Cyanobacteria Cells Research Articles

Bioplastic production by harnessing cyanobacteria-rich microbiomes for long-term synthesis

Departing from the conventional axenic and heterotrophic cultures, our research ventures into unexplored territory by investigating the potential of photosynthetic microbiomes for polyhydroxybutyrate (PHB) synthesis, a biodegradable polyester that presents a sustainable alternative to conventional plastics. Our investigation focused on a cyanobacteria-enriched microbiome, dominated by Synechocystis sp. and Synechococcus sp., cultivated in a 3 L photobioreactor under non-sterile conditions, achieving significant PHB production—up to 28 % dry cell weight (dcw) over a span of 108 days through alternating cycles of biomass growth and PHB accumulation. Nile Blue staining and Transmission Electron Microscope visualization allowed to successfully confirm the presence of PHB granules within cyanobacteria cells. Furthermore, the overexpression of PHA synthase during the accumulation phase directly correlated with the increased PHB production. Also, gene expression changes revealed glycogen as the primary storage compound, but under prolonged macronutrient stress, there was a shift of the carbon flux towards favoring PHB synthesis. Finally, analysis through Raman, Fourier- transform infrared spectroscopy and proton Nuclear Magnetic Resonance further validated the extracted polymer as PHB. Overall, it was demonstrated for the first time the feasibility of using phototrophic microbiomes to continuous production of PHB in a non-sterile system. This study also offers valuable insights into the metabolic pathways involved.

A Comprehensive Study of Light Quality Acclimation in Synechocystis Sp. PCC 6803.

Cyanobacteria play a key role in primary production in both oceans and fresh waters and hold great potential for sustainable production of a large number of commodities. During their life, cyanobacteria cells need to acclimate to a multitude of challenges, including shifts in intensity and quality of incident light. Despite our increasing understanding of metabolic regulation under various light regimes, detailed insight into fitness advantages and limitations under shifting light quality remains underexplored. Here, we study photo-physiological acclimation in the cyanobacterium Synechocystis sp. PCC 6803 throughout the photosynthetically active radiation (PAR) range. Using light emitting diodes (LEDs) with qualitatively different narrow spectra, we describe wavelength dependence of light capture, electron transport and energy transduction to main cellular pools. In addition, we describe processes that fine-tune light capture, such as state transitions, or the efficiency of energy transfer from phycobilisomes to photosystems (PS). We show that growth was the most limited under blue light due to inefficient light harvesting, and that many cellular processes are tightly linked to the redox state of the plastoquinone (PQ) pool, which was the most reduced under red light. The PSI-to-PSII ratio was low under blue photons, however, it was not the main growth-limiting factor, since it was even more reduced under violet and near far-red lights, where Synechocystis grew faster compared to blue light. Our results provide insight into the spectral dependence of phototrophic growth and can provide the foundation for future studies of molecular mechanisms underlying light acclimation in cyanobacteria, leading to light optimization in controlled cultivations.

Стрессорное воздействие биоцидных метаболитов актинобактерии Streptomyces geldanamycininus Z374 на цианобактерии Microcystis aeruginosa

Over the past decades, as a result of anthropogenic pollution and global warming, the frequency, intensity and geographical distribution of the mass development of microalgae and cyanobacteria in water bodies have significantly increased. The Microcystis species are responsible for most cases of the cyanobacterial blooms in freshwater bodies worldwide. Microcystis aeruginosa is the most commonly observed of them. In this work, we assessed the stress effect of isolated from actinobacteria Streptomyces geldanamycininus cyanocidal crude biocide Z374 (CB Z374) on the cyanobacteria M. aeruginosa. The results showed that CB Z374 significantly inhibited M. aeruginosa biomass. The CB Z374 half maximal effective concentration (EC50) for M. aeruginosa after 96 hours of treatment was 5 mg/L. The growth of M. aeruginosa with CB Z374 is characterized by an increase in the duration of the lag-phase, a decrease in the specific growth rate and biomass yield compared to the control. CB Z374 caused oxidative stress in cyanobacteria cells, determined by the elevated levels of hydrogen peroxide (H2O2) and malondialdehyde (MDA) up to 1.6 times, as well as an increased permeability of M. aeruginosa cell membranes by 1.5 times. The levels of superoxide dismutase (SOD) and catalase (CAT) activities and reduced glutathione (GSH) content raised in response to oxidative stress. M. aeruginosa growth inhibition was accompanied by a photosynthesis modification: the photosynthetic pigments phycobiliproteins and carotenoids content increases by 2.3 and 1.6 times respectively and the chlorophyll a content decreases by 1.2 times. CB Z374 inhibited M. aeruginosa photosynthesis, which was expressed in a decline in the maximum quantum efficiency of photosystem II – Fv/Fm by 10% and a reduction in the electron transfer rate (ETR) by 18%. We assume that oxidative stress and, as a result, cell membranes damage and photosynthesis inhibition are the main mechanisms of the cyanocidal action of CB Z374 on M. aeruginosa.

