Preparing synthetic biology for the world

Abstract

Synthetic Biology promises low-cost, exponentially scalable products and global health solutions in the form of self-replicating organisms, or "living devices." As these promises are realized, proof-of-concept systems will gradually migrate from tightly regulated laboratory or industrial environments into private spaces as, for instance, probiotic health products, food, and even do-it-yourself bioengineered systems. What additional steps, if any, should be taken before releasing engineered self-replicating organisms into a broader user space? In this review, we explain how studies of genetically modified organisms lay groundwork for the future landscape of biosafety. Early in the design process, biological engineers are anticipating potential hazards and developing innovative tools to mitigate risk. Here, we survey lessons learned, ongoing efforts to engineer intrinsic biocontainment, and how different stakeholders in synthetic biology can act to accomplish best practices for biosafety.

Keywords: biosafety research; containment of biohazards; risk assessment; synthetic biology.

Figure 1

Genetic safeguard strategies. Recombinant DNA (bright green) is introduced into the host chromosome (white wavy lines). Two pathways for engineered auxotrophy (A,B) kill synthetic organisms (blue) once they lose access to a supplement (+) in a controlled environment. The supplement either (A) suppresses a toxic gene product (−) or (B) provides nutrition to compensate for a genetic deletion (red X). The induced lethality system (C) produces a toxic gene product (−) in response to an inducer (i) such as IPTG, sucrose, arabinose, or heat. Gene-flow prevention (D) is accomplished by placing a toxic gene into the recombinant DNA (dark blue/bright green circle) in an immune host. Transfer of the recombinant plasmid kills unintended host cells.

Figure 2

Reported frequencies of engineered bacteria that escape various genetic safeguard systems. A 2-liter volume is represented here as a standard soft drink container (left). Lowest reported frequencies (shown on the y-axis, log scale) were multiplied by the estimated number of cells in 2-liters at 1 × 10⁸ cells/mL, where OD600 = 0.1 [BioNumbers record ID 10985 (Milo et al., 2009)]. The dashed line indicates the maximum survival limit (1000 cells per 2 liters) recommended by the National Institutes of Health (Wilson, 1993).

Figure 3

An illustration of the accumulation of damaged genetic safeguards in a population of synthetic organisms. When cells with intact safeguards (blue) escape physical containment (e.g., an accidental spill), an inducer (i) can be added to remove them from the environment (see Figure 1C). As the population grows, leaky expression of the lethal protein (−) reduces the viability of cells that carry functional safeguards. Mutation (X) of the lethal gene provides a growth advantage, thus cells that carry damaged safeguards (red) overwhelm the population. Cells with mutated safeguards do not respond to the cell death inducer (i). Consequently, it is difficult to remove the cells from the environment after an accidental release.