Search

In the next 10-20 years, several observatories will aim to detect the signatures of oxygenic photosynthesis on exoplanets, though targets must be carefully selected. Most known potentially habitable exo-planets orbit cool M-dwarf stars, which have limited emission in the photosynthetically active region of the spectrum (PAR, 400 < λ < 700 nm) used by Earth's oxygenic photoautotrophs. Still, recent experiments have shown that model cyanobacteria, algae, and non-vascular plants grow comfortably under simulated M-dwarf light, though vascular plants struggle. Here, we hypothesize that this is partly due to the different ways they harvest light, reflecting some general rule that determines how photosynthetic antenna structures may evolve under different stars. We construct a simple thermodynamic model of an oxygenic antenna-reaction centre supercomplex and determine the optimum structure, size and absorption spectrum under light from several star types. For the hotter G (e.g. the Sun) and K-stars, a small modular antenna is optimal and qualitatively resembles the PSII-LHCII supercomplex of higher plants. For the cooler M-dwarfs, a very large antenna with a steep 'energy funnel' is required, resembling the cyanobacterial phycobilisome. For the coolest M-dwarfs an upper limit is reached, where increasing antenna size further is subject to steep diminishing returns in photosynthetic output. We conclude that G- and K-stars could support a range of niches for oxygenic photo-autotrophs, including high-light adapted canopy vegetation that may generate detectable bio-signatures. M-dwarfs may only be able to support low light-adapted organisms that have to invest considerable resources in maintaining a large antenna. This may negatively impact global coverage and therefore detectability., (© 2024. The Author(s).)

Although most cyanobacteria grow in visible light (VL; λ = 400-700 nm), some cyanobacteria can also use far-red light (FRL; λ = 700-800 nm) for oxygenic photosynthesis by performing far-red light photoacclimation. These two types of cyanobacteria can be found in the same environment. However, how they respond to each other remains unknown. Here, we reveal that coculture stresses FRL-using Chlorogloeopsis fritschii PCC 9212 and VL-using Synechocystis sp. PCC 6803. No significant growth difference was found in Synechocystis sp. PCC 6803 between the coculture and the monoculture. Conversely, the growth of Chlorogloeopsis fritschii PCC 9212 was suppressed in VL under coculture. According to transcriptomic analysis, Chlorogloeopsis fritschii PCC 9212 in coculture shows low transcript levels of metabolic activities and high transcript levels of ion transporters, with the differences being more noticeable in VL than in FRL. The transcript levels of stress responses in coculture were likewise higher than in monoculture in Synechocystis sp. PCC 6803 under FRL. The low transcript level of metabolic activities in coculture or the inhibition of cyanobacterial growth indicates a possible negative interaction between these two cyanobacterial strains.IMPORTANCEThe interaction between two cyanobacterial species is the primary focus of this study. One species harvests visible light, while the other can harvest far-red and visible light. Prior research on cyanobacteria interaction concentrated on its interactions with algal, coral, and fungal species. Interactions between cyanobacterial species were, nevertheless, rarely discussed. Thus, we characterized the interaction between two cyanobacterial species, one capable of photosynthesis using far-red light and the other not. Through experimental and bioinformatic approaches, we demonstrate that when one cyanobacterium thrives under optimal light conditions, it stresses the remaining cyanobacterial species. We contribute to an ecological understanding of these two kinds of cyanobacteria distribution patterns. Cyanobacteria that utilize far-red light probably disperse in environments with limited visible light to avoid competition with other cyanobacteria. From a biotechnological standpoint, this study suggests that the simultaneous cultivation of two cyanobacterial species in large-scale cultivation facilities may reduce the overall biomass yield., Competing Interests: The authors declare no conflict of interest.

Cyanobacteria are photoautotrophic organisms that use light and water as a source of energy and electrons, respectively, to fix atmospheric carbon dioxide and release oxygen as a by-product during photosynthesis. However, photosynthesis and fitness of organisms are challenged by seasonal and diurnal fluctuations in light environments. Also, the distribution of cyanobacteria in a water column is subject to changes in the light regime. The quality and quantity of light change significantly in low and bright light environments that either limit photochemistry or result in photoinhibition due to an excess amount of light reaching reaction centers. Therefore, cyanobacteria have to adjust their light-harvesting machinery and cell morphology for the optimal harvesting of light. This adjustment of light-harvesting involves remodeling of the light-harvesting complex called phycobilisome or incorporation of chlorophyll molecules such as chlorophyll d and f into their light-harvesting machinery. Thus, photoacclimation responses of cyanobacteria at the level of pigment composition and cell morphology maximize their photosynthetic ability and fitness under a dynamic light environment. Cyanobacteria exhibit different types of photoacclimation responses that are commonly known as chromatic acclimation (CA). In this work, we discuss different types of CA reported in cyanobacteria and present a molecular mechanism of well-known type 3 CA where phycoerythrin and phycocyanin of phycobilisome changes according to light signals. We also include other aspects of type 3 CA that have been recently studied at a molecular level and highlight the importance of morphogenes, cytoskeleton, and carboxysome proteins. In summary, CA gives a unique competitive benefit to cyanobacteria by increasing their resource utilization ability and fitness., (© 2024 Scandinavian Plant Physiology Society.)

Cyanobacterial phycocyanin and phycoerythrin are gaining commercial interest due to their nutrition and healthcare values. This research analyzed the biomass accumulation and pigment production of two strains of Leptolyngbya under different combinations of light colors and intensities. The results showed that while Leptolyngbya sp.4 B1 (B1) produced all phycobiliproteins, Leptolyngbya sp.5 F2 (F2) only had phycocyanin and allophycocyanin. Both the color of the light and its light intensity affect the biomass accumulation and phycoerythrin concentration in strain B1. Although white light at medium intensity (50 μmol m-2 s-1) causes greater biomass accumulation (1.66 ± 0.13 gDW L-1), low-intensity (25 μmol m-2 s-1) green light induces lower biomass accumulation with twice the pigment content (87.70 ± 2.46 mg gDW -1), culminating in 71% greater productivity. In contrast, for the F2 strain, light intensity positively influenced biomass and pigment accumulation, being observed 2.25 ± 0.10 gDW L-1 under white light at 100 μmol m-2 s-1 and higher phycocyanin concentration (138.38 ± 3.46 mg gDW -1) under red light at 100 μmol m-2 s-1. These findings provide insights into optimizing the growth conditions by altering the intensity and wavelength of light for future production of phycocyanin and phycoerythrin from local cyanobacteria.

2-methylisoborneol (2-MIB) is an odiferous metabolite mainly produced by cyanobacteria, contributing to taste and odor problems in drinking water. The mechanisms involved in 2-MIB biosynthesis in cyanobacteria are not yet completely understood. This study investigated the effect of light availability and wavelength on growth, 2-MIB synthesis, and related gene expression in Pseudanabaena foetida var. intermedia. A significantly lower 2-MIB production was observed in P. foetida var. intermedia during the dark period of a 12-h photoperiod. Exposure to green light resulted in a significant decrease in 2-MIB production compared to white light and red light. The relative expression levels of 2-MIB-related genes in P. foetida var. intermedia were significantly lower during the dark period of a 12-h photoperiod and when cultured under green light. The expression of 2-MIB-related genes in cyanobacteria appears to be light-dependent. This study suggests that the demand for photopigment synthesis under unfavorable light conditions affects the 2-MIB synthesis in cyanobacteria., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Photosystems I and II are the photooxidoreductases central to oxygenic photosynthesis and canonically absorb visible light (400-700 nm). Recent investigations have revealed that certain cyanobacteria can acclimate to environments enriched in far-red light (700-800 nm), yet can still perform oxygenic photosynthesis in a process called far-red light photoacclimation, or FaRLiP. During this process, the photosystem subunits and pigment compositions are altered. Here, the current structural understanding of the photosystems expressed during FaRLiP is described. The design principles may be useful for guiding efforts to engineer shade tolerance in organisms that typically cannot utilize far-red light., Competing Interests: Declaration of competing interest The author declares that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in their paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Energy transfer from light-harvesting ketocarotenoids to the light-driven proton pump xanthorhodopsins has been previously demonstrated in two unique cases: an extreme halophilic bacterium 1 and a terrestrial cyanobacterium 2 . Attempts to find carotenoids that bind and transfer energy to abundant rhodopsin proton pumps 3 from marine photoheterotrophs have thus far failed 4-6 . Here we detected light energy transfer from the widespread hydroxylated carotenoids zeaxanthin and lutein to the retinal moiety of xanthorhodopsins and proteorhodopsins using functional metagenomics combined with chromophore extraction from the environment. The light-harvesting carotenoids transfer up to 42% of the harvested energy in the violet- or blue-light range to the green-light absorbing retinal chromophore. Our data suggest that these antennas may have a substantial effect on rhodopsin phototrophy in the world's lakes, seas and oceans. However, the functional implications of our findings are yet to be discovered., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)

