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We studied metabolic activity of the symbiont-bearing large benthic foraminifer Heterostegina depressa under different light conditions. Besides the overall photosynthetic performance of the photosymbionts estimated by means of variable fluorescence, the isotope uptake ( 13 C and 15 N) of the specimens (= holobionts) was measured. Heterostegina depressa was either incubated in darkness over a period of 15 days or exposed to an 16:8 h light:dark cycle mimicking natural light conditions. We found photosynthetic performance to be highly related to light supply. The photosymbionts, however, survived prolonged darkness and could be reactivated after 15 days of darkness. The same pattern was found in the isotope uptake of the holobionts. Based on these results, we propose that 13 C-carbonate and 15 N-nitrate assimilation is mainly controlled by the photosymbionts, whereas 15 N-ammonium and 13 C-glucose utilization is regulated by both, the symbiont and the host cells.

The increasing global demand for sustainable protein sources necessitates the exploration of alternative solutions beyond traditional livestock and crop-based proteins. Microalgae present a promising alternative due to their high protein content, rapid biomass accumulation, and minimal land and water requirements. Furthermore, their ability to thrive on non-arable land and in wastewater systems enhances their sustainability and resource efficiency. Despite these advantages, scalability and economical feasibility remain major challenges in microalgal protein production. This review explores recent advancements in microalgal protein cultivation and extraction technologies, including pulsed electric field, ultrasound-assisted extraction, enzyme-assisted extraction, and microwave-assisted extraction. These innovative techniques have significantly improved protein extraction efficiency, purity, and sustainability, while addressing cell wall disruption and protein recovery challenges. Additionally, the review examines protein digestibility and bioavailability, particularly in the context of human nutrition and aquafeed applications. A critical analysis of life cycle assessment studies highlights the environmental footprint and economical feasibility of microalgal protein production compared to conventional protein sources. Although microalgal protein production requires significant energy inputs, advancements in biorefinery approaches, carbon dioxide sequestration, and industrial integration can help mitigate these limitations. Finally, this review outlines key challenges and future research directions, emphasizing the need for cost reduction strategies, genetic engineering for enhanced yields, and industrial-scale process optimization. By integrating innovative extraction techniques with biorefinery models, microalgal proteins hold immense potential as a sustainable, high-quality protein source for food, feed, and nutraceutical applications.

Estimating algal biomass is a prerequisite for monitoring growth of microalgae. Especially for large-scale production sites, the measurements must be robust, reliable, fast and easy to obtain. We compare the relevant parameters, discuss potential hurdles and provide recommendations to tackle these issues. The focus is on optical density and in vivo autofluorescence of chlorophyll, which have proven to be ideal candidates for monitoring purposes. Beyond biomass, cell vitality is also crucial for maintaining cultures. While maximizing biomass yield is often the primary consideration, some applications require adverse growth conditions for the synthesis of high-quality compounds. The non-invasive technique of pulse-amplified modulated (PAM) fluorescence measurements provides an ideal tool and is increasingly being employed due to ever more affordable devices. We compared three devices and studied the robustness of the dark fluorescence yield of photosystem II (Fv/Fm) at various cell densities. Although the so-called inner filter effects influence the fluorescence signal, the resulting Fv/Fm remain stable and robust over a wide range of cell densities due to mutual effects.

Foraminifera are single-celled protists which are important mediators of the marine carbon cycle. In our study, we explored the potential impact of polystyrene (PS) microplastic particles on two symbiont-bearing large benthic foraminifera species— Heterostegina depressa and Amphistegina lobifera —over a period of three weeks, employing three different approaches: investigating (1) stable isotope (SI) incorporation—via 13 C- and 15 N-labelled substrates—of the foraminifera to assess their metabolic activity, (2) photosynthetic efficiency of the symbiotic diatoms using imaging PAM fluorometry, and (3) microscopic enumeration of accumulation of PS microplastic particles inside the foraminiferal test. The active feeder A. lobifera incorporated significantly more PS particles inside the cytoplasm than the non-feeding H. depressa, the latter accumulating the beads on the test surface. Photosynthetic area of the symbionts tended to decrease in the presence of microplastic particles in both species, suggesting that the foraminiferal host cells started to digest their diatom symbionts. Compared to the control, the presence of microplastic particles lead to reduced SI uptake in A. lobifera , which indicates inhibition of inorganic carbon and nitrogen assimilation. Competition for particulate food uptake was demonstrated between algae and microplastic particles of similar size. Based on our results, both species seem to be sensitive to microplastic pollution, with non-feeding H. depressa being more strongly affected.

Foraminifera are abundant unicellular organisms that play an important role in marine element cycles. A large benthic foraminifer obligatory bearing photosymbionts is Heterostegina depressa . We studied potential impacts of sunscreens available on the market on the activity of photosymbionts on H. depressa by means of pulse-amplitude modulated (PAM) fluorescence microscopy. We included four different sunscreens, with two of them sold as “conventional” and two more stated as “eco-friendly”. Further, the impact of pure Ensulizole (phenylbenzimidazole sulfonic acid) was tested, which is a common agent of sunscreens. Foraminifera were incubated at varying concentrations (10, 50 and 200 mgL −1 ) of different sunscreens and the pure Ensulizole for 14 days. The photosynthetic performance was measured after 1,3, 7 and 14 days. Pure Ensulizole had a strong negative impact on the photobionts, which was reflected by a significant reduction of the areal fluorescence signal. “Eco-friendly” sunscreens affected the health of foraminifera more severely compared to “conventional” ones. We assume that metal nanoparticles like titanium dioxide or zinc oxide of “eco-friendly” sunscreens are causing this impact, because these substances were already classified as toxic for several microorganisms.

