Scientists direct bacteria with expanded genetic code to evolve extreme heat tolerance

In recent years, scientists have engineered bacteria with expanded genetic codes that produce proteins made from a wider range of molecular building blocks, opening up a promising front in protein engineering.

Thermophiles, or thermophilic bacteria, are a type of extreme bacteria (extremophiles) that thrive in temperatures above 131 degrees Fahrenheit (55 Celsius).

Exposing bacteria with an artificially expanded genetic code to temperatures at which they cannot normally grow, the researchers found that some of the bacteria evolved new heat-resistant proteins that remain stable at temperatures where they would typically inactivate.

The scientists started by tweaking the genome of E. coli so that the bacteria could produce the protein homoserine o-succinyltransferase (metA) using a 21 amino acid code instead of the common 20 amino acid code. Above that temperature, metA begins to inactivate and the bacteria die. At this point, they let natural selection work. Heating the bacteria to 44 degrees Celsius, which is a temperature at which this bacteria cannot survive, the scientists put selective pressure on the bacteria population. As expected, some of the mutant bacteria were able to survive beyond their typical temperature ceiling, thanks to possessing a mutant metA that was more heat stable, all other bacteria died.

The researchers then identified the specific genetic sequence change that resulted in the mutant metA and found it was due to the unique chemical properties of one of their noncanonical amino acids that laboratory evolution exploited in a clever way to stabilize the protein.

Source: 

https://www.sciencedaily.com/releases/2018/11/181128082729.htm  Science Daily 

https://sciencing.com/examples-heatresistant-bacteria-20175.html  Heat-Resistant Bacteria