The current study is focused on the effects of artificial UV-B radiation on growth, proteins, and pigments, as well as the activities of several enzymatic and non-enzymatic antioxidant enzymes in some cyanobacterial strains. Cultures were maintained at 25 °C ± 1 °C under a white fluorescent tube of intensity 30-40 μE m -2s -1 with a 14:10 light and dark cycle in the laboratory and analyzed at an interval of 25, 32, 39, 46, and 53 days. The test cultures were exposed to UV-B stress for 24 h at the same intervals. We found that exposure to UV-B showed increased production of phycocyanin and carotenoids in four strains, namely, Scytonema javanicum, Nostoc muscorum, Aphanothece naegeli, and Synechococcus elongates. We also look into the effects of UV-B radiation on the proline content, non-protein thiols, radical scavenging activity, ascorbic acid, and tocopherol, total flavonoid content (TFC), total phenolic content (TPC) on these strains. Variation in the non-enzymatic antioxidants and expression levels of enzymatic enzymes and reducing power activity as compared to the non-irradiated control was found. Our study showed that cyanobacteria impart prominent antioxidant and radical scavenging properties which facilitate the defence mechanism against UV-B induced cell damage., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

The effect of a Mars-like UV flux and γ-radiation on the detectability of biomarkers in dried cells of Chroococcidiopsis sp. CCMEE 029 was investigated using a fluorescence sandwich microarray immunoassay. The production of anti- Chroococcidiopsis antibodies allowed the immunoidentification of a reduced, though still detectable, signal in dried cells mixed with phyllosilicatic and sulfatic Mars regolith simulants after exposure to 6.8 × 10 5 kJ/m 2 of a Mars-like UV flux. No signal was detected in dried cells that were not mixed with minerals after 1.4 × 10 5 kJ/m 2 . For γ-radiation ( 60 Co), no detectable variations of the fluorescence signal occurred in dried cells exposed to 113 kGy compared to non-irradiated dried cells. Our results suggest that immunoassay-based techniques could be used to detect life tracers eventually present in the martian subsurface in freshly excavated materials only if shielded from solar UV. The high structural integrity of biomarkers irradiated with γ-radiation that mimics a dose accumulated in 13 Myr at 2 m depth from the martian surface has implications for the potential detectability of similar organic molecules/compounds by future life-detection missions such as the ExoMars Rosalind Franklin rover.

Some cyanobacteria can perform far-red light photoacclimation (FaRLiP), which allows them to use far-red light (FRL) for oxygenic photosynthesis. Most of the cyanobacteria able to use FRL were discovered in low visible-light (VL; λ = 400-700 nm) environments that are also enriched in FRL (λ = 700-800 nm). However, these cyanobacteria grow faster in VL than in FRL in laboratory conditions, indicating that FRL is not their preferred light source when VL is available. Therefore, it is interesting to understand why such strains were primarily found in FRL-enriched but not VL-enriched environments. To this aim, we established a terrestrial model system with quartz sand to study the distribution and photoacclimation of cyanobacterial strains. A FaRLiP-performing cyanobacterium, Leptolyngbya sp. JSC-1, and a VL-utilizing model cyanobacterium, Synechocystis sp. PCC 6803, were compared in this study. We found that, although Leptolyngbya sp. JSC-1 can grow well in both VL and FRL, Synechocystis sp. PCC 6803 grows much faster than Leptolyngbya sp. JSC-1 in VL. In addition, the growth was higher in liquid cocultures than in monocultures of Leptolyngbya sp. JSC-1 or Synechocystis sp. PCC 6803. In an artificial terrestrial model system, Leptolyngbya sp. JSC-1 has an advantage when growing in coculture at greater depths by performing FaRLiP. Therefore, strong competition for VL and slower growth rate are possible reasons why FRL-utilizing cyanobacteria are found in environments with low VL intensities. This model system provides a valuable tool for future studies of cyanobacterial ecological niches and interactions in a terrestrial environment. IMPORTANCE This study uses sand columns to establish a terrestrial model system for the investigation of the distribution and acclimation of cyanobacteria to far-red light. Previous studies of this group of cyanobacteria required direct in situ samplings. The variability of conditions and abundances of the cyanobacteria in natural settings impeded detailed analyses and comparisons. Therefore, we established this model system under controlled conditions in the laboratory. In this system, the distribution and acclimation of two cyanobacteria were similar to the situation observed in natural environments, which validates that it can be used to study fundamental questions. Using this approach, we made the unanticipated observation that two cyanobacteria grow faster in coculture than in axenic cultures. This laboratory-based model system can provide a valuable new tool for comparing cyanobacterial strains (e.g., mutants and wild type), exploring interactions between cyanobacterial strains and interactions with other bacteria, and characterizing ecological niches of cyanobacteria.

The demand for natural antioxidants to be used in food industry is increasing, as synthetic antioxidants are toxic and have high production costs. Specifically, food processing and preservation require antioxidants resistant to thermal sterilization processes. In this study, twenty-five strains among microalgae and cyanobacteria were screened as antioxidants producers. The species Enallax sp., Synechococcus bigranulatus and Galdieria sulphuraria showed the highest content of chlorophyll a and total carotenoids. In vitro stability and antioxidant activity of the ethanolic extracts were performed. The results revealed that pigments present in the extracts, obtained from the previously mentioned species, were stable at room temperature and exhibited in vitro free radical scavenging potential with IC 50 values of 0.099 ± 0.001, 0.048 ± 0.001 and 0.13 ± 0.02 mg mL -1 , respectively. Biocompatibility assay showed that the extracts were not toxic on immortalized cell lines. The antioxidant activity was also tested on a cell-based model by measuring intracellular ROS levels after sodium arsenite treatment. Noteworthy, extracts were able to exert the same protective effect, before and after the pasteurization process. Results clearly indicate the feasibility of obtaining biologically active and thermostable antioxidants from microalgae. Green solvents can be used to obtain thermo-resistant antioxidants from cyanobacteria and microalgae which can be used in the food industry. Thus, the substitution of synthetic pigments with natural ones is now practicable., (© 2021. The Author(s), under exclusive licence to Springer Nature B.V.)

Mycosporine-like amino acids (MAAs) are small natural molecules having potent UV-absorbing and antioxidant properties. Hassallia byssoidea is one dominant cyanobacterium found all over the Konark stone monument, a UNESCO World Heritage site. We characterized mycosporine-alanine for the first time from H. byssoidea and studied its biosynthetic pathway from the whole genome data. We found D-alanyl-D-alanine carboxypeptidase, which might convert mycosporine-glycine to mycosporine-alanine by replacing glycine with alanine or by separate methylation, the mycosporine-glycine is converted to mycosporine-alanine. Our in vitro UV-B exposure experiment and exposure of H. byssoidea to natural sunlight show an increase in biosynthesis of mycosporine-alanine with 12 h of UV-B irradiation and high natural sunlight. We also found mycosporine-alanine to have good free radical scavenging activity with an IC 50 value of 1.98 mg/ml. Our results show due to the presence of mycosporine-alanine H. byssoidea probably tolerate the UV and high solar radiation and continue to colonize on the Konark stone monument as a dominant cyanobacterium., (Copyright © 2021 Elsevier B.V. All rights reserved.)

