Algal Cell Wall Research Articles

Crude fucoidan content in two North Atlantic kelp species, Saccharina latissima and Laminaria digitata\u2014seasonal variation and impact of environmental factors

Fucoidans are sulphated fucose-rich polysaccharides predominantly found in the cell walls of brown algae. The bioactive properties of fucoidans attract increasing interest from the medico-pharmaceutical industries and may drive an increase in demand of brown algae biomass. In nature, the biochemical composition of brown algae displays a seasonal fluctuation driven by environmental factors and endogenous rhythms. To cultivate and harvest kelps with high yields of fucoidans, knowledge is needed on seasonal variation and impact of environmental conditions on the fucoidan content of brown algae. The relations between the fucoidan content and key environmental factors (irradiance, nutrient availability, salinity and exposure) were examined by sampling natural populations of the common North Atlantic kelps, Saccharina latissima and Laminaria digitata, over a full year at Hanstholm in the North Sea and Aarhus in the Kattegat. In addition, laboratory experiments were carried out isolating the effects of the single factors. The results demonstrated that (1) seasonal variation alters the fucoidan content by a factor of 2–2.6; (2) interspecific differences exist in the concentrations of crude fucoidan (% of dry matter): L. digitata (11%) > S. latissima (6%); and (3) the effects of single environmental factors were not consistent between species or between different conspecific populations. The ambiguous response to single environmental factors complicates prospective directions for manipulating an increased content of fucoidan in a cultivation scenario and emphasizes the need for knowledge on performance of local kelp ecotypes.

Protective effect of fucoidans from tropical seaweeds against oxidative stress in HepG2 cells

Fucoidans are sulfated polysaccharides with proven pharmacological effects localized in the cell wall of marine brown algae. The majority of studies have been performed with temperate brown algal species, but in recent years, the evaluation of species from tropical areas has been growing. The aim of this study was to determine the protective effect of fucoidans extracted from the tropical brown seaweeds Dictyota ciliolata, Padina sanctae-crucis, and Sargassum fluitans, against oxidative stress (OS). The D. ciliolata fucoidan (FDc) exhibited the highest reactive oxygen species (ROS) scavenging activity (26%), followed by P. sanctae-crucis fucoidan (FPs) (22%) and S. fluitans fucoidan (FSf) (14%). No cytotoxic effect was detected for any of the extracted fucoidans at a concentration of 2 mg mL−1. Not only did the fucoidans tested show protective effect against OS by reducing ROS generation, but they also increased the glutathione (GSH) level and restored catalase (CAT) activity. Fucoidans obtained from tropical seaweeds could be used as a potential natural ingredient for functional foods.

Insoluble (1\u2009\u2192\u20093), (1\u2009\u2192\u20094)-\u03b2-D-glucan is a component of cell walls in brown algae (Phaeophyceae) and is masked by alginates in tissues

Brown algae are photosynthetic multicellular marine organisms. They belong to the phylum of Stramenopiles, which are not closely related to land plants and green algae. Brown algae share common evolutionary features with other photosynthetic and multicellular organisms, including a carbohydrate-rich cell-wall. Brown algal cell walls are composed predominantly of the polyanionic polysaccharides alginates and fucose-containing sulfated polysaccharides. These polymers are prevalent over neutral and crystalline components, which are believed to be mostly, if not exclusively, cellulose. In an attempt to better understand brown algal cell walls, we performed an extensive glycan array analysis of a wide range of brown algal species. Here we provide the first demonstration that mixed-linkage (1 → 3), (1 → 4)-β-d-glucan (MLG) is common in brown algal cell walls. Ultra-Performance Liquid Chromatography analyses indicate that MLG in brown algae solely consists of trisaccharide units of contiguous (1 → 4)-β-linked glucose residues joined by (1 → 3)-β-linkages. This regular conformation may allow long stretches of the molecule to align and to form well-structured microfibrils. At the tissue level, immunofluorescence studies indicate that MLG epitopes in brown algae are unmasked by a pre-treatment with alginate lyases to remove alginates. These findings are further discussed in terms of the origin and evolution of MLG in the Stramenopile lineage.

Ultrasonic zeppelin-shape transducer for algae oil extraction

Energy consumption worldwide is increasing each year. Alternative energy sources supplement these energy demands. Algae are one of such alternative energy sources. As oil needs to be extracted from the ground, algae are needed to be prepared for bio-fuel production. There are a few methods that are used for algae to crack open: chemical and mechanical. Among mechanical methods, the one that is suitable for that purpose is ultrasonication.The current paper presents an ultrasonic cylinder-shape transducer designed for that purpose. Commercial piezo-mechanical systems for algae processing are mostly ordinary longitudinal transducers. The efficiency of such systems is based on irradiation surface, which is normally about 1000mm2. In our system, we propose a different approach to increase the vibration area that produces a cavitation field needed to crack the cell wall of algae. Normally, the active end of transducers is immersed into a reservoir filled with algae-liquid mixture. We propose to create a vibrating reservoir as a part of transducer, thus enlarging the area of acoustic irradiation. Excitation is produced by two full-wave longitudinal transducers orientated opposite to each other and connected to a specifically designed resonant chamber.Experiments have been carried out using two colonial algae species, namely Scenedesmus acutus Meyen and single-cell Monoraphidium griffithii. Comparative experiments have been performed using the standard commercial ultrasonic system for algae processing and the proposed system. The key parameters obtained from the experiments include power consumption and destruction rate.

