Multi-omics for studying and understanding polar life.

Polar ecosystems are experiencing amongst the most rapid rates of regional warming on Earth. Here, we discuss 'omics' approaches to investigate polar biodiversity, including the current state of the art, future perspectives and recommendations. We propose a community road map to generate and more fully exploit multi-omics data from polar organisms. These data are needed for the comprehensive evaluation of polar biodiversity and to reveal how life evolved and adapted to permanently cold environments with extreme seasonality. We argue that concerted action is required to mitigate the impact of warming on polar ecosystems via conservation efforts, to sustainably manage these unique habitats and their ecosystem services, and for the sustainable bioprospecting of novel genes and compounds for societal gain.

[Photo-based examination for diabetic eye pathologies in a German ophthalmological practice without personal doctor-patient contact]. / Fotobasierte Untersuchung auf diabetische Augenveränderungen in einer deutschen Augenarztpraxis ohne direkten Arzt-Patienten-Kontakt.

BACKGROUND: An increasing number of patients suffering from diabetes require regular ophthalmological check-ups to diagnose and/or treat potential diabetic retinal disease. Some countries have already implemented systematic fundus assessments including artificial intelligence-based programs in order to detect sight-threatening retinopathy. The aim of this study was to improve the detection of diabetic fundus changes in Germany without examination by a doctor and to create an easy access to ophthalmological examinations. MATERIAL AND METHODS: In this prospective monocentric study 93 patients in need for a routine check-up for diabetic retinopathy were included. The study participants took up an offer of an examination (visual examination, non-mydriatic camera-based fundus examination) without doctor-patient contact. Patient satisfaction with the organization and examinations was assessed using a questionnaire. RESULTS: The mean age was 53.5 years (SD 13.6 years, 49.5% female) and 17 eyes (18.3%) showed a diabetic retinopathy which was detected using a camera-based examination. Within the small sample, no patient had to repeat the examination due to poor image quality. All categories of the questionnaire showed a good to very good satisfaction, indicating a high acceptance of the other examination form that took place at the ophthalmologist's premises. CONCLUSION: In our study in an ophthalmological practice a high level of acceptance among the patients interested in the screening for diabetic retinopathy without any direct patient-doctor contact was achieved. Our study shows a very good acceptance and feasibility. Future use of artificial intelligence in clinical practice may help to be able to screen many more patients as in this study imaging quality was very good.

Optimal Patient Adherence and Long-Term Treatment Outcomes of Neovascular Age-Related Macular Degeneration in Real-Life.

PURPOSE: To report on long-term real-life outcomes of anti-vascular endothelial growth factor (anti-VEGF) therapy in neovascular age-related macular degeneration (nAMD) with optimal patient adherence. METHODS: For this retrospective monocenter study, we identified 3217 eyes of 2793 patients that received a minimum of three intravitreal anti-VEGF injections for nAMD therapy between 2006 and 2014 at the University Eye Hospital Munich. From those, we included eyes with treatment-naïve nAMD, follow-up (FU) of ≥60 months and continuous adherence during FU. Primary measures were corrected visual acuity (VA), number of injections and visits as well as treatment regimen. RESULTS: We included 161 eyes of 125 patients with a mean FU of 8.0 ± 2.3 years. Mean VA at baseline was 60.1 letters (Snellen equivalent, 20/63). After the third year, mean VA declined constantly by 2-3 letters per year. After 5 and 8 years, 26.1% and 42.1% had lost at least 3 lines from baseline. Mean cumulative number of injections was 5.3 after the first year, and 23.9, 38.1, 48.5 after 5, 8, and 10 years. "Treat and extent" regimen with higher injection frequency correlated with better function. At time of last FU, 69.8% of eyes were under active treatment. Eyes with ≥70 letters at baseline correlated with better VA at the end of FU. CONCLUSIONS: Despite optimal patient adherence, visual function declined progressively in real-life nAMD therapy over long-term. The highest impact on treatment success is given by an early treatment start with individual but intensive anti-VEGF therapy.

The Role and Views of Ophthalmologists During the COVID-19 Pandemic.

