The effects of ultraviolet radiation on photosynthetic performance, growth and sunscreen compounds in aeroterrestrial biofilm algae isolated from building facades

Advancing sustainable seawater disinfection: Enhanced inactivation and mechanism of pulsed UV-LEDs irradiation on Tetraselmis sp

Ultraviolet light-emitting diodes (UV-LEDs), as a novel ultraviolet light source with flexible pulse mode, has gained significant attention for applications in water disinfection and food sterilization. This study investigated the comparative inactivation efficiency of Tetraselmis sp. with continuous and pulsed UV-LEDs irradiation, exploring different wavelengths, duty rates and pulse frequencies. The results reveal a significant enhancement in inactivation efficiency (p < 0.05) under pulsed conditions even at the same UV dose, with inactivation efficiency increasing as duty rate or pulse frequency decreases. The optimal conditions for achieving peak inactivation efficacy are identified as a duty rate of 50% and a pulse frequency of 5 Hz. Within this parameter space, pulsed irradiation leads to a remarkable 1.7-fold increase in inactivation efficiency at UV265 nm and a 1.5-fold increase at UV285 nm compared to continuous irradiation, respectively. Additionally, the disruptive impacts on photosynthetic performance are more pronounced with pulsed irradiation, particularly at the 5 Hz pulse frequency. In shed of these findings, the application of pulsed UV-LEDs irradiation emerges as a promising alternative to the conventional continuous UV disinfection methods in the area of seawater disinfection, offering higher disinfection efficacy and energy consumption.

Synergistic effects of salt and ultraviolet radiation on the rice-field cyanobacterium Nostochopsis lobatus HKAR-21

Environmental variation has a significant impact on how organisms, including cyanobacteria, respond physiologically and biochemically. Salinity and ultraviolet radiation (UVR)-induced variations in the photopigments of the rice-field cyanobacterium Nostochopsis lobatus HKAR-21 and its photosynthetic performance was studied. We observed that excessive energy dissipation after UVR is mostly caused by Non-Photochemical Quenching (NPQ), whereas photochemical quenching is important for preventing photoinhibition. These findings suggest that ROS production may play an important role in the UVR-induced injury. To reduce ROS-induced oxidative stress, Nostochopsis lobatus HKAR-21 induces the effective antioxidant systems, which includes different antioxidant compounds like carotenoids and enzymes such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX). The study indicates that Nostochopsis lobatus HKAR-21 exposed to photosynthetically active radiation + UV-A + UV-B (PAB) and PAB + NaCl (PABN) had significantly reduced photosynthetic efficiency. Furthermore, maximum ROS was detected in PAB exposed cyanobacterial cells. The induction of lipid peroxidation (LPO) has been investigated to evaluate the impact of UVR on the cyanobacterial membrane in addition to enzymatic defensive systems. The maximal LPO level was found in PABN treated cells. Based on the findings of this research, it was concluded that salinity and UVR had collegial effects on the major macromolecular components of the rice-field cyanobacterium Nostochopsis lobatus HKAR-21.

Palmelloid Formation and Cell Aggregation Are Essential Mechanisms for High Light Tolerance in a Natural Strain of Chlamydomonas reinhardtii

Photosynthetic organisms, such as higher plants and algae, require light to survive. However, an excessive amount of light can be harmful due to the production of reactive oxygen species (ROS), which cause cell damage and, if it is not effectively regulated, cell death. The study of plants' responses to light can aid in the development of methods to improve plants' growth and productivity. Due to the multicellular nature of plants, there may be variations in the results based on plant age and tissue type. Chlamydomonas reinhardtii, a unicellular green alga, has also been used as a model organism to study photosynthesis and photoprotection. Nonetheless, the majority of the research has been conducted with strains that have been consistently utilized in laboratories and originated from the same source. Despite the availability of many field isolates of this species, very few studies have compared the light responses of field isolates. This study examined the responses of two field isolates of Chlamydomonas to high light stress. The light-tolerant strain, CC-4414, managed reactive oxygen species (ROS) slightly better than the sensitive strain, CC-2344, did. The proteomic data of cells subjected to high light revealed cellular modifications of the light-tolerant strain toward membrane proteins. The morphology of cells under light stress revealed that this strain utilized the formation of palmelloid structures and cell aggregation to shield cells from excessive light. As indicated by proteome data, morphological modifications occur simultaneously with the increase in protein degradation and autophagy. By protecting cells from stress, cells are able to continue to upregulate ROS management mechanisms and prevent cell death. This is the first report of palmelloid formation in Chlamydomonas under high light stress.

Diversity and Distribution of Carotenogenic Algae in Europe: A Review

Microalgae are the richest source of natural carotenoids, which are valuable pigments with a high share of benefits. Often, carotenoid-producing algae inhabit specific biotopes with unfavorable or even extremal conditions. Such biotopes, including alpine snow fields and hypersaline ponds, are widely distributed in Europe. They can serve as a source of new strains for biotechnology. The number of algal species used for obtaining these compounds on an industrial scale is limited. The data on them are poor. Moreover, some of them have been reported in non-English local scientific articles and theses. This review aims to summarize existing data on microalgal species, which are known as potential carotenoid producers in biotechnology. These include Haematococcus and Dunaliella, both well-known to the scientific community, as well as less-elucidated representatives. Their distribution will be covered throughout Europe: from the Greek Mediterranean coast in the south to the snow valleys in Norway in the north, and from the ponds in Amieiro (Portugal) in the west to the saline lakes and mountains in Crimea (Ukraine) in the east. A wide spectrum of algal secondary carotenoids is reviewed: β-carotene, astaxanthin, canthaxanthin, echinenone, adonixanthin, and adonirubin. For convenience, the main concepts of biology of carotenoid-producing algae are briefly explained.

Microalgae growth rate multivariable mathematical model for biomass production

Background

The use of microalgae has been emerging as a potential technology to reduce greenhouse gases and bioremediate polluted water and produce high-value products as pigments, phytohormones, biofuels, and bioactive compounds. The improvement in biomass production is a priority to make the technology implementation profitable in every application mentioned before.

Methods

The present study was conducted to explore the use of microalgae from genus Chlorella and Tetradesmus for the generation of substances of interest with UV absorption capacity. A mathematical model was developed for both microalgae to characterize the production of microalgae biomass considering the effects of light intensity, temperature, and nutrient consumption. The model was programmed in MATLAB software, where the three parameters were incorporated into a single specific growth rate equation.

Results

It was found that the optimal environmental conditions for each genus (Chlorella T=36°C, and I<787 μmol/m²s; Tetradesmus T=23°C and I<150 μmol/m²s), as well as the optimal specific growth rate depending on the personalized values of the three parameters.

Conclussion

This work could be used in the production of microalgae biomass for the design and development of topical applications to replace commercial options based on compounds that compromise health and have a harmful impact on the environment.

Effects of changes in UV-B radiation levels on biofilm-forming organisms commonly found in cultural heritage surfaces

Accurate measuring and monitoring methods available since the 1980s have shown that the amount of Ultraviolet B (UV-B) radiation reaching the Earth's surface has increased as a result of degradation of the ozone layer. Since the adoption of the Montreal Protocol in 1987, ozone levels have been recovering successfully. However, in the context of the current climate change, other factors such as changes in cloud patterns and an increased incidence of natural disasters (e.g. fires) may be disrupting this recovery. The present study aimed to investigate the effects of different UV-B radiation levels on biofilms colonising heritage monuments. For this purpose, the effects of current UV-B levels on a biofilm composed of Synechocystis sp. (a cyanobacterium), Bracteacoccus minor (a green alga) and Fusarium sp. (a fungus) were compared at three points along a South-North transect: Portugal, Galicia (NW Spain) and Ireland (from highest to lowest UV-B radiation, respectively). Increased levels of UV-B radiation caused changes in the growth, physiological state and composition of subaerial biofilms, with cyanobacteria being more resistant than green algae to high levels of UV-B. A reduction of fungal growth and extracellular polymer substances (EPS) production was also observed, related to the reduction of biofilm aggregation at high UV-B levels.