β-cyclocitral induced rapid cell death of Microcystis aeruginosa

β-cyclocitral (BCC) is an odorous compound that can be produced by bloom-forming cyanobacteria, for example, Microcystis aeruginosa. BCC has been proposed to explain the rapid decline of cyanobacterial blooms in natural water bodies due to its lytic effects on cyanobacteria cells. However, few insights have been gained regarding the mechanisms of its lethality on cyanobacteria. In this study, M. aeruginosa was exposed to 0–300 mg/L BCC, and the physiological responses were comprehensively studied at the cellular, molecular, and transcriptomic levels. The result indicated that the lethal effect was concentration-dependent; 100 mg/L BCC only caused recoverable stress, while 150–300 mg/L BCC caused rapid rupture of cyanobacterial cells. Scanning electron microscope images suggested two typical morphological changes exposed to above 150 mg/LBCC: wrinkled/shrank with limited holes on the surface at 150 and 200 mg/L BCC exposure; no apparent shrinkage at the surface but with cell perforation at 250 and 300 mg/L BCC exposure. BCC can rapidly inhibit the photosynthetic activity of M. aeruginosa cells (40%∼100% decreases for 100–300 mg/L BCC) and significantly down-regulate photosynthetic system Ⅰ-related genes. Also, chlorophyll a (by 30%∼90%) and ATP (by ∼80%) contents severely decreased, suggesting overwhelming pressure on the energy metabolism in cells. Glutathione levels increased significantly, and stress response-related genes were upregulated, indicating the perturbation of intracellular redox homeostasis. Two cell death pathways were proposed to explain the lethal effect: apoptosis-like death as revealed by the upregulation of SOS response genes when exposed to 200 mg/L BCC and mazEF-mediated death as revealed by the upregulation of mazEF system genes when exposed to 300 mg/L BCC. Results of the current work not only provide insights into the potential role of BCC in inducing programmed cell death during bloom demise but also indicate the potential of using BCC for harmful algal control.

Cycles of solar ultraviolet radiation favor periodic expansions of cyanobacterial blooms in global lakes

Global warming and eutrophication are known to increase the prevalence of cyanobacterial blooms, posing a severe threat to the ecological stability and sustainability of water bodies. The long-term (over an annual time frame) effect of UV radiation on cyanobacterial blooms in lakes are rarely discussed though the substantial effects of high-intensity UV radiation on the growth inhibition of marine phytoplankton were studied. Here, we employed the datasets on surface solar UV radiation, nitrogen and phosphorus concentrations, and the annual scales and frequencies of cyanobacterial blooms in lakes across long-term spatial scales to probe the relationship of UV radiation with cyanobacterial blooms. The results indicated that enhanced solar UV radiation may unintentionally stimulate cyanobacterial growth and favor the expansions of cyanobacterial blooms in lakes around the world. The fluctuating UV radiation significantly affects the annual scales of cyanobacterial blooms in both eutrophic and oligotrophic lakes. Solar UV radiation enhances the positive impact of rising phosphorus levels on cyanobacterial blooms because UV radiation prompts the synthesis of polyphosphate in cyanobacteria cells, which helps cyanobacteria to alleviate the stress of UV light. The scales of cyanobacterial blooms are significantly impacted by solar UV radiation intensities as opposed to the annual frequency of cyanobacterial blooms. Furthermore, solar UV radiation fluctuation with a 9-year period over a 14-year main cycles significantly affects the periodicities of cyanobacterial blooms in global lakes, which provides a basis for predicting the peak value of the scales of cyanobacterial blooms in lakes. These findings opened up new avenues of inquiry into the mechanism and management strategies of cyanobacterial blooms in lakes worldwide.

