A constitutive stress response is a result of low temperature growth in the Antarctic green alga Chlamydomonas sp. UWO241

Generation of suspension cell cultures with high syringin content and anti-inflammatory activity through overexpressing glycotransferase SiUGT72BZ2 in Saussurea involucrata

The snow lotus species Saussurea involucrata (Kar. & Kir.) Sch.Bip., an endangered traditional Chinese herb, belongs to a genus of the Asteraceae family. Syringin present in S. involucrata stands as one of the predominant bioactive compounds. However, the biosynthetic pathway of syringin remains largely elusive. Here, S. involucrata suspension cell culture was subjected to methyl jasmonate (MeJA) treatment, which stimulated the synthesis of syringin, increasing its content by up to 3.9-fold. Comparative transcriptome analysis revealed that genes involved in syringin biosynthesis were generally upregulated in response to MeJA. Furthermore, two candidate UDP-glycosyltransferase genes, SiUGT72BZ2 and SiUGT72CY1, were identified through phylogenetic tree and expression profiling analyses. Overexpression of SiUGT72BZ2 (BZ2_OE) and SiUGT72CY1 (CY1_OE) in S. involucrata suspension cell cultures led to 15.2- and 5.9-fold higher syringin levels than empty vector control cultures, respectively. Notably, upregulation of SiUGT72BZ2 enhanced the biosynthesis of coniferin as well. In contrast, only trace amounts of coniferin were present in control and CY1_OE cell cultures. Subsequent anti-inflammatory assays using lipopolysaccharide (LPS)-stimulated RAW264.7 cells demonstrated that the extracts from these cell cultures possessed remarkable anti-inflammatory properties. Most strikingly, the BZ2_OE cultures exhibited superior anti-inflammatory effects compared to the control and CY1_OE. In conclusion, our research has not only identified the key enzymes in syringin synthesis but also, through genetic engineering, has generated novel cell culture resources enriched with syringin and coniferin, and enhanced anti-inflammatory activities, highlighting the potential of S. involucrata cell culture as an alternative for wild snow lotus resources.

Marine and terrestrial biostimulant elicitors of tolerance to cold stress

The increasing frequency of adverse environmental events, driven by ongoing climate change, has intensified the search for new technological alternatives in crop production and plant protection. Thermal stress can limit plant adaptation and negatively impact metabolism, physiology, morphology, and yield. Cold stress in plants has been extensively studied and can affect various stages of plant's life cycle, from seed formation to development, causing damage to cell membranes, impairing cell division, and disrupting water absorption. Consequently, researchers have focused on mitigating the impacts of abiotic stress by investigating bioactive molecules and biostimulants derived from various organisms, which enhance tolerance mechanisms in plants. In aquatic environments, macro- and microalgae have emerged as key sources of plant elicitors, providing extractable molecules such as polysaccharides, polyamines, polyphenols, and amino acids that enhance plant defense responses. Similarly, certain terrestrial plants have shown potential as sources of biostimulant compounds. Thus, this study aims to highlight advancements in crop systems by emphasizing the potential of algae-based and terrestrial biostimulant elicitors in enhancing tolerance to cold stress. Ultimately, the goal is to improve understanding of promising biological models for food production, fostering innovative developments that can contribute to economically and ecologically sustainable technologies.

Favored competition of Uroglena sp. against coexisting microorganisms in spring of lower temperatures: clarification through a systematic incubation study

Uroglena sp. is a major contributor to the fishy odor in drinking water, with temperature being a key factor regulating its growth. However, no study has yet detailed its effect on Uroglena sp.'s growth. Uroglena sp. mainly blooms in spring when temperatures are lower, though similar lower temperatures are also present in autumn and winter. Therefore, the objectives of this study were to investigate the growth and decline behavior of Uroglena sp. under different temperatures and to assess the impact of microorganism composition in different samples on the growth of Uroglena sp. To achieve the objectives of this study, surface water samples collected in May (spring), September (autumn), and January (winter) were incubated under different temperatures. Findings revealed that Uroglena sp. exhibited higher and more prolonged growth at a low temperature of 5 °C. Within the temperature range of 10 to 20 °C, Uroglena sp. exhibited less vigorous growth and lysed more rapidly. No growth was observed at 30 °C. The limited growth of Uroglena sp. at higher temperatures is attributed to an increased abundance of bacteria and competition with other microalgae including Nitzschia sp., Sphaerocystis sp., Scenedesmus sp., Fragilaria sp., Attheya sp., Golenkinia sp., Melosira sp., and Dinobryon sp. This indicates that the coexistence of microalgae and bacteria plays a significant role in the growth of Uroglena sp. The maximum concentration of Uroglena sp. during incubation was higher for the water sample of May compared to the sample of September and January, which reached about 2500 colony/mL at 5 °C for the sample of May. The generally higher growth of Uroglena sp. with the sample of May suggests that less significant microalgae competition in the season could create more favorable conditions for the bloom of Uroglena sp.