Submergence of the filamentous Zygnematophyceae Mougeotia induces differential gene expression patterns associated with core metabolism and photosynthesis

The streptophyte algal class Zygnematophyceae is the closest algal sister lineage to land plants. In nature, Zygnematophyceae can grow in both terrestrial and freshwater habitats and how they do this is an important unanswered question. Here, we studied what happens to the zygnematophyceaen alga Mougeotia sp., which usually occurs in permanent and temporary freshwater bodies, when it is shifted to liquid growth conditions after growth on a solid substrate. Using global differential gene expression profiling, we identified changes in the core metabolism of the organism interlinked with photosynthesis; the latter went hand in hand with measurable impact on the photophysiology as assessed via pulse amplitude modulation (PAM) fluorometry. Our data reveal a pronounced change in the overall physiology of the alga after submergence and pinpoint candidate genes that play a role. These results provide insight into the importance of photophysiological readjustment when filamentous Zygnematophyceae transition between terrestrial and aquatic habitats.

Differential Responses to UV-A Stress Recorded in Carotenogenic Microalgae Haematococcus rubicundus, Bracteacoccus aggregatus, and Deasonia sp

UV-A is the main ultraviolet component of natural (solar) radiation. Despite it, its effect on phototrophs is studied less than UV-B. Effects of UV-A on photosynthetic apparatus of three carotenoid-producing microalgae were elucidated. Photosynthetic activity was studied using chlorophyll fluorescence analysis. Cell extracts were evaluated by absorbance spectroscopy. On the one hand, there were some common features of three strains. In all cases the changes involved PSII primary photochemistry and antennae size. All strains accumulated UV-absorbing polar compounds. On the other hand, some responses were different. Upregulation of non-photochemical quenching was observed only in B. aggregatus BM5/15, whereas in other cases its level was low. H. rubicundus BM7/13 and Deasonia sp. NAMSU 934/2 accumulated secondary carotenoids, whereas B. aggregatus BM5/15 accumulated primary ones. Microscopic features of the cultures were also different. H. rubicundus BM7/13 and Deasonia sp. NAMSU 934/2 were represented mostly by solitaire cells or small cell clusters, lacking their green color; the cells of B. aggregatus BM5/15 formed aggregates from green cells. Cell aggregation could be considered as an additional UV-protecting mechanism. Finally, the strains differed by their viability. B. aggregatus BM5/15 was most resistant to UV-A, whereas massive cell death was observed in two other cultures.

Epiphytic phytoplankton in response to divergent air pollutants from urban and commercial zones of Chennai District, Tamil Nadu, India: A case study towards phytoplankton based Air Quality Index

Microalgae are an effective source of bioindicators to screen any changes of the natural ecosystem in the environment. With the increase in air pollution due to different potential sources, pollution monitoring stations are deployed across the nation with sophisticated analytical methodologies. However, phytoplankton can also serve as an indicator of air pollution as they possess the ability to absorb particulate contaminants. With previous studies on indicator species based on aquatic habitats, this study was carried out to comprehend the interaction between gaseous oxides of sulphur and nitrogen, particulate matter with diameter less than 10 and 2.5 μm (PM10, PM 2.5), with the population density, abundance and frequency of terrestrial epiphytic microalgae from residential and commercial areas of Chennai District, Tamil Nadu. There was a significant correlation between the members of Chlorophyceae, Bacillariophyceae and Cyanophyceae with the abovementioned air pollutants. Cluster analysis, CCA and NMDS analysis were done to find the interaction pattern. The results suggested few indicator species from genera Chlorella, Phormidium, Nitzschia, Navicula, Spirogyra and Oscillatoria. Species of Desmodesmus, Gleocapsa, Gleocyctis and Lyngbya can be considered as an addition to Palmer's list of tolerant species. During this study, the occurrence of filamentous Cladophora crispata is reported for the first time from Tamil Nadu, India. This study unveiled the list of microalgal species resistant to air pollutants from one of the highly polluted cities of India.

Sunscreen Effect Exerted by Secondary Carotenoids and Mycosporine-like Amino Acids in the Aeroterrestrial Chlorophyte Coelastrella rubescens under High Light and UV-A Irradiation

The microalga Coelastrella rubescens dwells in habitats with excessive solar irradiation; consequently, it must accumulate diverse compounds to protect itself. We characterized the array of photoprotective compounds in C. rubescens. Toward this goal, we exposed the cells to high fluxes of visible light and UV-A and analyzed the ability of hydrophilic and hydrophobic extracts from the cells to absorb radiation. Potential light-screening compounds were profiled by thin layer chromatography and UPLC-MS. Coelastrella accumulated diverse carotenoids that absorbed visible light in the blue-green part of the spectrum and mycosporine-like amino acids (MAA) that absorbed the UV-A. It is the first report on the occurrence of MAA in Coelastrella. Two new MAA, named coelastrin A and coelastrin B, were identified. Transmission electron microscopy revealed the development of hydrophobic subcompartments under the high light and UV-A exposition. We also evaluate and discuss sporopollenin-like compounds in the cell wall and autophagy-like processes as the possible reason for the decrease in sunlight absorption by cells, in addition to inducible sunscreen accumulation. The results suggested that C. rubescens NAMSU R1 accumulates a broad range of valuable photoprotective compounds in response to UV-A and visible light irradiation, which indicates this strain as a potential producer for biotechnology.

Ecophysiological, morphological, and biochemical traits of free-living Diplosphaera chodatii (Trebouxiophyceae) reveal adaptation to harsh environmental conditions

Single-celled green algae within the Trebouxiophyceae (Chlorophyta) are typical components of terrestrial habitats, which often exhibit harsh environmental conditions for these microorganisms. This study provides a detailed overview of the ecophysiological, biochemical, and ultrastructural traits of an alga living on tree bark. The alga was isolated from a cypress tree in the Botanical Garden of Innsbruck (Austria) and identified by morphology and molecular phylogeny as Diplosphaera chodatii. Transmission electron microscopy after high-pressure freezing (HPF) showed an excellent preservation of the ultrastructure. The cell wall was bilayered with a smooth inner layer and an outer layer of polysaccharides with a fuzzy hair-like appearance that could possibly act as cell-cell adhesion mechanism and hence as a structural precursor supporting biofilm formation together with the mucilage observed occasionally. The photosynthetic-irradiance curves of D. chodatii indicated low light requirements without photoinhibition at high photon flux densities (1580 μmol photons m^-2 s^-1) supported by growth rate measurements. D. chodatii showed a high desiccation tolerance, as 85% of its initial value was recovered after controlled desiccation at a relative humidity of ~10%. The alga contained the low molecular weight carbohydrates sucrose and sorbitol, which probably act as protective compounds against desiccation. In addition, a new but chemically not elucidated mycosporine-like amino acid was detected with a molecular mass of 332 g mol^-1 and an absorption maximum of 324 nm. The presented data provide various traits which contribute to a better understanding of the adaptive mechanisms of D. chodatii to terrestrial habitats.

