UVA Treatment Research Articles

Commentary: Chemiexcitation of melanin derivatives induces DNA photoproducts long after UV exposure.

Commentary: Chemiexcitation of melanin derivatives induces DNA photoproducts long after UV exposure.

Impact of exogenous stress on TGF‐β inducible early gene 1 in human skin cells

Keywords: oxidative stress; skin ageing; skin photoexposure; TGF-β; TGF-β inducible early gene-1

Effect of Keratocyte Supernatant on Epithelial Cell Migration and Proliferation After Corneal Crosslinking (CXL)

Purpose: To evaluate the effect of keratocyte supernatant (harvesting time, riboflavin concentration and UV-A-light illumination) on migration and proliferation of human corneal epithelial cells (HCECs) by CXL, in vitro.Methods: Primary human keratocytes isolated from 8 normal and 6 keratoconus corneas were cultured. Thereafter, keratocytes in 0%, 0.05% or 1% riboflavin solution were split into samples without and with 370 nm UVA-light-illumination. After removal of the riboflavin solution, keratocytes were incubated in the mentioned keratocyte culture medium at 37 °C and keratocyte supernatant was harvested after 5 and 24 hours. Keratocyte supernatant without riboflavin and UVA treatment, was used as control. HCECs were cultured until reaching confluence, the HCEC culture medium was replaced by the keratocyte supernatant and HCEC migration was analyzed using the wound-healing assay. HCEC proliferation was determined by the cell proliferation ELISA BrdU (colorimetric) kit. Statistical analysis was performed using a linear mixed model in the framework of a Generalized Estimating Equations (GEE) approach to analyze the effect of harvesting time, riboflavin concentration and UV-A-light illumination using IBM-SPSS version 22.Results: Riboflavin concentration, UVA-light illumination and harvesting time of normal or keratoconus keratocyte supernatant had no significant impact on HCEC proliferation (p > 0.10). Riboflavin concentration did not show significant impact on HCEC migration using normal or keratoconus keratocyte supernatant (p > 0.10), however, longer harvesting time of normal or keratoconus keratocyte supernatant significantly increased (p = 0.01 for both) and UVA-light illumination of keratoconus keratocyte supernatant (p < 0.001) significantly decreased HCEC migration.Conclusion: Harvesting time, riboflavin concentration and UV-A-light illumination of normal and keratoconus keratocyte cultures has no impact on proliferation of HCECs, in the short term. However, 24 hours harvesting time (both for normal and keratoconus keratocytes) increases and UVA-light-illumination of keratoconus keratocyte cultures decreases HCEC migration.

Cutaneous penetration of soft nanoparticles via photodamaged skin: Lipid-based and polymer-based nanocarriers for drug delivery

Photoaging is recognized as the factor damaging skin-barrier function. The aim of this study was to examine the impact of ultraviolet (UV) irradiation on the cutaneous penetration of soft nanoparticles, including nanostructured lipid carriers (NLCs) and poly(lactic-co-glycolic acid) polymer nanoparticles (PNs). In vitro cutaneous permeation of retinoic acid (RA) carried by nanoparticles was evaluated. In vivo nude mouse skin distribution of topically applied nanoparticles was observed by fluorescence and confocal microscopies. The association of nanoparticles with cultured keratinocytes was measured by flow cytometry and fluorescence microscopy. The average diameter and surface charge were 236nm and −32mV for NLCs, and 207nm and −12mV for PNs. The ultrastructural images of skin demonstrated that the application of UV produced a loss of Odland bodies and desmosomes, the organelles regulating skin-barrier function. UVA exposure increased skin deposition of RA regardless of nanoparticle formulation. UVB did not alter RA deposition from nanoparticles as compared to the non-treated group. Exposure to UVA promoted RA delivery into hair follicles from NLCs and PNs by 4.2- and 4.9-fold, respectively. The in vivo skin distribution also showed a large accumulation of Nile red-loaded nanoparticles in follicles after UVA treatment. The soft nanoparticles were observed deep in the dermis. PNs with higher lipophilicity showed a greater association with keratinocytes compared to NLCs. The cell association of PNs was increased by UVA application, whereas the association between NLCs and keratinocytes was reduced two times by UVA. It was concluded that both follicles and intercellular spaces were the main pathways for nanoparticle diffusion into photodamaged skin.

