Immobilized microalgae in biotechnology

Here we present a brief account of current data on immobilization of oxygenic phototrophic microorganisms—cyanobacteria and eukaryotic microalgae—in natural and artificial experimental systems. We emphasize that immobilization e.g. in biofilms is a basic, widespread in nature strategy ensuring the survival of microorganisms. Accordingly, the artificially immobilized microalgal cells might be considered as a special group of biomimetic materials. Special attention is paid to the effect(s) of different immobilization on the physiology of microalgal cells and their stress tolerance as well as productivity of microalgal cultures. A comparison of the advantages and drawbacks of different immobilization techniques and cell carriers is presented. The review concludes with outlook on the possibilities of using of the immobilized phototrophic cells in biotechnology. Specific areas include (but not limited to) the biomass and metabolites production and harvesting, removal of heavy metals, biocapture of nutrients from wastewater and destroying of organic pollutants are explored.     

Potential of sponges and microalgae for marine biotechnology

Marine organisms can be used to produce several novel products that have applications in new medical technologies, in food and feed ingredients and as biofuels. In this paper two examples are described: the development of marine drugs from sponges and the use of microalgae to produce bulk chemicals and biofuels. Many sponges produce bioactive compounds with important potential applications as medical drugs. Recent developments in metagenomics, in the culturing of associated microorganisms from sponges and in the development of sponge cell-lines have the potential to solve the issue of supply, which is the main limitation for sponge exploitation. For the production of microalgal products at larger scales and the production of biofuels, major technological breakthroughs need to be realized to increase the product yield.     

Biofilms: implications in bioremediation

Biofilms are assemblages of single or multiple populations that are attached to abiotic or biotic surfaces through extracellular polymeric substances. Gene expression in biofilm cells differs from planktonic stage expression and these differentially expressed genes regulate biofilm formation and development. Biofilm systems are especially suitable for the treatment of recalcitrant compounds because of their high microbial biomass and ability to immobilize compounds. Bioremediation is also facilitated by enhanced gene transfer among biofilm organisms and by the increased bioavailability of pollutants for degradation as a result of bacterial chemotaxis. Strategies for improving bioremediation efficiency include genetic engineering to improve strains and chemotactic ability, the use of mixed population biofilms and optimization of physico-chemical conditions. Here, we review the formation and regulation of biofilms, the importance of gene transfer and discuss applications of biofilm-mediated bioremediation processes.     

Screening of marine microalgae for bioremediation of cadmium-polluted seawater

Twenty four strains out of 191 marine microalgal strains exhibited cadmium (Cd) resistance. They were tested for their Cd removal ability in growth media containing 50 μM Cd. Six strains out of 19 green algae and one out of five cyanobacteria removed more than 10% of total Cd from the medium. The marine green alga Chlorella sp. NKG16014 showed the highest removal of Cd 48.7% of total. Cd removal by NKG16014 was further quantitatively evaluated by measuring the amount of cell adsorption and intracellular accumulation. After 12 days incubation, 67% of the removed Cd was accumulated intracellularly and 25% of the Cd removed was adsorbed on the algal cell surface. The maximum Cd adsorption (q_max) was estimated to be 37.0 mg Cd (g dry cells)⁻¹ using the Langmuir sorption model. The Cd removal by freeze-dried NKG16014 cells was also determined. Cd was more quickly adsorbed by dried cells than that by living cells, with a q_max of 91.0 mg Cd (g dry cells)⁻¹.     

Global plant-responding mechanisms to salt stress: physiological and molecular levels and implications in biotechnology

The increasing seriousness of salinization aggravates the food, population and environmental issues. Ameliorating the salt-resistance of plants especially the crops is the most effective measure to solve the worldwide problem. The salinity can cause damage to plants mainly from two aspects: hyperosmotic and hyperionic stresses leading to the restrain of growth and photosynthesis. To the adverse effects, the plants derive corresponding strategies including: ion regulation and compartmentalization, biosynthesis of compatible solutes, induction of antioxidant enzymes and plant hormones. With the development of molecular biology, our understanding of the molecular and physiology knowledge is becoming clearness. The complex signal transduction underlying the salt resistance is being illuminated brighter and clearer. The SOS pathway is the central of the cell signaling in salt stress. The accumulation of the compatible solutes and the activation of the antioxidant system are the effective measures for plants to enhance the salt resistance. How to make full use of our understanding to improve the output of crops is a huge challenge for us, yet the application of the genetic engineering makes this possible. In this review, we will discuss the influence of the salt stress and the response of the plants in detail expecting to provide a particular account for the plant resistance in molecular, physiological and transgenic fields.     