The effect of light intensity and inoculum volume on the occurrence of photooxidation for Leptolyngbya sp. QUCCCM 56 was investigated, to facilitate the transition from small-scale laboratory experiments to large-scale outdoor cultivation. Indoor, the strain was capable of growing at light intensities of up to 5600 µmol photons/m 2 /s, at inoculation densities as low as 0.1 g/L (10% inoculation volume vol/vol). Levels of chlorophyll and phycocyanin showed a significant decrease within the first 24 h, indicating some level of photooxidation, however, both were able to recover within 72 h. When cultivated under outdoor conditions in Qatar during summer, with average peak light intensities 1981 ± 41 μmol photons/m 2 /s, the strain had difficulties growing. The culture recovered after an initial adaptation period, and clear morphological differences were observed, such as an increase in trichome length, as well as coiling of multiple trichomes in tightly packed strands. It was hypothesized that the morphological changes were induced by UV-radiation as an adaptation mechanism for increased self-shading. Furthermore, the presence of contaminating ciliates could have also affected the outdoor culture. Both UV and contaminants are generally not simulated under laboratory environments, causing a mismatch between indoor optimizations and outdoor realizations., (© 2021 The Authors. Biotechnology and Bioengineering published by Wiley Periodicals LLC.)

Gloeobacter violaceus is a cyanobacteria species with a lack of thylakoids, while photosynthetic antennas, i.e., phycobilisomes (PBSs), photosystem II (PSII), and I (PSI), are located in the cytoplasmic membrane. We verified the hypothesis that blue-red (BR) light supplemented with a far-red (FR), ultraviolet A (UVA), and green (G) light can affect the photosynthetic electron transport chain in PSII and explain the differences in the growth of the G. violaceus culture. The cyanobacteria were cultured under different light conditions. The largest increase in G. violaceus biomass was observed only under BR + FR and BR + G light. Moreover, the shape of the G. violaceus cells was modified by the spectrum with the addition of G light. Furthermore, it was found that both the spectral composition of light and age of the cyanobacterial culture affect the different content of phycobiliproteins in the photosynthetic antennas (PBS). Most likely, in cells grown under light conditions with the addition of FR and G light, the average antenna size increased due to the inactivation of some reaction centers in PSII. Moreover, the role of PSI and gloeorhodopsin as supplementary sources of metabolic energy in the G. violaceus growth is discussed.

Motility is ubiquitous in prokaryotic organisms including the photosynthetic cyanobacteria where surface motility powered by type 4 pili (T4P) is common and facilitates phototaxis to seek out favorable light environments. In cyanobacteria, chemotaxis-like systems are known to regulate motility and phototaxis. The characterized phototaxis systems rely on methyl-accepting chemotaxis proteins containing bilin-binding GAF domains capable of directly sensing light, and the mechanism by which they regulate the T4P is largely undefined. In this study we demonstrate that cyanobacteria possess a second, GAF-independent, means of sensing light to regulate motility and provide insight into how a chemotaxis-like system regulates the T4P motors. A combination of genetic, cytological, and protein-protein interaction analyses, along with experiments using the proton ionophore carbonyl cyanide m-chlorophenyl hydrazine, indicate that the Hmp chemotaxis-like system of the model filamentous cyanobacterium Nostoc punctiforme is capable of sensing light indirectly, possibly via alterations in proton motive force, and modulates direct interaction between the cyanobacterial taxis protein HmpF, and Hfq, PilT1, and PilT2 to regulate the T4P motors. Given that the Hmp system is widely conserved in cyanobacteria, and the finding from this study that orthologs of HmpF and T4P proteins from the distantly related model unicellular cyanobacterium Synechocystis sp. strain PCC6803 interact in a similar manner to their N. punctiforme counterparts, it is likely that this represents a ubiquitous means of regulating motility in response to light in cyanobacteria., Competing Interests: The authors declare no competing interest.

Cyanobacteria and microalgae present in the aquatic or terrestrial environment may be emitted into the air and transported along with air masses over long distances. As a result of staying in the atmosphere, these organisms may develop a greater tolerance to stressful factors, but this topic is still relatively unknown. The main aim was to show an autecological characteristic of some airborne microalgae and cyanobacteria strains by a factorial laboratory experiment approach, including changes in irradiance, temperature, and salinity conditions. The additional purpose of this work was also to present part of the Culture Collection of Baltic Algae (CCBA) collection, which consists of airborne algae (AA) isolated from the atmospheric air of the southern Baltic Sea region. Altogether, 61 strains of airborne cyanobacteria and microalgae from the southern Baltic Sea region were isolated from May 2018 to August 2020. Selected microorganisms were tested in controlled laboratory conditions to identify their response to different irradiance (10-190 µmol photons m -2 s -1 ), temperature (13-23 °C), and salinity conditions (0-36 PSU). The highest numbers of cells (above 30 × 10 5 cell mL -1 ) were recorded for cyanobacterium Nostoc sp., and for diatoms Nitzschia sp., Amphora sp., and Halamphora sp. We found that for cyanobacterium Nostoc sp. as well as for green alga Coccomyxa sp. the maximum cell concentrations were recorded at the salinity of 0 PSU. Moreover, cyanobacteria Planktolyngbya contorta , Pseudanabaena catenata , Leptolyngbya foveolarum , Gloeocapsa sp., and Rivularia sp. were able to grow only at a salinity of 0 PSU. On the other hand, in the range of 16-24 PSU, the highest cell numbers of examined diatoms have been identified. Our research provided that deposited airborne microalgae and cyanobacteria showed full colonization potential. The present experiment suggests that the adaptive abilities of microorganisms, in particular those producing toxins, may contribute to the spread in the future. Thus, it may increase human exposure to their negative health effects. Any distinctive adaptations of the genera give them an additional competitive advantage and a greater chance for territorial expansion.

Background: Global warming directly influencing ozone layer depletion, which eventually is increasing ultraviolet radiation penetration having far-reaching impacts on living biota. This particularly influences the primary producer microalgae which are the basic unit of food webs in the aquatic habitats. Therefore, it is necessary to concentrate the research at this micro-level to understand the harmful impact of increased UV-B radiation ever before. Consequently, the present attempt aimed to focus on the influence of UV-B on growth criteria, photosynthetic pigments, some metabolites, and ultrastructure of the freshwater cyanobacteria, Planktothrix cryptovaginata (Microcoleaceae), Nostoc carneum (Nostocaceae), Microcystis aeruginosa (Microcystaceae), the Chlorophyte Scenedesmus acutus (Scenedesmaceae), and the marine Cyanobacterium Microcystis (Microcystaceae)., Methods: The cultures of investigated algae were subjected directly to different duration periods (1, 3, 5, and 7 h) of artificial UV-B in addition to unirradiated control culture and allowed to grow for 10 days, after which the algal samples were analyzed for growth, photosynthetic activities, primary metabolities and cellular ultrastructure., Results: A remarkable inhibitory influence of UV-B was observed on growth criteria (measured as optical density and dry weight) and photosynthetic pigments of P. cryptovaginata, N. carneum, M. aeruginosa, S. acutus, and marine Microcystis . Where increasing the exposure time of UV-B was accompanied by increased inhibition. The variation in carbohydrate and protein contents under UV stress was based on the exposure periods and the algal species. The variation in algal ultrastructure by UV-B stress was noticed by an Electron Microscope. Cells damage and lysis, cell wall and cell membrane ruptured and release of intracellular substances, loss of cell inclusion, plasmolysis and necrosis, or apoptosis of the algal cells were observed by exposure to 7 h of UV-B., Conclusion: Exposure to UV-B has a marked harmful impact on the growth, pigments, and metabolic activity, as well as the cellular ultrastructure of some cyanobacteria and chlorophytes.

