Salt and heat stress enhances hydrogen production in cyanobacteria.

Cyanobacteria are among the most suitable organisms for the capture of excessive amounts of CO2 and can be grown in extreme environments. In our research we use the single-celled freshwater cyanobacteria Synechococcus elongatus PCC7942 PAMCOD strain and Synechocystis sp. PCC6714 for the production of carbohydrates and hydrogen. PAMCOD strain and Synechocystis sp. PCC6714 synthesize sucrose when exposed to salinity stress, as their main compatible osmolyte. We examined the cell proliferation rate and the sucrose accumulation in those two different strains of cyanobacteria under salt (0.4 M NaCl) and heat stress (35 0C) conditions. The intracellular sucrose (mol sucrose content per Chl a) was found to increase by 50% and 108% in PAMCOD strain and Synechocystis sp. PCC6714 cells, respectively. As previously reported, PAMCOD strain has the ability to produce hydrogen through the process of dark anaerobic fermentation (Vayenos D, Romanos GE, Papageorgiou GC, Stamatakis K (2020) Photosynth Res 146, 235-245). In the present study, we demonstrate that Synechocystis sp. PCC6714 has also this ability. We further examined the optimal conditions during the dark fermentation of PAMCOD and Synechocystis sp. PCC6714 regarding H2 formation, increasing the PAMCOD H2 productivity from 2 nmol H2 h- 1 mol Chl a- 1 to 23 nmol H2 h- 1 mol Chl a- 1. Moreover, after the dark fermentation, the cells demonstrated proliferation in both double BG-11 and BG-11 medium enriched in NaNO3, thus showing the sustainability of the procedure.

Covalently Modified Kevlar Fabric Incorporating Graphene Oxide with Enhanced Antibacterial Properties and Preserved Strength.

This work describes a multi-step modification process for the covalent transformation of Kevlar fabric en route to the incorporation of graphene oxide (GO) nanosheets. Spectroscopic, thermal and microscopy imaging techniques have been employed to follow step-by-step the modification of Kevlar and the formation of the corresponding Kevlar-GO hybrid fabric. The level of Kevlar's functionalization can be controlled with the nitration time, the first reaction in the multi-sequence organic transformations, for obtaining the hybrid fabric with a content of GO up to 30 %. Most importantly, the covalent post-modification of Kevlar does not occur in the expense of the other excellent mechanical properties of the fabric. Under optimal conditions, the Kevlar-GO hybrid fabric shows a 20 % enhancement of the ultimate strength. Notably, when the Kevlar-GO hybrid fabric was exposed to cyanobacterial Synechococcus the bacteria growth was fully inhibited. Overall, the covalently modified fabric demonstrated significant antibacterial behavior, excellent strength and stability under common processes. Due to its simplicity, the methodology presented in this work not only promises to result in a standard procedure to functionalize the mer units of Kevlar with a variety of chemicals and nanomaterials but it can be also extended for the modification and hybridization of other fabrics.

Kevlar®, Nomex®, and VAR Modification by Small Organic Molecules Anchoring: Transfusing Antibacterial Properties and Improving Water Repellency.

The surface modification of fabrics composed of Kevlar®, Nomex®, or VAR was extensively investigated. Kevlar® and Nomex® are widely-utilized aramid materials, whereas VAR is a technical fabric comprising 64% viscose, 24% para-aramid (Kevlar®), 10% polyamide, and 2% antistatic fibers. Both aramid materials and cellulose/viscose exhibit exceptional mechanical properties that render them valuable in a wide range of applications. For the herein studied modification of Kevlar®, Nomex®, and VAR, we used small organic molecules 3-allyl-5,5-dimethylhydantoin (ADMH) and 3-(acrylamidopropyl)trimethylammonium chloride (APTAC), which were anchored onto the materials under study via graft polymerization. By doing so, excellent antibacterial properties were induced in the three studied fabrics. Their water repellency was improved in most cases as well. Extensive characterization studies were conducted to probe the properties of the modified materials, employing Raman and FTIR spectroscopies, Scanning Electron Microscopy (SEM), and thermogravimetric analysis (TGA).

Assessment of Synechococcus elongatus PCC 7942 as an option for sustainable wastewater treatment.

