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Receptor-like kinases (RLKs) detect external and internal signals, triggering responses essential for growth and adaptation. Among internal cues, cell wall integrity (CWI) sensing plays a key role, as changes in cell wall structure activate responses critical for development and defense. While RLKs are well-studied in vascular plants, their diversity and function remain largely unknown in green algae belonging to the Chlorophyta phylum, a group that is relevant for global oxygen production and carbon cycling. Due to their varied cell wall structures, Chlorophyta offer a useful system to study the origins of CWI sensing. In this study, we used advanced bioinformatics and AI-based tools to analyze RLKs in 34 Chlorophyta species, mapping their distribution, structural features, and similarity to plant RLKs. We identified 736 putative RLKs, expanding the known repertoire in green algae. Structural analyses showed a wide range of extracellular domains, including motifs related to plant CWI sensors: domains mediating protein interactions (e.g., Leucine Rich Repeats—LRR, Plasminogen Apple Nematod e-PAN, Armadillo repeat—ARM), cell wall remodeling (e.g., glycosyl hydrolases, lyases), and mechanosensing (e.g., Leucine-Proline-X-Threonine-Glycine motifs—LPXTG, Fibronectin). This diversity suggests that mechanisms for extracellular sensing and CWI monitoring emerged early in evolution. The results provide a basis for future studies on the function of RLKs in algae and their evolutionary links to vascular plant signaling.

The increasing discharge of untreated wastewater poses risks to ecosystems and public health, necessitating sustainable treatment strategies. Anaerobic digestion (AD) of sewage sludge offers several benefits including waste-volume reduction and sludge stabilization. However, it produces nutrient-rich effluents, requiring further treatment. Microalgae can remove nutrients while generating valuable biomass. This study aimed to evaluate the effect of CO2 concentration and reactor configuration on the performance of Chlorococcum sp. cultivated in AD effluent of municipal sewage sludge. Four CO2 levels (0.04, 3, 6, and 9%) was tested and 6% CO2 yielded the highest biomass (0.98 g L− 1) and CO2 fixation rate (162 mg L− 1 d− 1), while maintaining ammonium and phosphorous removal comparable to aeration with 3 and 9% CO2. This concentration was used in ALR, BC, and BC with carriers. The highest nutrient removal was achieved in BC, with 37.61% NH4⁺-N and 25.87% phosphorus reduction, whereas growth in ALR reached the highest cell density (81 × 106 cells mL− 1) in 9 days. Biomass composition was stable across reactors, with similar protein, carbohydrate, or fatty acid methyl esters content. These findings demonstrate that the Nordic Chlorococcum sp. grown in AD effluent can remove NH4⁺-N and phosphorus across a wide CO2 range (0.04–9%). Culturing in ALR is the preferred option for rapid growth. However, BC offered better nutrient removal and higher biomass production but required longer cultivation than ALR.

Microalgae hold great promise as sustainable feedstocks for a broad spectrum of biotechnological applications. However, their use is still constrained by the significant financial and energy demands of downstream processing, particularly biomass harvesting and extraction of high-value metabolites. A major barrier represents their robust, often biochemically complex cell wall that hinders efficient processing. Because cell-wall biosynthesis consumes large amounts of photosynthetically fixed carbon, the wall itself represents not only a major metabolic investment but also a largely untapped, renewable bioresource with significant industrial potential. To advance algal biotechnology, comprehensive knowledge of cell-wall structure, biosynthesis, and variability is essential. However, for Chlorophyta—the green algae most frequently used in biotechnological applications—available information on cell-wall composition remains fragmented. Existing studies often describe divergent or even contradictory findings, reflecting the remarkable diversity of cell-wall architectures within this phylum. This review addresses this knowledge gap by synthesizing and critically evaluating current research on Chlorophyta cell walls. An outline of the major structural components reported across species, including polysaccharides, glycoproteins and algaenan-like materials is provided. In addition, current industrial applications of these cell-wall components—ranging from biomaterials and bioactive compounds to environmentally friendly polymers—are discussed, along with their potential roles in future biotechnological innovations. By integrating these scattered data, the review aims to provide a unified perspective that supports both fundamental research and practical application. Ultimately, this review seeks to facilitate the development of more efficient biotechnological processes and to advance a more sustainable bioeconomy by strengthening the understanding of the biochemistry of Chlorophyta cell walls.

