Blue-green algae (cyanobacteria): prospects and perspectives

Summary Photosynthetic, prokaryotic blue-green algae (cyanobacteria) occur in a wide range of natural habitats of diverse ionic composition and as such, represent an important source of biological material for biosolar energy conversion programs using saline water. The gasvacuolate, filamentous Spirulina is grown in seminatural culture in Lake Texcoco, Mexico, as a major source of single-cell protein for animal nutrition. Pilot-scale trials in other areas of the world have also demonstrated the suitability of blue-green algae, including Spirulina, for growth under brackish conditions. The carbohydrate accumulation profiles of blue-green algae differ in isolates from freshwater, marine and hypersaline habitats, with a trend towards sucrose or trehalose accumulation in stenohaline freshwater strains grown in media containing NaCl, while euryhaline and marine forms frequently accumulate glucosylglycerol. Many halotolerant isolates from hypersaline habitats accumulate glycinebetaine in response to osmotic stress. This knowledge may provide scope for future improvement in the N₂ fixation rates of blue-green algae in saline media, using betaine-accumulating N₂-fixing strains in preference to other, saltsensitive isolates.     

A perspective: Photosynthetic production of fatty acid-based biofuels in genetically engineered cyanobacteria

Biofuels are expected to play a key role in the development of a sustainable, economical and environmentally safe source of energy. Microbes offer great potential for applications in technology based biofuel production. Three fundamental questions need to be addressed in order for the development of microbial synthesis of biofuels to be successful. Firstly, what energy resource platform could be used to make biofuels. Secondly, what type of biofuel is the ideal fuel molecule that should be targeted. Finally, what microbial system could be used to transform energy resources into the targeted biofuel molecules. In this perspective, the potential of using photosynthetic microbes (cyanobacteria in particular) in the solar energy driven conversion of carbon dioxide to fatty acid-based biofuels is explored.     

Fatty acid alkyl esters: perspectives for production of alternative biofuels

The global economy heads for a severe energy crisis: whereas the energy demand is going to rise, easily accessible sources of crude oil are expected to be depleted in only 10–20 years. Since a serious decline of oil supply and an associated collapse of the economy might be reality very soon, alternative energies and also biofuels that replace fossil fuels must be established. In addition, these alternatives should not further impair the environment and climate. About 90% of the biofuel market is currently captured by bioethanol and biodiesel. Biodiesel is composed of fatty acid alkyl esters (FAAE) and can be synthesized by chemical, enzymatic, or in vivo catalysis mainly from renewable resources. Biodiesel is already established as it is compatible with the existing fuel infrastructure, non-toxic, and has superior combustion characteristics than fossil diesel; and in 2008, the global production was 12.2 million tons. The biotechnological production of FAAE from low cost and abundant feedstocks like biomass will enable an appreciable substitution of petroleum diesel. To overcome high costs for immobilized enzymes, the in vivo synthesis of FAAE using bacteria represents a promising approach. This article points to the potential of different FAAE as alternative biofuels, e.g., by comparing their fuel properties. In addition to conventional production processes, this review presents natural and genetically engineered biological systems capable of in vivo FAAE synthesis.     

Biotechnological perspectives on algae: a viable option for next generation biofuels

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Mannan biotechnology: from biofuels to health

Mannans of different structure and composition are renewable bioresources that can be widely found as components of lignocellulosic biomass in softwood and agricultural wastes, as non-starch reserve polysaccharides in endosperms and vacuoles of a wide variety of plants, as well as a major component of yeast cell walls. Enzymatic hydrolysis of mannans using mannanases is essential in the pre-treatment step during the production of second-generation biofuels and for the production of potentially health-promoting manno-oligosaccharides (MOS). In addition, mannan-degrading enzymes can be employed in various biotechnological applications, such as cleansing and food industries. In this review, fundamental knowledge of mannan structures, sources and functions will be summarized. An update on various aspects of mannan-degrading enzymes as well as the current status of their production, and a critical analysis of the potential application of MOS in food and feed industries will be given. Finally, emerging areas of research on mannan biotechnology will be highlighted.     

Applications and perspectives of multi-parameter flow cytometry to microbial biofuels production processes

Conventional microbiology methods used to monitor microbial biofuels production are based on off-line analyses. The analyses are, unfortunately, insufficient for bioprocess optimization. Real time process control strategies, such as flow cytometry (FC), can be used to monitor bioprocess development (at-line) by providing single cell information that improves process model formulation and validation. This paper reviews the current uses and potential applications of FC in biodiesel, bioethanol, biomethane, biohydrogen and fuel cell processes. By highlighting the inherent accuracy and robustness of the technique for a range of biofuel processing parameters, more robust monitoring and control may be implemented to enhance process efficiency.     