Free fatty acids (FFA) generated in cyanobacterial cells can be utilized for the biodiesel that is required for our sustainable future. The combination of FFA and strong light induces severe photoinhibition of photosystem II (PSII), which suppresses the production of FFA in cyanobacterial cells. In the present study, we examined the effects of exogenously added FFA on the photoinhibition of PSII in Synechocystis sp. PCC 6803. The addition of lauric acid (12:0) to cells accelerated the photoinhibition of PSII by inhibiting the repair of PSII and the de novo synthesis of D1. α-Linolenic acid (18:3) affected both the repair of and photodamage to PSII. Surprisingly, palmitic (16:0) and stearic acids (18:0) enhanced the repair of PSII by accelerating the de novo synthesis of D1 with the mitigation of the photoinhibition of PSII. Our results show chemical potential of FFA in the regulation of PSII without genetic manipulation.

Background: UV radiation and its impact on living organisms became an essential concern over the past three decades and will be essential in the years to come. So, the present investigation was devoted to examining the impact of artificial UV-B radiation on the accumulation of amino acids and MDA contents as well as some antioxidant enzymes activities in three freshwater cyanobacterial species; Planktothrix cryptovaginata, Nostoc carneum and Microcystis aeruginosa , one freshwater green alga; Scenedesmus acutus and one marine cyanobacterium; Microcystis ., Methods: The algal cultures were exposed directly to artificial UV-B radiation for 1, 3, 5, and 7 hours and amino acids, MDA contents, and the antioxidant enzyme activities; CAT, POD, APX, and SOD were analyzed., Results: The data obtained indicated that alteration in MDA and antioxidant enzymes by UV stress depends on the algal species and the exposure time. The treatment of the investigated algae with different periods of UV-B exposure stimulated the biosynthesis of some individual amino acids and inhibited the accumulation of some others. In some cases, exposure to UV-B was accompanied by the disappearance of some amino acids. In addition, UV-B exposure for 3 hours stimulated the accumulation of total amino acids in M. aeruginosa and S. acutus , while 7 hours of UV-B enhanced the biosynthesis of total amino acids in M. aeruginosa only from the investigated algae., Conclusion: Exposure of some cyanobacteria and green algae to UV-B radiation stimulated the biosynthesis of some individual amino acids and inhibited the accumulation or accompanied by the disappearance of some others. However, the alteration in MDA and antioxidant enzymes by UV stress depends on the algal species and the exposure time.

Due to the recent advances in X-ray free electron laser techniques, bilin-containing cyanobacteriochrome photoreceptors have become prime targets for the ever-expanding field of time-resolved structural biology. However, to facilitate these challenging studies, it is essential that the time scales of any structural changes during the photocycles of cyanobacteriochromes be established. Here, we have used visible and infrared transient absorption spectroscopy to probe the photocycle of a model cyanobacteriochrome system, TePixJ. The kinetics span multiple orders of magnitude from picoseconds to seconds. Localized changes in the bilin binding pocket occur in picoseconds to nanoseconds, followed by more large-scale changes in protein structure, including formation and breakage of a second thioether linkage, in microseconds to milliseconds. The characterization of the entire photocycle will provide a vital frame of reference for future time-resolved structural studies of this model photoreceptor.

Cyanobacteriochromes (CBCRs) are small, bistable linear tetrapyrrole (bilin)-binding light sensors which are typically found as modular components in multidomain cyanobacterial signaling proteins. The CBCR family has been categorized into many lineages that roughly correlate with their spectral diversity, but CBCRs possessing a conserved DXCF motif are found in multiple lineages. DXCF CBCRs typically possess two conserved Cys residues: a first Cys that remains ligated to the bilin chromophore and a second Cys found in the DXCF motif. The second Cys often forms a second thioether linkage, providing a mechanism to sense blue and violet light. DXCF CBCRs have been described with blue/green, blue/orange, blue/teal, and green/teal photocycles, and the molecular basis for some of this spectral diversity has been well established. We here characterize AM1&#95;1499g1, an atypical DXCF CBCR that lacks the second cysteine residue and exhibits an orange/green photocycle. Based on prior studies of CBCR spectral tuning, we have successfully engineered seven AM1&#95;1499g1 variants that exhibit robust yellow/teal, green/teal, blue/teal, orange/yellow, yellow/green, green/green, and blue/green photocycles. The remarkable spectral diversity generated by modification of a single CBCR provides a good template for multiplexing synthetic photobiology systems within the same cellular context, thereby bypassing the time-consuming empirical optimization process needed for multiple probes with different protein scaffolds., Competing Interests: The authors declare no competing interest.

Rising global temperatures have been suggested to favor cyanobacteria over eukaryotic algae, but UV-B fluxes are also predicted to remain high and may interact with temperature to affect algal growth. To understand the interactive effects of temperature and UV-B radiation, cultures of Microcystis aeruginosa and Anabaena circinalis were grown at either 25 or 30°C and then exposed to an acute irradiance of UV-B (1.4 W m -2 ). Both species showed differences in growth rates at both temperature regimes. The growth rates of M. aeruginosa (0.41 ± 0.02 day -1 ) and A. circinalis (0.38 ± 0.01 day -1 ) were higher at 25 and 30°C, respectively. Rates of damage (k) and repair (r) were calculated from the kinetics of change in effective quantum yield, F v '/F m '. Analysis of the estimates of r and k shows that M. aeruginosa exhibited relatively high values for both parameters, compared to A. circinalis, at both growth temperatures. In both species, repair rates were higher at 30°C than at 25°C but in A. circinalis damage was also greater at the higher temperature. In contrast, M. aeruginosa showed a lower damage rate at the higher temperature. For both species, the ratio of r:k was higher at the higher temperature. However, the percent inhibition of effective quantum yield by UV-B was greater in A. circinalis than in M. aeruginosa as the r:k was lower A. circinalis. Therefore, it could be concluded that temperature may influence growth and bloom formation of cyanobacteria and that different species may respond differently to UV-B and temperature interactions., (© 2020 American Society for Photobiology.)

The evolution of oxygenic photosynthesis, respiration and photoperception are connected with the appearance of cyanobacteria. The key compounds, which are involved in these processes, are tetrapyrroles: open chain - bilins and cyclic - chlorophylls and heme. The latter are characterized by their covalent bond with the apoprotein resulting in the formation of biliproteins. This type of photoreceptors is unique in that it can perform important and opposite functions-light-harvesting in photosynthesis with the participation of phycobiliproteins and photoperception mediated by phycochromes and phytochromes. In this review, cyanobacterial phycobiliproteins and phytochrome Cph1 are considered from a comparative point of view. Structural features of these pigments, which provide their contrasting photophysical and photochemical characteristics, are analyzed. The determining factor in the case of energy migration with the participation of phycobiliproteins is blocking the torsional relaxations of the chromophore, its D-ring, in the excited state and their freedom, in the case of phytochrome photoisomerization. From the energetics point of view, this distinction is preconditioned by the height of the activation barrier for the photoreaction and relaxation in the excited state, which depends on the degree of the chromophore fixation by its protein surroundings., (© 2019 American Society for Photobiology.)

The cyanobacterium Acaryochloris marina MBIC 11017 (A. marina 11017) possesses chlorophyll d (Chl. d) peaking at 698 nm as photosystem reaction center pigments, instead of chlorophyll a (Chl. a) peaking at 665 nm. About 95% of the total chlorophylls is Chl. d in A. marina 11017. In addition, A. marina 11017 possesses phycobilisome (PBS) supercomplex to harvest orange light and to transfer the absorbing energy to the photosystems. In this context, A. marina 11017 utilizes both far-red and orange light as the photosynthetic energy source. In the present study, we incubated A. marina 11017 cells under monochromatic orange and far-red light conditions and performed transcriptional and morphological studies by RNA-seq analysis and electron microscopy. Cellular absorption spectra, transcriptomic profiles, and microscopic observations demonstrated that PBS was highly accumulated under an orange light condition relative to a far-red light condition. Notably, transcription of one cpcBA operon encoding the phycobiliprotein of the phycocyanin was up-regulated under the orange light condition, but another operon was constitutively expressed under both conditions, indicating functional diversification of these two operons for light harvesting. Taking the other observations into consideration, we could illustrate the photoacclimation processes of A. marina 11017 in response to orange and far-red light conditions in detail.