A GH19 lysozyme and peptidase from Myoviridae cyanophages lacking the typical holin-endolysin system exhibit lytic activity

Most of the dsDNA cyanophages employ holin-endolysin lysis systems to damage the host cells. This study aimed to elucidate the lytic activity of ORF91 and ORF117 in the cyanophage MaMV-DH01, which lacked a conventional cholinesterase system. These two proteins contained Lyz-like superfamily domains and were annotated as a member of GH family 19 (named DHGH19) and peptidase (named DHpeptidase), respectively. Overexpression of DHGH19 in E. coli over a 5 h course demonstrated potent bactericidal activity, evident from significant growth inhibition, membrane damage, and leakage of intracellular enzymes of E. coli cells. However, the lytic activity of DHpeptidase was relatively weaker, exhibiting a bacteriostatic effect. It was important to highlight that the specific mutation of enzyme-catalyzed residues in DHGH19 (E122 and E131) showed that these were the essential amino acids for DHGH19 to exert its bactericidal activity. Furthermore, the lytic function of DHGH19 and DHpeptidase on cyanobacteria cells was confirmed by their overexpression in the cyanobacterium Synechocystis sp. PCC6803. Overall, this study provides novel insights into the lytic mechanism of Myoviridae cyanophage, offering potential alternatives for the development of GH19 and peptidase as new antibacterial agents in the future.

Understanding the Risks of Diffusion of Cyanobacteria Toxins in Rivers, Lakes, and Potable Water.

Blue-green algae, or cyanobacteria, may be prevalent in our rivers and tap water. These minuscule bacteria can grow swiftly and form blooms in warm, nutrient-rich water. Toxins produced by cyanobacteria can pollute rivers and streams and harm the liver and nervous system in humans. This review highlights the properties of 25 toxin types produced by 12 different cyanobacteria genera. The review also covered strategies for reducing and controlling cyanobacteria issues. These include using physical or chemical treatments, cutting back on fertilizer input, algal lawn scrubbers, and antagonistic microorganisms for biocontrol. Micro-, nano- and ultrafiltration techniques could be used for the removal of internal and extracellular cyanotoxins, in addition to powdered or granular activated carbon, ozonation, sedimentation, ultraviolet radiation, potassium permanganate, free chlorine, and pre-treatment oxidation techniques. The efficiency of treatment techniques for removing intracellular and extracellular cyanotoxins is also demonstrated. These approaches aim to lessen the risks of cyanobacterial blooms and associated toxins. Effective management of cyanobacteria in water systems depends on early detection and quick action. Cyanobacteria cells and their toxins can be detected using microscopy, molecular methods, chromatography, and spectroscopy. Understanding the causes of blooms and the many ways for their detection and elimination will help the management of this crucial environmental issue.

Enhanced photocatalytic inactivation of Cylindrospermopsis raciborskii by modified TiO2/Ag3PO4: Efficiency and mechanism

To effectively inhibit the emerging harmful algae Cylindrospermopsis raciborskii, modified TiO2/Ag3PO4 (T-P25/A) with oxygen vacancies was successfully synthesized by tea polyphenol (TP) reduction and chemical deposition methods for algae removal under visible light. The creation of oxygen vacancies affected the band structure of P25 and improved the photocatalytic performance of the T-P25/A composite. The photogenerated holes (h+) and superoxide radicals (·O2–) are dominant reactive species in the photocatalytic system of T-P25/A, which yielded a 91.75 % inactivation rate to Cylindrospermopsis raciborskii (cyanobacteria cells) after 5 h of visible light irradiation. This degradation rate was about 1.5 and 1.7 times that of P25/A and Ag3PO4, respectively. Furthermore, the algal inactivation mechanism by T-P25/A under visible light was indicated by changes in morphological characteristics, cellular content degradation, oxidative species accumulation, and enzyme activity. This research provides valuable information about applicational prospects for the inactivation of harmful algal cells in real water bodies.

