The 1st International BioDesign Research Conference December 1st - 18th, 2020, Virtual

Synthetic Biology for Terraforming our planet

Blai Vidiella1,2,* , Josep Sardanyés3,4, Nuria Conde-Pueyo1,2, Ricard Solé1,2,5,*

1ICREA-Complex Systems Lab, Departament CEXS, Universitat Pompeu Fabra, Dr. Aiguader 88, 08003

Barcelona, Spain

2Institut de Biologia Evolutiva (CSIC-Universitat Pompeu Fabra), Pg. Marítim de la Barceloneta 37,

08003 Barcelona, Spain

3Centre de Recerca Matemàtica (CRM), Edicifi C, Campus de Bellaterra 08193, Bellaterra, Barcelona

4Barcelona Graduate School of Mathematics (BGSMath), Edicifi C, Campus de Bellaterra 08193,

Bellaterra, Barcelona

5Santa Fe Institute, 1399 Hyde Park Road, Santa Fe, NM 87501, USA

*Corresponding authors. Email: blai.vidiella@upf.edu and ricard.sole@upf.edu

Background

Planet Earth is currently under multiple threads because of the human activity1. As

result of the industrial development the oceans have been polluted (i.e. plastic and the

CO2 driven acidification), many megafauna species have become extinct, and because

of the emissions there is an increase in the global temperature. One precise example

what is already happening in the semiarid ecosystems. The increase in the temperature

is directly rising their aridity, producing vegetated landscapes became deserts2. This

will affect more than 40% of the land and a similar amount of the human population3.

Infront of these undesired effects, one possibility is the geoengineering. But another

possibility would be to take advantage of the biological agents (able to self-heal and

self-replicate) to restore the endangered ecosystems. Using synthetic biology, some

functions can be enhanced functions the so-called Terraformation4.

This strategy is based on modifying organisms already presents in the endangered

ecosystem to have new functions to improve the state from the ecosystem. One example,

could be the modification of cyanobacteria (i.e. Nostoc sp.) to produce more

polysaccharides to increase water retention, this would promote a better vegetation

resistance in front of the aridity rises5,6 (see Fig. 1). Other possibilities are the

introduction of organisms able to degrade plastic or oil at the ocean, or the CO2 fixation

by organisms that usually do not do it7. Some examples of organisms able to restore

ecosystems have been published recently. There are studies looking for kelp forest

increases in resilience using synthetic biology8. And another case is the symbionts

developed against the coral bleaching9.

Given that a single organism strategy could fail, there is the possibility to produce

synthetic microbiomes. It can be stablished communities of mutualistic interactions by

codependency (i.e. amino acid sharing). Thus, provoking a synthetic hypercycle which

growth rate should be higher than a single species growth6. This will reduce the

metabolic load that is needed for some function’s implementation. Moreover, the

inclusion of multiple organisms increases the possibilities for complex computations

The 1st International BioDesign Research Conference December 1st - 18th, 2020, Virtual

using a variety of inputs (i.e. associative learning10), implying the possibility of better

responses under environment variations.

Methods

In order to address this topic, we have done an extensive bibliographic research to

understand the current state of the different involved fields: ecology, mathematical

methods, and the last advances in the synthetic biology field (see Conde-Pueyo, et al

20206).

To test possible interventions, we have produced different mathematical models.

For the population dynamics (temporal response each specie) we have used mean-field

models5. In order to test the influence of the different strategies in semiarid ecosystems,

a more realistic model, we have simulated a spatial model where the influence of the

local and global rules are applied using a cellular automata11. Another, important source

Fig.1 Illustration of the multi-scale Terraformation effect in semiarid ecosystems. Editing

microorganisms from the ecosystem, change the behavior in multiple spatial scales, even

promoting changes in the ecosystem pattern configuration and its functionality.

The 1st International BioDesign Research Conference December 1st - 18th, 2020, Virtual

of differences with the models and the reality is the noise and possible environmental

fluctuations, for this reason we have also tested the models with Gillespie simulations11.