Programmed Cell Death (PCD) in eukaryotes is a regulated process occurring during development, cell differentiation and aging. Apoptosis is a particularly well studied morphotype of PCD, only observed in animal cells (metazoan). Its most definitive hallmark is the formation and release of membrane-enclosed extracellular vesicles called Apoptotic Bodies (ABs). Although apoptotic-like features have been described in plants, yeast, protozoa and phytoplankton, the production of ABs has been thought to be limited to multicellular animals. Here we report the production and release of extracellular ABs in a non-metazoan unicellular eukaryote, the cryptophyte alga Guillardia theta. Morphologies of G. theta cells during aging and pharmacologically-induced cell death confirm the presence of ABs and apoptosis in phytoplankton. G. theta ABs have similar composition to metazoan ABs, carrying DNA, proteins, lipids, carbohydrates, fragments of organelles and cytosol portions. Our results demonstrate that G. theta, a microalga that arose from secondary endosymbiosis, experiences apoptotic cell death in physiological conditions, similar to animal cells. Since secondary endosymbiosis occurred prior to the origin of multicellularity, our discovery questions the evolutionary origin of PCD.

Heavy metal contamination is of highest concern for the environment. Bioremediation, using microorganisms to adsorb and enrich heavy metals, offers an outstanding solution, especially when the pollutants appear at concentrations where physical/chemical methods are not efficient. This study presents a sustainable approach to heavy metal removal through the development of a microalgae-based sorbent supported on a copolymer produced entirely from recycled waste streams. The copolymer was synthesized by inverse vulcanization using sulfur recovered from petrochemical waste and waste cooking oil, demonstrating a circular use of industrial and household by-products. This sustainable, biobased sorbent was highly efficient in removing the heavy metals copper, cadmium and lead in a multi-element mixture at concentrations of industrial relevance. Kinetics and equilibrium parameters and even adsorption capacities improved drastically after immobilization of microalgae to the copolymer, compared to free-swimming microalgae or copolymer alone. The green microalga Chlorella vulgaris (13-1) immobilized to the copolymer removed more than 95% of the total Cu2+ and Cd2+ and 50% of the total Pb2+ within 8 h. Additionally, this sorbent is reusable; a desorption and regeneration step with 0.1M EDTA and CaCl2 allowed up to 98% recovery of the concentrated, bound heavy metals. Reusing the microalgal-copolymer sorbent in a second removal cycle resulted in removal rates of 75-99% of the initial ones. This novel sorbent allows not only sustainable and efficient removal of heavy metal mixtures from industrial wastewaters but also can be used in subsequent rounds during wastewater purification.

Flocculation is often regarded as a cost-effective and reliable method for microalgal harvesting. However, the traditional method often requires the addition of chemical agents to induce flocculation. This carries certain disadvantages including the chemical contamination of the biomass and the subsequent need to remove the flocculants from the medium. To address these issues, this study aimed to induce flocculation in a naturally non-flocculating strain (Chlorella vulgaris 13-1) without resorting to chemical additives, with the ultimate goal of increasing harvesting efficiency. Scanning electron microscopy showed that Scotelliopsis reticulata UFA-2, a naturally flocculating strain, produces extracellular polymeric substances (EPS) whereas 13-1 does not. As a result, two methods were used to induce flocculation in 13-1: co-cultivation of UFA-2 and 13-1, and insertion of EPS produced by UFA-2 into the growth medium of 13-1. The co-cultivation of 13-1 with UFA-2 significantly increased the flocculation efficiency compared to that of 13-1 alone (30 % higher flocculation efficiency after one hour of settling and 52 % higher after three hours of settling). Alternatively, the insertion of dry tightly-bound (TB) UFA-2 EPS into 13-1 cultures also improved flocculation efficiency (by 19 % compared to the control), while addition of soluble or loosely-bound (LB) EPS was less efficient (less than 1 % and 10 %, respectively). FTIR results showed that the composition of TB-EPS was different to that of LB and soluble EPS. TB-EPS contained higher proportions of proteins and different types of carbohydrates, potentially contributing to its increased efficacy in inducing flocculation in microalgae.