Arsenic uptake and metabolism by a marine cyanobacteria PCC7002

Cyanobacteria Synechococcus PCC7002 is a typical marine bacterium that can tolerate salinity at around 20 ppt. In this study, cyanobacterium PCC7002 cells were incubated in a controlled environmental chamber for one week. Three different arsenic V (AsV) concentrations were added to the culture to observe the cyanobacterium’s capability to arsenic uptake. The arsenic uptake was then compared to the control media (without AsV addition). The higher the arsenic concentration added to the media, the more Arsenic occurs in the cells. Cyanobacteria cells could take up arsenic from their media at the range of 60-90% of the total arsenic exposed to the media, which showed their high arsenic tolerance. Speciation analysis using tandem HPLC and ICPMS showed that As-sugar is the main arsenic species in the cells, while inorganic arsenic is the main arsenic species in the media. Further analysis for signal confirmation using LCMS showed that the transformation of inorganic AsV into organic arsenic (As-sugar) confirmed the biotransformation of arsenic in the cyanobacteria cells. This result proves the vital role of cyanobacteria in arsenic cycling and biotransformation in marine environments.

Functional Analysis of the Endopeptidase and Holin From Planktothrix agardhii Cyanophage PaV-LD.

A cyanophage PaV-LD, previously isolated from harmful filamentous cyanobacterium Planktothrix agardhii, was sequenced, and co-expression of its two ORFs in tandem, ORF123 and ORF124, inhibited growth on the model cyanobacterium Synechocystis sp. PCC6803 cells. However, the mechanism of action of ORF123 and ORF124 alone remains to be elucidated. In this study, we aimed to study the individual function of ORF123 or ORF124 from PaV-LD. Our data showed that the ORF123 encoded an endopeptidase, which harbored an M23 family peptidase domain and a transmembrane region. The expression of the endopeptidase in Escherichia coli alone revealed that the protein exhibited remarkable bacteriostatic activity, as evidenced by observation of growth inhibition, membrane damage, and leakage of the intracellular enzyme. Similarly, the holin, a membrane-associated protein encoded by the ORF124, showed weak bacteriostatic activity on E. coli. Moreover, deletion mutations indicated that the transmembrane domains of endopeptidase and holin were indispensable for their bacteriostatic activity. Meanwhile, the bacteriostatic functions of endopeptidase and holin on cyanobacteria cells were confirmed by expressing them in the cyanobacterium Synechocystis sp. PCC6803. Collectively, our study revealed the individual role of endopeptidase or holin and their synergistic bacteriolytic effect, which would contribute to a better understanding of the lytic mechanism of cyanophage PaV-LD.

Airborne microalgal and cyanobacterial diversity and composition during rain events in the southern Baltic Sea region

Airborne cyanobacteria and microalgae are commonly found in the atmosphere and may pose a serious human health risk. This study presents an innovative investigation of the washout efficiency of airborne cyanobacteria and microalgae in the Gulf of Gdańsk (southern Baltic Sea). For the first time, the number and type of cyanobacteria and microalgae were determined in rainwater samples and in air before and after rainfall events. The number of cyanobacteria and microalgae cells in the rainwater samples ranged, depending on, e.g., weather conditions, from 100 cells L–1 to 342.2 × 103 cells L–1. Several harmful taxa, such as Chlorococcum sp., Oocystis sp., Anabaena sp., Leptolyngbya sp., Nodularia sp., Pseudanabaena sp., Synechococcus sp., Synechocystis sp., and Gymnodinium sp., were noted in our study. Washing out by rain is extremely relevant to human health and decreases the chance that people inhale these species and their toxic metabolic products. The greatest diversity of airborne microalgae and cyanobacteria was recorded in July 2019, despite this being the period with the lowest number of cells in rainwater samples. Research conducted in the southern Baltic Sea region confirmed the relationship between the occurrence of cyanobacteria and microalgae in the air and blooms in the sea. It is worth emphasizing that the number of microalgae and cyanobacteria cells decreased by up to 87% after a rainfall event relative to that before the rainfall event. The obtained results significantly increase the level of knowledge about cyanobacteria and microalgae present in the air. By demonstrating the washout efficiencies of cyanobacteria and microalgae, the results indicate the potential of individual taxa to be removed from the atmosphere with rainfall. The findings of this study are helpful for further research on airborne microorganisms and air quality.

