Synthetic circuits designs for earth terraformation

A recent article presents some hypothetical  strategies to mitigate and repair some of the damage that humans have caused on earth.

Logic diagrams showing interactions between terraformation motifs. (Sole et al, 2015)

Logic diagrams showing interactions between terraformation motifs. (Sole et al, 2015)

Do you ever wonder what would happen if our planet can no longer support life as we know it? Ricard V. Sole and his colleagues  have, sharing some plausible hypothesis to remediate the impact that human beings have had on our planet. As stated by the authors, there are already some current efforts towards the implementation of remediation mechanisms. However, these strategies are presented as a passive way to act. Because of this the authors came up with more active strategies that employ designed organisms to ‘terraform’ the biosphere.

They consider different scenarios that will assure sustainability, setting boundaries to control the introduced synthetic organism. They present such scenarios, as motifs, where one of the main constraints are ecological interactions. Without any ecological constraints, as they point out, the newly introduced organism will enjoy a positive feedback loop, leading to a fast expansion that might end up with the dominance of the new organism. Through four different motifs, they propose to overcome such positive feedback, leading to a partial control over the synthetic organism. The motifs are composed either by three or two nodes. A host or resource, a synthetic organism and a wild-type organism compose the three nodes motif. The two nodes motif is reduced to only, a resource and a synthetic organism.

In the first motif, named ‘engineered mutualism’, the synthetic organism will be a genetically modified strain from a wild-type organism already present in the environment. The synthetic organism and the host will both directly interact and act positively on each other. The authors propose to engineer the mutualistic symbiosis properties using co-evolution of plants and bacteria under strong selection. Given that the synthetic organism comes from a wild type native organism, loss of the engineered properties won’t lead to environmental catastrophe.I think such dependence is not as direct as they think it will be, in particular when the designed motif is taken from laboratory conditions to the real world. There is always a way in nature to overcome such boundaries. The same opinion is shared by one of the article’s reviewers, Prof. Eörs Szathmary. He writes, “...the proposal is too optimistic, or indeed a bit naïve…I see no guarantee for the lack of escape mutants or recombinants.”

The second motif, ‘indirect cooperation’, is based on the same principle as motif one, however here the interaction is indirect. For such an interaction to occur a particular environment is needed, they mention an aqueous environment as an example. Some organisms to be employed on the design of such motif are cyanobacteria or some plant species. Here the main task of the synthetic organism is to ameliorate the environment to promote survival of other beneficial species.From my point of view, given that both, the wild type and synthetic organism interact with the host, it might be possible that the synthetic organism would either never succeed or take over the wild type organism, and then undesirable consequences could arise.

‘Function and die-design’ is the third motif. It is also composed of three nodes that later could turn into a two. Its main characteristic is the dependence of the organism to live upon a specific substrate or resource. The edited organism will perform a specific function and use the degradation of a particular waste as source of nutrients. The presence or absence of such waste will limit the survival of the synthetic organism. The authors propose Vibrio species since it has been reported to colonize plastic waste. Again, I believe such assumption is naive, living organisms are capable of using more than one source of nutrients to survive.

The final motif, ‘sewage synthetic microbiome’, relies on the use of a synthetic environment, human created, to control the survival of the synthetic organism. Since such synthetic organism comes from a wild type that is only able to grow in a particular environmental small modification in the living conditions will affect their survival. Another advantage is that there is no need to preserve the environment. There is also the possibility to use any foreign organism to generate the synthetic organism.In my opinion this could be the more successful scenario, since the environment already sets high boundaries, but I doubt that if a completely foreign organism is introduced it will be 100% contained in such environment.

The article caught me by surprise, and from the title, I thought that the authors would talk about extra-terrestrial scenarios, for instance Mars or the Moon terraformation. Dr. Tom Ellis, the article’s second reviewer, shared a similar sentiment in his comments. I also had the feeling that the hypotheses were more oriented towards bioremediation. I would like to have read more about genetic approaches to contain a synthetic organism. Checkpoints that not only rely on interactions between species, but also interactions within the synthetic organisms. They vaguely mention the use of xenobiotics components, however they don’t elaborate more on the topic. I am quite optimistic that in some years, with the generation of semi-synthetic bacteria, like the work by Dr. Floyd Romesberg, or minimal bacteria, work lead by the Craig Venter Institute, the motifs described in this article will be more plausible, since the designed organism will be easier to contain and control. In my opinion, more than one way of control is needed, life always finds the way to prosper.

Written by:

Daniela Garcia

Daniela is a PhD student in Biochemistry and Biophysics at LMU Munich. 

Edited by: Devang Mehta

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