Responses of a hot spring cyanobacterium under ultraviolet and photosynthetically active radiation: photosynthetic performance, antioxidative enzymes, mycosporine-like amino acid profiling and its antioxidative potentials

This study summarizes the response of a hot spring cyanobacterium Fischerella sp. strain HKAR-14, under simulated light conditions of ultraviolet radiation (UVR), photosynthetically active radiation (PAR), PAR + UV-A (PA) and PAR + UV-A + UV-B (PAB). Exposure to UVR caused a decline in growth and Chl a while total carotene content increased under PA and PAB. Maximum photochemical efficiency of photosystem II (F v /F m) and relative electron transport rate decreased significantly in PA and PAB exposure. Higher non-photochemical quenching and lower photochemical quenching values were observed in UVR-exposed samples as compared to the control. Levels of intracellular reactive oxygen species (ROS) increased significantly in PAB and PA. Fluorescence microscopic images showed an increase in green fluorescence, indicating the generation of ROS in UVR. The antioxidant machinery including superoxide dismutase, catalase and peroxidase showed an increase of 1.76-fold and 2.5-fold superoxide dismutase, 2.4-fold and 3.7-fold catalase, 1.83-fold and 2.5-fold peroxidase activities under PA and PAB, respectively. High-performance liquid chromatography equipped with photodiode array detector, electrospray ionization mass spectrometry, Fourier-transform infrared spectroscopy and nuclear magnetic resonance spectroscopy analyses reveal the occurrence of a single mycosporine-like amino acid, shinorine (λ max 332.3 ± 2 nm, m/z 333.1), with a retention time of 1.157 min. The electrochemical characterization of shinorine was determined by cyclic voltammetry. The shinorine molecule possesses electrochemical activity and represents diffusion-controlled process in 0.1 M (pH 7.0) phosphate buffer. An antioxidant assay of shinorine showed its efficient activity as antioxidant which increased in a dose-dependent manner.

Various potential techniques to reduce the water footprint of microalgal biomass production for biofuel-A review

Due to their rapid growth rates, high lipid productivity, and ability to synthesize value-added products, microalgae are considered as the potential biofuel feedstocks. However, among the several bottlenecks that are hindering the commercialization of microalgal biofuel synthesis, the issue of high water consumption is the least explored. This analysis, therefore, examines the factors that decide water use for the production of microalgae biofuel. Microalgae biodiesel water footprint varies from 3.5 to 3726 kg of water per kg of biodiesel. The study further investigates the cause for large variability in the estimation of the water footprint for microalgae fuel. Various strategies, including the reuse of harvested water, the use of high density cultivation that could be adopted for low water consumption in microalgal biofuel production are discussed. Specifically, the review identified a reciprocal relationship between biomass productivity and water footprint. On the basis of which the review emphasizes the significance of high density cultivation, which can be inexpensive and feasible relative to other water-saving techniques. With the setback of water scarcity due to the rapid industrialization in developing countries, the implementation of the cultivation system with a focus on minimizing the water consumption is inevitable for a successful large scale microalgal biofuel production.

Evo-physio: on stress responses and the earliest land plants

Embryophytes (land plants) can be found in almost any habitat on the Earth's surface. All of this ecologically diverse embryophytic flora arose from algae through a singular evolutionary event. Traits that were, by their nature, indispensable for the singular conquest of land by plants were those that are key for overcoming terrestrial stressors. Not surprisingly, the biology of land plant cells is shaped by a core signaling network that connects environmental cues, such as stressors, to the appropriate responses-which, thus, modulate growth and physiology. When did this network emerge? Was it already present when plant terrestrialization was in its infancy? A comparative approach between land plants and their algal relatives, the streptophyte algae, allows us to tackle such questions and resolve parts of the biology of the earliest land plants. Exploring the biology of the earliest land plants might shed light on exactly how they overcame the challenges of terrestrialization. Here, we outline the approaches and rationale underlying comparative analyses towards inferring the genetic toolkit for the stress response that aided the earliest land plants in their conquest of land.

Enigmatic Microalgae from Aeroterrestrial and Extreme Habitats in Cosmetics: The Potential of the Untapped Natural Sources

With the increasing demand for natural and safe products in cosmetics, algae with their diverse and valuable bioactive compounds are gaining vital importance. Until now, cosmetics have focused mainly on the use of freshwater and marine algae. However, algae are not restricted to aquatic habitats. They are found in essentially every type of aeroterrestrial and extreme environment on the Earth. There, they have to cope with harsh ecological conditions and have developed special strategies to thrive in these inimical habitats. Although not thoroughly studied, their adaptations include protective biochemical compounds which can find their application or are already used in the field of cosmetics. With proper cultivation techniques, algae from these habitats can provide novel sources of high-value functional products for the cosmetics industry, which have the advantage of being obtained in eco-friendly and cost-effective processes. However, it has to be considered that a few aeroterrestrial and extremophilic algae can be toxin producers, and in order to ensure conformity to the safe quality standards, all new ingredients must be properly tested. The aim of the present review is to unveil the hidden and underestimated potential of the enigmatic algae of aeroterrestrial and extreme habitats for the rapidly developing modern cosmetic industries.

Klebsormidin A and B, Two New UV-Sunscreen Compounds in Green Microalgal Interfilum and Klebsormidium Species (Streptophyta) From Terrestrial Habitats

The terrestrial green algal members of the genera Interfilum and Klebsormidium (Klebsormidiophyceae, Streptophyta) are found in biological soil crusts of extreme habitats around the world where they are regularly exposed, among other abiotic stress factors, to high levels of ultraviolet radiation (UVR). As a consequence those species synthesize and accumulate either one or two mycosporine-like amino acids (MAAs), but with a missing structural elucidation up to now. Therefore, in the present study both MAAs were chemically isolated and structurally elucidated. The two new compounds exhibit absorption maxima of 324 nm. MAA 1 has a molecular weight of 467 and MAA 2 of 305, and the latter (MAA 2) was identified as N-(4,5-dihydroxy-5-(hydroxymethyl)-2-methoxy-3-oxocyclohex-1-en-1-yl)-N-methylserine using one- and two-dimensional 1H and 13C-NMR spectroscopy. MAA 1 contains an additional sugar moiety. As trivial names for these two novel MAAs we suggest klebsormidin A and klebsormidin B. Different species from all previously described phylogenetic clades of Klebsormidiophyceae were chemically screened for their MAA composition in aqueous extracts using RP-HPLC and LC-MS. The novel klebsormidin A was present throughout all clades and hence could be suitable as a chemotaxonomic marker. Additionally, controlled UVR-exposure experiments with all investigated species showed that MAA biosynthesis and intracellular enrichment is strongly induced by short wavelengths, supporting the function of these compounds as natural UV-sunscreen as well as explaining the cosmopolitan distribution and ecological success of Interfilum and Klebsormidium in terrestrial habitats.

Bostrychines A-F, Six Novel Mycosporine-Like Amino-Acids and a Novel Betaine from the Red Alga Bostrychia scorpioides

Various red algae have repeatedly been reported to produce a variety of UV-absorbing mycosporine-like amino acids (MAAs), compounds that are well-known as natural sun-screens, as well as a plethora of betaines, metabolites which contribute to the osmotic balance under salt stress. Among other Rhodophyta, Bostrychia scorpioides, which is thriving as epiphyte on salt marsh plants in Europe and hence experiences extreme environmental conditions such as desiccation, UV-stress and osmotic stress, has barely been investigated for its secondary metabolites. In the present study, seven mycosporine like-amino acids and two betaines were isolated from Bostrychia scorpioides using various chromatographic techniques. Their structures were confirmed by Nuclear Magnetic Resonance (NMR) spectroscopy and High Resolution Mass Spectrometry (HRMS). Six MAAs and one betaine were chemically characterized as new natural products.

