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Abstract: The concept of “photosynthetic biofuels” envisions application of a single organism, acting both as photo-catalyst and producer of ready-made fuel. This concept was applied upon genetic engineering of the cyanobacterium Synechocystis, conferring the ability to generate volatile isoprene hydrocarbons from CO2 and H2O. Heterologous expression of the Pueraria montana (kudzu) isoprene synthase (IspS) gene in Synechocystis enabled photosynthetic isoprene generation in these cyanobacteria. Codon-use optimization of the kudzu IspS gene improved expression of the isoprene synthase in Synechocystis. Use of the photosynthesis psbA2 promoter, to drive the expression of the IspS gene, resulted in a light-intensity-dependent isoprene synthase expression. Results showed that oxygenic photosynthesis can be re-directed to generate useful small volatile hydrocarbons, while consuming CO2, without a prior requirement for the harvesting, dewatering and processing of the respective biomass. [Copyright &y& Elsevier]

The composition of photosystem II (PSII) in the chlorophyll (Chl) d-dominated cyanobacterium Acaryochloris marina MBIC 11017 was investigated to enhance the general understanding of the energetics of the PSII reaction center. We first purified photochemically active complexes consisting of a 47-kDa Chl protein (CP47), CP43' (PcbC), D1, D2, cytochrome b559, Psbl, and a small polypeptide. The pigment composition per two pheophytin (Phe) a molecules was 55 ± 7 Chl d, 3.0 ± 0.4 Chl a, 17 ± 3 α-carotene, and 1.4 ± 0.2 plastoquinone-9. The special pair was detected by a reversible absorption change at 713 nm (P713) together with a cation radical band at 842 nm. FTIR difference spectra of the specific bands of a 3-formyl group allowed assignment of the special pair. The combined results indicate that the special pair comprises a Chl d homodimer. The primary electron acceptor was shown by photo-accumulation to be Phe a, and its potential was shifted to a higher value than that in the Chl a/Phe a system. The overall energetics of PSII in the Chl d system are adjusted to changes in the redox potentials, with P713 as the special pair using a lower light energy at 713 nm. Taking into account the reported downward shift in the potential of the special pair of photosystem I (P740) in A. marina, our findings lend support to the idea that changes in photosynthetic pigments combine with a modification of the redox potentials of electron transfer components to give rise to an energetic adjustment of the total reaction system. [ABSTRACT FROM AUTHOR]

Plants and their green cousins cyanobacteria and algae use sunlight to drive the chemistry that lets them grow, survive and perform an amazing range of biochemical reactions. The ability of these organisms to use a freely available energy source makes them attractive as sustainable and renewable platforms for more than just food production. They are also a source of metabolic tools for engineering microbes for "green" chemistry. This Thematic Minireview Series discusses how green organisms capture light and protect their photosynthetic machinery from too much light; new structural snapshots of the clock complex that orchestrates signaling during the light/dark cycle; challenges for improving stress responses in crops; harnessing cyanobacteria as biofactories and efforts to engineer microbes for "green" biopolymer production. [ABSTRACT FROM AUTHOR]