Presence of a Na+-stimulated P-type ATPase in the plasma membrane of the alkaliphilic halotolerant cyanobacterium Aphanothece halophytica

Electrogenesis in Plasma Membrane Fraction of Halotolerant Microalga Dunaliella maritima and Effects of N,N'-Dicyclohexylcarbodiimide

The effects of N,N'-dicyclohexylcarbodiimide (DCCD), non-specific inhibitor of various transport systems functioning in biological membranes, on Na+-transporting P-type ATPase of the green halotolerant microalga Dunaliella maritima were studied in the experiments with vesicular plasma membranes isolated from the alga cells. The effects of DCCD on electrogenic/ion transport function of the enzyme and its ATP hydrolase activity were investigated. Electrogenic/ion transport function of the enzyme was recorded as a Na+-dependent generation of electric potential on the vesicle membranes with the help of the potential-sensitive probe oxonol VI. It was found that unlike many other ion-transporting ATPases, the Na+-ATPase of D. maritima is insensitive to DCCD. This agent did not inhibit either ATP hydrolysis catalyzed by this enzyme or its transport activity. At the same time DCCD affected the ability of the vesicle membranes to maintain electric potential generated by the D. maritima Na+-ATPase. The observed effects can be explained based on the assumption that DCCD interacts with the Na+/H+ antiporter in the plasma membrane of D. maritima.

Salt Tolerance and Desalination Abilities of Nine Common Green Microalgae Isolates

In recent years, decline of freshwater resources has been recognized as one of the main environmental problems on global level. In addition to the increasing extent of primary salinization due to climate change, secondary salinization caused by human interventions is also a significantly increasing problem, therefore, the development of various chemical-free, biological desalination and removal procedures will become increasingly important. In the present study, the salinity tolerance, salinity, and nutrient reducing ability of nine common freshwater microalgae species from the genera Chlorella, Chlorococcum, Desmodesmus, Scenedesmus, and Monoraphidium were investigated. Our results proved that the studied green microalgae species are halotolerant ones, which are able to proliferate in environments with high salt concentrations. Furthermore, most of the species were able to reduce conductivity and remove significant amounts of chloride (up to 39%) and nutrients (more than 90% nitrate). The results proved that nitrate removal of the studied species was not influenced by salt concentration, only indirectly via growth inhibition. However, the results also highlighted that N:P ratio of the medium has primarily importance in satisfactory phosphorous removal. It can be concluded that assemblages of the studied microalgae species could be able to adapt to changing conditions even of salt-rich wastewaters and improve water quality during bioremediation processes.

Bio-desalination of brackish and seawater using halophytic algae

Global demand for water is rising. A sustainable and energy efficient approach is needed to desalinate brackish sources for agricultural and municipal water use. Genetic variation among two algae species, Scenedesmus species (S. sp.) and Chlorella vulgaris (C. vulgaris), in their tolerance and uptake of salt (NaCl) was examined for potential bio-desalination of brackish water. Salt-tolerant hyper-accumulators were evaluated in a batch photobioreactors over salinity concentration ranging from 2 g/L to 20 g/L and different nutrient composition for their growth rate and salt-uptake. During algae growth phase, the doubling time varied between 0.63 and 1.81 days for S. sp. and 3.1 to 5.9 for C. vulgaris. The initial salt-uptake followed pseudo first order kinetics where the rate constant ranged between -3.58 and -7.68 day-1 reaching up to 30% in a single cycle. The halophyte algae S. sp. and C. vulgaris that were selected for pilot-scale studies here represent a promising new method for desalination of brackish waters. Halophytic technologies combined with the potential use of algae for biofuel, which offsets energy demand, can provide a sustainable solution for clean, affordable water and energy.

Biodesalination: a case study for applications of photosynthetic bacteria in water treatment

Shortage of freshwater is a serious problem in many regions worldwide, and is expected to become even more urgent over the next decades as a result of increased demand for food production and adverse effects of climate change. Vast water resources in the oceans can only be tapped into if sustainable, energy-efficient technologies for desalination are developed. Energization of desalination by sunlight through photosynthetic organisms offers a potential opportunity to exploit biological processes for this purpose. Cyanobacterial cultures in particular can generate a large biomass in brackish and seawater, thereby forming a low-salt reservoir within the saline water. The latter could be used as an ion exchanger through manipulation of transport proteins in the cell membrane. In this article, we use the example of biodesalination as a vehicle to review the availability of tools and methods for the exploitation of cyanobacteria in water biotechnology. Issues discussed relate to strain selection, environmental factors, genetic manipulation, ion transport, cell-water separation, process design, safety, and public acceptance.