Molecular mechanisms of proline-mediated tolerance to toxic heavy metals in transgenic microalgae

Pro has been shown to play an important role in ameliorating environmental stress in plants and microorganisms, including heavy metal stress. Here, we describe the effects of the expression of a mothbean delta(1)-pyrroline-5-carboxylate synthetase (P5CS) gene in the green microalga Chlamydomonas reinhardtii. We show that transgenic algae expressing the mothbean P5CS gene have 80% higher free-Pro levels than wild-type cells, grow more rapidly in toxic Cd concentrations (100 microM), and bind fourfold more Cd than wild-type cells. In addition, Cd-K edge extended x-ray absorption fine structure studies indicated that Cd does not bind to free Pro in transgenic algae with increased Pro levels but is coordinated tetrahedrally by sulfur of phytochelatin. In contrast to P5CS-expressing cells, Cd is coordinated tetrahedrally by two oxygen and two sulfur atoms in wild-type cells. Measurements of reduced/oxidized GSH ratios and analyses of levels of malondialdehyde, a product of the free radical damage of lipids, indicate that free Pro levels are correlated with the GSH redox state and malondialdehyde levels in heavy metal-treated algae. These results suggest that the free Pro likely acts as an antioxidant in Cd-stressed cells. The resulting increased GSH levels facilitate increased phytochelatin synthesis and sequestration of Cd, because GSH-heavy metal adducts are the substrates for phytochelatin synthase.     

Microbe-aliphatic hydrocarbon interactions in soil: implications for biodegradation and bioremediation

Aliphatic hydrocarbons make up a substantial portion of organic contamination in the terrestrial environment. However, most studies have focussed on the fate and behaviour of aromatic contaminants in soil. Despite structural differences between aromatic and aliphatic hydrocarbons, both classes of contaminants are subject to physicochemical processes, which can affect the degree of loss, sequestration and interaction with soil microflora. Given the nature of hydrocarbon contamination of soils and the importance of bioremediation strategies, understanding the fate and behaviour of aliphatic hydrocarbons is imperative, particularly microbe-contaminant interactions. Biodegradation by microbes is the key removal process of hydrocarbons in soils, which is controlled by hydrocarbon physicochemistry, environmental conditions, bioavailability and the presence of catabolically active microbes. Therefore, the aims of this review are (i) to consider the physicochemical properties of aliphatic hydrocarbons and highlight mechanisms controlling their fate and behaviour in soil; (ii) to discuss the bioavailability and bioaccessibility of aliphatic hydrocarbons in soil, with particular attention being paid to biodegradation, and (iii) to briefly consider bioremediation techniques that may be applied to remove aliphatic hydrocarbons from soil.     

CO2-converting enzymes for sustainable biotechnology: from mechanisms to application

1. Download : Download high-res image (168KB)
2. Download : Download full-size image

     

Population density-dependent metal tolerance: One possible basis and its ecological implications

A population density-dependent copper (Cu) resistance mechanism in a gram-negative soil bacterium, strain TDCd1, was shown to be inducible and was accompanied by changes in the protein composition of the outer membrane of the cell envelope. Characteristically, following inoculation of TDCd1 into Cu-supplemented growth media, there was a period of growth inhibition during which the number of individuals tolerant to Cu gradually increased, even though microcultural experiments indicated that some cells died during this period. We concluded that the population density dependency of the resistance mechanism resulted from the interactions between the rate of cell death, the time taken for Cu resistance to develop, and the size of the initial population. Therefore, the ability of relatively large populations of microorganisms to grow in metal-supplemented media under laboratory conditions may have little ecological significance for sparse populations in natural environments.     

Scientific Citizenship and good governance: implications for biotechnology

In the wake of public distrust regarding biotechnology, it has been suggested that the debate should be moved "upstream", whereby the public help to set research priorities. Although many scientists see this as an illogical reaction to a loss of faith in science, we argue that the boundaries between science and its technological applications have become blurred and this produces conflicts of interests that have led to this crisis of trust. Furthermore, this distrust is also a crisis in governance that calls for a new open and democratic approach to scientific research. We propose that the concept of Scientific Citizenship, based on good governance, will help to restore public trust and bridge the gap between science and the society that it serves. Integral to this is the suggestion that the governance of science forms part of the training for scientists.     

Microtubule dynamic instability: some possible physical mechanisms and their implications.

