s u m m a r y

Current energy production from biomass has a low efficiency due to energy losses at various levels in cellular metabolism. However, this process has the attractive feature of automatic self-reproduction, so that for the long term energy budget it is not necessary to invest energy in renewing the photosynthetic apparatus.


To engineer from scratch a self-reproducing biological solar energy converter with maximized efficiency, a combination of systems-biology- and synthetic-biology approaches will be required. This should be a long-term concerted effort in which geneticists, physiologists, molecular biologists, biochemists, physicists, and computational experts should join forces to maximize the translation of atomic-level understanding to high yield solar to fuel conversion and coupling it with downstream production processes.


This will require understanding of the living cell as a self-regulating, self-ordering, self-maintaining and adaptive entity and will eventually lead to a merger of life science and materials science. Life is based on interplay between diversification at the bottom, through random mutations, and selection from the top (i.e. at the organism level). Currently the basic understanding is still lacking regarding how to implement a smart matrix that provides the appropriate selection criteria for development, (genetic) adaptation and evolution into artificial systems with the desired properties. Bacteria generally live in ecosystems where tasks often are distributed over a multitude of species, and the steady state is maintained on a multi-organism level with high metabolic energy cost, in part because of the fluctuating environmental conditions. Alternatively, bacteria have become organelles like chloroplasts, embedded in a host matrix (eukaryotic plant cell) with lower metabolic costs.


Several cyanobacterial genomes have been sequenced already at an early stage in the genomics revolution, since 1996, and the investigation of their systems biology properties is progressing well. Chlamydomonas reinhardtii, a recently sequenced single cell green alga, has been put forward as the cell factory of the future? and biotechnology has produced variants that accumulate high quantities of polysaccharides. Time has come to design an artificial organism? at the drawing table, including the minimum of pathways that are required to produce an on-board solar energy to fuel system to drive cell-factories in an efficient way.


Cell factories with an on-board light-energy conversion system with optimal efficiency and convenience, can produce a wide variety of chemicals and chemical feedstocks in a sustainable manner. In this way efficiency gain and solar energy utilization go hand in hand.


Minimally metabolizing units will provide optimal production of desired target compounds including biomass; this includes systems in which biological waste can be converted to nutritious materials with self-reproducing devices containing only a single photo system. To develop this, a major challenge is to provide comprehensive insight into the systems biology of relevant photosynthetic organisms to provide a sound basis for the new design of photosynthetic cell factories. Major hurdles will be to understand and implement:


* Minimally metabolizing smart matrices

* Proper (genetic) adaptation modules, for guiding development and evolution towards the desired function.


This requires development of methods for new design of minimal life units, including physiological and genetic adaptation for evolutionary optimization strategies, systems design, specification of biological and biophysical mechanisms leading to the desired properties, and analysis of the control and sensitivity in the designed systems. This should lead to the development of minimal self-reproducing units that can be applied in a variety of production processes, including biomass and bio-energy production.


As an alternative, the design of an artificial chloroplast-type entity (i.e. without self-reproduction capability) embedded in a host matrix could be considered. This may further improve the efficiency.


The overall success of this approach will also depend on the inclusion of methods that allow for an efficient harvesting of end products, such as spontaneous aggregation of products, self sedimentation at the end of the (artificial) life cycle and facile drying of regimented biomass.

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