Whether it is a microscopically-small bacterium, a 90-metre-tall Redwood Tree, a 750-legged millipede or just a human, it is well known water and carbon compounds are critical molecules for survival. However, in addition to these elements (oxygen, hydrogen and carbon), nitrogen cannot be forgotten as an essential element to life itself. Nitrogen’s importance should not be surprising, considering that ~78% of the atmospheric make-up of this planet is gaseous nitrogen. It would be implausible not to have it as a building block for life on Earth when it is in such great abundance. The GreenSat team is currently working on an exciting project investigating nitrogen processes and its importance in agriculture, with the potential of growing crops for human consumption in space.
Nitrogen’s importance cannot be underplayed. For example, it is a fundamental component that makes up DNA. DNA consists of four nitrogenous1 bases (Fig 1) and these four units attribute to making every living being on this planet unique. DNA’s two strands (Fig 2) contain a unique line of code made of these four bases: A, C, G, and T (Fig 1). It is the combination of these units and the unique sequences they are in that makes up genes and genomes of whole organisms. The sequence of these bases in DNA is the fundamental difference between a human and a mouse, or a human and a banana (although the genetic similarity between a human and a mouse is ~90% and between a human and a banana is 50%!). In addition to making up DNA’s structure, nitrogen is essential to life because it is a component in the structure of proteins-includes enzymes that break down the food we eat and antibodies that fight diseases that invade our bodies (Fig 3).
The irony is that even though this life-depended element may be the majority of the atmosphere’s composition, the vast majority of living organisms (including humans) cannot obtain and use it from the air. All atmospheric nitrogen that is taken in when we breathe is just exhaled again. Nitrogen in the atmosphere exists as a gas, N2, with a triple bond between two nitrogen molecules and this gaseous, stable and inert state cannot be broken down by most living organisms because it requires a lot of energy to pull this molecule apart and use the nitrogen atoms.
Humans and other mammals can only take in nitrogen when it is in an organic form (Fig 4). All the nitrogen that animals need and use is made accessible by bacteria (also known as harmless ‘bugs’) living in soils. They are the only living things that can take gaseous nitrogen from the air and combining it with hydrogen or other elements to make inorganic compounds (Fig 4). These compounds are subsequently taken up from the soils through the roots of plants, such as vegetables or grasses, and turned into usable organic compounds for building DNA or proteins. The process by which bacteria can convert gaseous nitrogen into inorganic compounds (such as ammonia) is known as nitrogen fixation and is carried out by multiple specific groups of bacteria known as nitrogen-fixing bacteria (Fig 4). It is because of these bacteria we get our nitrogen source, whether it is directly eating plant products (such as vegetables) or through eating livestock and other animals (such as fish) that have eaten plant matter, thus carrying the nitrogen through the food chain. Without these bacteria that live in soils we would not be able to get the nitrogen source we need to stay alive and healthy.
GreenSat is currently focusing on the potential of nitrogen-fixing bacteria due to the vital process of nitrogen fixation in agriculture. Nitrogen is a fundamentally important element to life on Earth and we cannot exist without it- although this cannot be necessarily said for life on other planets without a nitrogen-rich atmosphere. Nevertheless, from a huge ecosystem narrowed down to an individual species, to a single organism, to a small cell and lastly to DNA, nitrogen is abundant and necessary for life on Earth.
– Scarlett Li-Williams