitochondria and photosynthesis in chloroplasts as molecules are delicately assembled and disassembled enzymatically with minimal energy input. I would imagine that the newly discovered nitrogen-fixing organelle would have similar systems. Stepwise low-energy enzymatic pathways.

Sussing out the details would make a great Ph.D. project. Or many, considering that the details of chloroplasts still haven’t been fully discovered.

Wendy

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Re: slower growing, less yield

Soybeans seem to do fine with their own source. Still require some fertilizer but much less than corn.

Its too soon to know how practical this will be but i think you can be sure people are looking into it.

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I almost understand your article because I am on lecture number 27 of a 72 lecture series on Biology by a professor at Duke University as part of a bunch of lectures offered by Wondrium. I am gobsmacked by the advances made in the half century since I last read a Biology text.

Your article confirms my belief that I need to keep learning just to keep up as I age.

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The residuals from legume growth on land are the foundation of crop rotation.

<=== currently in year 50 of a 3 crop rotation of wheat, soy and milo (a sub varietal of sorghum)

The soils are fortified with fermented lagoon waste, however.

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Physics is still physics so there is no free lunch. A lot of energy is used by those microbes to metabolize nitrogen gas. It has been calculated to be 16:1 ratio of ATP per nitrogen molecule.

Microorganisms that fix nitrogen require 16 moles of adenosine triphosphate (ATP) to reduce each mole of nitrogen (Hubbell & Kidder, 2009). Biological Nitrogen Fixation | Learn Science at Scitable.

There is a reason why only a small fraction of organisms can fix nitrogen. That energy use is a disadvantage in most habitats where other nitrogen sources are plentiful.

The Soybean plant itself does not fix nitrogen. Soybean associates with nitrogen-fixation bacteria that lives in the root nodules. This is an example of symbiosis or mutualism where two organisms form an association that is beneficial to both. Point is that the plant is not bearing the energy cost of fixing nitrogen.

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The plant is bearing the energy cost since it supplies the bacteria with glucose formed by photosynthesis.

Nitrogen is the rate-limiting element for plant growth in many situations. The plant may have plenty of solar energy so that’s not the rate-limiting factor.
Wendy

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Interesting because the parallel breakthrough in E. coli has to do with wastewater.

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That’s what I, too, was thinking.
It doesn’t have to be one or the other… it can be both N-fixing with a smaller fertilizer supplement.

The “plan” could also be GMO plants for N-fixing organelles… AND for symbiotic relationships with N-fixing microbes.

As @WendyBG alludes, once the rate limiting resource is met, then the next rate limiting resource can be tackled.

:face_with_monocle:
ralph

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I agree this is an excellent gene insertion opportunity. It might take a while to hit the right combination. But great potential when developed. Probably a dozen growing seasons to perfect.

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@pauleckler I think that’s way too optimistic. I’m sure that breaking the N2 triple bond will take a long series of enzymatic reactions. Just figuring out what they are will be difficult. It wouldn’t surprise me if the new organelle has its own genome, similar to mitochondria.

Wendy

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Maybe, but on the flip side, nitrogen is almost always a limiting nutrient in biological systems so having fixed nitrogen could increase yields.

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It may also eliminate the need for the tremendous amount of energy used to produce fertilizers.

Nitrogen fertilizer production consumes approximately 5200 PJ of fossil fuels

annually, primarily natural gas.

Urea is the major nitrogen fertilizer requiring 600–900 kg steam and 50–120 kWh electricity per ton.

The energy requirement of nitrogen fertilizer production could vary from 76.3 to 79.5 MJ/kg nitrogen. This is also associated with the release of up to 540 kg CO2 eq./tonne N production.

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I think Wendy is correct. Having generated genetically modified insects for basic research I can say that it is possible to introduce single genes into organisms. For example, a gene that conveys resistance to the active factor in Roundup is in GMO soybean. This allows using roundup to kill weeds without killing soybean. Similarly several genes that produce pesticide proteins have been put into GMO corn. One can also add genes that alter an existing biochemical pathway.

However, all that is much simpler than trying to install an entirely new biochemical pathway, which is what would be required to make corn capable of fixing nitrogen independent of microbes. To my knowledge that has never been done. In addition, known nitrogen fixation pathways require that oxygen levels be very low. That’s why N-fixation by bacteria in legumes occur in specialized root nodules. Don’t know how one would coax corn to start making those.

A short description of these issues is described here: https://csanr.wsu.edu/why-hasnt-biological-nitrogen-fixation-fixed-nitrogen-scarcity-in-the-world/

There are much simpler ways of addressing the Nitrogen issue. Rotations with cover crops for example. Cowpeas is a fast growing N-fixing legume that produces peas humans can eat and forage for animals. Periodically planting fields with cowpeas then tilling it under is a form of green fertilizer that can reduce the need for synthetic fertilizer.

Cowpeas make an excellent N source ahead of fall-planted crops and attract many beneficial insects that prey on pests. Used in California in vegetable systems and sometimes in tree crops, cowpeas also can be used on poor land as part of a soil-building cover crop sequence. Cowpeas - SARE

Using cover crops for soil improvement is not high tech, but it works.

Sunnhemp is another N-fixing plant commonly used in Asia for cover cropping and is being adopted in the southern US. It can produce about a 100 pounds of nitrogen per acre in about 10 weeks.

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On the other hand the mechanism to make amino acids and proteins is probably already present. Nitrogen to ammonia may be all thats required.

And personally i would not research one gene at a time sequentially. I would do dozens or hundreds at a time and hope you hit on one that works. In the process you will learn much about the bios geneome, which ones are essential for life, and what they do. Good solid info useful to have on an living system of interest.

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