Light quality affects chlorophyll biosynthesis and photosynthetic performance in Antarctic Chlamydomonas

The perennially ice-covered Lake Bonney in Antarctica has been deemed a natural laboratory for studying life at the extreme. Photosynthetic algae dominate the lake food webs and are adapted to a multitude of extreme conditions including perpetual shading even at the height of the austral summer. Here we examine how the unique light environment in Lake Bonney influences the physiology of two Chlamydomonas species. Chlamydomonas priscui is found exclusively in the deep photic zone where it receives very low light levels biased in the blue part of the spectrum (400-500 nm). In contrast, Chlamydomonas sp. ICE-MDV is represented at various depths within the water column (including the bright surface waters), and it receives a broad range of light levels and spectral wavelengths. The psychrophilic character of both species makes them an ideal system to study the effects of light quality and quantity on chlorophyll biosynthesis and photosynthetic performance in extreme conditions. We show that the shade-adapted C. priscui exhibits a decreased ability to accumulate chlorophyll and severe photoinhibition when grown under red light compared to blue light. These effects are particularly pronounced under red light of higher intensity, suggesting a loss of capability to acclimate to varied light conditions. In contrast, ICE-MDV has retained the ability to synthesize chlorophyll and maintain photosynthetic efficiency under a broader range of light conditions. Our findings provide insights into the mechanisms of photosynthesis under extreme conditions and have implications on algal survival in changing conditions of Antarctic ice-covered lakes.

Permanent Stress Adaptation and Unexpected High Light Tolerance in the Shade-Adapted Chlamydomonas priscui

The Antarctic photopsychrophile, Chlamydomonas priscui UWO241, is adapted to extreme environmental conditions, including permanent low temperatures, high salt, and shade. During long-term exposure to this extreme habitat, UWO241 appears to have lost several short-term mechanisms in favor of constitutive protection against environmental stress. This study investigated the physiological and growth responses of UWO241 to high-light conditions, evaluating the impacts of long-term acclimation to high light, low temperature, and high salinity on its ability to manage short-term photoinhibition. We found that UWO241 significantly increased its growth rate and photosynthetic activity at growth irradiances far exceeding native light conditions. Furthermore, UWO241 exhibited robust protection against short-term photoinhibition, particularly in photosystem I. Lastly, pre-acclimation to high light or low temperatures, but not high salinity, enhanced photoinhibition tolerance. These findings extend our understanding of stress tolerance in extremophilic algae. In the past 2 decades, climate change-related increasing glacial stream flow has perturbed long-term stable conditions, which has been associated with lake level rise, the thinning of ice covers, and the expansion of ice-free perimeters, leading to perturbations in light and salinity conditions. Our findings have implications for phytoplankton survival and the response to change scenarios in the light-limited environment of Antarctic ice-covered lakes.

Endometabolic profiling of pigmented glacier ice algae: the impact of sample processing

INTRODUCTION

Glacier ice algae, mainly Ancylonema alaskanum and Ancylonema nordenskiöldi, bloom on Greenland Ice Sheet bare ice surfaces. They significantly decrease surface albedo due to their purple-brown pigmentation, thus increasing melt. Little is known about their metabolic adaptation and factors controlling algal growth dynamics and pigment formation. A challenge in obtaining such data is the necessity of melting samples, which delays preservation and introduces bias to metabolomic analysis. There is a need to evaluate the physiological response of algae to melting and establish consistent sample processing strategies for metabolomics of ice microbial communities.

OBJECTIVES

To address the impact of sample melting procedure on metabolic characterization and establish a processing and analytical workflow for endometabolic profiling of glacier ice algae.

METHODS

We employed untargeted, high-resolution mass spectrometry and tested the effect of sample melt temperature (10, 15, 20 °C) and processing delay (up to 49 h) on the metabolome and lipidome, and complemented this approach with cell counts (FlowCam), photophysiological analysis (PAM) and diversity characterization.

RESULTS AND CONCLUSION

We putatively identified 804 metabolites, with glycerolipids, glycerophospholipids and fatty acyls being the most prominent superclasses (> 50% of identified metabolites). Among the polar metabolome, carbohydrates and amino acid-derivatives were the most abundant. We show that 8% of the metabolome is affected by melt duration, with a pronounced decrease in betaine membrane lipids and pigment precursors, and an increase in phospholipids. Controlled fast melting at 10 °C resulted in the highest consistency, and is our recommendation for future supraglacial metabolomics studies.

Photostasis and photosynthetic adaptation to polar life

Photostasis is the light-dependent maintenance of energy balance associated with cellular homeostasis in photoautotrophs. We review evidence that illustrates how photosynthetic adaptation in polar photoautrophs such as aquatic green algae, cyanobacteria, boreal conifers as well as terrestrial angiosperms exhibit an astonishing plasticity in structure and function of the photosynthetic apparatus. This plasticity contributes to the maintenance of photostasis, which is essential for the long-term survival in the seemingly inhospitable Antarctic and Arctic habitats. However, evidence indicates that polar photoautrophic species exhibit different functional solutions for the maintenance of photostasis. We suggest that this reflects, in part, the genetic diversity symbolized by inherent genetic redundancy characteristic of polar photoautotrophs which enhances their survival in a thermodynamically challenging environment.

