US scientists have developed a new technique to help them genetically modify bacteria. This new technology may prove to be a crucial step in the eventual creation of a man-made bacterium which, if achieved, would be the first-ever synthetic organism.
Reporting in the journal Science, a research team from the J. Craig Venter Institute (JCVI) in Rockville, Maryland and San Diego, California, described how they removed the genome from one type of bacteria, called Mycoplasma mycoides; transplanted it in to yeast; genetically modified it; and then successfully transplanted it into cells from another type of bacteria called Mycoplasma capricolum. The recipient M. capricolum cells were reprogrammed by the new genomes, and the resulting bacteria cells were of the M. mycoides type and carried the genetic modification.
This is an important achievement as scientists are unable to engineer the genomes of several strains of bacteria directly but can only do so by first transplanting the genome into yeast cells, which are easier to manipulate. In the past, when they then tried to transplant the modified genomes back into bacteria cells, the bacteria recognised and destroyed the introduced modified DNA, and so new bacteria cells carrying the engineered genomes could not be grown. Dr Sanjay Vashee, one of the leading members of the research team, explained to BBC News: 'bacteria have 'immune' systems that protect them from foreign DNA such as those from viruses'. In the new study, the researchers successfully bypassed this surveillance mechanism for the first time.
Bacteria recognise their own DNA by tagging it with molecules called methyl groups. The researchers used two methods to thwart this system. They either disabled the enzyme that detects DNA that is not marked with methyl groups in the recipient bacteria cells, or they added methyl tags to the modified DNA so that it appeared to be native bacteria DNA. Both methods prevented the engineered DNA from being attacked by the recipient bacteria, and enabled the reprogramming of the cells to become modified M. mycoides.
Last year, scientists at the JCVI created the first-ever artificial bacterium genome by stitching together molecules to create a string of DNA. So far they have been unable to transplant this synthetic genome into bacteria cells without it being destroyed by the recipient cell. Thus the new techniques may finally allow the researchers to insert the artificial genome into a cell and achieve reprogramming of the cell, thereby creating a functioning bacterium with a man-made genome - effectively, 'artificial life'.By genetically engineering bacteria, or even creating an entirely artificial species, scientists hope to be able to create bacteria to perform specific tasks, such as produce biofuels or absorb carbon dioxide from the atmosphere. However, many are concerned about the moral, ethical and safety issues surrounding this work. Dr Vashee commented: 'the team at JCVI continue to work with bioethicists, outside policy groups, [politicians], and the public to encourage discussion and understanding about the societal implications of their work and the field of synthetic genomics.'