Scientists, including one of Indian origin, have engineered E coli bacteria into producing large quantities of serine, an important bio-chemical used in detergents, tube feeding formula and as building blocks for many important chemicals.
"This discovery is quite unique and proves that we can actually adapt cells to tolerate large amounts of serine - something many people thought was not possible," said Professor Alex Toftgaard Nielsen from Technical University of Denmark.
Serine is an amino acid important for humans, because it is one of the 20 amino acids forming proteins in our bodies. Being highly water soluble, serine finds application as moisturiser in lotions of pharma and cosmetic industry.
There is a huge market for serine in the chemical industry, because it can be converted into other chemicals such as plastics, detergents, dietary supplements and a variety of other products.
Serine has been mentioned as one of the 30 most promising biological substances to replace chemicals from the oil industry, if the production costs can be reduced.
Fermentation by bacteria is the most common method of producing amino acids.
However, serine is toxic to the laboratory work horse E coli, which quickly "gives up", if the bacterium is to produce large amounts of the substance.
The first step in the development process was to produce E coli cells that could survive high concentrations of serine.
To achieve this, the scientists used so-called automated 'Adaptive Laboratory Evolution' (ALE) in which they first exposed the cells to a small amount of serine.
When the cells had grown accustomed to these conditions, the bacteria were transferred to a slightly higher concentration. The experiment was repeated several times with the cells best suited to tolerate serine.
This experiment required highly specialised robots, said study lead author, Hemanshu Mundhada from The Novo Nordisk Foundation Centre for Biosustainability (DTU Biosustain).
"Cell growth must be monitored 24 hours a day, and the cells must be transferred to new medium at a certain time of growth," said Mundhada.
The tolerant E coli cells were subsequently optimised genetically to produce serine, and in this way, they could suddenly produce 250 to 300 grammes of serine for each kg of sugar (glucose) added, which is the largest productivity seen for serine ever.
Serine is already produced in other microbes by converting glycine and methanol.
However, these microbes must first be grown in large quantities, after which the glycine - which is chemically produced - is added.
Glycine is relatively expensive, and therefore many are looking for cheaper and more sustainable production methods.
"We have shown that our E coli cells can use regular sugar and even residues from sugar production, molasses, in lower concentrations," said Mundhada.
The study was published in the journal Metabolic Engineering.
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