The use of fossil fuels is now widely accepted as unsustainable due to depleting resources and the accumulation of greenhouse gases in the environment that have already exceeded the "dangerously high" threshold of 450 ppm CO 2 -e. To achieve environmental and economic sustainability, fuel production processes are required that are not only renewable, but also capable of sequestering atmospheric CO 2 . Currently, nearly all renewable energy sources (e.g. hydroelectric, solar, wind, tidal, geothermal) target the electricity market, while fuels make up a much larger share of the global energy demand (∼66%). Biofuels are therefore rapidly being developed. Second generation microalgal systems have the advantage that they can produce a wide range of feedstocks for the production of biodiesel, bioethanol, biomethane and biohydrogen. Biodiesel is currently produced from oil synthesized by conventional fuel crops that harvest the sun's energy and store it as chemical energy. This presents a route for renewable and carbon-neutral fuel production. However, current supplies from oil crops and animal fats account for only approximately 0.3% of the current demand for transport fuels. Increasing biofuel production on arable land could have severe consequences for global food supply. In contrast, producing biodiesel from algae is widely regarded as one of the most efficient ways of generating biofuels and also appears to represent the only current renewable source of oil that could meet the global demand for transport fuels. The main advantages of second generation microalgal systems are that they: (1) Have a higher photon conversion efficiency (as evidenced by increased biomass yields per hectare): (2) Can be harvested batch-wise nearly all-year-round, providing a reliable and continuous supply of oil: (3) Can utilize salt and waste water streams, thereby greatly reducing freshwater use: (4) Can couple CO 2 -neutral fuel production with CO 2 sequestration: (5) Produce non-toxic and highly biodegradable biofuels. Current limitations exist mainly in the harvesting process and in the supply of CO 2 for high efficiency production. This review provides a brief overview of second generation biodiesel production systems using microalgae. AbbreviationsBTL biomass to liquid CFPP cold filter plugging point CO 2 -e-CO 2 equivalents of greenhouse gases NEB net energy balance LHC light harvesting complex OAE oceanic anoxic event PS photosystem

Photosystem II (PSII) complexes, isolated from spinach and the thermophilic cyanobacterium Synechococcus elongatus, were characterized by electron microscopy and single-particle image-averaging analyses. Oxygenevolving core complexes from spinach and Synechococcus having molecular masses of about 450 kDa and dimensions of "17.2 x 9.7 nm showed twofold symmetry indicative of a dimeric organization. Confirmation of this came from image analysis of oxygen-evolving monomeric cores of PSII isolated from spinach and Synechococcus having a mass of -240 kDa.

pure) were produced over a 10 -14-day period at a maximal rate of 4 ml h ؊1 (efficiency ‫؍‬ ϳ5 times the WT). Stm6 therefore represents an important step toward the development of future solar-powered H 2 production systems.

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Photosystem II (PSII) is the pigment protein complex embedded in the thylakoid membrane of higher plants, algae, and cyanobacteria that uses solar energy to drive the photosynthetic water-splitting reaction. This chapter reviews the primary, secondary, tertiary, and quaternary structures of PSII as well as the function of its constituent subunits. The understanding of in vivo organization of PSII is based in part on freeze-etched and freeze-fracture images of thylakoid membranes. These images show a resolution of about 40-50 A and so provide information mainly on the localization, heterogeneity, dimensions, and shapes of membrane-embedded PSII complexes. Higher resolution of about 15-40 A has been obtained from single particle images of isolated PSII complexes of defined and differing subunit composition and from electron crystallography of 2-D crystals. Observations are discussed in terms of the oligomeric state and subunit organization of PSII and its antenna components.

