Multiple-pathways light modulation in Pleurosigma strigosum bi-raphid diatom.

Ordered, quasi-ordered, and even disordered nanostructures can be identified as constituent components of several protists, plants and animals, making possible an efficient manipulation of light for intra- and inter- species communication, camouflage, or for the enhancement of primary production. Diatoms are ubiquitous unicellular microalgae inhabiting all the aquatic environments on Earth. They developed, through tens of millions of years of evolution, ultrastructured silica cell walls, the frustules, able to handle optical radiation through multiple diffractive, refractive, and wave-guiding processes, possibly at the basis of their high photosynthetic efficiency. In this study, we employed a range of imaging, spectroscopic and numerical techniques (including transmission imaging, digital holography, photoluminescence spectroscopy, and numerical simulations based on wide-angle beam propagation method) to identify and describe different mechanisms by which Pleurosigma strigosum frustules can modulate optical radiation of different spectral content. Finally, we correlated the optical response of the frustule to the interaction with light in living, individual cells within their aquatic environment following various irradiation treatments. The obtained results demonstrate the favorable transmission of photosynthetic active radiation inside the cell compared to potentially detrimental ultraviolet radiation.

Clinical Characteristics of Patients with Acute Ischemic Stroke Previously Vaccinated Against COVID-19.

OBJECTIVES: The aim of this study was to examine the clinical characteristics of patients with acute ischemic stroke which were previously vaccinated against Coronavirus Disease 2019 (COVID-19) and determine whether the vaccine had impact on outcome. MATERIALS AND METHODS: In this observational cohort study we analyzed the clinical characteristics of 58 patients with ischemic stroke, previously vaccinated against COVID-19. We analyzed demographic characteristics, risk factors, type of stroke and outcome. We also compared outcome of those patients with outcome in stroke patients hospitalized in the same period but not vaccinated, patients hospitalized during the pandemic, before vaccination began, and stroke patients hospitalized before the pandemic. Further, we compared mortality rate with mortality rate in patients who had acute ischemic stroke and COVID-19 simultaneously. RESULTS: The mean age of the patients was 71.0 years, most were male (58.6%), mostly with risk factors for stroke. In the largest number of patients, 17 (29.3%), the etiopathogenetic mechanism of stroke was atherosclerosis of the large arteries. Mortality in vaccinated patients was identical to mortality in stroke patients before pandemic, without significant difference from mortality in unvaccinated patients (13.8% versus 8.6%; p= 0.23). The mean NIHSS and mRS score at discharge for all examined groups were without significant difference. A significant difference in mortality was found between COVID-19 positive and COVID-19 negative stroke patients (37.8% versus 18.1%; p=0.001). CONCLUSIONS: There are no significant differences in clinical characteristics of stroke in vaccinated compared to unvaccinated patients. We did not find a connection between vaccination and stroke.

Underwater Light Manipulation by the Benthic Diatom Ctenophora pulchella: From PAR Efficient Collection to UVR Screening.

Several species of diatoms, unicellular microalgae which constitute the main component of phytoplankton, are characterized by an impressive photosynthetic efficiency while presenting a noticeable tolerance versus exposure to detrimental UV radiation (UVR). In particular, the growth rate of the araphid diatom Ctenophora pulchella is not significantly affected by harsh treatments with UVR, even in absence of detectable, specific UV-absorbing pigments and even if it is not able to avoid high UV exposure by motility. In this work we applied a multi-disciplinary approach involving numerical computation, photonics, and biological parameters in order to investigate the possible role of the frustule, micro- and nano-patterned silica shell which encloses the cell, in the ability of C. pulchella to efficiently collect photosynthetic active radiation (PAR) and to simultaneously screen the protoplasm from UVR. The characterization of the photonic properties of the frustule has been accompanied by in vivo experiments conducted in water in order to investigate its function as optical coupler between light and plastids.

Cultivation and Photophysiological Characteristics of Desmids in Moderately Saline Aquaculture Wastewater.

Although desmids typically inhabit freshwater environments characterized by low amounts of nutrients and low salinity, several desmid species have been recorded in eutrophic waters, indicating their adaptation to elevated pollution and conductivity. This study aimed to determine whether desmids could be used for remediation of moderately saline aquaculture wastewater (AWW) from a fish farm situated in the southeast of Sweden. Fourteen desmid strains isolated from different climates (tropical to polar) and trophic conditions (oligotrophic to eutrophic) were cultivated in diluted AWW and we estimated their growth rates, biomass, nutrient removal efficiency, chlorophyll fluorescence parameters and cellular C, N and P quotas. Despite being grown at moderate salinity, unfavourable N:P ratio, and relatively low light/temperature regime the eutrophic strains, Cosmarium humile, Cosmarium laeve and a meso-oligotrophic species Cosmarium impressulum, completely absorbed nitrate and phosphate from AWW media after 7 d, indicating their potential for remediation of fish effluents in colder climates. These species, along with the typical eutrophic species, Cosmarium meneghinii and Staurastrum chaetoceras, had biomass in the range 0.45-1.19 g · L-1 while maximum growth rates ranged from 0.36 to 0.51 · d-1 , similar to published rates for several fast-growing green microalgae cultivated in various AWW types. Tropical desmids had distinctly high values of saturating irradiance (Ik  > 1,000 µmol photons · m-2  · s-1 ), and, along with eutrophic desmids, had high potential electron transport (rETRmax  > 155 rel. units). Hence, the desmids studied demonstrated inherent photophysiological responses corresponding to their climate and trophic origin under the suboptimal growth conditions.