Phycobiliproteins from cyanobacteria: Chemistry and biotechnological applications

Phycobiliproteins are a group of water soluble proteins with an associated chromophore, responsible for the light-harvesting in cyanobacteria. They are divided in four main types: phycoerythrin, phycocyanin, phycoerythrocyanin and allophycocyanin, and they are characterized according to their structure and light quality absorption. Phycobiliproteins from cyanobacteria have been described as potential bioactive compounds, and recognized as high-valued natural products for biotechnological applications. Moreover, phycobiliproteins have been associated to antioxidant, anticancer and anti-inflammatory capacities among others. Thus, in order to produce phycobiliproteins from cyanobacteria for industrial application, it is necessary to optimize the whole bioprocess, including the processing parameters (such as light, nitrogen and carbon source, pH, temperature and salinity) that affects the growth and phycobiliprotein accumulation, as well as the optimization of phycobiliproteins extraction and purification. The aim of this review is to give an overview of phycobiliproteins not only in terms of their chemistry, but also in terms of their biotechnological applicability and the advances and challenges in the production of such compounds.     

Isolation of photosynthetic catalysts from cyanobacteria.

Methods are described for the isolation of ferredoxins I and II, cytochrome c-553, cytochrome f, cytochrome c-550 and plastocyanin from large quantities of various cyanobacteria. The amino acid composition of cytochrome c-550 is reported. There is a variation in the relative amounts of these proteins in different batches of cells which may relate to the nutritional status of the organisms.     

Cytochrome f from spinach and cyanobacteria. Purification and characterization

Cytochrome f has been purified from spinach chloroplasts and from the photosynthetic membranes of the cyanobacterium Spirulina maxima. The spinach protein has an isoelectric point of 5.2 and gives a single band on isoelectric focusing gels. The S. maxima cytochrome shows a major band with a pI of 4.01 and a minor band with a pI of 3.97. S. maxima cytochrome f has a molecular weight approximately 38,000 and is monomeric, while the spinach protein is slightly smaller, approximately 36,000 daltons, and aggregates to form an octamer. S. maxima cytochrome f has an E'0 of +339 mV which is close to that of cytochromes f from higher plants. The NH2-terminal amino acid sequences of the cytochromes show striking similarities. Spinach cytochrome f shows a clear preference for oxidation by spinach plastocyanin and S. maxima cytochrome f is more readily oxidized by its in vivo reaction partner, cytochrome c553.     

An NAD-specific glutamate dehydrogenase from cyanobacteria. Identification and properties

The unicellular cyanobacterium Synechocystis sp. PCC 6803 presents a hexameric NAD-specific glutamate dehydrogenase with a molecular mass of 295 kDa. The enzyme differs from the NADP-glutamate dehydrogenase found in the same strain and is coded by a different gene. NAD-glutamate dehydrogenase shows a high coenzyme specificity, catalyzes preferentially glutamate formation and presents Km values for ammonium, NADH and 2-oxoglutarate of 4.5 mM, 50 microM and 1.8 mM respectively. An animating role for the enzyme is discussed.     

Bioactive compounds from cyanobacteria and microalgae: an overview

Cyanobacteria (blue-green algae) are photosynthetic prokaryotes used as food by humans. They have also been recognized as an excellent source of vitamins and proteins and as such are found in health food stores throughout the world. They are also reported to be a source of fine chemicals, renewable fuel and bioactive compounds. This potential is being realized as data from research in the areas of the physiology and chemistry of these organisms are gathered and the knowledge of cyanobacterial genetics and genetic engineering increased. Their role as antiviral, anti-tumour, antibacterial, anti-HIV and a food additive have been well established. The production of cyanobacteria in artificial and natural environments has been fully exploited. In this review the use of cyanobacteria and microalgae, production processes and biosynthesis of pigments, colorants and certain bioactive compounds are discussed in detail. The genetic manipulation of cyanobacteria and microalgae to improve their quality are also described at length.     