The Photosystem I (PSI) reaction center in cyanobacteria is comprised of ~96 chlorophyll (Chl) molecules, including six specialized Chl molecules denoted Chl1A/Chl1B (P 700 ), Chl2A/Chl2B, and Chl3A/Chl3B that are arranged in two branches and function in primary charge separation. It has recently been proposed that PSI from Chroococcidiopsis thermalis (Nürnberg et al. (2018) Science 360, 1210-1213) and Fischerella thermalis PCC 7521 (Hastings et al. (2019) Biochim. Biophys. Acta 1860, 452-460) contain Chl f in the positions Chl2A/Chl2B. We tested this proposal by exciting RCs from white-light grown (WL-PSI) and far-red light grown (FRL-PSI) F. thermalis PCC 7521 with femtosecond pulses and analyzing the optical dynamics. If Chl f were in the position Chl2A/Chl2B in FRL-PSI, excitation at 740 nm should have produced the charge-separated state P 700 + A 0 - followed by electron transfer to A 1 with a τ of ≤25 ps. Instead, it takes ~230 ps for the charge-separated state to develop because the excitation migrates uphill from Chl f in the antenna to the trapping center. Further, we observe a strong electrochromic shift at 685 nm in the final P 700 + A 1 - spectrum that can only be explained if Chl a is in the positions Chl2A/Chl2B. Similar arguments rule out the presence of Chl f in the positions Chl3A/Chl3B; hence, Chl f is likely to function solely as an antenna pigment in FRL-PSI. We additionally report the presence of an excitonically coupled homo- or heterodimer of Chl f absorbing around 790 nm that is kinetically independent of the Chl f population that absorbs around 740 nm., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Photosynthetic organisms need to sense and respond to fluctuating environmental conditions, to perform efficient photosynthesis and avoid the formation of harmful reactive oxygen species. Cyanobacteria have developed a photoprotective mechanism that decreases the energy arriving at the reaction centers by increasing thermal energy dissipation at the level of the phycobilisome, the extramembranal light-harvesting antenna. This mechanism is triggered by the photoactive orange carotenoid protein (OCP). In this study, we characterized OCP and the related photoprotective mechanism in non-stressed and light-stressed cells of three different strains of Planktothrix that can form impressive blooms. In addition to changing lake ecosystemic functions and biodiversity, Planktothrix blooms can have adverse effects on human and animal health as they produce toxins (e.g., microcystins). Three Planktothrix strains were selected: two green strains, PCC 10110 (microcystin producer) and PCC 7805 (non-microcystin producer), and one red strain, PCC 7821. The green strains colonize shallow lakes with higher light intensities while red strains proliferate in deep lakes. Our study allowed us to conclude that there is a correlation between the ecological niche in which these strains proliferate and the rates of induction and recovery of OCP-related photoprotection. However, differences in the resistance to prolonged high-light stress were correlated to a better replacement of damaged D1 protein and not to differences in OCP photoprotection. Finally, microcystins do not seem to be involved in photoprotection as was previously suggested., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Chlorophyll (Chl) f and d are the most recently discovered chlorophylls, enabling cyanobacteria to harvest near-infrared radiation (NIR) at 700-780 nm for oxygenic photosynthesis. Little is known about the occurrence of these pigments in terrestrial habitats. Here, we provide first details on spectral photon irradiance within the photic zones of four terrestrial cave systems in concert with a detailed investigation of photopigmentation, light reflectance and microbial community composition. We frequently found Chl f and d along the photic zones of caves characterized by low light enriched in NIR and inhabited by cyanobacteria producing NIR-absorbing pigments. Surprisingly, deeper parts of caves still contained NIR, an effect likely attributable to the reflectance of specific wavelengths by the surface materials of cave walls. We argue that the stratification of microbial communities across the photic zones of cave entrances resembles the light-driven species distributions in forests and aquatic environments., (© 2019 Society for Applied Microbiology and John Wiley & Sons Ltd.)

Far-red absorbing chlorophylls are constitutively present as chlorophyll (Chl) d in the cyanobacterium Acaryochloris marina , or dynamically expressed by synthesis of Chl f , red-shifted phycobiliproteins and minor amounts of Chl d via far-red light photoacclimation in a range of cyanobacteria, which enables them to use near-infrared-radiation (NIR) for oxygenic photosynthesis. While the biochemistry and molecular physiology of Chl f -containing cyanobacteria has been unraveled in culture studies, their ecological significance remains unexplored and no data on their in situ activity exist. With a novel combination of hyperspectral imaging, confocal laser scanning microscopy, and nanoparticle-based O 2 imaging, we demonstrate substantial NIR-driven oxygenic photosynthesis by endolithic, Chl f -containing cyanobacteria within natural beachrock biofilms that are widespread on (sub)tropical coastlines. This indicates an important role of NIR-driven oxygenic photosynthesis in primary production of endolithic and other shaded habitats., Competing Interests: MK, ET, MM, MJ, AL, NF, KK No competing interests declared, (© 2020, Kühl et al.)

Crocosphaera is a major dinitrogen (N 2 )-fixing microorganism, providing bioavailable nitrogen (N) to marine ecosystems. The N 2 -fixing enzyme nitrogenase is deactivated by oxygen (O 2 ), which is abundant in marine environments. Using a cellular scale model of Crocosphaera sp. and laboratory data, we quantify the role of three O 2 management strategies by Crocosphaera sp.: size adjustment, reduced O 2 diffusivity, and respiratory protection. Our model predicts that Crocosphaera cells increase their size under high O 2 Using transmission electron microscopy, we show that starch granules and thylakoid membranes are located near the cytoplasmic membranes, forming a barrier for O 2 The model indicates a critical role for respiration in protecting the rate of N 2 fixation. Moreover, the rise in respiration rates and the decline in ambient O 2 with temperature strengthen this mechanism in warmer water, providing a physiological rationale for the observed niche of Crocosphaera at temperatures exceeding 20°C. Our new measurements of the sensitivity to light intensity show that the rate of N 2 fixation reaches saturation at a lower light intensity (∼100 μmol m -2 s -1 ) than photosynthesis and that both are similarly inhibited by light intensities of >500 μmol m -2 s -1 This suggests an explanation for the maximum population of Crocosphaera occurring slightly below the ocean surface. IMPORTANCE Crocosphaera is one of the major N 2 -fixing microorganisms in the open ocean. On a global scale, the process of N 2 fixation is important in balancing the N budget, but the factors governing the rate of N 2 fixation remain poorly resolved. Here, we combine a mechanistic model and both previous and present laboratory studies of Crocosphaera to quantify how chemical factors such as C, N, Fe, and O 2 and physical factors such as temperature and light affect N 2 fixation. Our study shows that Crocosphaera combines multiple mechanisms to reduce intracellular O 2 to protect the O 2 -sensitive N 2 -fixing enzyme. Our model, however, indicates that these protections are insufficient at low temperature due to reduced respiration and the rate of N 2 fixation becomes severely limited. This provides a physiological explanation for why the geographic distribution of Crocosphaera is confined to the warm low-latitude ocean., (Copyright © 2019 Inomura et al.)

Chromatic acclimation (CA) encompasses a diverse set of molecular processes that involve the ability of cyanobacterial cells to sense ambient light colors and use this information to optimize photosynthetic light harvesting. The six known types of CA, which we propose naming CA1 through CA6, use a range of molecular mechanisms that likely evolved independently in distantly related lineages of the Cyanobacteria phylum. Together, these processes sense and respond to the majority of the photosynthetically relevant solar spectrum, suggesting that CA provides fitness advantages across a broad range of light color niches. The recent discoveries of several new CA types suggest that additional CA systems involving additional light colors and molecular mechanisms will be revealed in coming years. Here we provide a comprehensive overview of the currently known types of CA and summarize the molecular details that underpin CA regulation.

