In their paper “Synthetic circuit designs for Earth terraformation,” Ricard Sole, Raul Montanez and Salvador Duran-Nebreda posit a novel systems-approach design for synthetic organisms (synths) to be used for reversing human impacts on Earth’s climate systems. This work was conducted by the authors at the ICREA Complex Systems Lab at the Pompeu Fabra University in Barcelona, Spain.
The motifs envisioned by Sole and his colleagues do not necessarily apply to solving any one environmental problem but rather serve as guidelines for the development of synthetic organisms in general, preventing unforeseen and potentially hazardous consequences of misguided synths they colloquially name the “Jurassic Park Effect.”
These “terriformation motifs,” or “Sole Motifs,” can be used in any application of synths; though the pressing issue of climate change is what motivated their development. More specifically than anthropogenic climate change, though, are the motivations of stopping and reversing our detrimental impacts on global ecosystem equilibria to prevent what the authors term “catastrophic shifts” in ecosystems that we depend on, stemming from nonlinear, rapidly accelerating changes set in motion by human actions.
Numerous methods of combating climate change have been introduced since awareness of the problem first became prevalent.These methods range from passive mitigation of anthropogenic greenhouse gas sources and adaptation by humans towards sustainable practices in our new self-imposed climate system, to more active efforts to reverse climate change via geoengineering techniques. Additionally, no one method will likely be used alone, rather it will take a suite of activities, both passive and active, to halt the degradation of, and reverse the changes already made to, global climate systems. And a path of inaction is surely to lead to more harm to humans in the altered biosphere than even the simplest methods of passive mitigation.
To actively and rapidly reverse the effects of anthropogenic climate change through geoengineering is a controversial idea. The endeavor would be enormously costly, likely have very limited impact, and has the potential to cause much more harm with unknown consequences or runaway cascading feedback loops. An alternative to this large scale effort, supported by the authors, is through the imitation of natural biological systems. This involves engineering synthetic microorganisms that help to actively reverse human-caused environmental degradation either through supporting existing natural systems that sequester carbon, fix nitrogen or clean water, increasing the system’s natural capacity, or through a synth that actively performs one of these actions independent form a naturally occurring system.
The development of synthetic biology benefits from access to an already immense catalog of lifeforms and biological processes that we have studied in nature. Already the technology exists to make modifications to organisms, a practice used in research as well as pharmaceutical industries.
Through the use of synthetic biology, any scale of the biosphere can be targeted – from the smallest microorganism ecosystem in a layer of soil to planetary-scale systems of carbon dioxide cycles and sinks. Organisms, through reproduction, are scalable, unlike a purpose-built geoeingeering project which would perform only within a single scale level. Not only does synthetic biology offer scale advantages, but also cost advantages against geoengineering techniques because a small initial population is adequate to start a much larger operational population of syths.
To help synthetic organisms serve as ecosystem engineers, the “Sole Motifs” were developed to guide the logical structures that would be built into any synthetic organism. These motifs are designed to prevent any unintended consequences by providing fail-safes and firewalls in the design of synths. Four motifs are presented by the authors as logic system diagrams. The variables involved are the host (H), the synthetic organism (SYN), the wild type organism (WT) from which the synth is derived, water (W ) and a xenobiotic resource (R). The host constitutes the target that the process is trying to improve, whether this is a single species or entire ecosystem. The synth is derived from a genetically modified extant wild type organism native to the target ecosystem. Water serves as an example of an indirect means of interaction between the synth and its host, an interaction that benefits the host – another means might be production of fixed nitrogen, a change of soil chemistry, or any other product of the synth. The xenobiotic resource can be introduced to the system as a result of deliberate or non-deliberate human action, and serves to limit the activity of the synth.
The following two motifs describe a synthetic organism that is tied to natural ecosystem processes to provide the necessary fail-safes.
The first motif describes a synth that is kept in check by a mutualistic partner, where the synth will only grow and spread alongside this partner. This system involves a double positive feedback where the synth provides a benefit to the partner and the partner provides a benefit to the synth. The failure mode of this motif would be the synth dying off or reverting back to its wild type, unmodified, organism. This failure would occur when the engineered synth is no longer beneficial to the system and the partner no longer reciprocates its benefit to the synth.