Evaluation of Moringa oleifera Extract as a Biocoagulant to Remove Microcystis aeruginosa Cells and Dissolved Metabolites

Cyanobacteria are microorganisms capable of releasing toxic metabolites in freshwater, deleterious to humans and other living organisms even in very low concentrations. Removing both cyanobacteria cells and their metabolites in conventional water treatment systems is still a challenge that needs to be addressed. This paper evaluated the use of Moringa oleifera saline extract and polyaluminum chloride (PACl) as coagulants in order to remove cells and metabolites of M. aeruginosa from water. Samples consisted of synthetic water spiked with humic acid and M. aeruginosa cells, with a final turbidity of 25 NTU. Coagulation/flocculation/dissolved air flotation (C/D/DAF) tests were performed with 50 mg/L of M. oleifera coagulant, combined with different proportions of PACl (10–50%). For removal of metabolites, 25 μg/L of microcystin and 50 ng/L of 2-MIB and geosmin were spiked in water samples. The best results were obtained with 70:30 M. oleifera:PACl, achieving removal efficiencies of 81.37%, 74.69%, and 71.06% for turbidity, color, and cell density, respectively. For microcystin, 2-MIB, and geosmin, after filtration (30 min), global removal efficiencies (clarification + filtration) of 99.45%, 62.37%, and 100%, respectively, were obtained, using Sand+GAC filter. The results suggest that the substitution of PACl by M. oleifera extract can be a good option to remove cyanobacteria cells from water, and high removal efficiencies of metabolites can be achieved after the complete proposed treatment.

Common architectures in cyanobacteria Prochlorococcus cells visualized by X-ray diffraction imaging using X-ray free electron laser

Visualization of intracellular structures and their spatial organization inside cells without any modification is essential to understand the mechanisms underlying the biological functions of cells. Here, we investigated the intracellular structure of cyanobacteria Prochlorococcus in the interphase by X-ray diffraction imaging using X-ray free-electron laser. A number of diffraction patterns from single cells smaller than 1 µm in size were collected with high signal-to-noise ratio with a resolution of up to 30 nm. From diffraction patterns, a set of electron density maps projected along the direction of the incident X-ray were retrieved with high reliability. The most characteristic structure found to be common among the cells was a C-shaped arrangement of 100-nm sized high-density spots, which surrounded a low-density area of 100 nm. Furthermore, a three-dimensional map reconstructed from the projection maps of individual cells was non-uniform, indicating the presence of common structures among cyanobacteria cells in the interphase. By referring to the fluorescent images for distributions of thylakoid membranes, nucleoids, and carboxysomes, we inferred and represented their spatial arrangements in the three-dimensional map. The arrangement allowed us to discuss the relevance of the intracellular organization to the biological functions of cyanobacteria.

Alkyltrimethylammonium (ATMA) surfactants as cyanocides - Effects on photosynthesis and growth of cyanobacteria

Cyanobacteria and their toxins present potential hazard to consumers of water from lakes, reservoirs and rivers, thus their removal via water treatment or at the source, is essential. Here, we report that alkyltrimethylammonium (ATMA) surfactants, such as octadecyltrimethylammonium (ODTMA) bromide, act as cyanocides that efficiently inhibit photosynthesis and growth of cyanobacteria. Green algae were found less sensitive than cyanobacteria to ATMA compounds. Fluorescence measurements and microscopic observations demonstrated that cyanobacteria cells (Aphanizomenon or Microcystis) disintegrate and lose their metabolic activity (photosynthesis) upon exposure to ATMA bromides (estimated ED50(1hr) ranged between 1.5 and 7 μM for ODTMA-Br or hexadecyltrimethylammonium (HDTMA) bromide). Other ATMA compounds, such as tetradecyltrimethylammonium (TDTMA) or dodecyltrimethylammonium (DDTMA) bromides had similar inhibitory effect but their toxicity to cyanobacteria (measured as ED50(1hr) for photosynthetic efficiency) decreased, as the length of the alkyl chain decreased. All ATMA compounds used in this study showed lower toxicity to green algae than to cyanobacteria. A toxicity mechanism for ATMA cations is proposed, based on real time fluorescence signals and on alteration of cell ultra-structure revealed by electron microscopy. The present study sheds light on the toxic effect of ATMA surfactants on cyanobacteria and its potential application for controlling the occurrence of cyanobacterial bloom in lakes, reservoirs or rivers to secure the safety of drinking water and to mitigate and manage bloom events.