PURPOSE: The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic forced ophthalmologists to adjust their working conditions to ensure patient and staff safety, while still providing effective and timely treatment. This international survey among ophthalmologists was initiated to capture what actions ophthalmologists were taking and what their opinions were on the risks of infection in their workplace, the delay in treatment, the use of telemedicine and telephone for appointments, and the regional specifications and measures implemented by the respective authorities. METHODS: An open-source web tool was used to develop an online survey, to which ophthalmologists worldwide were invited via e-mail using international mailing lists (Media Mice, Singapore; Texere Publishing Inc, USA; CGO Gerling) and incentivized using a lottery. The physicians provided their level of agreement relating to the offered statements and gave free answers to the questions regarding the actions taken (conducted November 5th 2020 to December 20th 2020). RESULTS: After 91,000 invitations, responses were collected from 1122 ophthalmologists. Despite the use of large international mailing lists, mainly doctors from Europe participated. Half of the participants expressed great concern about possible SARS-CoV-2 infection in their patients. A significant number of younger ophthalmologists (≤50 years: 76.9%, n = 313; >50 years: 69.6%, n = 181) feared the delays that COVID-19 could cause to treatment. Reductions in patient numbers were broadly observed, with more ophthalmologists of younger age reporting greater declines. Nearly all ophthalmologists indicated that they provided disinfectant and the majority also used masks and questionnaires for screening. For 60.3% (n = 412) of ophthalmologists, telephone calls reduced the risk of 'no-shows'; 71.6% (n = 497) disagreed that telemedical evaluation is possible without slit lamp findings and fundus photos; and 57.0% of participants felt content with the governmental measures during the COVID-19 pandemic. CONCLUSION: The COVID-19 pandemic has significantly influenced the work of ophthalmologists. Based on the limited response rate, certain statements were only possible to evaluate for the European Union: with a noticeable reduction in patient numbers, delay in treatment was a major worry. Measures to protect and reassure patients should be undertaken, especially regarding those with vision-threatening diseases requiring treatment.

Big data simulations for capacity improvement in a general ophthalmology clinic.

PURPOSE: Long total waiting times (TWT) experienced by patients during a clinic visit have a significant adverse effect on patient's satisfaction. Our aim was to use big data simulations of a patient scheduling calendar and its effect on TWT in a general ophthalmology clinic. Based on the simulation, we implemented changes to the calendar and verified their effect on TWT in clinical practice. DESIGN AND METHODS: For this retrospective simulation study, we generated a discrete event simulation (DES) model based on clinical timepoints of 4.401 visits to our clinic. All data points were exported from our clinical warehouse for further processing. If not available from the electronic health record, manual time measurements of the process were used. Various patient scheduling models were simulated and evaluated based on their reduction of TWT. The most promising model was implemented into clinical practice in 2017. RESULTS: During validation of our simulation model, we achieved a high agreement of mean TWT between the real data (229 ± 100 min) and the corresponding simulated data (225 ± 112 min). This indicates a high quality of the simulation model. Following the simulations, a patient scheduling calendar was introduced, which, compared with the old calendar, provided block intervals and extended time windows for patients. The simulated TWT of this model was 153 min. After implementation in clinical practice, TWT per patient in our general ophthalmology clinic has been reduced from 229 ± 100 to 183 ± 89 min. CONCLUSION: By implementing a big data simulation model, we have achieved a cost-neutral reduction of the mean TWT by 21%. Big data simulation enables users to evaluate variations to an existing system before implementation into clinical practice. Various models for improving patient flow or reducing capacity loads can be evaluated cost-effectively.

Enlargement rate of geographic atrophy before and after secondary CNV conversion with associated anti-VEGF treatment.

BACKGROUND: To study the enlargement rate of primary geographic atrophy (GA) before and after diagnosis of a secondary choroidal neovascularization (CNV) treated with anti-vascular endothelial growth factor (VEGF) therapy. METHODS: Five hundred twenty-two consecutive eyes with primary GA were screened for the development of a complicating secondary CNV. Geographic atrophy was measured on blue autofluorescence (BAF) by two readers and calculated into mean growth rate before and after CNV diagnosis. RESULTS: Ten eyes of six patients were included in the study (six study eyes with GA complicated by CNV, four GA only partner eyes). Follow-up was 1.42 ± 0.48 years before and 3.64 ± 2.73 years after CNV. There was no significant difference between mean growth rate before and after CNV (1.58 ± 0.99 vs. 1.39 ± 0.65 mm2/year; p = 0.44) or between study and partner eyes (p = 0.86). Over a mean time of 3.64 ± 2.73 years, a mean of 8.3 ± 2.8 anti-VEGF injections were given. No correlation between the amount of anti-VEGF injections and change in growth rate could be observed (r = 0.58; p = 0.23). CONCLUSION: In this pilot study, primary GA enlargement did not seem to be influenced by a secondary CNV. No association between the intensity of anti-VEGF treatment and changes in atrophy enlargement rates were found. Further studies with larger sample sizes are warranted.

