Many synthetic biologists are interested in engineering microbial communities for a variety of purposes. One might try to change human gut communities to cure obesity or help anxiety. Or, one might engineer a microbial community to purify water or produce high-value drugs or chemical compounds. Synthetic biologists are especially proud of the fact that the cost of DNA synthesis is dropping exponentially, much as computing power doubles every eighteen months. If this trend continues, one day synthetic biologists might be able to cheaply control the state of a microbial community by continually introducing an engineered function into a community. However, this might come at a real environmental cost.
Here’s my idea on how one can control microbial communities. My research shows that it is possible for maladaptive genes (or microbes) to beat out better-adapted genes (or microbes) in a population: if the maladaptive variants are introduced at a high enough rate, migration can overcome natural selection. By spending energy to introduce genes or microbes, synthetic biologists can change the evolutionary equilibrium of the population.
If gene synthesis is cheap, one can drown out unwanted evolved strains by flooding the population with the engineered gene or microbe. If one introduces whole genomes or microbes, one could crash a microbial community by drowning out rare strains—if these rare strains are part of a syntrophy, it is possible for the entire community to crash. One could also use viral vectors to spread a focal engineered gene across microbes in a community. In this case I expect the focal gene would spread across genomes as well as within genomes (multiple copies would be introduced within a genome). This second case is interesting, because I expect that the population might evolve resistance to being infected by the viral vector if the engineered gene carries a fitness cost (especially if the cost depends on copy number). Of course, the outcome will depend on the particular mechanism by which the virus transfers genes.
In short, the easiest way for a synthetic biologist to control a microbial community—by flooding the community with engineered genes or microbes—has the potential to affect natural communities if enough synthetic microbes escape their engineered surroundings. Second, I can imagine companies using this idea to make addictive probiotics: that is, microbes that help people with gastrointestinal (or other) problems by changing the state of the gut from diseased to healthy, but in such a way that the patient needs a permanent medication regime (introduction of the engineered strain) to prevent a disease state from recurring.
In my mind, the problem with synthetic biology is social, not scientific. I don’t think the public should fund the research of low-empathy scientists who develop products without caring whether or not they will hurt people. I believe that knowledge is always a public good—but the problem is that many technologies have the potential to cause harm, and the people who profit from such technologies usually prefer to ignore the possibility of others being hurt, and they usually fail to pay the cost when disaster strikes. Many scientists (including my PhD advisor Richard Lenski) have been thinking about these issues with regard to synthetic biology for decades. For those interested in reading further, I refer to some papers on this topic at the end of this post.
I believe that publicly-funded scientists have a duty to the public. Therefore, I believe that publicly-funded scientists should make their voice heard about technologies that have the potential to cause more harm than good. Externalizing disasters to others makes economic sense, but it is immoral and makes the world a worse place for all.
Lenski, R. E. 1987. The infectious spread of engineered genes. Pp. 99-124 in J. R. Fowle, III, editor. Application of Biotechnology: Environmental and Policy Issues. American Association for the Advancement of Science, Washington, D.C.
Lenski, R. E., and T. T. Nguyen. 1988. Stability of recombinant DNA and its effects on fitness. Trends in Ecology and Evolution 3:S18-S20.
Lenski, R. E. 1991. Quantifying fitness and gene stability in microorganisms. Pp. 173-192 in L. R. Ginzburg, editor. Assessing Ecological Risks of Biotechnology. Butterworth-Heinemann, Boston.
Levin, B. R., and F. M. Stewart. 1977. Probability of establishing chimeric plasmids in natural populations of bacteria. Science 196:218–220.
Tiedje, J. M., R. K. Colwell, Y. L. Grossman, R. Hodson, R. E. Lenski, R. N. Mack, and P. J. Regal. 1989. The planned introduction of genetically engineered organisms: ecological considerations and recommendations. Ecology 70:298-315.