GABA shunt deficiencies and accumulation of reactive oxygen species under UV treatments: insight from Arabidopsis thaliana calmodulin mutants

Environmental stimuli such as UV, paraquat, and H2O2 can induce reactive oxygen species (ROS) production and impair the cellular redox equilibrium. ROS are controlled by a complex network of ROS metabolizing enzymes and play a major signaling role in different compartments of plants cell. GABA, alanine, and glutamate are all GABA shunt-related metabolites that are accumulated in response to oxidative stress. In this study, T-DNA insertion mutants of 7 calmodulin genes (CAM) in Arabidopsis thaliana were used to determine the role of specific CaM in tolerance of plants to oxidative stress induced by ultraviolet (UVA and UVB) treatments. Seedlings growth, seeds germination, reactive oxygen species accumulation, and changes in GABA shunt metabolites levels were determined. Only cam4 mutants showed significant tolerance to UVA and UVB treatments over the other cam mutants during seed germination. Oxidative damage measured as level of MDA caused by UV treatment was found in root and shoot tissues of cam1, cam4, cam5-4, and cam6-1 of Arabidopsis cam mutants. In response to UVA treatment, the shunt metabolites accumulated in root and shoot tissues after 30 min. As a result of UVB treatment, GABA accumulated after 30 min while alanine and glutamate accumulated after 60 min only in root tissue. There was a significant increase in GABA, alanine, and glutamate levels after 30, 60, and 90 min UVA treatments in root and shoot tissue of cam1, cam3-2, cam4, cam5-1, cam5-2, cam6-1, cam7-1 mutants. On the other hand, all shunt metabolites levels were significantly accumulated in root of cam1, cam4, cam5-4, and cam6-1 and only in shoot tissue of cam5-4 and cam6-1 mutants in response to 30, 60, and 90 min UVB treatment. Our results show that cam mutants are sensitive to induced-oxidative stress in response to both UV treatments especially cam1, cam4, cam5-4, cam6-1, and cam7-1 mutants for seed germination and ROS accumulation. Accumulation of GABA shunt metabolites under induced-oxidative stress via UV treatments demonstrates that GABA shunt pathway, GABA metabolites accumulation, and Ca+2/CaM-mediating signaling mechanisms are major components of antioxidant machinery associated with ROS scavenging, H2O2 equilibrium, maintaining balance of cellular redox state, and acquiring tolerance in cellular signaling in response to UV stress in Arabidopsis seedlings.

Photolytic degradation of sulfamethoxazole and trimethoprim using UV-A, UV-C and vacuum-UV (VUV)

The photolytic degradation of the non-degradable pharmaceuticals sulfamethoxazole (SMX) and trimethoprim (TMP) in an aqueous solution was investigated using three kinds of low-pressure mercury lamp UV-A (352 nm), UV-C (254 nm), and vacuum-UV (VUV, 185 nm and 254 nm). The degradation rates were highly dependent on the target compounds as well as the UV sources. No degradation of the target compounds was observed using UV-A treatment, because there was no overlap between the UV-A emission spectrum and absorption spectrum of the target compounds. On the other hand, UVC and VUV revealed higher reactivity. The results also indicated that SMX had a greater potential to react photochemically than TMP. Among the UV sources, VUV was the most effective process for the degradation of target compounds. Furthermore, the addition of oxidants such as hydrogen peroxide (H2O2) and sodium persulfate (Na2S2O8) to the reaction system improved the overall degradation rate significantly.The experimental results for the VUV-irradiated samples with the addition of methanol as a hydroxyl radical scavenger revealed that hydroxyl radicals contribute significantly to the elimination of the target compound. Overall, the degradation rate of the target compounds was in the order: VUV = UV-C > UV-A for sulfamethoxazole and VUV/H2O2 > VUV/ Na2S2O8 > VUV >UV-C >UV-A for trimethoprim.

