In a drive to improve the environmental safety of genetically modified (GM) organisms, scientists have created the first GM microbes that can only survive in the presence of designer compounds not found in nature.
The work represents a major step towards the creation of GM life forms that are completely reconfigured to perform an important job and then die without a trace when their task is done.
Vats of GM microbes are already used to make various chemicals, drugs and dairy products, but the newly designed organisms could be safe enough to use outside, for example, to clean up oil spills or break down toxic chemicals on contaminated land. Other bugs based on the same procedure might be put in drinks as probiotics to cure diseases.
Scientists at Harvard and Yale universities made changes throughout the genome of E. coli bugs to make them resistant to viruses and reliant on designer amino acids to survive. Amino acids are the building blocks of the proteins the organisms need to live and multiply.
The researchers call the new microbes “genetically recoded organisms” because they have a new kind of genetic code that ensures they can only thrive when fed the synthetic amino acids.
A similar procedure could be used to improve GM crops, but the task is far tougher because plants have about 10 times as many genes that are used to make proteins.
Scientists have created GM bugs before that need a particular chemical to survive, but the safety mechanism has always been vulnerable. The bugs might find the chemical in the environment, pick up DNA from other microbes that lets them use other nutrients, or mutate into a form that can survive without the chemical.
In two separate papers published in the journal Nature, teams led by George Church at Harvard and Farren Isaacs at Yale demonstrate that their designer bugs are far less able to overcome the “kill” mechanism engineered into their DNA.
This is because the E. coli was engineered in such way that it would need tens of precise mutations to survive without the artificial amino acid. In addition, the synthetic amino acid the bugs live on was designed to look like no other compound found in nature, slashing the chances of the bugs finding a way to live off a similar natural compound.
In laboratory tests, Church grew a trillion of the modified E. coli and found that none evolved to survive without the synthetic amino acid. Farren’s tests involving 100-billion engineered E. coli found the same.
Other changes to the microbes’ DNA made them resistant to viruses that attack bacteria, giving them a built-in defence against infections that can wipe out fermentation and other industrial processes that rely on healthy microbes. To spread, viruses need to hijack a cell’s molecular machinery, but the genetic changes in the E. coli made it extremely hard for them to do that.
Church said he developed the procedure to prevent GM bugs spreading after spillages, leaks or their intentional use in the wild. “You want to get ahead of these things rather than wait until you have a problem,” he said. “It’s good to get a safety mechanism in place.”
Isaacs said the new technique endowing engineered bugs with safeguards will pave the way for their more widespread use. – © Guardian News & Media 2015