Impact of Sub-Retinal Fluid on the Long-Term Incidence of Macular Atrophy in Neovascular Age-related Macular Degeneration under Treat & Extend Anti-Vascular Endothelial Growth Factor Inhibitors.

Sub-retinal fluid (SRF) has been discussed as a protective factor against macular atrophy in eyes with neovascular age-related macular degeneration (nAMD).To gauge the impact of SRF on macular atrophy, a database of 310 nAMD eyes was screened for eyes manifesting an SRF-only phenotype under treat & extend anti-VEGF treatment, defined as nAMD expressing CNV exudation beyond the three monthly anti-VEGF loading doses by SRF only without any signs of exudative intra-retinal fluid (IRF) for ≥3 years. Incidence of macular atrophy and treatment responses were evaluated on multimodal imaging, including optical coherence tomography (OCT), blue autofluorescence (BAF) and near-infrared (NIR) confocal scanning laser ophthalmoscopy and fluorescence and indocyanine green angiography (FAG/ICGA). In total, 27 eyes (8.7%) of 26 patients with a mean follow-up of 4.2 ± 0.9 (3-5) years met the inclusion criteria. Mean age was 72 ± 6 (range: 61-86) years. The SRF only phenotype was seen from baseline in 14 eyes (52%), and in 13 eyes (48%) after a mean 1.0 ± 1.3 (1-3) injections. In years 1 to 5, mean 7.5, 5.9, 6.1, 6.1 and 7.0 anti-VEGF injections were given (p = 0.33). Cumulative macular atrophy incidence was 11.5% at year 1, 15.4% throughout years 2 to 4, and 22.4% at year 5. In conclusion, eyes manifesting activity by SRF only in treat & extend anti-VEGF regimen for nAMD seem to exhibit rather low rates of macular atrophy during long-term follow-up. SRF might be an indicator of a more benign form of nAMD.

Evaluation of Functional Outcomes and OCT-Biomarkers after Intravitreal Dexamethasone Implant for Postoperative Cystoid Macular Edema in Vitrectomized Eyes.

PURPOSE: To evaluate the efficacy of dexamethasone implant (DEX) for the treatment of postoperative cystoid macular edema (PCME) in vitrectomized eyes and to investigate visual and morphological OCT predictive factors. METHODS: In this retrospective study, eyes with PCME after vitrectomy were treated with at least one DEX injection and were observed over 12 months. Indications for surgery were epiretinal membrane (ERM) or rhegmatogenous retinal detachment (RRD) without macular involvement. Prior treatments, if any, were noted. Best corrected visual acuity (BCVA), central foveal thickness (CFT), and OCT morphology including the presence of intraretinal cysts/fluid or subretinal fluid (IRF/SRF) and ellipsoid zone (EZ) continuity were evaluated. Correlations between OCT measures and visual outcomes were analyzed by the generalized estimating equations procedure. RESULTS: Forty-six eyes with ERM and 15 eyes with RRD were enrolled. The ERM group was more likely to gain BCVA than RRD (odds ratio (OR), 1.168; 95% confidence interval (CI), 1.003-1.360; p=0.046). The absence of SRF (OR, 0.860; 95% CI, 0.743-0.995; p=0.043) was predictive of worse BCVA, whereas the integrity of EZ (OR, 1.094; 95% CI, 0.951-1.257; p=0.209) or naïve status (OR, 0.946; 95% CI, 0.871-1.137, p=0.853) was not. Eyes with a worse baseline BCVA were more likely to gain >1 line after 12 months (OR, 1.485; 95% CI, 1.171-1.884; p=0.001). CONCLUSION: The efficacy of the treatment of PCME in vitrectomized eyes seems to be affected by baseline BCVA, the absence of SRF, and the indication for surgery. Naïve status appears not to play any significant role in the prediction of BCVA. This trial is registered with DRKS00018955.