Many phycological applications require the growth and maintenance of pure algae cultures. In some research areas, such as biochemistry and physiology, axenic growth is essential to avoid misinterpretations caused by contaminants. Nonetheless, axenicity—defined as the state of only a single strain being present, free of any other organism—needs to be verified. We compare the available methods to assess axenicity. We first purified unialgal Limnospira fusiformis cultures with an established series of axenicity treatments, and by including two additional treatment steps. The presumable axenic cultures were then tested for their axenic state by applying conventional tests on LB (lysogeny broth) agar-plates, 16S rRNA gene amplicon sequencing, flow-cytometry and epifluorescence microscopy. Only the plate tests indicated axenic conditions. We found a linear relationship between total cell counts of contaminants achieved by flow cytometry and epifluorescence microscopy, with flow cytometry counts being consistently higher. In addition, 16S rRNA gene amplicon sequencing demonstrated its superiority by not only being an efficient tool for axenicity testing, but also for identification of persistent contaminants. Although classic plate tests are still commonly used to verify axenicity, we found the LB-agar-plate technique to be inappropriate. Cultivation-independent methods are highly recommended to test for axenic conditions. A combination of flow-cytometry and 16S rRNA gene amplicon sequencing complement each other and will yield the most reliable result.

The cytoplasm of characean internodal cells is characterized by a stationary layer of cortical chloroplast files and a mobile endoplasm moving along subcortical actin bundles. Occasionally, chloroplasts detach from the cortex and are passively carried along with the endoplasmic flow. Previous studies revealed that local irradiation with intense light causes chloroplast bleaching followed by a release into the endoplasm (“window formation”). We found that endoplasmic chloroplasts of Chara australis resettle at the window and align parallel to the streaming direction. The process takes several weeks with neither chloroplast division nor growth of proplastids being involved. Both release and re-attachment are actin-dependent. Resettled chloroplasts showed slightly, but significantly lower maximum quantum efficiency (Fv/Fm) values as compared with control regions. Extremely low Fv/Fm values were measured in chloroplasts at the border of the window even after three months indicating longevity, although with serious damage. In higher plants, a protein complex is responsible for the motility and anchorage of chloroplasts, with CHUP1 ( C HLOROPLAST U NUSUAL P OSITIONING 1) being an essential part. We discovered a homologous form CaCHUP1, encoding a polypeptide of 1201 amino acids with a calculated molecular mass of about 130 kDa. When transiently expressed in epidermal cells of Nicotiana benthamiana leaves, fluorescently tagged CaCHUP1 localizes to chloroplasts. We assume that CaCHUP1 is involved in the anchorage of chloroplasts and in the polymerization of actin filaments, but not in active movement. Our study revealed that endoplasmic chloroplasts can re-anchor at the cell cortex thereby refilling chloroplast-free regions, which we interpret as a repair mechanism after various kinds of damage. It confirms that chloroplasts use different strategies for repositioning, either via polymerization of cp-actin or via cytoplasmic streaming.

Biopolymers such as chitosan and pectin are currently attracting significant attention because of their unique properties, which are valuable in the food industry and pharmaceutical applications. These properties include non-toxicity, compatibility with biological systems, natural decomposition ability, and structural adaptability. The objective of this study was to assess the performance of two different ratios of pectin–chitosan polyelectrolyte composite (PCPC) after applying them as a coating to commercially pure titanium (CpTi) substrates using electrospraying. The PCPC was studied in ratios of 1:2 and 1:3, while the control group consisted of CpTi substrates without any coating. The pull-off adhesion strength, cytotoxicity, and antibacterial susceptibility tests were utilized to evaluate the PCPC coatings. In order to determine whether the composite coating was the result of physical blending or chemical bonding, the topographic surface parameters were studied using Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM). PCPC (1:3) had the highest average cell viability of 93.42, 89.88, and 86.85% after 24, 48, and 72 h, respectively, as determined by the cytotoxicity assay, when compared to the other groups. According to the Kirby–Bauer disk diffusion method for testing antibacterial susceptibility, PCPC (1:3) showed the highest average diameter of the zone of inhibition, measuring 14.88, 14.43, and 11.03 mm after 24, 48, and 72 h of incubation, respectively. This difference was highly significant compared to Group 3 at all three time periods. PCPC (1:3) exhibited a significantly higher mean pull-off adhesion strength (521.6 psi) compared to PCPC (1:2), which revealed 419.5 psi. PCPC (1:3) coated substrates exhibited better surface roughness parameters compared to other groups based on the findings of the AFM. The FTIR measurement indicated that both PCPC groups exhibited a purely physical blending in the composite coating. Based on the extent of these successful in vitro experiments, PCPC (1:3) demonstrates its potential as an effective coating layer. Therefore, the findings of this study pave the way for using newly developed PCPC after electrospraying coating on CpTi for dental implants.

Rivers are impacted by microbial faecal pollution from various sources. We report on a short-term faecal pollution event at the pre-alpine Austrian river Traisen caused by the large cultural event FM4 Frequency music festival, with around 200,000 visitors over 4 days. We observed a massive increase of the faecal indicator bacteria (FIB) intestinal enterococci during the event, while Escherichia coli concentrations were only slightly elevated. This increase poses a significant potential health threat to visitors and people recreating downstream of the festival area. A plausible explanation for the uncoupling of the two FIBs may have been a differential persistence caused by a combination of factors including water temperature, solar radiation, and the excessive presence of personal care products (PCPs) in the river water. However, a potential impact of PCPs on FIB assay performance cannot be ruled out. Our observations are relevant for other intensively used bathing sites; detailed investigations on persistence and assay performance of the FIB in response to different ingredients of PCPs are highly recommended. We conclude that for future festivals at this river or other festivals taking place under similar settings, a more effective management is necessary to reduce deterioration in water quality and minimise health risks.