We have worked out a rapid 1-day test based on photosynthesis measurements to estimate suitable growth temperature of microalgae cultures. To verify the proposed procedure, several microalgae-Chlorella, Nostoc, Synechocystis, Scenedesmus, and Cylindrospermum-were cultured under controlled laboratory conditions (irradiance, temperature, mixing, CO 2 , and nutrient supply) to find the optima of photosynthetic activity using the range between 15 and 35 °C. These activities were recorded at each temperature step after 2 h of acclimation which should be sufficient as oxygen production and the PQ cycle are regulated by fast processes. Photosynthetic activity was measured using three techniques-oxygen production/respiration, saturating pulse analysis of fluorescence quenching, and fast fluorescence induction kinetics-to estimate the temperature optima which should correspond to high growth rate. We measured all variables that might have been directly related to growth-photosynthetic oxygen evolution, maximum photochemical yield of PSII, F v /F m , relative electron transport rate rETR max , and the transients V j and V i determined by fast fluorescence induction curves. When the temperature optima for photosynthetic activity were verified in growth tests, we found good correlation. For most of tested microalgae strains, temperature around 30 °C was found to be the most suitable at this setting. We concluded that the developed test can be used as a rapid 1-day pre-screening to estimate a suitable growth temperature of microalgae strains before they are cultured in a pilot scale.

Cyanobacteriochrome photoreceptors are linear tetrapyrrole-binding photoreceptors that are distantly related to the canonical phytochrome photoreceptors. The chromophore-binding region of the cyanobacteriochromes consists of only a cGMP-phosphodiesterase/adenylate cyclase/FhlA (GAF) domain, while that of the phytochromes consists of three domains, including the GAF domain. Most of the canonical phytochromes homogenously show red/far-red reversible photoconversion. Conversely, the cyanobacteriochrome photoreceptors are highly diverse in the colors of light they sense. Since the discovery of the first cyanobacteriochrome photoreceptor around 15 years ago, physiological, biochemical, and biophysical studies on cyanobacteriochromes have been extensively performed to date. In this review, we focus on color-tuning mechanisms of diverse cyanobacteriochromes., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Phototrophic cyanobacteria are limited in growth locations by their need for visible light and must also cope with intermittent ultraviolet radiation (UVR), especially in extreme environments such as deserts and on early Earth. One survival method for cyanobacteria is growing endolithically within minerals such as micas, gypsum, and quartz minerals. However, the capability of different mica minerals to protect cyanobacteria from UVR, while at the same time allowing transmission of photosynthetically active radiation (PAR), has only been minimally examined. In this study, we performed laboratory incubation experiments to demonstrate that a model filamentous cyanobacterium, Leptolyngbya sp., can colonize micas, such as muscovite, phlogopite, and biotite. After inoculation experiments confirmed that these cyanobacteria grew between the sheets of mica, Leptolyngbya sp. colonies were exposed to UVB and UVC for up to 24 hrs, and the level of survival was determined using chlorophyll a and carotenoid assays. Of the three micas investigated, muscovite, being an Fe-poor and Al-rich mica, provided the least attenuation of UVR, however it transmitted the most visible light. Fe-rich biotite provided the best UVR shielding. Phlogopite, apparently because of its intermediate amount of Fe, showed the greatest ability to shield UVR while still transmitting an adequate amount of visible light, making it the ideal habitat for the cyanobacterium. Upon exposure to UVR, significant shifts in several important fatty acids of the cyanobacterium were detected such as linolenic acid and oleic acid, 18:3ω3 and 18:1ω9c, respectively. These cellular changes are interpreted to be a consequence of UVR and other accessory stress (such as O3)., Competing Interests: The authors have declared that no competing interests exist.

The objective of this study, for the first time, was to optimize Amazonian cyanobacterial culture conditions for improving cell productivity and lipid content, by analyzing the effect of light intensity and nitrogen concentration, for empirically evaluating biodiesel quality parameters. The strains Synechocystis sp. CACIAM05, Microcystis aeruginosa CACIAM08, Pantanalinema rosaneae CACIAM18, and Limnothrix sp. CACIAM25, were previously identified by morphological and molecular analysis (16S rRNA) and were selected based on their production of chlorophyll a and dry cell weight. Then, factorial planning (2 2 ) with central points was applied, with light intensity and NaNO 3 concentration as independent variables. As response variables, cell productivity and lipid content were determined. Statistical analysis indicated that for all strains, the independent variables were statistically significant for cell productivity. Analysis of the fatty acid composition demonstrated diversity in the composition of the fatty acid profile from the experimental planning assays of each strain. The Biodiesel Analyzer software predicted the biodiesel quality parameters. CACIAM05 and CACIAM25 obtained better parameters with low levels of light intensity and NaNO 3 concentration, whereas CACIAM08 and CACIAM18 obtained better parameters with low NaNO 3 concentrations and high luminous intensity.

Cyanobacteria have evolved various photoacclimation processes to perform oxygenic photosynthesis under different light environments. Chromatic acclimation (CA) is a widely recognized and ecologically important type of photoacclimation, whereby cyanobacteria alter the absorbing light colors of a supermolecular antenna complex called the phycobilisome. To date, several CA variants that regulate the green-absorbing phycoerythrin (PE) and/or the red-absorbing phycocyanin (PC) within the hemi-discoidal form of phycobilisome have been characterized. In this study, we identified a unique CA regulatory gene cluster encoding yellow-green-absorbing phycoerythrocyanin (PEC) and a rod-membrane linker protein (CpcL) for the rod-shaped form of phycobilisome. Using the cyanobacterium Leptolyngbya sp. PCC 6406, we revealed novel CA variants regulating PEC (CA7) and the rod-shaped phycobilisome (CA0), which maximize yellow-green light-harvesting capacity and balance the excitation of photosystems, respectively. Analysis of the distribution of CA gene clusters in 445 cyanobacteria genomes revealed eight CA variants responding to green and red light, which are classified based on the presence of PEC, PE, cpcL, and CA photosensor genes. Phylogenetic analysis further suggested that the emergence of CA7 was a single event and preceded that of heterocystous strains, whereas the acquisition of CA0 occurred multiple times. Taken together, these results offer novel insights into the diversity and evolution of the complex cyanobacterial photoacclimation mechanisms., (Copyright © 2019 The Author. Published by Elsevier Inc. All rights reserved.)

In diverse terrestrial cyanobacteria, Far-Red Light Photoacclimation (FaRLiP) promotes extensive remodeling of the photosynthetic apparatus, including photosystems (PS)I and PSII and the cores of phycobilisomes, and is accompanied by the concomitant biosynthesis of chlorophyll (Chl) d and Chl f. Chl f synthase, encoded by chlF, is a highly divergent paralog of psbA; heterologous expression of chlF from Chlorogloeopsis fritscii PCC 9212 led to the light-dependent production of Chl f in Synechococcus sp. PCC 7002 (Ho et al., Science 353, aaf9178 (2016)). In the studies reported here, expression of the chlF gene from Fischerella thermalis PCC 7521 in the heterologous system led to enhanced synthesis of Chl f. N-terminally [His] 10 -tagged ChlF 7521 was purified and identified by immunoblotting and tryptic-peptide mass fingerprinting. As predicted from its sequence similarity to PsbA, ChlF bound Chl a and pheophytin a at a ratio of ~ 3-4:1, bound β-carotene and zeaxanthin, and was inhibited in vivo by 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Cross-linking studies and the absence of copurifying proteins indicated that ChlF forms homodimers. Flash photolysis of ChlF produced a Chl a triplet that decayed with a lifetime (1/e) of ~ 817 µs and that could be attributed to intersystem crossing by EPR spectroscopy at 90 K. When the chlF 7521 gene was expressed in a strain in which the psbD1 and psbD2 genes had been deleted, significantly more Chl f was produced, and Chl f levels could be further enhanced by specific growth-light conditions. Chl f synthesized in Synechococcus sp. PCC 7002 was inserted into trimeric PSI complexes.