Microalgae metabolites: A rich source for food and medicine

Microalgae are one of the important components in food chains of aquatic ecosystems and have been used for human consumption as food and as medicines. The wide diversity of compounds synthesized from different metabolic pathways of fresh and marine water algae provide promising sources of fatty acids, steroids, carotenoids, polysaccharides, lectins, mycosporine-like amino acids, halogenated compounds, polyketides, toxins, agar agar, alginic acid and carrageenan. This review discusses microalgae used to produce biological substances and its economic importance in food science, the pharmaceutical industry and public health.

Mexican Microalgae Biodiversity and State-Of-The-Art Extraction Strategies to Meet Sustainable Circular Economy Challenges: High-Value Compounds and Their Applied Perspectives

In recent years, the demand for naturally derived products has hiked with enormous pressure to propose or develop state-of-the-art strategies to meet sustainable circular economy challenges. Microalgae possess the flexibility to produce a variety of high-value products of industrial interests. From pigments such as phycobilins or lutein to phycotoxins and several polyunsaturated fatty acids (PUFAs), microalgae have the potential to become the primary producers for the pharmaceutical, food, and agronomical industries. Also, microalgae require minimal resources to grow due to their autotrophic nature or by consuming waste matter, while allowing for the extraction of several valuable side products such as hydrogen gas and biodiesel in a single process, following a biorefinery agenda. From a Mexican microalgae biodiversity perspective, more than 70 different local species have been characterized and isolated, whereas, only a minimal amount has been explored to produce commercially valuable products, thus ignoring their potential as a locally available resource. In this paper, we discuss the microalgae diversity present in Mexico with their current applications and potential, while expanding on their future applications in bioengineering along with other industrial sectors. In conclusion, the use of available microalgae to produce biochemically revenuable products currently represents an untapped potential that could lead to the solution of several problems through green technologies. As such, if the social, industrial and research communities collaborate to strive towards a greener economy by preserving the existing biodiversity and optimizing the use of the currently available resources, the enrichment of our society and the solution to several environmental problems could be attained.

Assessment of fungi proliferation and diversity in cultural heritage: Reactions to UV-C treatment

Fungi are present in natural and non-touristic caves due to the presence of organic matter provided mainly by insects or animals such as bats. In show caves, however, tourist infrastructure and the visitors themselves are an important source of organic matter. In addition, photosynthetic biofilms provide a high amount of carbon and nitrogen sources for fungi. This study was conducted to identify the fungal communities present in caves along with the potential use of UV-C treatment against their proliferation. Thus, fungal communities proliferating in biofilms in six French and Swiss show caves were analyzed using high throughput sequencing. The results show 385 species recorded, some of them previously described in cases of fungal outbreak. This preliminary study also aimed to test the use of UV-C light as an environmentally friendly method to treat fungal proliferation. Six fungal strains, from three different sources (Lascaux cave, La Glacière cave, a church in Vicherey, France), were cultivated in an agar dish. Spores, mycelia and the entire colony were irradiated using several UV-C intensities. Results showed that four of the six fungi spores and mycelium died following a low-intensity UV-C treatment (2 kJ m^-2, 160 s), though Ochroconis lascauxensis and Penicillium bilaiae spores showed higher resistance. Finally, it was demonstrated that the fungal colony could resist the UV-C light due to a shadow effect. The structure of the fungal colony was affected from the periphery to its inner part. However, after four 30 kJ m^-2 treatments (39 min irradiation) all strains there definitively eradicated. Further studies will be necessary to examine the potential of UV-C light under cave conditions as a preventive and curative treatment.

Arctic, Antarctic, and temperate green algae Zygnema spp. under UV-B stress: vegetative cells perform better than pre-akinetes

Species of Zygnema form macroscopically visible mats in polar and temperate terrestrial habitats, where they are exposed to environmental stresses. Three previously characterized isolates (Arctic Zygnema sp. B, Antarctic Zygnema sp. C, and temperate Zygnema sp. S) were tested for their tolerance to experimental UV radiation. Samples of young vegetative cells (1 month old) and pre-akinetes (6 months old) were exposed to photosynthetically active radiation (PAR, 400-700 nm, 400 μmol photons m^-2 s^-1) in combination with experimental UV-A (315-400 nm, 5.7 W m^-2, no UV-B), designated as PA, or UV-A (10.1 W m^-2) + UV-B (280-315 nm, 1.0 W m^-2), designated as PAB. The experimental period lasted for 74 h; the radiation period was 16 h PAR/UV-A per day, or with additional UV-B for 14 h per day. The effective quantum yield, generally lower in pre-akinetes, was mostly reduced during the UV treatment, and recovery was significantly higher in young vegetative cells vs. pre-akinetes during the experiment. Analysis of the deepoxidation state of the xanthophyll-cycle pigments revealed a statistically significant (p < 0.05) increase in Zygnema spp. C and S. The content of UV-absorbing phenolic compounds was significantly higher (p < 0.05) in young vegetative cells compared to pre-akinetes. In young vegetative Zygnema sp. S, these phenolic compounds significantly increased (p < 0.05) upon PA and PAB. Transmission electron microscopy showed an intact ultrastructure with massive starch accumulations at the pyrenoids under PA and PAB. A possible increase in electron-dense bodies in PAB-treated cells and the occurrence of cubic membranes in the chloroplasts are likely protection strategies. Metabolite profiling by non-targeted RP-UHPLC-qToF-MS allowed a clear separation of the strains, but could not detect changes due to the PA and PAB treatments. Six hundred seventeen distinct molecular masses were detected, of which around 200 could be annotated from databases. These results indicate that young vegetative cells can adapt better to the experimental UV-B stress than pre-akinetes.

Composition and functional property of photosynthetic pigments under circadian rhythm in the cyanobacterium Spirulina platensis

Circadian rhythm is an important endogenous biological signal for sustainable growth and development of cyanobacteria in natural ecosystems. Circadian effects of photosynthetically active radiation (PAR), ultraviolet-A (UV-A) and ultraviolet-B (UV-B) radiations on pigment composition have been studied in the cyanobacterium Spirulina platensis under light (L)/dark (D) oscillation with a combination of 4/20, 8/16, 12/12, 16/8, 20/4 and 24/24 h time duration. Circadian exposure of PAR + UV-A (PA) and PAR + UV-A + UV-B (PAB) showed more than twofold decline in Chl a, total protein and phycocyanin (PC) in light phase and significant recovery was achieved in dark phase. The fluorescence emission wavelength of PC was shifted towards lower wavelengths in the light phase of PAB in comparison to P and PA whereas the same wavelength was retrieved in the dark phase. The production of free radicals was accelerated twofold in the light phase (24 h L) whereas the same was retrieved to the level of control during the dark phase. Oxidatively induced damage was alleviated by antioxidative enzymes such as catalase (CAT), peroxidase (POD), superoxide dismutase (SOD) and ascorbate peroxidase (APX) in the light phase (0-24-h L) whereas the dark phase showed significant inhibition of the same enzymes. Similar characteristic inhibition of free radicals and recovery of PC was observed inside cellular filament after circadian rhythm of 24/24 h (L/D). Circadian exposure of P, PA and PAB significantly altered the synthesis and recovery of pigments that could be crucial for optimization and sustainable production of photosynthetic products for human welfare.