Cyclic peptides and depsipeptides from cyanobacteria: A review

An elaborate array of structurally-novel and biologically-active cyclic peptides and depsipeptides are found in blue-green algae (cyanobacteria). Several of these compounds possess structures that are similar to those of natural products from marine invertebrates. Most of these cyclic peptides and depsipeptides, such as the microcystins and the lyngbyatoxins, will probably only be useful as biochemical research tools. A few, however, have the potential for development into useful commercial products. For example, cryptophycin-1, a novel inhibitor of microtubule assembly fromNostoc sp GSV 224, shows impressive activity against a broad spectrum of solid tumors implanted in mice, including multidrug-resistant ones, and majusculamide C, a microfilament-depolymerizing agent fromLyngbya majuscula, shows potent fungicidal activity and may have use in the treatment of resistant fungal-induced diseases of domestic plants and agricultural crops.     

Towards new enzymes for biofuels: lessons from chitinase research

Enzymatic conversion of structural polysaccharides in plant biomass is a key issue in the development of second generation ('lignocellulosic') bioethanol. The efficiency of this process depends in part on the ability of enzymes to disrupt crystalline polysaccharides, thus gaining access to single polymer chains. Recently, new insights into how enzymes accomplish this have been obtained from studies on enzymatic conversion of chitin. First, chitinolytic microorganisms were shown to produce non-hydrolytic accessory proteins that increase enzyme efficiency. Second, it was shown that a processive mechanism, which is generally considered favorable because it improves substrate accessibility, might in fact slow down enzymes. These findings suggest new focal points for the development of enzyme technology for depolymerizing recalcitrant polysaccharide biomass. Improving substrate accessibility should be a key issue because this might reduce the need for using processive enzymes, which are intrinsically slow and abundantly present in current commercial enzyme preparations for biomass conversion. Furthermore, carefully selected substrate-disrupting accessory proteins or domains might provide novel tools to improve substrate accessibility and thus contribute to more efficient enzymatic processes.     

A carotenoid-protein from cyanobacteria

Easily solubilized carotenoid-containing proteins have been found in aqueous extracts from three genera of cyanobacteria. The three proteins have been purified, and the absorption spectra have been determined to be virtually identical with absorption maxima at 495 and 465 nm. During the purification the orange protein spontaneously changed to a red protein with a single, broad absorption maximum at 505 nm. The orange protein showed a molecular weight of 47 000 on gel filtration while that of the red protein was 26 700. Sodium dodecyl sulfate polacrylamide gel electrophoresis indicated a single polypeptide of M_r 16 000 in both the red and orange forms, but this method removed the chromophore from the proteins. The main carotenoid component of the complex was determined to be 3′-hydroxy-4-keto-ββ-carotenoid or 3′-hydroxyechinenone. The number of carotenoid molecules per molecule of orange protein of molecular weight 47 000 was between 20 and 40. The stoichiometry of carotenoid to protein seemed reasonably constant.     

Engineering of microorganisms for the production of biofuels and perspectives based on systems metabolic engineering approaches

The increasing oil price and environmental concerns caused by the use of fossil fuel have renewed our interest in utilizing biomass as a sustainable resource for the production of biofuel. It is however essential to develop high performance microbes that are capable of producing biofuels with very high efficiency in order to compete with the fossil fuel. Recently, the strategies for developing microbial strains by systems metabolic engineering, which can be considered as metabolic engineering integrated with systems biology and synthetic biology, have been developed. Systems metabolic engineering allows successful development of microbes that are capable of producing several different biofuels including bioethanol, biobutanol, alkane, and biodiesel, and even hydrogen. In this review, the approaches employed to develop efficient biofuel producers by metabolic engineering and systems metabolic engineering approaches are reviewed with relevant example cases. It is expected that systems metabolic engineering will be employed as an essential strategy for the development of microbial strains for industrial applications.     

Synthetic biology for biofuels: Building designer microbes from the scratch

The ultimate goal in the production of biofuels is to produce fuels identical or similar to petroleum-derived transportation fuels more efficiently and in commercial quantities. Synthetic biologists have been engineering microbes to synthesize biofuels, such as butanol and fatty acid- or isoprenoid-based fuels, which are nearly identical to gasoline and diesel. One of the most urgent demands along this direction is to attain a solid framework for characterizing and standardizing the biological parts and devices. It seems quite promising because biotechnologies specially based on miniaturizations have been making a big contribution to this work. Therefore, in this review, recent advances and difficulties in the biofuel field are discussed, along with the advances of synthetic biology, which will make it possible to create designer microorganisms that produce economically viable next generation biofuels, aside from bioethanol, from corn or sugar cane, and biodiesel from plant or animal oils.