UV resistance of bacteria isolated from the marine cyanobacterium Moorea producens has not been observed previously, findings which highlight how unsafe germicidal UV irradiation for sterilization of air, food, and water could be. Further, UV resistance of Bacillus licheniformis is being observed for the first time. This study focused on bacteria isolated from the marine cyanobacterium M. producens collected off the Kenyan coast at Shimoni, Wasini, Kilifi, and Mida. UV irradiance of isolates (302 nm, 70 W/m 2 , 0-1 hr) established B. licheniformis as the most UV resistant strain, with the following order of taxon resistance: Bacilli> γ proteobacteria > Actinobacteria. UV resistance was independent of pigmentation. The maximum likelihood phylogenetic distance determined for both B. licheniformis and Bacillus aerius relative to M. producens CCAP 1446/4 was 2.0. Survival of B. licheniformis upon UV irradiance followed first-order kinetics (k = 0.035/min, R 2  = 0.88). Addition of aqueous extracts (2, 10, 20 and 40 mg/ml) of this B. licheniformis strain on the less resistant Marinobacterium stanieri was not significant, however, the commercial sunscreen benzophenone-3 (BP-3) positive control and the time of irradiance were significant. Detection of bacteria on M. producens filaments stained with acridine orange confirmed its nonaxenic nature. Although the chemistry of UV resistance in cyanobacteria has been studied in depth revealing for example the role of mycosporine like amino acids (MAAs) in UV resistance less is known about how bacteria resist UV irradiation. This is of interest since cyanobacteria live in association with bacteria., (© 2018 The Authors. MicrobiologyOpen published by John Wiley & Sons Ltd.)

The dependence on temperature of tryptophan fluorescence lifetime in trimeric photosystem I (PSI) complexes from cyanobacteria Synechocystis sp. PCC 6803 during the heating of pre-frozen to - 180 °C in the dark or in the light-activated preparations has been studied. Fluorescence lifetime in samples frozen in the light was longer than in samples frozen in the dark. For samples in 65% glycerol at λ reg  = 335 nm and at 20 °C, the lifetime of components were as follows: τ 1  ≈ 1.2 ns, τ 2  ≈ 4.9 ns, and τ 3  ≈ 20 ns. The contribution of the first component was negligible. To analyze the contribution of components 2 and 3 derived from frozen-thawed samples, two temperature ranges from - 180 to - 90 °C and above - 90 °C are considered. In doing so, the contributions of these components appear antiphase course to each other. The dependence on temperature of these contributions is explained by the influence of the microconformational protein dynamics on the tryptophan fluorescence lifetime. In the present work, a comparative analysis of temperature-dependent conformational dynamics and electron transfer in cyanobacterial PSI (Schlodder et al., in Biochemistry 37:9466-9476, 1998) and Rhodobacter sphaeroides reaction center complexes (Knox et al., in J Photochem Photobiol B 180:140-148, 2018) was also carried out.

In the ESA space experiment BIOMEX (BIOlogy and Mars EXperiment), dried Chroococcidiopsis cells were exposed to Mars-like conditions during the EXPOSE-R2 mission on the International Space Station. The samples were exposed to UV radiation for 469 days and to a Mars-like atmosphere for 722 days, approaching the conditions that could be faced on the surface of Mars. Once back on Earth, cell survival was tested by growth-dependent assays, while confocal laser scanning microscopy and PCR-based assay were used to analyze the accumulated damage in photosynthetic pigments (chlorophyll a and phycobiliproteins) and genomic DNA, respectively. Survival occurred only for dried cells (4-5 cell layers thick) mixed with the martian soil simulants P-MRS (phyllosilicatic martian regolith simulant) and S-MRS (sulfatic martian regolith simulant), and viability was only maintained for a few hours after space exposure to a total UV (wavelength from 200 to 400 nm) radiation dose of 492 MJ/m 2 (attenuated by 0.1% neutral density filters) and 0.5 Gy of ionizing radiation. These results have implications for the hypothesis that, during Mars's climatic history, desiccation- and radiation-tolerant life-forms could have survived in habitable niches and protected niches while transported.

BIOMEX (BIOlogy and Mars EXperiment) is an ESA/Roscosmos space exposure experiment housed within the exposure facility EXPOSE-R2 outside the Zvezda module on the International Space Station (ISS). The design of the multiuser facility supports-among others-the BIOMEX investigations into the stability and level of degradation of space-exposed biosignatures such as pigments, secondary metabolites, and cell surfaces in contact with a terrestrial and Mars analog mineral environment. In parallel, analysis on the viability of the investigated organisms has provided relevant data for evaluation of the habitability of Mars, for the limits of life, and for the likelihood of an interplanetary transfer of life (theory of lithopanspermia). In this project, lichens, archaea, bacteria, cyanobacteria, snow/permafrost algae, meristematic black fungi, and bryophytes from alpine and polar habitats were embedded, grown, and cultured on a mixture of martian and lunar regolith analogs or other terrestrial minerals. The organisms and regolith analogs and terrestrial mineral mixtures were then exposed to space and to simulated Mars-like conditions by way of the EXPOSE-R2 facility. In this special issue, we present the first set of data obtained in reference to our investigation into the habitability of Mars and limits of life. This project was initiated and implemented by the BIOMEX group, an international and interdisciplinary consortium of 30 institutes in 12 countries on 3 continents. Preflight tests for sample selection, results from ground-based simulation experiments, and the space experiments themselves are presented and include a complete overview of the scientific processes required for this space experiment and postflight analysis. The presented BIOMEX concept could be scaled up to future exposure experiments on the Moon and will serve as a pretest in low Earth orbit.

Cyanobacteria are an evolutionarily and ecologically important group of prokaryotes. They exist in diverse habitats, ranging from hot springs and deserts to glaciers and the open ocean. The range of environments that they inhabit can be attributed in part to their ability to sense and respond to changing environmental conditions. As photosynthetic organisms, one of the most crucial parameters for cyanobacteria to monitor is light. Cyanobacteria can sense various wavelengths of light and many possess a range of bilin-binding photoreceptors belonging to the phytochrome superfamily. Vital cellular processes including growth, phototaxis, cell aggregation and photosynthesis are tuned to environmental light conditions by these photoreceptors. In this Review, we examine the physiological responses that are controlled by members of this diverse family of photoreceptors and discuss the signal transduction pathways through which these photoreceptors operate. We highlight specific examples where the activities of multiple photoreceptors function together to fine-tune light responses. We also discuss the potential application of these photosensing systems in optogenetics and synthetic biology.

Stratospheric ozone depletion is mostly marked over the Antarctic and to a lesser extent over the Arctic, though recent reports have revealed that this also occurs at lower latitudes. Continued depletion of ozone in the lower stratosphere allows more UVR to reach the Earth's surface. Furthermore, it is projected that surface water temperatures will increase by between 0.2 and 2.0°C by the year 2060 and this will directly or indirectly influence algal growth. The interactions between environmental factors are complicated by the existence of different strains (ecotypes) of the same species that may respond differently. To understand the interactive effects of temperature and UV-B on two strains of Anabaena circinalis, we investigated the damaging effects of UV-B on cell numbers and photosynthetic characteristics and also examined the effect of temperature on the capacity of cells to recover from such stress. Both strains of A. circinalis responded differently in terms of survival, photosynthetic characteristics and recovery with interactions between temperature and UV-B. This could be due to the variations in strain-specific photoreactive mechanisms. This needs to be explored further including more strains and species before definitive conclusions can be reached about effects of global change on cyanobacteria generally., (© 2018 The American Society of Photobiology.)

Microbial mats and stromatolites are widespread in Hamelin Pool, Shark Bay, however the phototrophic capacity of these systems is unknown. This study has determined the optical properties and light-harvesting potential of these mats with light microsensors. These characteristics were linked via a combination of 16S rDNA sequencing, pigment analyses and hyperspectral imaging. Local scalar irradiance was elevated over the incident downwelling irradiance by 1.5-fold, suggesting light trapping and strong scattering by the mats. Visible light (400-700 nm) penetrated to a depth of 2 mm, whereas near-infrared light (700-800 nm) penetrated to at least 6 mm. Chlorophyll a and bacteriochlorophyll a (Bchl a) were found to be the dominant photosynthetic pigments present, with BChl a peaking at the subsurface (2-4 mm). Detailed 16S rDNA analyses revealed the presence of putative Chl f-containing Halomicronema sp. and photosynthetic members primarily decreased from the mat surface down to a depth of 6 mm. Data indicated high abundances of some pigments and phototrophic organisms in deeper layers of the mats (6-16 mm). It is proposed that the photosynthetic bacteria present in this system undergo unique adaptations to lower light conditions below the mat surface, and that phototrophic metabolisms are major contributors to ecosystem function.