Video microscopic observation of a population of microtubules at steady state of assembly shows individual microtubules which interconvert between phases of growing and shrinking. The average duration of either phase is strongly affected by the tubulin concentration. Close to the steady-state (or 'critical') concentration, the mean excursion lengths may be of cellular dimensions, suggesting that dynamic instability can function as a control mechanism for the spatial organization of microtubule arrays. Numerical modelling, based on a limited number of assumptions, illustrates the transition behaviour, and the polar nature of this instability. The basic concept is that tubulin-GTP adds to a terminal position of the microtubule lattice and causes hydrolysis of the tubulin-GTP at a previously terminal lattice position [1, 2]. The predictions of this model can be evaluated experimentally. Further, examination of the consequences of introducing into the lattice a molecule such as a tubulin-drug complex, with altered capacity for helical propagation, provides a quantitative model for substoichiometric inhibition of microtubule dynamics and growth. This principle could have a more general relevance to mechanisms of regulation of microtubules within the cytoskeleton.     

LC-PUFA from photosynthetic microalgae: occurrence, biosynthesis, and prospects in biotechnology

Microalgae offer potential for numerous commercial applications, among them the production of long-chain polyunsaturated fatty acids (LC-PUFAs). These valuable fatty acids are important for a variety of nutraceutical and pharmaceutical purposes, and the market for these products is continually growing. An appropriate ratio of LC-PUFA of the ω-3 and ω-6 groups is vital for "healthy" nutrition, and adequate dietary intake has strong health benefits in humans. Microalgae of diverse classes are primary natural producers of LC-PUFA. This mini-review presents an introductory overview of LC-PUFA-related health benefits in humans, describes LC-PUFA occurrence in diverse microalgal classes, depicts the major pathways of their biosynthesis in microalgae, and discusses the prospects for microalgal LC-PUFA production.     

Albumin and mammalian cell culture: implications for biotechnology applications

Albumin has a long historical involvement in design of media for the successful culture of mammalian cells, in both the research and commercial fields. The potential application of albumins, bovine or human serum albumin, for cell culture is a by-product of the physico-chemical, biochemical and cell-specific properties of the molecule. In this review an analysis of these features of albumin leads to a consideration of the extracellular and intracellular actions of the molecule, and importantly the role of its interactions with numerous ligands or bioactive factors that influence the growth of cells in culture: these include hormones, growth factors, lipids, amino acids, metal ions, reactive oxygen and nitrogen species to name a few. The interaction of albumin with the cell in relation to these co-factors has a potential impact on metabolic and biosynthetic activity, cell proliferation and survival. Application of this knowledge to improve the performance in manufacturing biotechnology and in the emerging uses of cell culture for tissue engineering and stem cell derived therapies is an important prospect.     

Potential of industrial biotechnology with cyanobacteria and eukaryotic microalgae

1. Download : Download high-res image (253KB)
2. Download : Download full-size image

     

Microalgal and bacterial auxin biosynthesis: implications for algal biotechnology

1. Download : Download high-res image (149KB)
2. Download : Download full-size image

     

In vitro culture and conservation of microalgae: Applications for aquaculture, biotechnology and environmental research

Summary Microalgae are a highly diverse group of unicellular organisms comprising the eukaryotic protists and the prokaryotic cyanobacteria or blue-green algae. The microalgae have a unique environmental status; being virtually ubiquitous in euphotic aquatic niches, they can occupy extreme habitats ranging from tropical coral reefs to the polar regions, and they contribute to half of the globe’s photosynthetic activity. Furthermore, they form the basis of the food chain for more than 70% of the world’s biomass. Microalgae are a valuable environmental and biotechnological resource, and the aim of this review is to explore the use of in vitro technologies in the conservation and sustainable exploitation of this remarkable group of organisms. The first part of the review evaluates the importance of in vitro methods in the maintenance and conservation of microalgae and describes the central role of culture collections in applied algal research. The second part explores the application of microalgal in vitro technologies, particularly in the context of the aquaculture and biotechnology industries. Emphasis is placed upon the exploitation of economically important algal products including aquaculture feed, biomass production for the health care sector, green fertilizers, pigments, vitamins, antioxidants, and antimicrobial agents. The contribution that microalgae can make to environmental research is also appraised; for example, they have an important role as indicator organisms in environmental impact assessments. Similarly, designated culture collection strains of microalgae are used for ecotoxicity testing. Throughout the review, emphasis is placed on the application of in vitro techniques for the continued advancement of microalgal research. The paper concludes by assessing future perspectives for the novel application of microalgae and their products.     

Cytoplasmic inheritance and its implications for animal biotechnology

At fertilization, the mammalian sperm transmits the haploid paternal genome. However, it also carries a variety of other factors into the oocyte that have the potential to affect embryo development. These include mRNAs left over from spermatogenesis, mitochondria with their own DNA, cytoskeletal and contractile elements, remnants of the sperm plasma membrane and, in many species, the sperm centriole. While most of these elements are eliminated, some play essential roles in early embryogenesis. In this review, I summarize the latest information on these phenomena and indicate some of the implications for animal biotechnology and, in particular, cloning.