Inactivation of Salmonella by nitrogen gas plasma generated by a static induction thyristor as a pulsed power supply

Salmonella is one of the most important causative agents of food borne infections in terms of food hygiene. In this study, we investigated whether N2 gas plasma, generated by applying a short high-voltage pulse to N2 using a static induction thyristor power supply (1.5 kilo pulse per second), exhibited a bactericidal/disinfecting effect against Salmonella. Viable cell number of Salmonella was efficiently decreased with a decimal reduction time (D value) of 0.178 min (initial slope) and 3.105 min (single-slope approximation). Plasma treatment altered the surface structure of Salmonella, as observed by scanning electron microscopy. In addition, this treatment induced a marked degradation in O antigen. Polymerase chain reaction (PCR) analysis also suggested that the Salmonella genomic DNA was damaged by the plasma treatment. Reactive chemical products (hydrogen peroxide-like chemicals), ultraviolet light (UV-A) and slight temperature elevations were observed during the operation of the gas plasma device. Viable cell number versus intensity of each potential bactericidal factor were used to identify the primary mechanism of disinfection of Salmonella. Although equivalent levels of UV-A or heat treatment did not inactivate Salmonella, treatment with a low concentration of hydrogen peroxide efficiently inactivated the bacteria. Our results suggest the N2 gas plasma generates reactive chemical species that alter components of Salmonella such as the cell surface as well as damaging the genomic DNA. The combined effect of these reactive species is to induce cell death.

Effect of prestorage UV-A, -B, and -C radiation on fruit quality and anthocyanin of 'Duke' blueberries during cold storage.

Ultraviolet (UV)-A, -B, and -C were radiated to full-ripe blueberries (cv. 'Duke'), and their effects on fruit qualities and phytonutrients during subsequent cold storage were investigated. The blueberries were exposed to each UV light at 6 kJ/m(2) and then stored at 0 °C for 28 days. Weight loss and decay of the fruits after UV treatment were significantly decreased during the cold storage. The total phenolics and antioxidant activities of blueberries after UV-B and -C treatments were always higher than those of the control and UV-A treatment. Individual anthocyanins were markedly increased during the 3 h after the UV-B and -C treatments. The correlation matrix between total phenolics, anthocyanins, and antioxidant activity measured by the 2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonic acid) assay indicated a significantly close correlation with the individual anthocyanin contents. It was confirmed that the prestorage treatments of UV-B and -C increased the storability and phytochemical accumulation of the full-ripe 'Duke' blueberries during cold storage.

Development of refractoriness of HO-1 induction to a second treatment with UVA radiation and the involvement of Nrf2 in human skin fibroblasts.

UVA treatment of cultured human skin fibroblasts (FEK4) has been shown previously to reduce transcriptional activation of heme oxygenase 1 (HO-1) following a second dose of UVA radiation, a phenomenon known as refractoriness. This study demonstrates that the levels of HO-1 protein are also reduced after a second dose of UVA radiation as are Nrf2 levels, and there is less accumulation of Nrf2 in the nucleus where as Bach1 does accumulate in the nucleus. Cell viability is further reduced and cell membrane damage increased as compared with a single UVA treatment when an initial UVA treatment was followed by a second dose. Knockdown of Nrf2 by siRNA (siNrf2) targeting caused additional refractoriness of HO-1 protein induction to a second UVA or heme treatment and this treatment also further enhanced cell damage by a second dose of UVA radiation. However, transfection with Nrf2 caused less refractoriness of HO-1 to a second dose of UVA and reduced cell damage by a second dose of UVA radiation. These findings are consistent with the proposal that Nrf2 is involved in HO-1 refractoriness and could serve as a cytoprotective factor against cell damage caused by repeated exposure to moderate doses of UVA radiation. We propose that protection by the Nrf2-HO-1 pathway protection may have clinical relevance since human skin is exposed repeatedly to UVA radiation.