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Solar energy capture, conversion into chemical energy and biopolymers by photoautotrophic organisms, is the basis for almost all life on Earth. A broad range of organisms have developed complex molecular machinery for the efficient conversion of sunlight to chemical energy over the past 3 billion years, which to the present day has not been matched by any man-made technologies. Chlorophyll photochemistry within photosystem II (PSII) drives the water-splitting reaction efficiently at room temperature, in contrast with the thermal dissociation reaction that requires a temperature of ca. 1550 K. The successful elucidation of the high-resolution structure of PSII, and in particular the structure of its Mn(4)Ca cluster provides an invaluable blueprint for designing solar powered biotechnologies for the future. This knowledge, combined with new molecular genetic tools, fully sequenced genomes, and an ever increasing knowledge base of physiological processes of oxygenic phototrophs has inspired scientists from many countries to develop new biotechnological strategies to produce renewable CO(2)-neutral energy from sunlight. This review focuses particularly on the potential of use of cyanobacteria and microalgae for biohydrogen production. Specifically this article reviews the predicted size of the global energy market and the constraints of global warming upon it, before detailing the complex set of biochemical pathways that underlie the photosynthetic process and how they could be modified for improved biohydrogen production.

Membranes enriched in photosystem TI were isolated from spinach and further solubilised using n-octyl 8-D-glucopyranoside (OctGlc) and n-dodecyl P-D-maltoside (DodClc,). The OctGlc preparation had high rates of oxygen evolution and when subjected to size-exclusion HPLC and sucrose density gradient centrifugation, in the presence of DodGlc,, separated into dimeric (430 kDa), monomeric (236 kDa) photosystem I1 cores and a fraction containing photosystem I1 light-harvesting complex (Lhcb) proteins. The dimeric core fraction was more stable, contained higher levels of chlorophyll, 8-carotene and plastoquinone per photosystem I1 reaction centre and had a higher oxygen-evolving activity than the monomeric cores. Their subunit composition was similar (CP43, CP47, DI, D2, cytochrome b 559 and several lower-molecular-mass components) except that the level of 33-kDa extrinsic protein was lower in the monomeric fraction. Direct solubilisation of photosystem-11-enriched membranes with DodGlc,, followed by sucrose density gradient centrifugation, yielded a super complex (700 kDa) containing the dimeric form of the photosystem I1 core and Lhcb proteins: Lhcbl, Lhcb2, Lhcb4 (CP29), and LhcbS (CP26). Like the dimeric and monomeric photosystem I1 core complexes, the photosystem 11-LHCII complex had lost the 23-kDa and 17-kDa extrinsic proteins, but maintained the 33-kDa protein and the ability to evolve oxygen. It is suggested. with a proposed model, that the isolated photosystem 11-LHCII super complex represents an in vivn organisation that can sometimes form a lattice in granal membranes K K~V O K~S :dimer; photosynthesis; photosystem 11; spinach; structure.Photosystem I1 (PSII) is a pigment-protein complex embedded in the thylakoid membrane of higher plants, algae, and cyanobacteria. By utilizing sunlight, it catalyses the splitting of water into protons, electrons, and molecular oxygen. This is the most strongly oxidizing reaction known to occur in biology. The primary photochemical process driving this highly oxidizing reaction takes place in the reaction centre of PSII which, when isolated, consists of the D1 and D2 subunits, cytochrome b 559 (cyt b 559), and the psbl gene product (Nanba and Satoh, 1987;Barber et al., 1987). The reaction centre proteins are closely associated with two other chlorophyll-a-binding proteins (CP47 and CP43). as well as the oxygen-evolving complex (OEC) composed of a four-atom cluster of manganese and the 33-kDa PsbO extrinsic protein (Ikeuchi et al., 1985). Unlike cyanobacteria, higher plants and algae have two additional extrinsic proteins associated with the OEC which have apparent molecular masses of 23 kDa and 17 kDa (PsbP and PsbQ proteins, respectively) (Murata and Miyao, 1985). Higher plants and green algae also have chlorophyll-ah-binding antenna systems that transfer excitation energy to the PSII reaction centre rather than phycobilisomes, which function in the same way in red algae and cyanobacteria (Jansson, 1994). The chlorophyll-nlh-binding antenna consists of LHCII (Lhcbl, b2, a...