Aberrant light sensing and motility in the green alga Chlamydomonas priscuii from the ice-covered Antarctic Lake Bonney

The Antarctic green alga Chlamydomonas priscuii is an obligate psychrophile and an emerging model for photosynthetic adaptation to extreme conditions. Endemic to the ice-covered Lake Bonney, this alga thrives at highly unusual light conditions characterized by very low light irradiance (<15 μmol m-2 s-1), a narrow wavelength spectrum enriched in blue light, and an extreme photoperiod. Genome sequencing of C. priscuii exposed an unusually large genome, with hundreds of highly similar gene duplicates and expanded gene families, some of which could be aiding its survival in extreme conditions. In contrast to the described expansion in the genetic repertoire in C. priscuii, here we suggest that the gene family encoding for photoreceptors is reduced when compared to related green algae. This alga also possesses a very small eyespot and exhibits an aberrant phototactic response, compared to the model Chlamydomonas reinhardtii. We also investigated the genome and behavior of the closely related psychrophilic alga Chlamydomonas sp. ICE-MDV, that is found throughout the photic zone of Lake Bonney and is naturally exposed to higher light levels. Our analyses revealed a photoreceptor gene family and a robust phototactic response similar to those in the model Chlamydomonas reinhardtii. These results suggest that the aberrant phototactic response in C. priscuii is a result of life under extreme shading rather than a common feature of all psychrophilic algae. We discuss the implications of these results on the evolution and survival of shade adapted polar algae.

Temperature stress in psychrophilic green microalgae: Minireview

Photosynthetic algae are the main primary producers in polar regions, form the basis of polar food webs, and are responsible for a significant portion of global carbon fixation. Many cold-water algae are psychrophiles that thrive in the cold but cannot grow at moderate temperatures (≥20°C). Polar regions are at risk of rapid warming caused by climate change, and the sensitivity of psychrophilic algae to rising temperatures makes them, and the ecosystems they inhabit, particularly vulnerable. Recent research on the Antarctic psychrophile Chlamydomonas priscuii, an emerging algal model, has revealed unique adaptations to life in the permanent cold. Additionally, genome sequencing of C. priscuii and its relative Chlamydomonas sp. ICE-L has given rise to a plethora of computational tools that can help elucidate the genetic basis of psychrophily. This minireview summarizes new advances in characterizing the heat stress responses in psychrophilic algae and examines their extraordinary sensitivity to temperature increases. Further research in this field will help determine the impact of climate change on psychrophiles from threatened polar environments.

Palmelloid formation in the Antarctic psychrophile, Chlamydomonas priscuii, is photoprotective

Cultures of the obligate, Antarctic psychrophile, Chlamydomonas priscuii grown at permissive low temperature (8°C) are composed of flagellated, single cells, as well as non-motile, multicellular palmelloids. The relative proportions of the two cell types are temperature dependent. However, the temperature dependence for palmelloid formation is not restricted to psychrophilic C. priscuii but appears to be a general response of mesophilic Chlamydomonas species (C. reinhardtii and C. raudensis) to non-permissive growth temperatures. To examine potential differences in photosynthetic performance between single cells versus palmelloids of the psychrophile, a cell filtration technique was developed to separate single cells from palmelloids of C. priscuii grown at 8°C. Flow cytometry was used to estimate the diameter of isolated single cells (≤5 μm) versus isolated palmelloids of varying size (≥8 μm). Compared to single cells, palmelloids of C. priscuii showed a decrease in the abundance of light-harvesting complex II (LHCII) proteins with a 2-fold higher Chl a/b ratio. A decrease in both lutein and β-carotene in palmelloids resulted in carotenoid pools which were 27% lower in palmelloids compared to single cells of the psychrophile. Chlorophyll fluorescence analyses of the isolated fractions revealed that maximum photochemical efficiency of PSII (F_v/F_m) was comparable for both single cells and palmelloids of C. priscuii. However, isolated palmelloids exhibited lower excitation pressure, measured as 1 - qL, but higher yield of PSII (Φ_PSII) and 50% higher rates of electron transport (ETR) than single cells exposed to high light at 8°C. This decreased sensitivity to high light in isolated palmelloids compared to single cells was associated with greater non-regulated dissipation of excess absorbed energy (Φ_NO) with minimal differences in Φ_NPQ in C. priscuii in response to increasing irradiance at low temperature. The ratio Φ_NO/Φ_NPQ observed for isolated palmelloids of C. priscuii developed at 8°C (1.414 ± 0.036) was 1.38-fold higher than Φ_NO/Φ_NPQ of isolated single cells (1.021 ± 0.018) exposed to low temperature combined with high light (1,000 μmol m^-2 s^-1). The differences in the energy quenching capacities between palmelloids and single cells are discussed in terms of enhanced photoprotection of C. priscuii palmelloids against low-temperature photoinhibition.