Due to its relatively simple structure and rapid rate of reproduction, the bacteria E. coli are favored in scientific research. The bugs have been used to do everything from creating antibiotics to manufacturing propane to serving as the engines behind the creation of a natural deep blue dye known as indigoidine. Now, researchers have paired E. coli with robots to create a power duo that just might revolutionize the production of serine, a key amino acid used in manufacturing.
Serine is found in all human beings where it's used to create proteins. It has also found a home in the manufacturing sector though, where it is used as a moisturizer in lotions and an ingredient in detergents. What's more, because it is easily converted into other chemicals like plastics, it provides another avenue to creating products in a more environmentally friendly way than relying on petrochemicals.
Currently, serine can be produced by microbes chewing on glycine, another amino acid. However, the process involves needing to raise a large crop of the bugs and then adding the chemically-produced glycine to the mix, which is fairly costly. Researchers at the Technical University of Denmark (TUD) have found what they believe is a more affordable option.
"We have shown that our E. coli cells can use regular sugar and even residues from sugar production, molasses, in lower concentrations," says TUD's Hemanshu Mundhada, lead study author. "And we have seen promising results with less expensive sugars, which makes it even more attractive to produce serine in E. coli."
Because E. coli can divide every 20 to 60 minutes, raising a large colony is a relatively fast process. However, serine is toxic to the bacteria so it hasn't been used as an engine to create the amino acid because it simply dies off as serine concentrations increase.
To overcome this challenge, the researchers used a process called Adaptive Laboratory Evolution or ALE. Through this process, the E. coli cells were exposed to increasing concentrations of serine every time they showed resistance to lower dosages. In this ladder-style approach, the end result is a colony of E. coli that could withstand high concentrations of serine.
But executing the ALE process requires moving the E. coli to higher and higher concentrations at very precise times. So precise, in fact, that robots were assigned the task.
"Cell growth must be monitored 24 hours a day, and the cells must be transferred to new mediums at a certain time of growth," said Mundhada. "Moreover, we have so many samples, it would be almost impossible to monitor all the cells manually. Therefore, it is crucial that we use ALE robots."
After the robots did their job raising the serine-resistant bacteria, the new, tougher E. coli cells were genetically engineered to produce 250 to 300 g (about 9-11 oz) of serine for every kilogram of sugar they were fed. The researchers say this is the largest productivity ratio ever achieved for the chemical.
The DUT team is now working with a company to refine the process for large-scale serine production. Their work has been published in the journal, Genetic Engineering.
Source: Technical University of Denmark
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