[Functional analysis of promoter fragments of salt-tolerance related genes in Spirulina]

In this work, the functions of promoter fragments of two potential salt-tolerance related genes of Spirulina (Spirulina platensis Geitl.) were studied using green fluorescent protein gene (gfp) as a reporter. The promoter structures of two salt-tolerance related genes of Spirulina were predicted using online promoter prediction software. pMD18-T and pUC18 vectors were used to clone the promoter sequences as well as the gfp gene and kanamycine resistance (kan) gene. The fragments containing pro-gfp-kanr were further cloned into pKW1188 vector and the resulting recombinant plasmids were then transformed into a host strain Synechocystis sp. (Synechocystis pevalekii Ercegovic) PCC6803. The resulting bacterial strains were grown under various concentrations of salinity for defining time intervals. The bacterial fluorescence was observed using laser confocal microscope. Our results showed that the transgenic bacteria grown at different concentrations of salinity for various periods produced varying fluorescence intensities. The bacteria treated with NaCl at the concentrations of 0.4mol/L to 0.6mol/L for 6 to 8 h showed the strongest fluorescent intensity. From the result of high salt induced expression of gfp, we predicted that the genes under control of these two promoters are likely to play important roles in the salt tolerance of Spirulina. Accordingly, we believed that a research platform for the studying functions of the promoters of the salt-tolerance related genes in Spirulina has been developed with the gfp as a reporter, the kanr gene as the selection marker, and Synechocystis. sp. PCC6803 as the expression host.

Contribution of a sodium ion gradient to energy conservation during fermentation in the cyanobacterium Arthrospira (Spirulina) maxima CS-328

Sodium gradients in cyanobacteria play an important role in energy storage under photoautotrophic conditions but have not been well studied during autofermentative metabolism under the dark, anoxic conditions widely used to produce precursors to fuels. Here we demonstrate significant stress-induced acceleration of autofermentation of photosynthetically generated carbohydrates (glycogen and sugars) to form excreted organic acids, alcohols, and hydrogen gas by the halophilic, alkalophilic cyanobacterium Arthrospira (Spirulina) maxima CS-328. When suspended in potassium versus sodium phosphate buffers at the start of autofermentation to remove the sodium ion gradient, photoautotrophically grown cells catabolized more intracellular carbohydrates while producing 67% higher yields of hydrogen, acetate, and ethanol (and significant amounts of lactate) as fermentative products. A comparable acceleration of fermentative carbohydrate catabolism occurred upon dissipating the sodium gradient via addition of the sodium-channel blocker quinidine or the sodium-ionophore monensin but not upon dissipating the proton gradient with the proton-ionophore dinitrophenol (DNP). The data demonstrate that intracellular energy is stored via a sodium gradient during autofermentative metabolism and that, when this gradient is blocked, the blockage is compensated by increased energy conversion via carbohydrate catabolism.

Na+-stimulated ATPase of alkaliphilic halotolerant cyanobacterium Aphanothece halophytica translocates Na+ into proteoliposomes via Na+ uniport mechanism

Background

When cells are exposed to high salinity conditions, they develop a mechanism to extrude excess Na⁺ from cells to maintain the cytoplasmic Na⁺ concentration. Until now, the ATPase involved in Na⁺ transport in cyanobacteria has not been characterized. Here, the characterization of ATPase and its role in Na⁺ transport of alkaliphilic halotolerant Aphanothece halophytica were investigated to understand the survival mechanism of A. halophytica under high salinity conditions.

