Photosynthesis: “Plug and play”?

A sustainable development of our society during the foreseeable future requires a dramatic increase in the contribution of natural photosynthesis to the production of energy carriers and commodity materials, so that the current linear flow of carbon from fossil resources to CO2 can be transformed into a closed carbon cycle (1). To make this transition possible it is necessary to engineer natural photosynthesis into a form in which relevant products are formed directly from CO2 and water, via the so-called ‘direct conversion approach’(2, 3). This ‘direct conversion’ requires engineered phototrophic organism for a wide range of products, which can be approached from two opposite directions: (i) Engineering the existing phototrophs and transforming them into efficient product-forming organisms, accompanied by genome reduction, and (ii) transferring the capacity to photosynthesize to already established (chemo-autotrophic) cell factories. The latter approach may also require providing the recipient cells with the capacity to grow autotrophically, i.e. to fix CO2, and can be referred to in popular terms as a ‘plug-and-play’ approach. Yet another approach for “direct conversion” includes (iii) constructing a hybrid biotic/abiotic system (4), for example combining an established microbial cell factory with synthetic water splitting catalyst to energize the reduction of CO2.

All these approaches will result in designer organisms that can function as a phototrophic cell factory and they all require a thorough knowledge about the minimal requirement for photosynthesis. An extra complication for (i) and (ii) is the fact that photosynthesis comes in at least 3 different forms: oxygenic photosynthesis, various forms of anoxygenic photosynthesis and retinal-based photosynthesis (5). The most recent proposals for increasing the efficiency of oxygenic photosynthesis fully underline the timeliness of the ‘plug and play’ approach (6).

This workshop will be considered a success if: (i) the minimum requirements for transfer of the relevant forms of photosynthesis to a suitable recipient can be defined; (ii) the requirements for the transformation to autotrophy can be pinpointed; and (iii) the benefits and risks of the ‘genome reduction’ and the ‘transfer of phototrophy’ approach can be compared quantitatively. The conclusions on these three aspects will be put in writing and submitted for publication in the peer-reviewed literature.

A successful workshop will be a very significant stimulus for the researchers in the Dutch photosynthesis community, and also those in the green and white sectors of biotechnology. Additionally, it will accommodate both researchers from academia and their counterparts from industry. Many of those who are currently in the photosynthesis research community are collaborating in the research program Towards BioSolar Cells (7), funded by the Dutch government, and of which the first phase will end in 2016. The Netherlands Society for Biotechnology (8) coordinates research activities in biotechnology (and synthetic biology) in the Netherlands.

The purpose of this workshop is to bring together an elite of researchers world over working in various aspects of photosynthesis research (e.g. physiological-, ecological-, and application-oriented aspects) with those from the field of metabolic modeling and synthetic biology, to explore and compare strategies towards the ‘construction’ of optimized phototrophic organisms that can be used for sustainability applications.

References:

1] Dolman AJ, van der Werf GR, van der Molen MK, Ganssen G, Erisman JW, Strengers B (2010) A carbon cycle science update since IPCC AR-4. Ambio 39: 402-412.

2] (a) Angermayr SA, Hellingwerf KJ, Lindblad P, de Mattos MJ (2009) Energy biotechnology with cyanobacteria. Curr Opinion Biotechnol. 20: 257-263; (b) Branco Dos Santos F, Du W, Hellingwerf KJ (2014) Synechocystis: Not Just a Plug-Bug for CO2, but a Green E. coli. Frontiers Bioenergetics and Biotechnology 2: 36.

3) Aro EM (2016) From first generation biofuels to advanced solar biofuels. AMBIO 45(1): S24-S31.  

4] Torella JP, Gagliardi CJ, Chen JS, Bediako DK, Colon B, Way JC, Silver PA, Nocera DG (2015) Efficient solar-to-fuels production from a hybrid microbial-water-splitting catalyst system. PNAS 112: 2337-2342

5] Fuhrman JA, Schwalbach MS, Stingl U (2008) Proteorhodopsins: an array of physiological roles? Nature Reviews Microbiology 6: 488-494.

6] Ort DR, Merchant SS, Alric J, Barkan A, Blankenship RE, Bock R, Croce R, Hanson MR, Hibberd JM, Long SP, Moore TA, Moroney J, Niyogi KK, Parry MA, Peralta-Yahya PP, Prince RC, Redding KE, Spalding MH, van Wijk KJ, Vermaas WF, von Caemmerer S, Weber AP, Yeates TO, Yuan JS, Zhu XG (2015) Redesigning photosynthesis to sustainably meet global food and bioenergy demand. Proc Natl Acad Sci USA 112: 8529-8536.

7] http://www.biosolarcells.nl/

8] NBV; http://nbv.kncv.nl/

Brief outline of the contents of the workshop

Each day will start with two to three lectures, each giving an introduction to one of the major six themes of the workshop (see below). Upon general discussion scheduled to follow each main lecture, a set of specific questions, propositions and hypotheses will be formulated that warrant thorough further discussion/investigation and literature searches. Every afternoon time is reserved for solving these problems, preferably occurring in small working groups of 4 or 5 researchers, to find relevant literature, formulate models, design strategies, urgent experiments, etc. The outcomes of each working group will be discussed and evaluated together with all participants in a Plenary Discussion Session at the end of the day.

There is time scheduled for up to 5 short communications each day. These presentations are mainly reserved for junior participants of the workshop, related to the theme of the day. The six main themes are (with proposed principal contributors between brackets):

Day 1: Introduction: ‘direct conversion’; modeling of growth and metabolism; and achievements of synthetic biology (Hellingwerf, Bruggeman, Bailey).

Day 2: Multiple modes of phototrophy; definition and identification of plug-in modules for photosynthesis and other metabolic activities (Pinhassi (tentative), Bauer, Aro).

Day 3: Autotrophic metabolism based on the Calvin- Benson Cycle and other pathways, its modelling and compartmentalization (Antonov, Steuer, Kerfeld).

Day 4: Carbon allocation in oxygenic photosynthetic cell factories and comparison of optimization through large-scale genome reduction and via ‘plug and play’ design (Pade, Branco dos Santos, Mayfield)