Response of neovascular central serous chorioretinopathy to an extended upload of anti-VEGF agents.

PURPOSE: To determine the anatomical and functional outcomes of an extended 6-month intravitreal anti-vascular endothelial growth factor (anti-VEGF) upload in choroidal neovascularization (CNV) secondary to chronic central serous chorioretinopathy (CSCR). METHODS: A retrospective database analysis was performed applying the following inclusion criteria: (1) diagnosis of CSCR, (2) diagnosis of secondary CNV, and (3) treatment of at least six consecutive injections of anti-VEGF. Outcome measures included the change of central retinal subfield thickness, remodeling of the pigment epithelium detachments, and change in visual function. RESULTS: Twenty-one eyes of 21 patients were included. Mean patient age was 65 ± 8.3 years, and 35% of the patients (n = 8) were female. Mean disease duration before diagnosis of CNV was 48 ± 25.3 months. Mean central retinal thickness decreased from 346 ± 61 to 257 ± 57 µm (p < 0.01) after the sixth injection while mean visual acuity improved from 0.65 ± 0.35 to 0.49 ± 0.29 (logMAR; p < 0.01). Of note, an extended upload of six as opposed to three injections yielded an additional mean central retinal thickness reduction (280 ± 46 µm vs. 257 ± 57 µm, p = 0.038). Significant CNV remodeling was observed as a decrease in pigment epithelium detachment (PED) vertical (p = 0.021) and horizontal diameter (p = 0.024) as well as PED height (p < 0.01). CONCLUSION: An extended anti-VEGF upload of six consecutive injections seems to be effective in inducing CNV remodeling and fluid resorption in CNV complicating chronic CSCR.

One- and two-year visual outcomes from the Moorfields age-related macular degeneration database: a retrospective cohort study and an open science resource.

OBJECTIVES: To analyse treatment outcomes and share clinical data from a large, single-centre, well-curated database (8174 eyes/6664 patients with 120 756 single entries) of patients with neovascular age-related macular degeneration (AMD) treated with anti-vascular endothelial growth factor (VEGF). By making our depersonalised raw data openly available, we aim to stimulate further research in AMD, as well as set a precedent for future work in this area. SETTING: Retrospective, comparative, non-randomised electronic medical record (EMR) database cohort study of the UK Moorfields AMD database with data extracted between 2008 and 2018. PARTICIPANTS: Including one eye per patient, 3357 eyes/patients (61% female). Extraction criteria were ≥1 ranibizumab or aflibercept injection, entry of 'AMD' in the diagnosis field of the EMR and a minimum of 1 year of follow-up. Exclusion criteria were unknown date of first injection and treatment outside of routine clinical care at Moorfields before the first recorded injection in the database. MAIN OUTCOME MEASURES: Primary outcome measure was change in VA at 1 and 2 years from baseline as measured in Early Treatment Diabetic Retinopathy Study letters. Secondary outcomes were the number of injections and predictive factors for VA gain. RESULTS: Mean VA gain at 1 year and 2 years were +5.5 (95% CI 5.0 to 6.0) and +4.9 (95% CI 4.2 to 5.6) letters, respectively. Fifty-four per cent of eyes gained ≥5 letters at 2 years, 63% had stable VA (±≤14 letters), 44% of eyes maintained good VA (≥70 letters). Patients received a mean of 7.7 (95% CI 7.6 to 7.8) injections during year 1 and 13.0 (95% CI 12.8 to 13.2) injections over 2 years. Younger age, lower baseline VA and more injections were associated with higher VA gain at 2 years. CONCLUSION: This study benchmarks high quality EMR study results of real life AMD treatment and promotes open science in clinical AMD research by making the underlying data publicly available.

Cluster binding studies with two anti-Thomsen-Friedenreich (anti-core-1, CD176, TF) antibodies: Evidence for a multiple TF epitope.