Results

The purified enzyme catalyzed the hydrolysis of ATP in the presence of Na⁺ but not K⁺, Li⁺ and Ca²⁺. The apparent K_m values for Na⁺ and ATP were 2.0 and 1.2 mM, respectively. The enzyme is likely the F₁F₀-ATPase based on the usual subunit pattern and the protection against N,N'-dicyclohexylcarbodiimide inhibition of ATPase activity by Na⁺ in a pH-dependent manner. Proteoliposomes reconstituted with the purified enzyme could take up Na⁺ upon the addition of ATP. The apparent K_m values for this uptake were 3.3 and 0.5 mM for Na⁺ and ATP, respectively. The mechanism of Na⁺ transport mediated by Na⁺-stimulated ATPase in A. halophytica was revealed. Using acridine orange as a probe, alkalization of the lumen of proteoliposomes reconstituted with Na⁺-stimulated ATPase was observed upon the addition of ATP with Na⁺ but not with K⁺, Li⁺ and Ca²⁺. The Na⁺- and ATP-dependent alkalization of the proteoliposome lumen was stimulated by carbonyl cyanide m - chlorophenylhydrazone (CCCP) but was inhibited by a permeant anion nitrate. The proteoliposomes showed both ATPase activity and ATP-dependent Na⁺ uptake activity. The uptake of Na⁺ was enhanced by CCCP and nitrate. On the other hand, both CCCP and nitrate were shown to dissipate the preformed electric potential generated by Na⁺-stimulated ATPase of the proteoliposomes.

Conclusion

The data demonstrate that Na⁺-stimulated ATPase from A. halophytica, a likely member of F-type ATPase, functions as an electrogenic Na⁺ pump which transports only Na⁺ upon hydrolysis of ATP. A secondary event, Na⁺- and ATP-dependent H⁺ efflux from proteoliposomes, is driven by the electric potential generated by Na⁺-stimulated ATPase.

Large-scale collection and annotation of full-length enriched cDNAs from a model halophyte, Thellungiella halophila

BACKGROUND

Thellungiella halophila (also known as Thellungiella salsuginea) is a model halophyte with a small plant size, short life cycle, and small genome. It easily undergoes genetic transformation by the floral dipping method used with its close relative, Arabidopsis thaliana. Thellungiella genes exhibit high sequence identity (approximately 90% at the cDNA level) with Arabidopsis genes. Furthermore, Thellungiella not only shows tolerance to extreme salinity stress, but also to chilling, freezing, and ozone stress, supporting the use of Thellungiella as a good genomic resource in studies of abiotic stress tolerance.

RESULTS

We constructed a full-length enriched Thellungiella (Shan Dong ecotype) cDNA library from various tissues and whole plants subjected to environmental stresses, including high salinity, chilling, freezing, and abscisic acid treatment. We randomly selected about 20,000 clones and sequenced them from both ends to obtain a total of 35 171 sequences. CAP3 software was used to assemble the sequences and cluster them into 9569 nonredundant cDNA groups. We named these cDNAs "RTFL" (RIKEN Thellungiella Full-Length) cDNAs. Information on functional domains and Gene Ontology (GO) terms for the RTFL cDNAs were obtained using InterPro. The 8289 genes assigned to InterPro IDs were classified according to the GO terms using Plant GO Slim. Categorical comparison between the whole Arabidopsis genome and Thellungiella genes showing low identity to Arabidopsis genes revealed that the population of Thellungiella transport genes is approximately 1.5 times the size of the corresponding Arabidopsis genes. This suggests that these genes regulate a unique ion transportation system in Thellungiella.

CONCLUSION

As the number of Thellungiella halophila (Thellungiella salsuginea) expressed sequence tags (ESTs) was 9388 in July 2008, the number of ESTs has increased to approximately four times the original value as a result of this effort. Our sequences will thus contribute to correct future annotation of the Thellungiella genome sequence. The full-length enriched cDNA clones will enable the construction of overexpressing mutant plants by introduction of the cDNAs driven by a constitutive promoter, the complementation of Thellungiella mutants, and the determination of promoter regions in the Thellungiella genome.

ATP in current biotechnology: regulation, applications and perspectives

Adenosine tri-phosphate (ATP), the most important energy source for metabolic reactions and pathways, plays a vital role in the growth of industrial strain and the production of target metabolites. In this review, current advances in manipulating ATP in industrial strains, including altering NADH availability, and regulating NADH oxidation pathway, oxygen supply, proton gradient, the electron transfer chain activity and the F(0)F(1)-ATPase activity, are summarized and discussed. By applying these strategies, optimal product concentrations, yields and productivity in industrial biotechnology have been achieved. Furthermore, the mechanisms by which ATP extends the substrate utilization spectra and enhances the ability to challenge harsh environmental stress have been elucidated. Finally, three critical issues related to ATP manipulation have been addressed.