Cyanophycin is a natural biopolymer, first identified in 1887. This polymer is created and stored by various bacteria, most notably cyanobacteria, often referred to as blue-green algae. It is composed of amino acids but is not made by ribosomes, the cellular machinery that typically builds proteins. Due to its unique chemical structure and properties, scientists are exploring how this bacterial product can be leveraged for a range of uses in both industrial and medical fields.
Cyanophycin’s Natural Purpose
In the bacterial world, cyanophycin functions as a storage container, holding reserves of nitrogen, carbon, and energy. This allows bacteria to thrive in environments where nutrients might be scarce or available only intermittently. When conditions are favorable, the bacteria produce and accumulate cyanophycin as large, insoluble granules within their cytoplasm. These granules act as a pantry, keeping the stored resources inert and inaccessible until they are needed for growth and survival.
The structure of cyanophycin makes it an effective storage molecule, particularly for nitrogen. It is a polypeptide with a backbone of poly-aspartic acid. Attached to each aspartic acid unit is another amino acid, arginine. Arginine is rich in nitrogen, so by linking many of these molecules together, the bacterium creates a dense, compact nitrogen reserve. This is especially advantageous for nitrogen-fixing cyanobacteria, which can convert atmospheric nitrogen into a usable form.
When the environment becomes nutrient-poor, the bacterium activates specific enzymes called cyanophycinases to break down the polymer. This process releases dipeptides—small units of one aspartic acid and one arginine molecule—which are then further broken down into individual amino acids. This regulated system allows the organism to mobilize its stored nitrogen and carbon for survival. For some cyanobacteria, this storage system allows them to separate energy production through photosynthesis from nitrogen fixation, which must occur in an oxygen-free environment.
From Bacteria to the Laboratory
To harness cyanophycin for human use, scientists need to produce it in quantities greater than what can be extracted from its natural sources. The solution lies in biotechnology and the use of genetically engineered microorganisms. Researchers have successfully transferred the gene responsible for producing cyanophycin synthetase, the enzyme that builds the polymer, from cyanobacteria into common laboratory bacteria like Escherichia coli (E. coli). This turns the host bacterium into a factory dedicated to manufacturing cyanophycin.
This production method allows for controlled and efficient synthesis of the biopolymer. By cultivating these recombinant E. coli in large-scale fermenters, scientists can induce them to produce cyanophycin up to significant portions of their cellular dry weight, with yields as high as 24% to 30%. The production process can be fine-tuned by adjusting culture conditions, such as the growth medium and temperature, to maximize output.
Once produced inside the bacteria, the cyanophycin granules can be isolated and purified. A common method involves an acid extraction procedure that separates the polymer from the rest of the cellular components. This biotechnological approach is scalable, enabling the production of cyanophycin at the kilogram scale for commercial applications.
Potential Applications in Industry and Medicine
The properties of cyanophycin make it a versatile material with applications across several fields. Its biodegradability is an advantage, positioning it as an eco-friendly alternative to polymers derived from fossil fuels. When cyanophycin is processed, its polyaspartic acid backbone can be isolated. This water-soluble polymer is useful as a water-softening agent in detergents, an anti-corrosion agent, and as a component in agricultural products to improve water retention in soil.
Cyanophycin also serves as a source of high-purity chemicals. The arginine that makes up half of its structure is a commercially valuable amino acid used in dietary supplements, sports nutrition products, and pharmaceuticals due to its role in cardiovascular function. By breaking down cyanophycin, pure arginine can be efficiently produced. This biological production method offers a sustainable alternative to traditional chemical synthesis.
In the medical field, the biocompatibility of cyanophycin and its derivatives allows for advanced applications. Because it is made of amino acids, the polymer and its breakdown products are generally well-tolerated by the human body. This makes it a candidate for developing drug delivery systems to encapsulate and transport therapeutic agents to specific targets within the body. Materials derived from cyanophycin, such as hydrogels, are also being investigated for use in tissue engineering as scaffolds that can support cell growth and tissue regeneration.