The production of food for cats begins with plants. Plants use nitrogen to make protein, one of the key components of cat food. In the natural environment, nitrogen is found as di-nitrogen, a molecule consisting of two nitrogen atoms bound tightly together and composing about 78% of the atmosphere. Plants can’t use this form of nitrogen to make protein, they need to begin with “fixed” nitrogen.
When life first evolved, nitrogen was fixed by the action of lightening. In the high temperature of a lightening bolt, oxygen is able to substitute for the second nitrogen atom in di-nitrogen to form nitrogen oxide. Plants are then able to further substitute the oxygen with suitable functional groups to form the various amino acids that combine to make protein. Lightening is not the only way nitrogen is fixed.
Symbiosis is another process critical for the fixation of enough nitrogen for making the protein we need. Legumes enter a cooperative relationship with independently living bacteria. The legume provides the bacteria with a safe living space along with sugars and nutrients, and in return, the bacteria provide fixed nitrogen that they make from di-nitrogen from the air. The bacteria are called rhizobia. Nitrogen is fixed as ammonia in this case.
Natural fixation of nitrogen has also recently been observed to occur with only the third-ever identified “organelle”. Mitochondria in eukaryotes and chloroplasts in plant and algal cells are the first and second discovered organelles. These nitrogen fixing organelles are called nitroplasts and they occur in certain alga. Nitroplasts, mitochondria and chloroplasts are thought to have originally been independent single cell organisms captured and internalized within other single cell organisms hundreds of millions of years ago with the joined organisms living symbiotically at first. The conversion to an organelle seems to involve the shedding of absorbed species genetic information, instead, relying on the hosts material.
At some point in the 20th century, it began to occur to chemists that natural nitrogen fixation processes could only support limited food production. German chemists carried out research that led to the development of the Haber-Bosch process. By combining di-nitrogen with di-hydrogen at high temperature and pressure, ammonia is formed. Today, plenty of fixed nitrogen fertilizer is produced this way.