Industrial wastewaters are recognized as a valuable resource, however, their disposal without proper treatment can result in environmental deterioration. The associated environmental/operational cost of wastewater treatment necessitates upgrade of applied processes towards the goals of sustainability and mitigation of climate change. The implementation of cyanobacteria-based processes can contribute to these goals via resources recovery, production of high-value products, carbon fixation and green-energy production. The present study evaluates the cyanobacterium Synechococcus elongatus PCC 7942 (S7942) as a biological component for novel and sustainable alternatives to typical biological nutrient removal processes. Valuable results regarding cultivation temperature boundaries, applied disinfection techniques and analytical methods, as well as regarding relations between parameters expressing S7942 biomass concentration are presented. The results show that at typical industrial wastewater temperatures, S7942 efficiently grew and removed nitrates from treated snack-industry's wastewater. Moreover, in cultures with treated and relatively saline dairy wastewater, its growth rate slightly decreased, but nevertheless nitrates removal rate remained efficiently high. A comparison between typical denitrification processes and the proposed nutrient removal process indicated that a S7942-based system may constitute an alternative or a supplementary to denitrification process. Thus, Synechococcus elongatus PCC 7942 proved to be a potent candidate towards sustainable industrial wastewater treatment applications.

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 13.5 mol 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.

The extraordinary longevity of kleptoplasts derived from the Ross Sea haptophyte Phaeocystis antarctica within dinoflagellate host cells relates to the diminished role of the oxygen-evolving Photosystem II and to supplementary light harvesting by mycosporine-like amino acid/s.

The haptophyte Phaeocystis antarctica and the novel Ross Sea dinoflagellate that hosts kleptoplasts derived from P. antarctica (RSD; R.J. Gast et al., 2006, J. Phycol. 42 233-242) were compared for photosynthetic light harvesting and for oxygen evolution activity. Both chloroplasts and kleptoplasts emit chlorophyll a (Chl a) fluorescence peaking at 683nm (F683) at 277K and at 689 (F689) at 77K. Second derivative analysis of the F689 band at 77K revealed two individual contributions centered at 683nm (Fi-683) and at 689 (Fi-689). Using the p-nitrothiophenol (p-NTP) treatment of Kobayashi et al. (Biochim. Biophys. Acta 423 (1976) 80-90) to differentiate between Photosystem (PS) II and I fluorescence emissions, we could identify PS II as the origin of Fi-683 and PS I as the origin of Fi-689. Both emissions could be excited not only by Chl a-selective light (436nm) but also by mycosporine-like amino acids (MAAs)-selective light (345nm). This suggests that a fraction of MAAs must be proximal to Chls a and, therefore, located within the plastids. On the basis of second derivative fluorescence spectra at 77K, of p-NTP resolved fluorescence spectra, as well as of PSII-driven oxygen evolution activities, PS II appears substantially less active (~1/5) in dinoflagellate kleptoplasts than in P. antarctica chloroplasts. We suggest that a diminished role of PS II, a known source of reactive oxygen species, and a diminished dependence on nucleus-encoded light-harvesting proteins, due to supplementary light-harvesting by MAAs, may account for the extraordinary longevity of RSD kleptoplasts.

Effects of exogenous ß-carotene, a chemical scavenger of singlet oxygen, on the millisecond rise of chlorophyll a fluorescence of cyanobacterium Synechococcus sp. PCC 7942.

Singlet-excited oxygen (1O 2* ) has been recognized as the most destructive member of the reactive oxygen species (ROS) which are formed during oxygenic photosynthesis by plants, algae, and cyanobacteria. ROS and 1O 2* are known to damage protein and phospholipid structures and to impair photosynthetic electron transport and de novo protein synthesis. Partial protection is afforded to photosynthetic organism by the ß-carotene (ß-Car) molecules which accompany chlorophyll (Chl) a in the pigment-protein complexes of Photosystem II (PS II). In this paper, we studied the effects of exogenously added ß-Car on the initial kinetic rise of Chl a fluorescence (10-1000 µs, the OJ segment) from the unicellular cyanobacterium Synechococcus sp. PCC7942. We show that the added ß-Car enhances Chl a fluorescence when it is excited at an intensity of 3000 µmol photons m-2 s-1 but not when excited at 1000 µmol photons m-2 s-1. Since ß-Car is an efficient scavenger of 1O 2* , as well as a quencher of 3Chl a * (precursor of 1O 2* ), both of which are more abundant at higher excitations, we assume that the higher Chl a fluorescence in its presence signifies a protective effect against photo-oxidative damages of Chl proteins. The protective effect of added ß-Car is not observed in O2-depleted cell suspensions. Lastly, in contrast to ß-Car, a water-insoluble molecule, a water-soluble scavenger of 1O 2* , histidine, provides no protection to Chl proteins during the same time period (10-1000 µs).