Metacaspases are cysteine proteases present in plants, fungi and protists. While the association of metacaspases with cell death is studied in a range of organisms, their native substrates are largely unknown. Here, we explored the in vivo proteolytic landscape of the two metacaspases, CrMCA-I and CrMCA-II, present in the green freshwater alga Chlamydomonas reinhardtii, using mass spectrometry-based degradomics approach, during control conditions and salt stress. Comparison between the cleavage events of CrMCA-I and CrMCA-II in metacaspase mutants revealed unique cleavage preferences and substrate specificity. Degradome analysis demonstrated the relevance of the predicted metacaspase substrates to the physiology of C. reinhardtii cells and its adaptation during salt stress. Functional enrichment analysis indicated an involvement of CrMCA-I in the catabolism of carboxylic acids, while CrMCA-II plays an important role in photosynthesis and translation. Altogether, our findings suggest distinct cellular functions of the two metacaspases in C. reinhardtii during salt stress response.

With climate change, droughts are expected to be more frequent and severe, severely impacting plant biomass and quality. Here, we show that overexpressing the Arabidopsis gene AtFtsHi3 (FtsHi3OE) enhances drought-tolerant phenotypes without compromising plant growth. AtFtsHi3 encodes a chloroplast envelope pseudo-protease; knock-down mutants (ftshi3-1) are found to be drought tolerant but exhibit stunted growth. Altered AtFtsHi3 expression therefore leads to drought tolerance, while only diminished expression of this gene leads to growth retardation. To understand the underlying mechanisms of the enhanced drought tolerance, we compared the proteomes of ftshi3-1 and pFtsHi3-FtsHi3OE (pFtsHi3-OE) to wild-type plants under well-watered and drought conditions. Drought-related processes like osmotic stress, water transport, and abscisic acid response were enriched in pFtsHi3-OE and ftshi3-1 mutants following their enhanced drought response compared to wild-type. The knock-down mutant ftshi3-1 showed an increased abundance of HSP90, HSP93, and TIC110 proteins, hinting at a potential downstream role of AtFtsHi3 in chloroplast pre-protein import. Mathematical modeling was performed to understand how variation in the transcript abundance of AtFtsHi3 can, on the one hand, lead to drought tolerance in both overexpression and knock-down lines, yet, on the other hand, affect plant growth so differently. The results led us to hypothesize that AtFtsHi3 may form complexes with at least two other protease subunits, either as homo- or heteromeric structures. Enriched amounts of AtFtsH7/9, AtFtsH11, AtFtsH12, and AtFtsHi4 in ftshi3-1 suggest a possible compensation mechanism for these proteases in the hexamer.

Anaerobic digestion is a promising method for organic waste treatment. While the obtained digestate can function as fertilizer, the liquid fraction produced is rather problematic to discharge due to its high nitrogen and chemical oxygen demand contents. Microalgae have great potential in sustainable nutrient removal from wastewater. This study aimed at evaluating native Swedish microalgae cultivation (batch operation mode, 25°C and continuous light of 80 μmol m−2 s−1) on anaerobic digestion effluent of pulp and paper sludge (PPS) or chicken manure (CKM) to remove ammonium and volatile fatty acids (VFAs). While algal strains, Chlorella vulgaris, Chlorococcum sp., Coelastrella sp., Scotiellopsis reticulata and Desmodesmus sp., could assimilate VFAs as carbon source, acetic acid was the most preferred. Higher algal biomass and cell densities were achieved using PPS compared to CKM. In PPS, Coelastrella sp. and Chlorella vulgaris reached the highest cell densities after 15 days, about 79 × 106 and 43 × 106 cells mL−1, respectively. Although in PPS, ammonium was completely assimilated (195 mg L−1), this was only 46% (172 mg L−1) in CKM. Coelastrella sp. produced the highest biomass concentration independently of the medium (1.84 g L−1 in PPS and 1.99 g L−1 in CKM). This strain is a promising candidate for nutrient removal and biomass production in the aforementioned media, followed by Chlorella vulgaris and Chlorococcum sp. They have great potential to reduce the environmental impact of industrial anaerobic digestion effluents in Nordic countries.