Structures arising from actin-based cell membrane movements, including ruffles, lamellipodia, and filopodia, play important roles in a broad spectrum of cellular functions, such as cell motility, axon guidance in neurons, wound healing, and micropinocytosis. Previous studies investigating these cell membrane dynamics often relied on pharmacological inhibition, RNA interference, and constitutive active/dominant negative protein expression systems. However, such studies did not allow the modulation of protein activity at specific regions of cells, tissues, and organs in animals with high spatial and temporal precision. Recently, optogenetic tools for inducing cell membrane dynamics have been developed which address several disadvantages of previous techniques. In a recent study, we developed a powerful optogenetic tool, called the Magnet system, to change cell membrane dynamics through Tiam1 and PIP3 signal transductions with high spatial and temporal resolution. In this review, we summarize recent advances in optogenetic tools that allow us to induce actin-regulated cell membrane dynamics and unique membrane ruffles that we discovered using our Magnet system., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Photoinhibition, or cell damage caused by excessively intense light is a major issue for the industrial use of cyanobacteria. To investigate the mechanism of responses to extreme high light intensity, gene expression analysis was performed using the model cyanobacterium Synechocystis sp. PCC 6803 (PCC 6803) cultured under various light intensities. The culture profile data demonstrated that, in contrast to the slow cell growth observed under low light intensities (30 and 50 μmol m -2  s -1 ), maximal cell growth was observed under mid light conditions (300 and 1000 μmol m -2  s -1 ). PCC 6803 cells exhibited photoinhibition when cultured under excessive high light intensities of 1100 and 1300 μmol m -2  s -1 . From the low to the mid light conditions, the expression of genes related to light harvesting systems was repressed, whereas that of CO 2 fixation and of D1 protein turnover-related genes was induced. Gene expression data also revealed that the down-regulation of genes related to flagellum synthesis (pilA2), pyridine nucleotide transhydrogenase (pntA and pntB), and sigma factor (sigA and sigF) represents the key responses of PCC 6803 under excessive high light conditions. The results obtained in this study provide further understanding of high light tolerance mechanisms and should help to improve the productivity of bioprocess using cyanobacteria., (Copyright © 2018 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.)

Cyanobacteria must balance separate demands for energy generation, carbon assimilation, and biomass synthesis. We used shotgun proteomics to investigate proteome allocation strategies in the model cyanobacterium Synechocystis sp. PCC 6803 as it adapted to light and inorganic carbon (C i ) limitation. When partitioning the proteome into seven functional sectors, we find that sector sizes change linearly with growth rate. The sector encompassing ribosomes is significantly smaller than in E. coli, which may explain the lower maximum growth rate in Synechocystis. Limitation of light dramatically affects multiple proteome sectors, whereas the effect of C i limitation is weak. Carbon assimilation proteins respond more strongly to changes in light intensity than to C i . A coarse-grained cell economy model generally explains proteome trends. However, deviations from model predictions suggest that the large proteome sectors for carbon and light assimilation are not optimally utilized under some growth conditions and may constrain the proteome space available to ribosomes., (Copyright © 2018 The Author(s). Published by Elsevier Inc. All rights reserved.)

Many studies have focused on the interactive effects of temperature increases due to global warming and nutrient enrichment on phytoplankton communities. Recently, non-temperature effects of climate change (e.g., decreases in wind speed and increases in solar radiation) on large lakes have received increasing attention. To evaluate the relative contributions of both temperature and non-temperature effects on phytoplankton communities in a large eutrophic subtropical shallow lake, we analyzed long-term monitoring data from Lake Taihu, China from 1997 to 2016. Results showed that Lake Taihu's spring phytoplankton biovolume and composition changed dramatically over this time frame, with a change in dominant species. Stepwise multiple linear regression models indicated that spring phytoplankton biovolume was strongly influenced by total phosphorus (TP), light condition, wind speed and total nitrogen (TN) (radj2 = 0.8, p < 0.01). Partial redundancy analysis (pRDA) showed that light condition accounted for the greatest variation of phytoplankton community composition, followed by TP and wind speed, as well as the interactions between TP and wind speed. Our study points to the additional importance of non-temperature effects of climate change on phytoplankton community dynamics in Lake Taihu., Competing Interests: The authors have declared that no competing interests exist.

Microorganisms developing in the liner of the spent fuel pool (SFP) and the fuel transfer channel (FTC) of a Nuclear Power Plant (NPP) can form high radiation resistant biofilms and cause corrosion. Due to difficulties and limitations to obtain large samples from SFP and FTC, cotton swabs were used to collect the biofilm from the wall of these installations. Molecular characterization was performed using massively parallel sequencing to obtain a taxonomic and functional gene classification. Also, samples from the drainage system were evaluated because microorganisms may travel over the 12-meter column of the pool water of the Brazilian Nuclear Power Plant (Angra1), which has been functioning since 1985. Regardless of the treatment of the pool water, our data reveal the unexpected presence of Fungi (Basidiomycota and Ascomycota) as the main contaminators of the SFP and FTC. Ustilaginomycetes (Basidiomycota) was the major class contributor (70%) in the SFP and FTC reflecting the little diversity in these sites; nevertheless, Proteobacteria, Actinobacteria, Firmicutes (Bacilli) were present in small proportions. Mapping total reads against six fungal reference genomes indicate that there is, in fact, a high abundance of fungal sequences in samples collected from SFP and FTC. Analysis of the ribosomal internal transcribed spacer (ITS) 1 and 2 regions and the protein found in the mitochondria of eukaryotic cells, cytochrome b (cytb) grouped our sample fungi in the clade 7 as Ustilago and Pseudozyma. In contrast, in the drainage system, Alphaproteobacteria were present in high abundances (55%). The presence of Sphingopyxis, Mesorhizobium, Erythrobacter, Sphingomonas, Novosphingobium, Sphingobium, Chelativorans, Oceanicaulis, Acidovorax, and Cyanobacteria was observed. Based on genomic annotation data, the assessment of the biological function found a higher proportion of protein-coding sequences related to respiration and protein metabolism in SFP and FTC samples. The knowledge of this biological inventory present in the system may contribute to further studies of potential microorganisms that might be useful for bioremediation of nuclear waste., Competing Interests: The author has declared that no competing interests exist.

Cyanobacteria are among the oldest living organisms on this planet, existing since more than 3 billion years. They are ideal organisms for investigating biological processes such as photosynthesis, respiration, circadian rhythm, photoregulation of gene expression, developmental gene rearrangements, and specialized cell differentiation. They are nearly ubiquitous in distribution, have colonized a wide range of ecosystems including soil, air, dry rock, and aquatic systems, and even occupy extreme niches that are inaccessible to other organisms. Such wide ecological distribution reflects their capacity to acclimate to extreme environments. They show great adaptive abilities and have survived various adverse physiological growth conditions like desiccation, high temperatures, extreme pH, cold, osmosis, salt, light, nitrogen, and high salinity. Their ancient origin and surviving through numerous stresses during evolution indicates their remarkable capabilities to survive and prevail under different environmental and man-made stresses. It has been hypothesized that similar and overlap stress response mechanisms help them to survive different stresses. It has been stated that responses against stresses like radiation has been accidental-exhibited because of similar response against desiccation stress, which has prevailed more during evolution. These overlaps and similarities in stress responses have been instrumental in making these organisms a large class of biological entities today. Present review discuss about stress tolerance in cyanobacteria against two extreme stresses - desiccation and gamma radiation. It also discuss the commonality and underlying molecular mechanisms in these two stress responses., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)