Polyols and UV-sunscreens in the Prasiola-clade (Trebouxiophyceae, Chlorophyta) as metabolites for stress response and chemotaxonomy

In many regions of the world, aeroterrestrial green algae of the Trebouxiophyceae (Chlorophyta) represent very abundant soil microorganisms, and hence their taxonomy is crucial to investigate their physiological performance and ecological importance. Due to a lack in morphological features, taxonomic and phylogenetic studies of Trebouxiophycean algae can be a challenging task. Since chemotaxonomic markers could be a great assistance in this regard, 22 strains of aeroterrestrial Trebouxiophyceae were chemically screened for their polyol-patterns as well as for mycosporine-like amino acids (MAAs) in their aqueous extracts using RP-HPLC and LC-MS. d-sorbitol was exclusively detected in members of the Prasiolaceae family. The novel MAA prasiolin and a related compound ("prasiolin-like") were present in all investigated members of the Prasiola-clade, but missing in all other tested Trebouxiophyceae. While prasiolin could only be detected in field material directly after extraction, the "prasiolin-like" compound present in the other algae was fully converted into prasiolin after 24 h. These findings suggest d-sorbitol and prasiolin-like compounds are suitable chemotaxonomic markers for the Prasiolaceae and Prasiola-clade, respectively. Additional UV-exposure experiments with selected strains show that MAA formation and accumulation can be induced, supporting their role as UV-sunscreen.

Different Resistance to UV-B Radiation of Extracellular Polymeric Substances of Two Cyanobacteria from Contrasting Habitats

The effects of UV-B radiation (UVBR) on photosynthetic activity (Fv/Fm) of aquatic Synechocystis sp. and desert Chroococcus minutus and effects on composition and fluorescence property of extracellular polymeric substances (EPSs) from Synechocystis sp. and C. minutus were comparatively investigated. The desert cyanobacterium species C. minutus showed higher tolerance of PSII activity (Fv/Fm) to UVBR than the aquatic Synechocystis sp., and the inhibited PSII activity of C. minutus could be fully recovered while that of Synechocystis sp. could be partly recovered. UVBR had significant effect on the yield and biochemical composition of EPS of both species. Protein-like and humic acid-like substances were detected in EPS from Synechocystis sp., and protein-like and phenol-like fluorescent compounds were detected in EPS from C. minutus. Proteins in EPS of desert and aquatic species were significantly decomposed under UVBR, and the latter was more easily decomposed. The polysaccharides were much more resistant to UVBR than the proteins for both species. Polysaccharides of Synechocystis sp. was degraded slightly but those of C. minutus was little decomposed. The higher tolerance to UVBR of the desert cyanobacterium can be attributed to the higher resistance of its EPS to photodegradation induced by UVBR in comparison with the aquatic species.

Bioweathering Potential of Cultivable Fungi Associated with Semi-Arid Surface Microhabitats of Mayan Buildings

Soil and rock surfaces support microbial communities involved in mineral weathering processes. Using selective isolation, fungi were obtained from limestone surfaces of Mayan monuments in the semi-arid climate at Yucatan, Mexico. A total of 101 isolates representing 53 different taxa were studied. Common fungi such as Fusarium, Pestalotiopsis, Trichoderma, and Penicillium were associated with surfaces and were, probably derived from airborne spores. In contrast, unusual fungi such as Rosellinia, Annulohypoxylon, and Xylaria were predominantly identified from mycelium particles of biofilm biomass. Simulating oligotrophic conditions, agar amended with CaCO3 was inoculated with fungi to test for carbonate activity. A substantial proportion of fungi, in particular those isolated from mycelium (59%), were capable of solubilizing calcium by means of organic acid release, notably oxalic acid as evidenced by ion chromatography. Contrary to our hypothesis, nutrient level was not a variable influencing the CaCO3 solubilization ability among isolates. Particularly active fungi (Annulohypoxylon stygium, Penicillium oxalicum, and Rosellinia sp.) were selected as models for bioweathering experiments with limestone-containing mesocosms to identify if other mineral phases, in addition to oxalates, were linked to bioweathering processes. Fungal biofilms were seen heavily covering the stone surface, while a biomineralized front was also observed at the stone-biofilm interface, where network of hyphae and mycogenic crystals was observed. X-ray diffraction analysis (XRD) identified calcite as the main phase, along with whewellite and wedellite. In addition, lower levels of citrate were detected by Attenuated Total Reflectance-Fourier-Transform Infrared Spectroscopy (ATR-FTIR). Overall, our results suggest that a diverse fungal community is associated with limestone surfaces insemi-arid climates. A subset of this community is geochemically active, excreting organic acids under quasi-oligotrophic conditions, suggesting that the high metabolic cost of exuding organic acids beneficial under nutrient limitation. Oxalic acid release may deteriorate or stabilize limestone surfaces, depending on microclimatic dynamics.

Prasiolin, a new UV-sunscreen compound in the terrestrial green macroalga Prasiola calophylla (Carmichael ex Greville) Kützing (Trebouxiophyceae, Chlorophyta)

We introduced a novel combination of chromatographic techniques for the purification and analysis of a new UV-sunscreen mycosporine-like amino acid (MAA) in the terrestrial green alga Prasiola calophylla. Prasiola calophylla (Carmichael ex Greville) Kützing (Trebouxiophyceae, Chlorophyta) is a typical member of terrestrial algal communities in temperate Europe, where it regularly experiences various stress conditions including strong diurnal and seasonal fluctuations in ultraviolet radiation (UVR). As a photoprotective mechanism Prasiola species and other related Trebouxiophycean taxa synthesize a mycosporine-like amino acid (MAA) as natural sunscreen whose chemical structure was unknown so far. In the present study a new methodological approach is described for the isolation, purification and structural elucidation of this novel sunscreen in P. calophylla. The new compound exhibits an absorption maximum at 324 nm (in the short ultraviolet-A), a molecular weight of 333 and a molecular extinction coefficient of 12.393 M(-1) cm(-1), and could be identified as N-[5,6 hydroxy-5(hydroxymethyl)-2-methoxy-3-oxo-1-cycohexen-1-yl] glutamic acid using one- and two-dimensional (1)H and (13)C-NMR spectroscopy. As trivial name for this novel MAA we suggest 'prasiolin'. The ecologically essential function of prasiolin for UVR-protection in terrestrial algae of the Trebouxiophyceae is discussed.

Enhancing plant productivity while suppressing biofilm growth in a windowfarm system using beneficial bacteria and ultraviolet irradiation

Common problems in a windowfarm system (a vertical and indoor hydroponic system) are phytopathogen infections in plants and excessive buildup of biofilms. The objectives of this study were (i) to promote plant health by making plants more resistant to infection by using beneficial biosurfactant-producing Pseudomonas chlororaphis around the roots and (ii) to minimize biofilm buildup by ultraviolet (UV) irradiation of the water reservoir, thereby extending the lifespan of the whole system with minimal maintenance. Pseudomonas chlororaphis-treated lettuce grew significantly better than nontreated lettuce, as indicated by enhancement of color, mass, length, and number of leaves per head (p < 0.05). The death rate of the lettuce was reduced by ∼ 50% when the lettuce was treated with P. chlororaphis. UV irradiation reduced the bacteria (4 log reduction) and algae (4 log reduction) in the water reservoirs and water tubing systems. Introduction of P. chlororaphis into the system promoted plant growth and reduced damage caused by the plant pathogen Pythium ultimum. UV irradiation of the water reservoir reduced algal and biofilm growth and extended the lifespan of the system.

