Science

Hungry plants could learn a thing or two from nitrogen-fixing bacteria

Hungry plants could learn a th...
Researchers have engineered bacteria to absorb nitrogen from the air, with the eventual goal of developing plants that can do the same
Researchers have engineered bacteria to absorb nitrogen from the air, with the eventual goal of developing plants that can do the same
View 2 Images
Researchers on the team, from left: Himadri Pakrasi, Michelle Liberton, Deng Liu and Maitrayee Bhattacharyya-Pakrasi
1/2
Researchers on the team, from left: Himadri Pakrasi, Michelle Liberton, Deng Liu and Maitrayee Bhattacharyya-Pakrasi
Researchers have engineered bacteria to absorb nitrogen from the air, with the eventual goal of developing plants that can do the same
2/2
Researchers have engineered bacteria to absorb nitrogen from the air, with the eventual goal of developing plants that can do the same

Nitrogen is a vital nutrient for plants, and although there's plenty of it drifting around in the air, they can only pull it out of the ground – hence the need for artificial fertilizer. But now, researchers at Washington University in St Louis have engineered bacteria that can efficiently suck nitrogen out of the air, and the long-term goal is to develop crops that can do the same.

About 78 percent of the Earth's atmosphere is made up of nitrogen, but the legume family is among the very few plants that are able to tap into that rich resource (known as nitrogen fixing). The vast majority rely on absorbing the nutrient through their roots, but soil can often be lacking, requiring fertilizer to be spread onto crops.

Developing plants that can essentially "fertilize" themselves through the air could be a huge boon to agriculture and the environment. In a recent study, researchers engineered soybean plants to have more nitrogen-carrying proteins, which kicked the plants into overdrive. Another technique, infusing seeds with nitrogen-fixing bacteria, could be applied to almost any plant.

Similar bacteria were the focus for the new study. The WUSTL researchers set out to isolate the nitrogen-fixing genes in cyanobacteria. In particular, they focused on a species known as Cyanothece, which uses a circadian rhythm to photosynthesize during the day and fix nitrogen at night.

Researchers on the team, from left: Himadri Pakrasi, Michelle Liberton, Deng Liu and Maitrayee Bhattacharyya-Pakrasi
Researchers on the team, from left: Himadri Pakrasi, Michelle Liberton, Deng Liu and Maitrayee Bhattacharyya-Pakrasi

The team determined which genes were responsible for this biological clock, and spliced them into another cyanobacteria species, Synechocystis, to see if it could pick up the nitrogen-fixing ability. And sure enough, it did.

After the removal of oxygen, which is produced through photosynthesis and interferes with the nitrogen fixation, and the addition of 35 new genes, Synechocystis was able to fix nitrogen at a rate of about two percent that of Cyanothece. Not great, but it's a start. But the bugs upped their game when the team removed some of the added genes: with only 24 Cyanothece genes, Synechocystis' nitrogen fixing increased to over 30 percent of Cyanothece's rate.

"This means that the engineering plan is feasible," says Himadri Pakrasi, lead researcher on the study. "I must say, this achievement was beyond my expectation."

The research is a step towards the team's ultimate goal of finding a way to genetically engineer plants that are able to fix nitrogen. Doing so could increase the yield of crops and reduce the need for fertilizer, which can be environmentally costly to produce and hazardous once it leaches into natural waterways.

The research was published in the journal mBio.

Source: Washington University in St Louis

3 comments
piperTom
I'd love to say "don't do it", but technology marches whether it's dangerous or not. Let's say these guys are successful... at first, only farmers use it and that's great. Later, these types of plants leak into the general environment; they out-compete natural plants. The GMO plants proper and the other plants suffer. The whole natural environment changes. I like the forest like it is now. But then, I would like it as it WAS before all the chestnuts died out, too.
re-update
I know quite a lot about this as I've spent some time researching it.
In the natural world, soil is filled with microorganisms; 'bacteria' or soil biota that is made up of various creatures including fungi and enzymes who all perform specific roles; many or most of which help the plant and maintain soil health as detritus is dropped on it and left to decompose.
With modern farming, we use chemical fertilizer which kills these microorganisms. Some of the fertilizer is absorbed; some is washed away by rain, and much oxidises in the atmosphere forming nitrous oxides - a powerful GHG.
Really what we should be doing is using the waste products created throughout the agricultural process - either crop or livestock waste streams. The interesting thing to do is to capture the methane that is released when this waste decomposes, and utilise it instead of its geological variant.
And then we put the remaining carbon and nutrients back on the soil. This completes the circle of nutrient return, to a certain degree, and is better than simply using chemicals.
But the further interesting thing is that by not using chemical fertilizer, this allows the soil biota to survive. And so by having a level of pre-existing soil health, those microbes that fix nitrogen, living around and even within plants and crops, can be added to by additional strains (or just a random group of healthy bacteria rhyzomes etc) - thus doing a better job than chemical crop treatments, including pesticides and other treatments.
Biocontrols as they are called have been used for years in India, but Monsanto have recently brought out a range of products based on these biota that they advertise as augmenting, or replacing traditional crop controls.
So these bacteria perform a wide variety of functions - however the use of substrate from biogas AD units significantly increases their ability to maintain healthy colonies and in turn maintain soil health.
Signguy
God prescribed the best solution by having the people plant the seventh year but not Harvest it and turn it under so that it would lie fallow for a year. The result of this is that it would reactivate all of the bacteria back to the soil that would give them all the nutrition they needed to plant for another 6 years.