A version of the engineered mutualism motif is through indirect cooperation or facilitation. In this case the synth modifies an environmental factor that benefits a host organism or ecosystem, which in turn, through a similar double positive feedback, benefits the synth. Again the failure mode of indirect cooperation would occur when the synth no longer benefits the host and stops receiving its own benefits from the host causing either death or mutation back to its wild type.
An example of the latter motif in action would be through the modification of cyanobacteria that produce polysaccharides. These chemicals improve soil quality and through supporting the soil crust ecosystem, enhance the rate of carbon sequestration by organisms in the soil crust.
These next motifs describe a system that requires a xenobiotic, human controlled or derived, resource to limit the activity of the synthetic organism.
“Function and Die” Design
The Function and Die motif ties the activity of the synth to a resource that itself is a function of the environmental degradation the synth is designed to counteract. This ensures that when the synth restores an environment to a desired state, the resource it depends on decreases, shutting down the productivity of the synth. If new factors arise and degradation again increases, more of the resulting resource will be produced, encouraging synth growth and beginning the process of environmental restoration to counteract the new degradation.
Plastic garbage is an example of a candidate resource to engineer the synths to depend on, as a source of energy or habitat to attach to. The synths then work on their bioremediation task and if successful the plastic available would decrease, limiting the synth population and shutting down their task once complete. Because no process would result in total completion, there will exist a small population of synths in dynamic equilibrium with their resource, ready to respond to any further drastic environmental degradation.
“Sewage” Synthetic Microbiome
This last motif describes a specific application of the “Function and die” design, but where the xenobiotic resource is actively controlled by humans. The authors describe waste treatment facilities as “an end part of the city metabolism” that offer an opportunity to modify an existing microbiome to perform environmental remediation functions.
Existing members of sewage system microbiomes could be engineered without too much concern about preserving wild type species since they exist wholly within human infrastructure, and cannot exist outside of it. The availability of this human manufactured habitat acts as the resource that is controlled to limit synth activity. At the end of the waste treatment processes, these organisms will die from osmotic shock in the ocean.
The Sewage Synthetic Microbiome also provides an interesting testing ground for the other motifs as well. It is a dynamic system similar in many ways to natural ecosystems but within human control with a low chance of catastrophic failure while experimenting with engineered failure modes for more sensitive natural ecosystems.
These frameworks of synthetic organism circuits of feedback and fail-safes are only the first step in developing synths to perform environmental remediation. Technologies for engineering synthetic organisms already exist, but must be further developed and tested before applying these methods on a large scale.
The initial margin for error will be high, but, through careful design and experimentation, can be reduced as this technology is further explored. Social acceptance would only come through understanding of the science behind the technology, as there would likely be resistance to the idea of solving the problem of environmental modification through further modification.
There could also be economic incentives to develop these technologies. Initially the motifs described could be used in abiotic applications such as self-healing concrete with calcium-carbonate producing bacteria, or in biomedical technologies of new active drug systems that work with the body’s natural defense mechanisms. These initial uses of this technology could lead to wider acceptance when eventually applying synthetic organisms to ecosystem remediation.
The Sewage Synthetic Microbiome motif could serve as the first large scale testing ground for these technologies, and in turn change the way we process human waste products. This may possibly reduce costs of current waste treatment operations while also performing secondary cost saving functions such as maintaining sewage infrastructure through self-repair or cleaning. And if these synth microbiomes are designed to sequester carbon from the atmosphere, their use could result in economic benefit though carbon credit programs.
The authors argue that these active methods of modifying Earth’s ecosystems are required in order to quell the ecosystem degradation that has already occurred in the Anthropocene due to unintended or misguided ecosystem modification. Natural ecosystems are dynamic enough to have some built in tolerance to human impacts, and the four motifs described hope to expand upon those natural strengths to help ecosystems recover from impacts beyond their range of tolerance. For humans to be a part of Earth’s biosphere without damaging it, the authors state that we must enhance our own interactions with it through engineering mutually beneficial relationships such as the motifs described. This would create an Anthropocene defined not by human degradation of existing systems but by closer ties between human systems and Earth’s biosphere.
Sole, R.; Montanez, R.; Duran-Nebreda, S. Synthetic circuit designs for Earth terraformation. arXiv:1503.05043 [q-bio.QM]. <http://arxiv.org/abs/1503.05043>