LA JOLLA, Calif., Jan. 13 (UPI) -- Researchers said Monday they have manipulated an organism successfully to make it produce an unnatural amino acid in addition to its natural counterparts.
"It's a bona fide unnatural organism now," said lead researcher Ryan Mehl, previously at Scripps Research Institute where the study was conducted and currently an assistant professor of chemistry at Franklin and Marshall College in Lancaster, Pa.
Manufacturing this unnatural bacterium could lead to the manipulation of others to manufacture antibiotics, enzymes or other compounds for human use, Mehl said. By adding a novel amino acid, another protein building block, the bacterium could produce proteins not found in nature and with unknown potential, he said.
"We're predicting that in certain cases it might be the Achilles heel, in some it might be the Golden Egg," Mehl told United Press International.
The Scripps researchers used a strain of the common bacterium Escherichia coli and replaced a chunk of its genetic code called a stop codon -- whose function is to halt protein-making machinery -- with a code for the unnatural amino acid, p-aminophenylalanine, or pAF.
As is common practice with scientists manipulating bacteria, the study's authors also altered the E. coli so it would not survive outside of the laboratory.
Mehl said the extra amino acid did not affect the bacterium's growth. The stop codon chosen was one that occurs least frequently in the E. coli strain used in the experiment, he said.
Also, out of the few hundred possible replacements, only 10 to 20 percent of candidate stop codons actually were replaced by pAF.
"If we used a different stop codon, one that's used more, it would kill the organism," Mehl said.
The evolutionary implications of the research could be profound, Mehl noted.
Successfully creating unnatural bacteria demonstrates that the organisms could have arisen naturally through evolution, Mehl explained. However, such organisms have not arisen, and one of the questions the researchers are asking is why.
"We have no idea why we have only 20 amino acids," Mehl said.
Chris Anderson, another of the study's authors, suggested that researchers pit a 21-amino-acid organism in an evolutionary race against a 20-amino-acid organism. On a practical level, if the modified organism "wins," researchers could manipulate bacteria to produce chemicals beneficial to humans.
Anderson noted using bacteria rather than higher organisms, such as cows, would be much more efficient economically as bacteria are less expensive to grow and maintain. The possibility provides another perk: It would alleviate ethical issues surrounding the use of higher animals to produce therapeutic proteins.
Until further research is conducted, commented John Hershey, professor of biological chemistry at the University of California, Davis, "If I were a company, I wouldn't put my money there."
However, he added: "It has some potential. If these bugs will grow, that's something that could be useful."