Quantitative analysis of the effects of morphological changes on extracellular electron transfer rates in cyanobacteria

BackgroundUnderstanding the extracellular electron transport pathways in cyanobacteria is a major factor towards developing biophotovoltaics. Stressing cyanobacteria cells environmentally and then probing changes in physiology or metabolism following a significant change in electron transfer rates is a common approach for investigating the electron path from cell to electrode. However, such studies have not explored how the cells’ concurrent morphological adaptations to the applied stresses affect electron transfer rates. In this paper, we establish a ratio to quantify this effect in mediated systems and apply it to Synechococcus elongatus sp. PCC7942 cells grown under different nutritional regimes.ResultsThe results provide evidence that wider and longer cells with larger surface areas have faster mediated electron transfer rates. For rod-shaped cells, increase in cell area as a result of cell elongation more than compensates for the associated decline in mass transfer coefficients, resulting in faster electron transfer. In addition, the results demonstrate that the extent to which morphological adaptations account for the changes in electron transfer rates changes over the bacterial growth cycle, such that investigations probing physiological and metabolic changes are meaningful only at certain time periods.ConclusionA simple ratio for quantitatively evaluating the effects of cell morphology adaptations on electron transfer rates has been defined. Furthermore, the study points to engineering cell shape, either via environmental conditioning or genetic engineering, as a potential strategy for improving the performance of biophotovoltaic devices.

Bioprocesses of hydrogen production by cyanobacteria cells and possible ways to increase their productivity

Due to the depletion and increasing cost of fossil fuels, the production of cyanobacteria-based hydrogen as eco-friendly and renewable energy for the future seems promising. The paper describes the current state of research in the field of hydrogen yield by cyanobacteria. The use of cyanobacteria as potential producers of hydrogen is particularly relevant and beneficial as they form hydrogen from water as a result of solar energy conversion. However, production is a complex biotechnological process, and the main obstacle is the low ability of cyanobacteria to produce hydrogen. The prospects for the development of cyanobacterium-based hydrogen energy can be improved by a complex approach of increasing hydrogen productivity by cyanobacteria cells. First of all, it is the achievement of genetic engineering, the construction of genetic mutants of cyanobacteria with great potential in hydrogen production, followed by a correctly chosen metabolic approach to increase its yield and the development of innovative methods of their cultivation. Thus, the widespread adoption of this technology requires additional R&D with large investments.

COMBINED EFFECT OF REACTIVE OXYGEN FORMS AND SHUNGITE ON THE GROWTH AND DEVELOPMENT OF CYANOBACTERIA

It has been shown that hydrogen peroxide, singlet oxygen and shungite affect the development of the population of cyanobacteria Anabaena variabilis and Synechocystis sp. PCC 6803 in different directions. The growth of cyanobacteria culture slows down in the presence of photosensitizer and hydrogen peroxide. In this case, the number of cells depends on the amount of shungite in the environment. Cyanobacteria Anabaena variabilis and Synechocystis sp. PCC 6803 grow better in the presence of 10 g/L shungite, but growth is suppressed at 100 g/L. Shungite at 10 g/L protectes cultures from the toxic effects of Bengal pink and hydrogen peroxide, which was determined by the level of photosynthesis efficiency and cell amounts. The growth of Anabaena variabilis (in terms of optical density at 680 nm) has been found to slow down in the presence of only hydrogen peroxide relative to the control. The growth of Anabaena variabilis in the presence of shungite and hydrogen peroxide is restored to the level of control samples. The number of cyanobacterium Synechocystis sp. PCC 6803 cells slows down significantly in the presence of singlet oxygen. Being combined with singlet oxygen, shungite partially inactivates the action of Bengal pink. At the end of the experiment, the growth of the culture is restored to 60% compared to the control. A similar relationship is observed when evaluating the effectiveness of photosynthesis of cyanobacteria Anabaena variabilis and Synechocystis sp. PCC 6803. Thus, singlet oxygen is more toxic than hydrogen peroxide. This may be due to different mechanisms of action of hydrogen peroxide and singlet oxygen on cyanobacteria growth. Depending on the content in the water, shungite can stimulate or inhibit the growth of cyanobacteria cells, inactivate the action of a toxicant.

Synechococcus elongatus PCC7942: a cyanobacterium cell factory for producing useful chemicals and fuels under abiotic stress conditions.