Wastewater disinfection using ultraviolet (UVA, UVC) and solar radiation

Nowadays, water availability and quality represent a major challenge. In 2050, the United Nations Organization predicts that 44% of the world population will face severe water scarcity. Countries located in sub-humid and semi-arid regions of the world will be especially concerned for this problem, because of their low supply of rainwater. The aim of this study is to suggest the disinfection treatment by irradiation as a complement wastewater treatment to obtain a safe microbial quality of water and permit its reuse. This last is limited to 1.000 CFU/100 ml (i.e. equivalent to 3 log) of fecal coliforms by the Algerian and WHO standards. The experiments were conducted to disinfect wastewater by UVA, UVC, and solar radiation. The UVA and UVC disinfection treatments were carried out using an experimental bench composed of three flat-bottom flasks and three Erlenmeyers of 2 L each. The solar disinfection treatment was experimented using a 30 L-tubular photoreactor in a stationary and a dynamic flow. The disinfection results indicate a reduction in 2.47 log of total coliforms, 3 log reduction of fecal coliforms, 2.67 log reduction of streptococci, 3.17 log reduction of staphylococci, 0.08 log reduction of yeasts, 0.19 log reduction of molds, and a reduction of 1.17 log of sulfite-spores.

UVA-photoactivated riboflavin effect on isolated vaginal tissues derived from pelvic organ prolapse cases.

To determine the optimal riboflavin exposure time before UVA irradiation and to study the effects of exogenous collagen on the mechano-tensile stiffness of isolated vaginal tissue strips after riboflavin UVA photoactivation. Vaginal tissue strips from pelvic organ prolapse (POP) cases were soaked in 0.1% riboflavin (0, 10, 20, 30 min), exposed to UVA photoactivation, and tensile stiffness was measured with a tensiometer. Collagen solution was injected (0.2 mL) into each strip, exposed to riboflavin with or without UVA photoactivation, and tensile stiffness was measured (n=6). Vaginal tissues treated with riboflavin for 10, 20 or 30 min followed by UVA irradiation displayed 21.2, 32.4 and 33.9% stronger tensile stiffness, respectively. Exogenous collagen administered before riboflavin UVA photoactivation resulted in 20% improvement in tensile stiffness. The tensile stiffness of vaginal tissues injected with collagen without the riboflavin UVA treatment was similar to control tissues. The results demonstrated increased tensile stiffness in isolated POP-derived vaginal tissues after riboflavin UVA photoactivation suggesting improved mechanical properties from collagen cross-linking. Administering exogenous collagen before riboflavin UVA treatment also improved tensile stiffness. More studies are needed to corroborate the present minimally invasive approach for strengthening vaginal tissues.

Study on Spatial Distribution of UVA Radiant Intensity for Ballast Water Treatment

UVA is seldom applied in UV inactivation or disinfection, however, it may be more suitable for underwater photo-catalysis treatment. Since the wavelength of UVA is longer than UVC, the former has higher transmission ability and encounter less disturbance of suspending substances in water. Also, the exciting wavelength of UVA is between 365nm and 413nm which coincides with the wavelength of UVA. Hence, the spatial distribution of UVA radiation is studied for a 15W UVA lamp. The decaying tendencies of UVA radiation intensity were probed over horizontal and vertical distance, behind large amounts of experimental data. Optimal radiation conditions plan to be detected based on the research to guide the UVA treatment.