International conference on "Photosynthesis research for sustainability-2015" in honor of George C. Papageorgiou", September 21-26, 2015, Crete, Greece.

During September 21-26, 2015, an international conference entitled ''Photosynthesis Research for Sustainability-2015'' was held in honor of George C. Papageorgiou at the Conference Center of the Orthodox Academy of Crete, an exceptionally beautiful location right on the Mediterranean Sea coast, Kolymvari, Chania, Crete, (Greece) (see http://photosynthesis2015.cellreg.org/ ). The meeting was held under the auspices of the Greek "General Secretariat for Research and Technology" (GSRT). We first provide a brief introduction and key contributions of George C. Papageorgiou, the honored scientist, and then information on the conference, on the speakers, and the program. A special feature of this conference was awards given to 13 young investigators, who are recognized in this Report. Several photographs are also included; they show the pleasant ambience at this conference. We invite the readers to the next conference on "Photosynthesis Research for Sustainability-2016," which will honor Nathan Nelson and T. Nejat Veziroglu; it will be held during June 19-25, 2016, in Pushchino, Moscow Region, Russia (see http://photosynthesis2016.cellreg.org/ ).

The non-foliar hypoxic photosynthetic syndrome: evidence for enhanced pools and functionality of xanthophyll cycle components and active cyclic electron flow in fruit chlorenchyma.

MAIN CONCLUSION: Green fruits display a high engagement in CEF and enhanced VAZ cycle activity as a response to the demands imposed by their internal aerial conditions, particularly low O 2 , due to gas exchange limitations. In the present study, we used HPLC analysis, post-illumination changes in fluorescence yield under varying O2 and CO2 partial pressures and absorbance changes at 820 nm induced by far-red light to assess the carotenoid composition, the functionality of the xanthophyll cycle (VAZ) and the possibility of an active cyclic e (-) flow (CEF) in the fully exposed green fruits from Nerium oleander and Rosa sp. Equally exposed, mature leaves served as controls. Compared to leaves, fruits display less total chlorophylls and carotenoids but higher Car/Chl ratio, mainly shaped by the increased pools of the VAZ cycle components, in both species. The enhanced VAZ pool size in fruits is combined with a higher mid-day de-epoxidation state (DEPS). Moreover, fruits exhibit considerably lower levels of oxidizable P700, a faster re-reduction of PSI and significantly higher relative magnitude of CEF, irrespective of the O2/CO2 levels applied. We conclude that the higher VAZ investment may serve the enhanced heat dissipation needs in fruits, in the presence of a suppressed linear e (-) flow. In addition, the elevated potential of CEF may replenish the ATP lost due to hypoxia and concurrently facilitate the development of adequate non-photochemical quenching (NPQ), through its contribution to ΔpH increase. Since other non-foliar green organs exhibit a similar photosynthetic pattern, we argue that this may reflect a common strategy for green tissues under similar micro-environmental conditions, particularly hypoxia.

SYNTHESIS OF N-SULFOPROPYLATED HYPERBRANCHED POLYETHYLENEIMINE WITH ENHANCED BIOCOMPATIBILITY AND ANTIMICROBIAL ACTIVITY.

Hyperbranched polyethyleneimine having 25,000Da molecular weight was functionalized by a simple sulfopropylation reaction, affording a novel N-sulfopropylated PEI derivative (PEI-SO3-). The successful introduction of N-sulfopropyl and sulfobetaine groups to the amino groups of PEI was spectroscopically confirmed. Furthermore, the antibacterial and anti-cyanobacterial activity of PEI-SO3- in comparison to the parent PEI were investigated on two type heterotrophic bacteria, i.e., Gram (-) Escherichia coli and Gram (+) Staphylococcus Aureus bacteria, and one type of autotrophic cyanobacterium, i.e. Synechococcus sp. PCC 7942. Both PEI-SO3- and PEI showed an enhanced, concentration-dependent antibacterial and anti-cyanobacterial activity against the tested bacteria strains, with PEI-SO3- exhibiting higher activity than the parent PEI, signifying that the introduction of the sulfopropyl and sulfobetaine groups to the PEI amino groups enhanced the antibacterial anti-cyanobacterial properties of PEI. In the case of cyanobacteria, PEI-SO3- was found to affect the integrity of the photosynthetic system by the inhibition of Photosystem-II electron transport activity. Cytocompatibility and hemocompatibility studies revealed that PEI-SO3- exhibits high biocompatibility, suggesting that PEI-SO3- could be considered as an attractive antibacterial and anti-cyanobacterial candidate for various applications in the disinfection industry and also against the harmful cyanobacterial blooms.