Heritage materials and biofouling mitigation through UV-C irradiation in show caves: state-of-the-art practices and future challenges

Biofouling, i.e., colonization of a given substrate by living organisms, has frequently been reported for heritage materials and particularly on stone surfaces such as building facades, historical monuments, and artworks. This also concerns subterranean environments such as show caves, in which the installation of artificial light for tourism has led to the proliferation of phototrophic microorganisms. In Europe nowadays, the use of chemicals in these very sensitive environments is scrutinized and regulated by the European Union. New and environmentally friendly processes must be developed as alternative methods for cave conservation. For several years, the UV irradiation currently used in medical facilities and for the treatment of drinking water has been studied as a new innovative method for the conservation of heritage materials. This paper first presents a review of the biofouling phenomena on stone materials such as building facades and historical monuments. The biological disturbances induced by tourist activity in show caves are then examined, with special attention given to the methods and means to combat them. Thirdly, a general overview is given of the effects of UV-C on living organisms, and especially on photosynthetic microorganisms, through different contexts and studies. Finally, the authors' own experiments and findings are presented concerning the study and use of UV-C irradiation to combat algal proliferation in show caves. Both laboratory and in situ results are summarized and synthesized from their previously published works. The application of UV in caves is discussed and further experiments are proposed to enhance research in this domain.

Use of lanthanides to alleviate the effects of metal ion-deficiency in Desmodesmus quadricauda (Sphaeropleales, Chlorophyta)

Lanthanides are biologically non-essential elements with wide applications in technology and industry. Their concentration as environmental contaminants is, therefore, increasing. Although non-essential, lanthanides have been proposed (and even used) to produce beneficial effects in plants, even though their mechanisms of action are unclear. Recently, it was suggested that they may replace essential elements. We tested the effect of low concentrations of lanthanides on the common freshwater microalga Desmodesmus quadricauda, grown under conditions of metal ion-deficiency (lower calcium or manganese concentrations). Our goal was to test if lanthanides can replace essential metals in their functions. Physiological stress was recorded by studying growth and photosynthetic activity using a pulse amplitude modulation (PAM) fluorimeter. We found that nutrient stress reduced parameters of growth and photosynthesis, such as maximal quantum yield, relative electron transport rate, photon capturing efficiency and light saturation irradiance. After adding low concentrations of five lanthanides, we confirmed that they can produce a stimulatory effect on microalgae, depending on the nutrient (metal) deprivation. In the case of a calcium deficit, the addition of lanthanides partly alleviated the adverse effects, probably by a partial substitution of the element. In contrast, with manganese deprivation (and at even lower concentrations), lanthanides enhanced the deleterious effect on cellular growth and photosynthetic competence. These results show that lanthanides can replace essential elements, but their effects on microalgae depend on stress and the nutritional state of the microalgae, raising the possibility of environmental impacts at even low concentrations.

Responses of a rice-field cyanobacterium Anabaena siamensis TISTR-8012 upon exposure to PAR and UV radiation

The effects of PAR and UV radiation and subsequent responses of certain antioxidant enzymatic and non-enzymatic defense systems were studied in a rice field cyanobacterium Anabaena siamensis TISTR 8012. UV radiation resulted in a decline in growth accompanied by a decrease in chlorophyll a and photosynthetic efficiency. Exposure of cells to UV radiation significantly affected the differentiation of vegetative cells into heterocysts or akinetes. UV-B radiation caused the fragmentation of the cyanobacterial filaments conceivably due to the observed oxidative stress. A significant increase of reactive oxygen species in vivo and DNA strand breaks were observed in UV-B exposed cells followed by those under UV-A and PAR radiation, respectively. The UV-induced oxidative damage was alleviated due to an induction of antioxidant enzymatic/non-enzymatic defense systems. In response to UV irradiation, the studied cyanobacterium exhibited a significant increase in antioxidative enzyme activities of superoxide dismutase, catalase and peroxidase. Moreover, the cyanobacterium also synthesized some UV-absorbing/screening substances. HPLC coupled with a PDA detector revealed the presence of three compounds with UV-absorption maxima at 326, 331 and 345 nm. The induction of the biosynthesis of these UV-absorbing compounds was found under both PAR and UV radiation, thus suggesting their possible function as an active photoprotectant.

A rapid phenol toxicity test based on photosynthesis and movement of the freshwater flagellate, Euglena agilis Carter

Phenol, a monosubstituted aromatic hydrocarbon with various commercial uses, is a major organic constituent in industrial wastewaters. The ecotoxic action of phenol for aquatic environment is well known. In this study, rapid phenol toxicity tests (1h) were developed based on chlorophyll a (Chl a) fluorescence and the movement parameters of the freshwater flagellate, Euglena agilis Carter. Phenol significantly reduced the maximum quantum yield (Fv/Fm) of photosystem II (PS II) and the maximum photosynthetic electron transport rate (rETRmax) with median effective concentration (EC50) values of 8.94 and 4.67 mM, respectively. Phenol reduced the motility and triggered change in the swimming velocity of the test organism. Among the parameters tested, velocity was the most sensitive biomarker with an EC50 of 3.17 mM. The EC50 values for Fv/Fm, motility, and velocity appear to overlap the permitted levels of phenol. In conclusion, the photosynthesis and movement of E. agilis can be fast and sensitive risk assessment parameters for the evaluation of phenol toxicity in municipal and industrial effluents.

Global ubiquity and local endemism of free-living terrestrial protists: phylogeographic assessment of the streptophyte alga Klebsormidium

Despite considerable research attention during the last 10 years, the distribution and biogeography of protists remain as highly controversial issues. The presumably huge population sizes and unlimited dispersal capabilities should result in protist ubiquity. However, recent molecular investigations suggest that protist communities exhibit strong biogeographic patterns. Here, we examined the biogeographic pattern of a very common green algal genus Klebsormidium. We evaluated the geographic distribution of rbcL genotypes for 190 isolates sampled in six sampling regions located in Europe, North America and Asia. Measures of correlation between genetic and geographic distance matrices revealed a differential distribution pattern on two geographic levels. Globally, the populations were genetically homogeneous; locally, the genotypes were patchily distributed. We hypothesized that a local fine-scale structuring of genotypes may be caused by various ecological factors, in particular, by the habitat differentiation of particular genotypes. Our investigations also identified a large number of new, previously unrecognized lineages. A total of 44 genotypes were identified and more than 66% of these were reported for the first time.

Influence of local climate and climate change on aeroterrestrial phototrophic biofilms

Aeroterrestrial phototrophic biofilms colonize natural and man-made surfaces and may damage the material they settle on. The occurrence of biofilms varies between regions with different climatic conditions. The aim of this study was to evaluate the influence of meteorological factors on the growth of aeroterrestrial phototrophs. Phototrophic biomass was recorded on roof tiles at six sites within Germany five times over a period of five years and compared to climatic parameters from neighboring weather stations. All correlating meteorological factors influenced water availability on the surface of the roof tiles. The results indicate that the frequency of rainy days and not the mean precipitation per season is more important for biofilm proliferation. It is also inferred that the macroclimate is more important than the microclimate. In conclusion, changed (regional) climatic conditions may determine where in central Europe global change will promote or inhibit phototrophic growth in the future.

