<p>Various photosynthetic bacteria have been found to be amenable to genetic modification. While cyanobacteria have a natural transformation system, many of the purple bacteria also can be transformed. This is an important property for applying synthetic biology approaches, where synthetic cassettes are made and incorporated into chassis organisms. Hence, it becomes now possible to design photosynthetic bacteria <em>à la carte</em> by incorporating in a single host multiple photobricks that supply the appropriate ratio of reducing equivalents and ATP that is optimal for producing high value products with negative carbon footprints. For the latter, we envisage any model compound but for the present proposal focus on the amino acids alanine, phenylalanine or aspartate, compounds with a relatively high value per photon (Ducat et al 2011). </p>
Hence, it becomes now possible to design photosynthetic bacteria 'à la carte' by incorporating in a single host multiple photobricks that supply the appropriate ratio of reducing equivalents and ATP that is optimal for producing high value products with negative carbon footprints. For the latter, we envisage any model compound but for the present proposal focus on the amino acids alanine, phenylalanine or aspartate, compounds with a relatively high value per photon (Ducat et al 2011).
Photosynthetic bacteria have evolved for over 2.5 Billion years in the free-living state, can cope with most wavelengths of visible and infrared light, and have large metabolic diversity as they are oxygenic or anoxygenic phototrops. In addition, several bacteria and archaea have developed photoheterotrophic growth and contain retinal-based photoproteins, termed rhodopsins, that are in fact light-driven proton or sodium pumps. Moreover, new members of these phototrophic prokaryotes continue to be discovered and many have be characterized at the metagenome level. This fantastic diversity allows not only an enormous flexibility in light energy harvesting potential but provides the option to exploit a wide array of systems for the light-induced production of ATP, with or without the production of reducing equivalents. We here designate these systems photobricks.
By using synthetic biology approaches, it becomes now possible to design photosynthetic bacteria à la carte by incorporating multiple and synergistic photobricks into a single transformable host. The concept of photosynthetic biology à la carte is proposed here as a novel approach to generate production systems with a negative carbon footprint. In this approach, the photoreactive systems of the photobricks – embedded in an suitable microbial chassis - supply the appropriate ratio of reducing equivalents and energy that is optimal for converting carbon dioxide into relevant high value model compounds, such as amino acids or their precursors. In this photosynthetic biology cycle we foresee the following tasks: (1) Designing the best combination of photobricks and chassis hosts for the production of high value model compounds; (2) Predicting the flux dynamics and light wavelengths needed to run the system by using a combination of biochemical, metabolic and biophysical models; (3) Constructing and validating the relevant parts of this system, and (4) Incorporating the experimental data into the models and optimizing these, closing the photosystems biology cycle.
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