Fatty acids as chemotaxonomic and ecophysiological traits in green microalgae (desmids, Zygnematophyceae, Streptophyta): A discriminant analysis approach.

Desmids (Zygnematophyceae) are a group of poorly studied green microalgae. The aim of the present study was to identify fatty acids (FAs) that could be used as biomarkers in desmids in general, and to determine FAs as traits within different ecophysiological desmid groups. FA profiles of 29 desmid strains were determined and analysed with respect to their geographic origin, trophic preference and age of cultivation. It appeared that merely FAs present in relatively large proportions such as palmitic, linoleic, α-linolenic and hexadecatrienoic acids could be used as biomarkers for reliable categorization of this microalgal group. Linear discriminant analysis applied to three a priori defined groups of desmids, revealed clear strain-specific characteristics regarding FA distribution, influenced by climate and trophic conditions at the source sites as well as by the age of culture and growth phase. Accordingly, when considering FAs for the determination of lower taxonomic ranks we recommend using the term "trait" instead of "biomarker", as the latter designates unchangeable "fingerprint" of a specific taxon. Furthermore, despite that desmids were regarded as microalgae having stable genomes, long-term cultivation appeared to cause modifications in FA metabolic pathways, evident as a larger proportion of stearidonic acid in desmid strains cultivated over extensive time periods (>35 years).

Ultrastructure of Cosmarium strains (Zygnematophyceae, Streptophyta) collected from various geographic locations shows species-specific differences both at optimal and stress temperatures.

Plant species collected from various climatic zones and stressed in vitro at various temperatures reveal changes in cellular ultrastructure which are in accordance with the climate at their sampling sites. This observation initiated the investigation to establish if stress at different temperatures may cause diverse extents of changes in the ultrastructure of microalgal strains originating from different geographic zones. The study revealed that the six Cosmarium strains demonstrated ultrastructural characteristics that were consistent with their source location under optimal, low and high temperature conditions, pointing to their preference to specific climatic niches. Interestingly, chloroplasts of all of the Cosmarium strains correspond to a sun-adapted type, which is concomitant with earlier statements that these strains are rendered as high-light adapted algae. The Cosmarium strains developed multiple ultrastructural responses which enabled them to cope with excessive temperatures, occasionally occurring in desmid natural habitats. The appearance of cubic membranes and increased number of plastoglobules may represent the first line in protection against high-temperature stress, which is accompanied by the alteration of protein synthesis and the appearance of stress granules in order to preserve cell homeostasis. However, the prolonged warm- or cold-temperature stress obviously initiated the programmed cell death, as concluded from the appearance of several ultrastructural features observed in all of the Cosmarium strains. The fair acclimation possibilities and the ability to undergo programmed cell death in order to save the population, certainly favor the cosmopolitan distribution of the genus Cosmarium.

Xanthophyll cycle pool size and composition in several Cosmarium strains (Zygnematophyceae, Streptophyta) are related to their geographic distribution patterns.

The photosynthetic behaviour and composition of photosynthetic pigments of four Cosmarium strains collected from different geographic areas were examined under moderate and photoinhibitory white light by means of PAM fluorometry and high-performance liquid chromatography. Generally, all of the Cosmarium strains displayed the photosynthetic performance and the composition of xanthophyll cycle pigments corresponding to that of high-light adapted plants and algae, when grown under the standard laboratory conditions. However, photoinhibitory treatments provoked several strain- and species-specific characteristics despite the long-term cultivation in laboratory conditions. The typical arctic taxon, C. crenatum var. boldtianum, displayed an incomplete violaxanthin cycle yielding an accumulation of antheraxanthin during high light stress, which is considered as an adaptation to occasional high irradiances in the polar zone due to the albedo. So far, the violaxanthin/antheraxanthin turnover was known only in some prasinophycean algae. Antheraxanthin actively participated in the heat dissipation from PSII centres in C. crenatum, as concluded from a significant positive correlation between non-photochemical quenching (NPQ) and the quantity of antheraxanthin. In contrast, all the other Cosmarium strains displayed a complete violaxanthin de-epoxidase action during the high light treatments, as judged from the relatively high production of zeaxanthin which participated in thermal dissipation of excess energy.

Protection strategies of Cosmarium strains (Zygnematophyceae, Streptophyta) isolated from various geographic regions against excessive photosynthetically active radiation.

Numerous in vitro investigations have suggested that macroalgae exhibit regular geographic and depth distribution patterns in accordance with the light and temperature predominance at their habitats; however, there have been only a few similar studies concerning microalgae. We examined the potential influence of irradiance on patterns of distribution of four Cosmarium strains isolated from various climatic zones and cultured long term (>15 years) under a constant temperature-light regime. All the Cosmarium strains demonstrated physiological responses that were consistent with the light intensity prevailing at their source location, confirming that these responses are genetically preserved, as concluded from chlorophyll fluorescence and oxygen evolution rates measurements. Addition of inhibitors of chloroplast-encoded protein synthesis (chloramphenicol and streptomycin) and violaxanthin de-epoxidase (dithiothreitol) indicated that the Cosmarium strains developed "sun- or shade-plant" protection strategies, in accordance with the climate at their sampling sites. The polar Cosmarium strains exhibited a "shade-plant strategy"-to suffer some photoinhibition, but acquire increasing protection from photoinhibited PSII centers, whereas the tropical strains displayed a "sun-plant strategy"-to counteract photoinhibition of PSII by a high rate of repair of photoinhibited PSII reaction centers and a high xanthophyll cycle turnover.