UV-induced effects on growth, photosynthetic performance and sunscreen contents in different populations of the green alga Klebsormidium fluitans (Streptophyta) from alpine soil crusts

Members of the green algal genus Klebsormidium (Klebsormidiales, Streptophyta) are typical components of biological soil crust communities worldwide, which exert important ecological functions. Klebsormidium fluitans (F. Gay) Lokhorst was isolated from an aeroterrestrial biofilm as well as from four different biological soil crusts along an elevational gradient between 600 and 2350 m in the Tyrolean and South Tyrolean Alps (Austria, Italy), which are characterised by seasonally high solar radiation. Since the UVtolerance of Klebsormidium has not been studied in detail, an ecophysiological and biochemical study was applied. The effects of controlled artificial ultraviolet radiation (UVR; <9 W m(-2) UV-A, <0.5 W m(-2) UV-B) on growth, photosynthetic performance and the capability to synthesise mycosporine-like amino acids (MAAs) as potential sunscreen compounds were comparatively investigated to evaluate physiological plasticity and possible ecotypic differentiation within this Klebsormidium species. Already under control conditions, the isolates showed significantly different growth rates ranging from 0.42 to 0.74 μm day(-1). The UVR effects on growth were isolate specific, with only two strains affected by the UV treatments. Although all photosynthetic and respiratory data indicated strain-specific differences under control conditions, UV-A and UV-B treatment led only to rather minor effects. All physiological results clearly point to a high UV tolerance in the K. fluitans strains studied, which can be explained by their biochemical capability to synthesize and accumulate a putative MAA after exposure to UV-A and UV-B. Using HPLC, a UV-absorbing compound with an absorption maximum at 324 nm could be identified in all strains. The steady-state concentrations of this Klebsormidium MAA under control conditions ranged from 0.09 to 0.93 mg g(-1) dry weight (DW). While UV-A led to a slight stimulation of MAA accumulation, exposure to UV-B was accompanied by a strong but strain-specific increase of this compound (5.34-12.02 mg(-1) DW), thus supporting its function as UV sunscreen. Although ecotypic differences in the UVR response patterns of the five K. fluitans strains occurred, this did not correlate with the altitude of the respective sampling location. All data indicate a generally high UV tolerance which surely contributes to the aeroterrestrial lifestyle of K. fluitans in soil crusts of the alpine regions of the European Alps.

Green algae in alpine biological soil crust communities: acclimation strategies against ultraviolet radiation and dehydration

Green algae are major components of biological soil crusts in alpine habitats. Together with cyanobacteria, fungi and lichens, green algae form a pioneer community important for the organisms that will succeed them. In their high altitudinal habitat these algae are exposed to harsh and strongly fluctuating environmental conditions, mainly intense irradiation, including ultraviolet radiation, and lack of water leading to desiccation. Therefore, green algae surviving in these environments must have evolved with either avoidance or protective strategies, as well as repair mechanisms for damage. In this review we have highlighted these mechanisms, which include photoprotection, photochemical quenching, and high osmotic values to avoid water loss, and in some groups flexibility of secondary cell walls to maintain turgor pressure even in water-limited situations. These highly specialized green algae will serve as good model organisms to study desiccation tolerance or photoprotective mechanisms, due to their natural capacity to withstand unfavorable conditions. We point out the urgent need for modern phylogenetic approaches in characterizing these organisms, and molecular methods for analyzing the metabolic changes involved in their adaptive strategies.

Unusual phenolic compounds contribute to ecophysiological performance in the purple-colored green alga zygogonium ericetorum (zygnematophyceae, streptophyta) from a high-alpine habitat

The filamentous green alga Zygogonium ericetorum (Zygnematophyceae, Streptophyta) was collected in a high-alpine rivulet in Tyrol, Austria. Two different morphotypes of this alga were found: a purple morph with a visible purple vacuolar content and a green morph lacking this coloration. These morphotypes were compared with respect to their secondary metabolites, ultrastructure, and ecophysiological properties. Colorimetric tests with aqueous extracts of the purple morph indicated the presence of soluble compounds such as phenolics and hydrolyzable tannins. High-performance liquid chromatography-screening showed that Z. ericetorum contained several large phenolic peaks with absorption maxima at ∼280 nm and sometimes with minor maxima at ∼380 nm. Such compounds are uncommon for freshwater green microalgae, and could contribute to protect the organism against increased UV and visible (VIS) irradiation. The purple Z. ericetorum contained larger amounts (per dry weight) of the putative phenolic substances than the green morph; exposure to irradiation may be a key factor for accumulation of these phenolic compounds. Transmission electron microscopy of the purple morph showed massive vacuolization with homogenous medium electron-dense content in the cell periphery, which possibly contains the secondary compounds. In contrast, the green morph had smaller, electron-translucent vacuoles. The ecophysiological data on photosynthesis and desiccation tolerance indicated that increasing photon fluence densities led to much higher relative electron transport rates (rETR) in the purple than in the green morph. These data suggest that the secondary metabolites in the purple morph are important for light acclimation in high-alpine habitats. However, the green morph recovered better after 4 d of rehydration following desiccation stress.

Potential for green microalgae to produce hydrogen, pharmaceuticals and other high value products in a combined process

Green microalgae for several decades have been produced for commercial exploitation, with applications ranging from health food for human consumption, aquaculture and animal feed, to coloring agents, cosmetics and others. Several products from green algae which are used today consist of secondary metabolites that can be extracted from the algal biomass. The best known examples are the carotenoids astaxanthin and β-carotene, which are used as coloring agents and for health-promoting purposes. Many species of green algae are able to produce valuable metabolites for different uses; examples are antioxidants, several different carotenoids, polyunsaturated fatty acids, vitamins, anticancer and antiviral drugs. In many cases, these substances are secondary metabolites that are produced when the algae are exposed to stress conditions linked to nutrient deprivation, light intensity, temperature, salinity and pH. In other cases, the metabolites have been detected in algae grown under optimal conditions, and little is known about optimization of the production of each product, or the effects of stress conditions on their production. Some green algae have shown the ability to produce significant amounts of hydrogen gas during sulfur deprivation, a process which is currently studied extensively worldwide. At the moment, the majority of research in this field has focused on the model organism, Chlamydomonas reinhardtii, but other species of green algae also have this ability. Currently there is little information available regarding the possibility for producing hydrogen and other valuable metabolites in the same process. This study aims to explore which stress conditions are known to induce the production of different valuable products in comparison to stress reactions leading to hydrogen production. Wild type species of green microalgae with known ability to produce high amounts of certain valuable metabolites are listed and linked to species with ability to produce hydrogen during general anaerobic conditions, and during sulfur deprivation. Species used today for commercial purposes are also described. This information is analyzed in order to form a basis for selection of wild type species for a future multi-step process, where hydrogen production from solar energy is combined with the production of valuable metabolites and other commercial uses of the algal biomass.

Molecular diversity of phototrophic biofilms on building stone

Composition and diversity of aeroterrestrial phototrophic microbial communities are up to now poorly understood. Here, we present a comparative study addressing the composition of algal communities on sandstone substrata based upon the analysis of rRNA gene clone libraries from environmental samples and crude cultures. From a west-facing, shaded wall area of the mediaeval castle ruin Gleichen (Thuringia, Germany), sequences mainly related to the green algae Prasiococcus and Trebouxia (Trebouxiophyceae) were retrieved. A south-west-facing, sun-exposed wall area was mainly colonized by Apatococcus and a Phyllosiphon-related alga. Just a few species, in particular Stichococcus-related strains, were ubiquitous in both areas. Samples from a basement vault exposed to low irradiance exhibited Chlorophyceae like Chromochloris and Bracteacoccus. Thus, most green algae on the daylight-exposed walls were affiliated to Trebouxiophyceae, whereas Chlorophyceae were dominant in samples taken from the site kept under low irradiance. Accordingly, cyanobacterial communities were different: the sun-exposed area was dominated by Synechococcus-related organisms, while on the shaded wall area, cyanobacteria were almost absent. The filamentous Leptolyngbya dominated samples from the basement vault. Scanning electron microscopy revealed endolithic algal morphotypes (coccoid algae and diatoms) dominant in open pores between mineral particles. Here, the organisms may be also involved in biogenic weathering of stone.

