Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - Protoeukaryotes (Multicompartmental Designs For Protocells)

Teaser

Origin of cellularity on early earth has been one of the most long-standing mysteries in science-how did first cells emerge in a world devoid of biological evolution from non-living components? To answer this question, many protocellular models have been proposed which to...

Summary

Origin of cellularity on early earth has been one of the most long-standing mysteries in science-how did first cells emerge in a world devoid of biological evolution from non-living components? To answer this question, many protocellular models have been proposed which to some degree mimic the functions of living cells. Protocells are encapsulated microsystems capable of a range of integrated biomimetic processes, such as gene expression, RNA-mediated replication and minimal metabolism. Most of the current designs of protocells are simple involving a single type of compartments or simply demonstrate the spatial coupling of enzymatic reactions across different subcompartments (organelles). The next step which will be key to get closer to mimicking biological systems is to make the different compartments interact dynamically, regulating each other’s functions to give rise to a state similar to “homeostasis”.

Protocells can also be perceived as smart micromachines whose adaptive and self-referential properties would find applications in emerging technologies aimed at addressing some of the societal challenges of the European Union. For example, sensing/sequestration of specific molecules can be used in clinical diagnosis or in environmental remediation; selective/stimulated exchange of materials with the environment is valuable in targeted drug delivery; transduction of external energy into chemical energy would find utility in microscale bioreactors. The advantages of protocells for these applications are ease/cost of manufacture, robustness and integration onto the environment.

The focus is to develop multi-compartmentalized protocellular systems which can exhibit self-regulation which so widely seen in biological systems. The objectives pursued are:
1. Construct protoeukaryotes capable of self-regulation of function or metabolite levels.
2. Construct protoeukaryotes capable of locomotion through reversible control of gas vesicles.
3. Protocellular hosts for cyanobacteria as endosymbionts for light energy harvesting.

The conclusions of the project are -
- By employing stimuli responsive polymer gates on membranes of protocells we have achieved self-actuation of the membrane properties.
- Buoyancy mediated motility has been achieved in microcapsules
- By spontaneous uptake of chloroplasts by polymer microdroplets (coacervates) enabled the realisation of protocells with light harvesting capabilities.

Work performed

To achieve the objectives of the project, we have designed and constructed different types of hierarchically structured protocells such as colloidosomes, polyion-microcapsules and coacervate microdroplets.
For the objective 1, we prepared hierarchical colloidosomes with pH-responsive polymer gates for regulating the diffusion through the protocell membrane with pH. The protocells were designed to host a pH-modulating enzymatic reaction which enabled the self-actuation of the membranes diffusion properties to regulate proto-metabolic reactions.
For the objective 2, polyion-capsules were prepared and the microbubble nucleation, growth and dissolution were studied in these capsules to achieve motility based on reversible buoyancy.
For the realization of objective 3, we employed chloroplasts in lieu of cyanobacteria to lend coacervate microdroplets light harvesting properties.

The key results of the project have been disseminated using different channels depending on the target audience. For the scientific audience, three manuscripts of scientific articles have been prepared. Two of them have been published in International journals – one in Nature Chemistry (Volume 10, 1154-1163, 2018) and the other in Chemical Communications.(Volume 54, 3594-3597, 2018). The first article has been highlighted in the journal Nature 560, 530, 2018 and by other news outlets - University of Bristol News, EurekAlert!, Phys.org, Long Room, Science Daily, Minimal Life and Chemistry World. The second article has been highlighted in Chemistry World.
In accordance with the regulations of Horizon 2020, the publications are/will be deposited in the repository of the University of Bristol, PURE, and will be made open access (the first article is still under embargo, its PURE ID number is 175764207). The second article has been published as a gold open access in Chemical communications. In addition to scientific articles, the results have been presented in the various scientific conferences such as \'Gordon Research Conference in Systems Chemistry (Maine, 2018)\', 23rd CRSI National Symposium in Chemistry, Bhopal, India (2018), BrisSynBio Conference (Bristol, 2018) and 5th International Conference on Multifunctional, Hybrid and Nanomaterials (Lisbon, 2017)

The results were also disseminated in the form of invited talks at various venues such as Gordon Research Conference in Systems Chemistry (Maine, 2018), Indian Institute of Technology Bombay (India, 2018), Indian Institute for Science Education and Research Bhopal, Bhopal (India, 2018)and Eindhoven University of Technology, Eindhoven (Netherlands, 2017).

For the general audience, we have worked in collaboration with the Centre for Public Engagement of the University of Bristol to participate in the following Outreach activities as part of the European Researcher’s Night 2018.

Final results

The progress beyond the state of the art:

- Microcompartments were able to harness buoyancy forces for motility for the first time to achieve programmable trajectories, execute oscillations and trigger chemical reactions.
- Biological organelles such as chloroplasts were for the first time stabilised in microcompartment to achieve light harvesting protocells

We have created protocells capable of functions such as self-regulation, locomotion and light harvesting. The motility of the protocells has been used for the flotation of macroscopic objects, self-sorting of mixed protocell communities and the delivery of a biocatalyst from an inert to chemically active environment. These results highlight new opportunities to constructing programmable micro-compartmentalized colloids with buoyancy-derived motility. For example, the oscillatory motion of the buoyant protocells could be used to transfer the motile microcapsules in and out of light- or dark-rich zones established in the upper and lower layers of a water column, respectively. In so doing, it should be feasible to couple the enzyme-powered buoyancy to the triggering of photoinduced processes within the protocells to establish a rudimentary form of phototrophic behaviour. With regard to the light harvesting protocells, given the current need for clean energy and carbon dioxide remediation, chloroplasts are an attractive photoactive target to encapsulate or stabilize in ‘ex situ’ environments. Indeed, chloroplasts have been stabilized in silica-based inert matrices for use as artificial photosynthetic bioreactors, and the extension to dispersed soft matter systems such as coacervates and vesicles could provide new opportunities in flow-based systems and patterned droplet arrays. In the latter case, the ability to spontaneously produce uniform arrays of droplet-isolated chloroplasts might provide a novel route to photosynthetically active micro-chips for biomimetic water splitting.