Results

Terraformation strategy can be applied to a variety of different environments and

problematics. The basic schema is to take an already present organism and modify it to

change the ecosystem behavior in front of anthropogenic effects (Fig.1). Given that we

must use already present organism (WT), the introduction of a synthetic organism (S)

implies a competition for the resources between the two strains (Fig.2a). Moreover,

depending on the genetic modifications, this acquired function could be loss in time (𝜇).

Despite the differences between the ecosystems to restore, using the minimal

structure of competition and mutation to the interactions with the environment or other

species there can be defined the so-called Terrformation motifs12. When the SYN

organism needs the pollutant to replicate a function-and-die response. If the resource is

not present, the engineered organism will disappear. The sewages and landfills are

anthropogenic ecosystems from which we can take profit to degrade toxins, or for

instance fixate CO2 (Fig.2e).

The other two motifs are result of the cooperation of the synthetic organism with a third

specie (i.e. vegetation). The direct cooperation is based in the symbiosis stablished by

nutrient sharing, for instance nitrogen fixation (Fig.3b). Addressing aridity in semiarid

ecosystems, the water retention is prioritized. For this reason, increases in humidity

(reduction of evaporation) would help vegetation to persist. This is the perfect example

of indirect cooperation (Fig.3c), where a synthetic organism can be added to the original

Fig. 2 Terraformation motifs. a Competition between the synthetic organisms and the

wild type, depending on the synthetic growth and mutation rate both organisms

could coexist (b). In the function-and-die motif (c) the interesting synthetic

characteristics are the degradation efficiency (𝜂) and the mutation rate (𝜇). Finally,

the behavior of the sewage motif (e) can be observed in panel f. Figure adapted from

Solé et al 20185.

The 1st International BioDesign Research Conference December 1st - 18th, 2020, Virtual

soil microbiome (the soil-crust, Fig.3a). Moreover, the effect of inoculating synthetic

organisms to the soil-crust with that take profit of the surrounding vegetation

(cooperative terraformation) or having better heat resistance (increase in dispersal),

improve the vegetation resilience11 (se Fig.4).

Fig. 3 Terraformation motifs where the synthetic organisms are symbionts possibly applied to

vegetation. a Soil-crust illustration from Belnap et al 200313illustrating the possibilities for

engineering the micro-ecosystem. In b and c are the direct and indirect cooperation

motifs. In the panels d and e there can be seen the system behavior depending on

different conditions (extinction, coexistence, or exclusion). f and g are cuts in the

parameter spaces (orange line in d and e). Figure from Conde-Pueyo et al 20206.

Fig. 4 Two different strategies of Engineered soil-crust could sustain the vegetation in more

degraded conditions. a Schematic view of both strategies (orange and blue lines). The effect on

the critical degradation rate of both strategies (parameters 𝛼 and 𝛽) can be seen in panel b

using a mean-field model and a cellular automata in c. Figure adapted from Vidiella et al

202011.

The 1st International BioDesign Research Conference December 1st - 18th, 2020, Virtual

Conclusion

Theoretical results indicate that small alterations in the microbiome of some ecosystems,

could be enough to make them more resilient to the current climate change conditions.

Funding

B.V., N.C.-P., R.S. have been funded by PR01018-EC-H2020-FET-Open MADONNA

project, partially funded by European Research Council Advanced Grant (SYNCOM),

and the Botin Foundation (Banco Santander through its Santander Universities Global

Division). R.S. also counted with the support of the FIS2015-67616-P grant, the Santa

Fe Institute, and the support of Secretaria d’Universitats i Recerca del Departament

d’Economia i Coneixement de la Generalitat de Catalunya. J.S. has been funded by a

“Ramón y Cajal” contract RYC-2017-22243, and by the MINECO grant MTM2015-

71509-C2-1-R and the Spain’s “Agencia Estatal de Investigación” grant RTI2018-

098322-B-I00, as well as by the CERCA Programme of the Generalitat de Catalunya.

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