Changes in phenolic compounds and cellular ultrastructure of arctic and antarctic strains of Zygnema (Zygnematophyceae, Streptophyta) after exposure to experimentally enhanced UV to PAR ratio

Ultraviolet (UV) radiation has become an important stress factor in polar regions due to anthropogenically induced ozone depletion. Although extensive research has been conducted on adaptations of polar organisms to this stress factor, few studies have focused on semi-terrestrial algae so far, in spite of their apparent vulnerability. This study investigates the effect of UV on two semi-terrestrial arctic strains (B, G) and one Antarctic strain (E) of the green alga Zygnema, isolated from Arctic and Antarctic habitats. Isolates of Zygnema were exposed to experimentally enhanced UV A and B (predominant UV A) to photosynthetic active radiation (PAR) ratio. The pigment content, photosynthetic performance and ultrastructure were studied by means of high-performance liquid chromatography (HPLC), chlorophyll a fluorescence and transmission electron microscopy (TEM). In addition, phylogenetic relationships of the investigated strains were characterised using rbcL sequences, which determined that the Antarctic isolate (E) and one of the Arctic isolates (B) were closely related, while G is a distinct lineage. The production of protective phenolic compounds was confirmed in all of the tested strains by HPLC analysis for both controls and UV-exposed samples. Moreover, in strain E, the content of phenolics increased significantly (p = 0.001) after UV treatment. Simultaneously, the maximum quantum yield of photosystem II photochemistry significantly decreased in UV-exposed strains E and G (p < 0.001), showing a clear stress response. The phenolics were most probably stored at the cell periphery in vacuoles and cytoplasmic bodies that appear as electron-dense particles when observed by TEM after high-pressure freeze fixation. While two strains reacted moderately on UV exposure in their ultrastructure, in strain G, damage was found in chloroplasts and mitochondria. Plastidal pigments and xanthophyll cycle pigments were investigated by HPLC analysis; UV A- and UV B-exposed samples had a higher deepoxidation state as controls, particularly evident in strain B. The results indicate that phenolics are involved in UV protection of Zygnema and also revealed different responses to UV stress across the three strains, suggesting that other protection mechanisms may be involved in these organisms.

UV-B affects photosynthesis, ROS production and motility of the freshwater flagellate, Euglena agilis Carter

The effects of ultraviolet B (UV-B; 295-320 nm) radiation on certain vital physiological (photosynthesis), biochemical (production of reactive oxygen species - ROS) and behavioral (motility and orientation) characteristics were investigated in the unicellular photoautotroph, Euglena agilis Carter. The photosynthetic performance of E. agilis was recorded after exposure of between 15 and 60 min followed by a period of recovery lasting 6-24h under dim light (5-10 μmol photons m(-2) s(-1)). The maximum quantum yield of PS II (F(v)/F(m)) was reduced to 65% and 14% of initial values immediately following 15 and 30 min UV-B exposure, but recovered to 100 and 86% of the initials, respectively. Values of rETR(max) in E. agilis exposed to 15 min UV-B were similar to those of the initials, but a 30 min UV exposure resulted in 75% reduction of rETR(max) with only a 43% recovery as compared with the initial after 24h recovery. After a 60 min UV-B exposure, there were no Chl a fluorescence signals, and hence no F(v)/F(m) or rETR(max). A UV dose-dependent increase in DCFH-DA fluorescence was found in E. agilis cells, reflecting an increase in ROS production. After exposures to UV-B for between 15 and 60 min, the percentages of motile cells in the population decreased to 76, 39 and 15%, respectively. Following 24h in dim light, the percentage of motile cells increased to between 66% and 95% of the initial value. The velocity of non-irradiated cells was 60 μm s(-1), which decreased to 16-35 μm s(-1) immediately following exposure for 15-60 min. After periods of time in dim light (6, 12 and 24h) velocities had recovered to between 44 and 81% of the initial value. In untreated controls, the r-value was 0.23, indicating random movement of E. agilis, but it increased to 0.35 and 0.72 after exposure to UV-B for 30 and 60 min, respectively. There was a tendency towards vertical downward movement of cells proportional to the duration of exposure. The compactness of E. agilis decreased from 2.9 in controls to 1.8-2.3 in cells treated with UV-B although significant recovery followed. UV-B dose-dependent interaction between photosynthetic activity, ROS production and movement is discussed in terms of a UV-protective mechanism in E. agilis.

Different biogeographic patterns of prokaryotes and microbial eukaryotes in epilithic biofilms

Microbial biogeography studies expend much effort in determining whether environmental selection or stochastic processes related to dispersal are more important in shaping community composition. While both types of factors are possibly influential, it is tacitly assumed that protists, or microbial eukaryotes in general, behave biogeographically as prokaryotes because of their small physical size. However, direct evidence for this in exactly the same environment and at the same phylogenetic depth is lacking. In this study, we compared the structure of both prokaryotic and eukaryotic components of microbial communities forming biofilms on mineral substrates in different geographic locations at the level of small-subunit (SSU) rRNA-based operational taxonomic units (OTUs). These microbial communities are subjected to strong environmental selection and contain significant proportions of extremophilic microorganisms adapted to desiccation and UV radiation. We find that the nature of the substrate as well as climatic variables and geography influences microbial community structure. However, constrained correspondence analyses and distance-decay curves showed that, whereas the substrate type was the most significant factor structuring bacterial communities, geographic location was the most influential factor for microbial eukaryote communities. Biological explanations implying a higher dispersal success for bacteria combined with more mobile lifestyles for predatory protists may underlie these different prokaryote versus microbial eukaryote biogeographic patterns.

Sunlight-exposed biofilm microbial communities are naturally resistant to chernobyl ionizing-radiation levels

Background

The Chernobyl accident represents a long-term experiment on the effects of exposure to ionizing radiation at the ecosystem level. Though studies of these effects on plants and animals are abundant, the study of how Chernobyl radiation levels affect prokaryotic and eukaryotic microbial communities is practically non-existent, except for a few reports on human pathogens or soil microorganisms. Environments enduring extreme desiccation and UV radiation, such as sunlight exposed biofilms could in principle select for organisms highly resistant to ionizing radiation as well.

Methodology/Principal Findings

To test this hypothesis, we explored the diversity of microorganisms belonging to the three domains of life by cultivation-independent approaches in biofilms developing on concrete walls or pillars in the Chernobyl area exposed to different levels of radiation, and we compared them with a similar biofilm from a non-irradiated site in Northern Ireland. Actinobacteria, Alphaproteobacteria, Bacteroidetes, Acidobacteria and Deinococcales were the most consistently detected bacterial groups, whereas green algae (Chlorophyta) and ascomycete fungi (Ascomycota) dominated within the eukaryotes. Close relatives to the most radio-resistant organisms known, including Rubrobacter species, Deinococcales and melanized ascomycete fungi were always detected. The diversity of bacteria and eukaryotes found in the most highly irradiated samples was comparable to that of less irradiated Chernobyl sites and Northern Ireland. However, the study of mutation frequencies in non-coding ITS regions versus SSU rRNA genes in members of a same actinobacterial operational taxonomic unit (OTU) present in Chernobyl samples and Northern Ireland showed a positive correlation between increased radiation and mutation rates.

Conclusions/Significance

Our results show that biofilm microbial communities in the most irradiated samples are comparable to non-irradiated samples in terms of general diversity patterns, despite increased mutation levels at the single-OTU level. Therefore, biofilm communities growing in sunlight exposed substrates are capable of coping with increased mutation rates and appear pre-adapted to levels of ionizing radiation in Chernobyl due to their natural adaptation to periodical desiccation and ambient UV radiation.