Sucrose, a compatible osmolyte in cyanobacteria, functions both as an energy reserve and as osmoprotectant. Sugars are the most common substrates used by microorganisms to produce hydrogen (H2) by means of anaerobic dark fermentation. Cells of the unicellular, non-nitrogen fixing, freshwater cyanobacterium Synechococcus elongatus PCC7942 accumulate sucrose under salt stress. In the present work, we used this cyanobacterium and a genetically engineered strain of it (known as PAMCOD) to investigate the optimal conditions for (a) photosynthetic activity, (b) cell proliferation and (c) sucrose accumulation, which are necessary for H2 production via anaerobic dark fermentation of the accumulated sucrose. PAMCOD (Deshnium et al. in Plant Mol Biol 29:897-902, 1995) contains the gene codA that codes for choline oxidase, the enzyme which converts choline to the zwitterion glycine betaine. Glycine betaine is a compatible osmolyte which increases the salt tolerance of Synechococcus elongatus PCC7942. Furthermore, glycine betaine maintains cell proliferation under salt stress and results in increased sucrose accumulation. In the present study, we examine the environmental factors, such as the NaCl concentration, the culture medium pH, and the carbon dioxide content of the air bubbled through it. At optimal conditions, sucrose accumulated in the cyanobacteria cells up to 13.5mol per mole Chl a. Overall, genetically engineered Synechococcus elongatus PCC7942 produces sucrose in sufficient quantities such that it may be a viable alternative (a) to sucrose synthesis, and (b) to H2 formation via anaerobic dark fermentation.

Potential use of C-phycocyanin in non-alcoholic fatty liver disease

C-phycocyanin (C-PC) is a kind of photosynthetically assisted pigment, which is ubiquitous in cyanobacteria cells. We investigated the effect of C-PC on non-alcoholic fatty liver disease (NAFLD) and its mechanism. Through oil red O staining, TC/TG detection, liver SOD/MDA detection and liver H&E staining, we found that C-PC could significantly reduce the lipid accumulation in the steatosis L02 cells and the liver of non-alcoholic steatohepatitis (NASH) mice, and improve the antioxidant capacity of liver. The results of Western Blotting showed that C-PC upregulated the expression of AMPK phosphorylation and downregulated SREBP-1c and its target genes ACC and FAS expression levels. Furthermore, C-PC also upregulated the expression of transcription factor PPARα, which was regulated by AMPK, and its target genes CPT1 level. In addition, C-PC could promote AMPK phosphorylation in hepatocytes while increasing the phosphorylation level of ACC in vivo and in vitro. Besides, C-PC could also improve the liver inflammatory infiltration by upregulated the expression of PPARγ and downregulated the expression of CD36, IL6 and TNFα. These results indicate that C-PC may improve hepatic lipid accumulation and inflammation in the non-alcoholic fatty liver mice by activating AMPK pathway of hepatocytes. The finding provides important help for the research and development of C-PC in the nutraceuticals and therapeutics of NAFLD.

Removal of Microcystis aeruginosa and control of algal organic matters by potassium ferrate(VI) pre-oxidation enhanced Fe(II) coagulation

The problem of cyanobacteria blooms during potable water production has generated wide concern. Ferrate(VI) serving as a pre-oxidation tactic was first applied to enhance conventional Fe(II) coagulation for Microcystis aeruginosa-laden water treatment at lab scale. Results demonstrated that ferrate(VI) pre-oxidation could successfully destabilize algae cells through destroying the protective organic layer. The residual ferrate(VI) together with post-added Fe(II) could provoke a comproportionation reaction, where large amounts of Fe hydrolyzates [Fe(OH)3] are formed. The in-situ Fe(OH)3 with abundant reactive surface is responsible for the promotion of flocs growth by facilitating the clustering and cross-linking of algal organic matters (AOM) and cyanobacteria cells, simultaneously resulting in satisfactory reductions in OD680, turbidity and UV254. Overdose of ferrate(VI) could cause severe cell destruction along with the release of intracellular organic matter (IOM), which may impair the water quality by increasing the concentration of dissolved organic carbon (DOC) and the disinfection by-products formation potential (DBPFP). Meanwhile, considering the Fe residual in settled water, the optimal ferrate(VI) dose (20 µM) and Fe(II) dose (80 µM) were proposed. Besides, the synergistic effect of both the degradation by ferrate(VI) and the adsorption by in-situ Fe(OH)3 contributed to the removal of DOC and Microcystin-LR. This study suggests that ferrate(VI) might be a potential candidate for pre-treatment to assist Fe(II) coagulation when addressing algae-laden water.