When dealing with bacteria in a lab setting, it is often a requirement to ensure that the risk of the bacteria escaping from containment is as minimized as possible. This is especially so if developing bacteria that produce a substance that one wouldn’t want to allow to get into the wild.
Escape Risk and Non-Competitiveness
In most situations when dealing with genetically modified bacteria, this isn’t the case. A quintessential example is modified E. coli that has been made to produce insulin, which is now the primary source for the medicine worldwide. The production of insulin is a complicated process and requires a lot of energy investment on the part of the bacteria while giving no meaningful benefit back.
Due to this, if the E. coli somehow got into the wild, it would not be able to survive and compete against its wild-type relatives, due to the energy drain from insulin production. This is also true for many non-bacterial genetically modified organisms as well, such as the Aquadvantage salmon.
But, even so, a certain amount of the public is concerned about all such modifications, justified or not. So scientists have worked in the past and present to come up with biocontainment methods that eliminate risk of escape. There are two common methods employed to achieve this goal.
The first is to engineer a so-called “suicide switch” into the bacteria’s genes. In the case of crops, this may also be known in a different form as “Terminator genes”. While they have never been used in the latter, they have seen a significant amount of use in bacterial work as they help to control the spread of the modified bacteria before dying off after a set number of reproductive generations.
The second trick is to enact a nutritional dependence within the bacteria. This means making their biology require the consumption of a particular chemical and, lacking it, they would die. In previous research, this has involved adding non-standard amino acids into the bacterial genome, making them require those be provided.
Another unique method within nutritional deficits is requiring a particular synthetic chemical, such as benzothiazole, in order to re-activate temporarily the critical genes in the bacterial genomes. Without a constant supply of the chemical, the genes will turn off again and the bacteria will die because of it.
The Cost of Raising Bacteria
All of these act as different options for containing modified E. coli and other bacteria. However, many of them require either complicated alterations or, more often, expensive or limited chemical options. Due to the very nature of biocontainment, the chemical dependence used needs to not be found in the wild, meaning that it must either be made through some human process or just be capable of being made synthetically in a lab.
Thanks to this, a large amount of the available alternatives can be hard to come by in significant quantities, making industrial production of certain genetically modified bacterial products impossible. Combined with this are concerns of escape mutants arising, individual bacteria that develop a mutation that gets them around the nutritional deficiency.
The question is, how to design a modified bacterial species that requires an easily accessible, but synthetic chemical and has a reduced chance of mutating out of this change?
A Phosphorus Understanding
Researchers at Hiroshima University in Japan decided to find a workaround to this issue. They began from the most simplest of bases: phosphorus. An essential component of life and found throughout nature in the form of phosphate and some other variations. This understanding let them to look into bacterial subspecies, such as Pseudomonas stutzeri lines, that are able to process phosphite and hypophosphite into usable forms.
These two chemical types of phosphorus cannot be found naturally in the wild in almost every case and are only derived from industrial settings. Additionally, the molecular transporter this bacteria uses to move these forms of phosphorus in and out of the cell cannot move phosphate. This makes it a prime candidate for biocontaining bacteria to require phosphite in order to change it into usable phosphate, while not being able to intake phosphate from its surroundings.
With E. coli as their model, the scientists knocked out all the other bacterial genes allowing it to transport phosphate and transgenically added in the phosphite transporter. Then they let their cultures divide generation after generation for more than 21 days. With a rate of one new cell duplication every 20 minutes to an hour, one can measure just how many generations this involved.
Reduced Risk and Hopefully Reduced Regulation
It took longer than this time period for just a single escape mutant to form, making this modified E. coli line the best and lowest frequency of escape mutant generation yet. Since it is impossible to permanently stop eventual mutations from occurring, having such a long time period for even a single escape mutation to form makes this new type of bacterial biocontainment the greatest candidate to date for use in future genetic modification research and industrial production.
Helpfully, as previously noted, phosphite is a common byproduct from industrial manufacturing, meaning it is easy to come by for use in bacterial mediums, bypassing the other complication as well. And its extreme rarity in the wild means the likelihood of any amount that would serve as a food source for the modified bacteria is statistically non-existent.
Thanks to this and the work by the Hiroshima University researchers, this new tool for biocontainment should allow even more research and application for bacterial biotechnology. While concerns of escape for almost all of these genetically modified bacteria shouldn’t be relevant due to their non-competitiveness and no real risk of harm, this technique will hopefully reduce regulation requirements in the future for biotech undertakings.
Photo CCs: E coli at 10000x from Wikimedia Commons