Antibodies to carbohydrate epitopes are often of the IgM isotype and require multiple binding for sufficient avidity. Therefore clusters of epitopes are preferred antigenic sites in these cases. We have examined the type of clusters recognized by two anti-Thomsen-Friedenreich (TF, core-1, CD176) IgM antibodies, NM-TF1 and NM-TF2, using several different sets of TF-carrying synthetic glycoconjugates in ELISA experiments. To our surprise, the single most important factor determining binding strength was a close vicinity of several TF glycans at distances of ≤1 nm. Considering the known dimensions of IgM antibodies, our data strongly suggest that a cluster of up to four TF moieties, presenting as a "multiple epitope", is required to attach to a single combining site in order to result in adequate binding strength. This effect can also be achieved by "surrogate-multiple epitopes" consisting of separate TF-carrying molecules in close vicinity. In addition, it was found that serine-linked TFs are stronger bound than threonine-linked TFs by both antibodies. This peculiar type of cluster recognition may contribute to improved avidity and explicit tumor specificity.

Evaluation of a computed-tomography-based assessment scheme in treatment decision-making for isolated orbital floor fractures.

INTRODUCTION: Treatment decisions for fractures of the orbital floor are based on clinical appearance, ophthalmological examination, and computed tomography (CT) scans. In extensive fractures, decisions are easily made between conservative and surgical treatment. However, objective parameters are rare in inconclusive cases. MATERIALS AND METHODS: Our retrospective study included 106 patients with unilateral isolated orbital floor fractures. Correlations between preoperative ophthalmological examinations and specific CT parameters were performed. RESULTS: The defect size of the fracture appeared to be significantly associated with the presence of diplopia. CT-morphological parameters and preoperative ophthalmological results showed statistical significance for diplopia and incarceration of inferior rectus muscle (IRM), diplopia and displacement of IRM, decreased mobility and incarceration of IRM, and decreased mobility and displacement of IRM. DISCUSSION: Our clinical assessment scheme for CT scans of orbital floor fractures is aimed at facilitating treatment decision making using four CT-based variables. As critical size defects of the orbital floor of ≥2 cm2 are likely to cause clinically significant posterior displacement of the globe, resulting in enophthalmos, the proposed parameters offer a readily accessible and easy to evaluate scheme that helps to identify patients in need of surgical intervention.

Differences in corneal clinical findings after standard and accelerated cross-linking in patients with progressive keratoconus.

BACKGROUND: The purpose of this study was to identify differences in clinical corneal findings after standard and accelerated epithelial off cross-linking (CXL) during a long-term follow-up. METHODS: Two hundred forty-one patients (184 male) were included in this monocentric, retrospective, non-randomized and unmasked study. One hundred forty-eight eyes were treated with the accelerated protocol and 138 with the standard protocol with epithelial off CXL, if diagnosed with keratoconus and a progression in Kmax of more than one dioptre during the preceding 6 months, plus a minimal pachymetry measurement of 400 µm in keratometry (Pentacam, Oculus GmbH, Wetzlar, Germany). Exclusion criteria were previous surgery, other corneal conditions or age above 50 years. Follow-up time was 36 months with clinical examination and keratometry at every visit. Outcome measures were the observed rate of corneal changes, differences between treatment groups and correlation with keratometry measurements. RESULTS: In patients with accelerated CXL, significantly more clear corneas were seen at three (p = 0.015) and six (p = 0.002) months after surgery than following the standard protocol. The rate of clear corneas dropped from 52.2% pre-operation (OP) to a minimum of 19.3% after 6 months in the standard protocol group compared with 50.7% clear corneas pre-OP and a minimum of 40.8% in the accelerated group. In the standard protocol group, more striae were found 3 months after intervention than in the accelerated group (p = 0.05). CONCLUSIONS: In patients with accelerated CXL, fewer morphological corneal changes were observed than after conventional CXL. However, rarely, corneal changes persisted for a long time.

Using Electronic Health Records to Build an Ophthalmologic Data Warehouse and Visualize Patients' Data.