Effect of monochromatic UV-A LED irradiation on the growth of tomato seedlings

Effect of 376 nm UV-A LED irradiation on the growth and morphology of tomato seedlings was studied. Tomato seedlings were grown under the 658 nm red LEDs or the red LED supplemented with two irradiation levels of the UV-A. The growth and development of tomato seedlings were significantly enhanced under the red light supplemented with the UV-A. Under the UV-A treatments, the tomato seedlings became more compact, the growth of plant organs was balanced, the leaf area was increased, and the total plant fresh and dry weights were also enhanced. Our findings suggested that the 376 nm UV-A from LEDs had a beneficial effect on the growth and development of tomato seedlings as similarly to the blue light.

The Oncogene ATF3 Is Potentiated by Cyclosporine A and Ultraviolet Light A

Cutaneous squamous cell carcinoma (SCC) represents the most important cutaneous complication following organ transplantation. It develops mostly on sun-exposed areas. A recent study showed the role of activating transcription factor 3 (ATF3) in SCC development following treatment with calcineurin inhibitors. It has been reported that ATF3, which may act as an oncogene, is under negative calcineurin/nuclear factor of activated T cells (NFAT) control and is upregulated by calcineurin inhibitors. Still, these findings do not fully explain the preferential appearance of SCC on chronically sun-damaged skin. We analyzed the influence of UV radiation on ATF3 expression and its potential role in SCC development. We found that ATF3 is a specifically induced AP1 member in SCC of transplanted patients. Its expression was strongly potentiated by combination of cyclosporine A and UVA treatment. UVA induced ATF3 expression through reactive oxygen species-mediated nuclear factor erythroid 2-related factor 2 (NRF2) activation independently of calcineurin/NFAT inhibition. Activated NRF2 directly binds to ATF3 promoter, thus inducing its expression. These results demonstrate two mechanisms that independently induce and, when combined together, potentiate the expression of ATF3, which may then force SCC development. Taking into account the previously defined role of ATF3 in the SCC development, these findings may provide an explanation and a mechanism for the frequently observed burden on SCCs on sun-exposed areas of the skin in organ transplant recipients treated by calcineurin inhibitors.

Modulation of Specific Apoptotic DNA Fragmentation after Short Term Exposure to Natural UVR in Fish Larvae

The goal of this study was to determine the short-term effects of the quality (UV-A/UV-B ratio) and quantity (irradiance) of natural ultraviolet radiation (UVR) on the apoptosis levels in Yellow perch (Perca flavescens) larvae. Apoptosis, or programmed cell death, is an essential event in many physiological processes as well as in pathological conditions. Western blots were used to measure the expression of several key proteins of the apoptotic cascade, such as p53, Bax, Bcl-2, and PARP-1, whereas specific apoptotic DNA fragmentation was measured by an ELISA assay. We predicted that higher UVR exposure would be related to higher levels of apoptosis. Our results showed that specific apoptotic DNA fragmentation was reduced by visible light + UV-A as well as by visible light + UV-A and UV-B treatments although it was not significantly affected by light quantity. However, the expression of p53, Bax/Bcl-2 ratio and PARP-1 were not significantly affected in larvae by the quantity or the quality of the light after two days of exposure. Altogether our results suggest that UVR may modulate the apoptotic process in Yellow perch larvae proposing an interesting role for this stressor on the early development of living organism under natural exposure condition.

Generalized morphea successfully treated with extracorporeal photochemotherapy (ECP).

A patient is presented with generalized morphea whose disease completely resolved after combination therapy with extracorporeal photopheresis and broad band UVA treatments.

Clinicopathological Evaluation and Outcome of Mycosis Fungoides

Although mycosis fungoides is the most common cutaneous T-cell lymphoma, its etiopathogenesis has not been clarified definitively and there is no standard and curative treatment method. Medical records of 57 patients diagnosed with mycosis fungoides by clinical and histopathological findings were retrospectively reviewed in our clinic. Complete blood count, erythrocyte sedimentation rate, peripheral blood smear, biochemical findings, chest radiographs, and computerized tomography of all patients were reviewed; patients were staged using TNM system. The clinical presentation was classical patch/plaque form in 44patients and other forms in 13. According to TNM staging, 9patients were stage 1a, 38 were stage 1b, 5 were 2a, and 2 were stage 3, and 2 were stage 4a. The pathological findings were basal alignment of lymphocytes, reticular fibroplasia, atypical lymphocytes, and epidermotropism. Remission was achieved by topical imiquimod in 2patients, phototherapy in 30, and phototherapy and systemic treatment in 8. Remission rate with narrow band UV B was 72%, and that of psoralen UV A was 85.71%. Ten patients in remission had recurrence. Age, sex, duration of disease, and clinical presentation had no effect on remission or recurrence of mycosis fungoides. Reticular fibroplasia is a supporting histopathological finding in mycosis fungoides, together with basal alignment of lymphocytes, atypical lymphocytes and epidermotropism. Topical imiquimod treatment for local lesions and phototherapy for widespread lesions are effective, and psoralen UVA treatment seems to be more efficient than narrow band UVB.

Simultaneous increases in specific growth rate and specific lipid content of Chlorella vulgaris through UV‐induced reactive species

A challenge in algae-based bio-oil production is to simultaneously enhance specific growth rates and specific lipid content. We have demonstrated simultaneous increases in both the above in Chlorella vulgaris through reactive species (RS) induced under ultraviolet (UV) A and UVB light treatments. We postulated that the changes in photosystem (PS) stoichiometry and antenna size were responsible for the increases in specific growth rate. UVB treatment excited PSII, which resulted in a twofold to sevenfold increase in PSII/PSI ratio compared to control. An excited PSII caused a 2.7-fold increase in the specific levels of superoxide and a twofold increase in the specific levels of hydroxyl radicals. We have established that the increased specific intracellular RS (si-RS) levels increased the PSII antenna size by a significant 10-fold as compared to control. In addition, the 8.2-fold increase in specific lipid content was directly related to the si-RS levels. We have also demonstrated that the RS induced under UVA treatment led to a 3.2-fold increase in the saturated to unsaturated fatty acid ratio. Based on the findings, we have proposed and demonstrated a UV-based strategy, which achieved an 8.8-fold increase in volumetric lipid productivity.

Sak1 kinase interacts with Pso2 nuclease in response to DNA damage induced by interstrand crosslink-inducing agents in Saccharomyces cerevisiae

By isolating putative binding partners through the two-hybrid system (THS) we further extended the characterization of the specific interstrand cross-link (ICL) repair gene PSO2 of Saccharomyces cerevisiae. Nine fusion protein products were isolated for Pso2p using THS, among them the Sak1 kinase, which interacted with the C-terminal β-CASP domain of Pso2p. Comparison of mutagen-sensitivity phenotypes of pso2Δ, sak1Δ and pso2Δsak1Δ disruptants revealed that SAK1 is necessary for complete WT-like repair. The epistatic interaction of both mutant alleles suggests that Sak1p and Pso2p act in the same pathway of controlling sensitivity to DNA-damaging agents. We also observed that Pso2p is phosphorylated by Sak1 kinase in vitro and co-immunoprecipitates with Sak1p after 8-MOP+UVA treatment. Survival data after treatment of pso2Δ, yku70Δ and yku70Δpso2Δ with nitrogen mustard, PSO2 and SAK1 with YKU70 or DNL4 single-, double- and triple mutants with 8-MOP+UVA indicated that ICL repair is independent of YKu70p and DNL4p in S. cerevisiae. Furthermore, a non-epistatic interaction was observed between MRE11, PSO2 and SAK1 genes after ICL induction, indicating that their encoded proteins act on the same substrate, but in distinct repair pathways. In contrast, an epistatic interaction was observed for PSO2 and RAD52, PSO2 and RAD50, PSO2 and XRS2 genes in 8-MOP+UVA treated exponentially growing cells.

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.