PURPOSE: To develop a near-real-time data warehouse (DW) in an academic ophthalmologic center to gain scientific use of increasing digital data from electronic medical records (EMR) and diagnostic devices. DESIGN: Database development. METHODS: Specific macular clinic user interfaces within the institutional hospital information system were created. Orders for imaging modalities were sent by an EMR-linked picture-archiving and communications system to the respective devices. All data of 325 767 patients since 2002 were gathered in a DW running on an SQL database. A data discovery tool was developed. An exemplary search for patients with age-related macular degeneration, performed cataract surgery, and at least 10 intravitreal (excluding bevacizumab) injections was conducted. RESULTS: Data related to those patients (3 142 204 diagnoses [including diagnoses from other fields of medicine], 720 721 procedures [eg, surgery], and 45 416 intravitreal injections) were stored, including 81 274 optical coherence tomography measurements. A web-based browsing tool was successfully developed for data visualization and filtering data by several linked criteria, for example, minimum number of intravitreal injections of a specific drug and visual acuity interval. The exemplary search identified 450 patients with 516 eyes meeting all criteria. CONCLUSIONS: A DW was successfully implemented in an ophthalmologic academic environment to support and facilitate research by using increasing EMR and measurement data. The identification of eligible patients for studies was simplified. In future, software for decision support can be developed based on the DW and its structured data. The improved classification of diseases and semiautomatic validation of data via machine learning are warranted.

Impact of oral consumption of heat-treated Bacteroides xylanisolvens DSM 23964 on the level of natural TFα-specific antibodies in human adults.

It is now generally accepted that the human body exists in close synergy with the gut microbiome and that this cross-talk plays an essential role in human health and disease. One facet from the many interactions between the microbiome and the immune system is the induction of natural antibodies to commensal bacterial glycans, such as blood group antigens, the alpha-Gal epitope or the Thomsen-Friedenreich (TFα) antigen. Since we have observed that certain species of the commensal genus Bacteroides express the TFα antigen, we examined whether the oral dietary supplementation of a pasteurised Bacteroides xylanisolvens strain might be able to enhance the level of natural anti-TFα antibodies in healthy adults. The data obtained from a double-blind, placebo-controlled study involving 140 healthy volunteers and lasting 8 weeks revealed that the oral uptake of this strain was indeed able to increase the level of TFα-specific immunoglobulin M serum antibodies. The effect was dose-dependent but remained - at any doses - within the physiological range determined before intervention. Furthermore, the effect reverted after stopping the intake. The results support the idea of the microbiome inducing the generation of systemic antigen-specific antibodies against sugar epitopes. They also demonstrate the possibility to modulate essential regulatory or defence processes through dietary supplementation of selected commensal bacteria with the aim to assist human health.

Blood group antigen A type 3 expression is a favorable prognostic factor in advanced NSCLC.

OBJECTIVES: Several blood group-related carbohydrate antigens are prognosis-relevant markers of tumor tissues. A type 3 (repetitive A) is a blood group antigen specific for A1 erythrocytes. Its potential expression in tumor tissues has so far not been examined. MATERIAL AND METHODS: We have evaluated its expression in normal lung and in lung cancer using a novel antibody (A69-A/E8). For comparison an anti-A antibody specific to A types 1 and 2 was used, because its expression on lung cancer tissue has been previously reported to be of prognostic relevance. Resected tissue samples of 398 NSCLC patients were analyzed in immunohistochemistry using tissue microarrays. RESULTS AND CONCLUSIONS: Expression of A type 3 was not observed in non-malignant lung tissues. A type 3 was expressed on tumor cells of around half of NSCLC patients of blood group A1 (p<0.001). Whereas no prognostic effect for A type 1/2 antigen was observed (p=0.562), the expression of A type 3 by tumor cells indicated a highly significant favorable prognosis among advanced NSCLC patients (p=0.011) and in NSCLC patients with lymphatic spread (p=0.014). Univariate prognostic results were confirmed in a Cox proportional hazards model. In this study we present for the first time prognostic data for A type 3 antigen expression in lung cancer patients. Prospective studies should be performed to confirm the prognostic value of A type 3 expression for an improved risk stratification in NSCLC patients.

What controls the expression of the core-1 (Thomsen-Friedenreich) glycotope on tumor cells?

Malignant transformation is tightly connected with changes in the glycosylation of proteins and lipids, which in turn are contributing to the invasive and metastatic behavior of tumor cells. One example of such changes is demasking of the otherwise hidden core-1 structure, also known as Thomsen-Friedenreich antigen, which is a highly tumor-specific glycotope and potentially a cancer stem cell marker. This review summarizes what is known about the mechanism(s) of its expression on tumor cells. New data reveal a close connection between tumor metabolism and Golgi function. Based on these data, we suggest that the expression of this antigen is also a marker of aerobic glycolysis.

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.