Natural resource landscapes of a marine bacterium reveal distinct fitness-determining genes across the genome.

Heterotrophic bacteria exploit diverse microhabitats in the ocean, from particles to transient gradients. Yet the degree to which genes and pathways can contribute to an organism's fitness on such complex and variable natural resource landscapes remains poorly understood. Here, we determine the gene-by-gene fitness of a generalist saprophytic marine bacterium (Vibrio sp. F13 9CS106) on complex resources derived from its natural habitats - copepods (Apocyclops royi) and brown algae (Fucus vesiculosus) - and as reference substrates, glucose and the polysaccharide alginate, derived from brown algal cell walls. We find that resource complexity strongly buffers fitness costs of mutations, and that anabolic rather than catabolic pathways are more stringently required, likely due to functional redundancy in the latter. Moreover, while carbohydrate-rich algae requires several synthesis pathways, protein-rich Apocyclops does not, suggesting this ancestral habitat for Vibrios is a replete medium with metabolically redundant substrates. We also identify a candidate fitness trade-off for algal colonization: deletion of mshA increases mutant fitness. Our results demonstrate that gene fitness depends on habitat composition, and suggest that this generalist uses distinct resources in different natural habitats. The results further indicate that substrate replete conditions may lead to relatively relaxed selection on catabolic genes.

Global Distribution Patterns and Pangenomic Diversity of the Candidate Phylum “Latescibacteria” (WS3)

We investigated the global distribution patterns and pangenomic diversity of the candidate phylum "Latescibacteria" (WS3) in 16S rRNA gene as well as metagenomic data sets. We document distinct distribution patterns for various "Latescibacteria" orders in 16S rRNA gene data sets, with prevalence of orders sediment_1 in terrestrial, PBSIII_9 in groundwater and temperate freshwater, and GN03 in pelagic marine, saline-hypersaline, and wastewater habitats. Using a fragment recruitment approach, we identified 68.9 Mb of "Latescibacteria"-affiliated contigs in publicly available metagenomic data sets comprising 73,079 proteins. Metabolic reconstruction suggests a prevalent saprophytic lifestyle in all "Latescibacteria" orders, with marked capacities for the degradation of proteins, lipids, and polysaccharides predominant in plant, bacterial, fungal/crustacean, and eukaryotic algal cell walls. As well, extensive transport and central metabolic pathways for the metabolism of imported monomers were identified. Interestingly, genes and domains suggestive of the production of a cellulosome-e.g., protein-coding genes harboring dockerin I domains attached to a glycosyl hydrolase and scaffoldin-encoding genes harboring cohesin I and CBM37 domains-were identified in order PBSIII_9, GN03, and MSB-4E2 fragments recovered from four anoxic aquatic habitats; hence extending the cellulosomal production capabilities in Bacteria beyond the Gram-positive Firmicutes In addition to fermentative pathways, a complete electron transport chain with terminal cytochrome c oxidases Caa3 (for operation under high oxygen tension) and Cbb3 (for operation under low oxygen tension) were identified in PBSIII_9 and GN03 fragments recovered from oxygenated and partially/seasonally oxygenated aquatic habitats. Our metagenomic recruitment effort hence represents a comprehensive pangenomic view of this yet-uncultured phylum and provides insights broader than and complementary to those gained from genome recovery initiatives focusing on a single or few sampled environments.IMPORTANCE Our understanding of the phylogenetic diversity, metabolic capabilities, and ecological roles of yet-uncultured microorganisms is rapidly expanding. However, recent efforts mainly have been focused on recovering genomes of novel microbial lineages from a specific sampling site, rather than from a wide range of environmental habitats. To comprehensively evaluate the genomic landscape, putative metabolic capabilities, and ecological roles of yet-uncultured candidate phyla, efforts that focus on the recovery of genomic fragments from a wide range of habitats and that adequately sample the intraphylum diversity within a specific target lineage are needed. Here, we investigated the global distribution patterns and pangenomic diversity of the candidate phylum "Latescibacteria" Our results document the preference of specific "Latescibacteria" orders to specific habitats, the prevalence of plant polysaccharide degradation abilities within all "Latescibacteria" orders, the occurrence of all genes/domains necessary for the production of cellulosomes within three "Latescibacteria" orders (GN03, PBSIII_9, and MSB-4E2) in data sets recovered from anaerobic locations, and the identification of the components of an aerobic respiratory chain, as well as occurrence of multiple O2-dependent metabolic reactions in "Latescibacteria" orders GN03 and PBSIII_9 recovered from oxygenated habitats. The results demonstrate the value of phylocentric pangenomic surveys for understanding the global ecological distribution and panmetabolic abilities of yet-uncultured microbial lineages since they provide broader and more complementary insights than those gained from single-cell genomic and/or metagenomic-enabled genome recovery efforts focusing on a single sampling site.

Insights into the Evolution of Hydroxyproline-Rich Glycoproteins from 1000 Plant Transcriptomes.

The carbohydrate-rich cell walls of land plants and algae have been the focus of much interest given the value of cell wall-based products to our current and future economies. Hydroxyproline-rich glycoproteins (HRGPs), a major group of wall glycoproteins, play important roles in plant growth and development, yet little is known about how they have evolved in parallel with the polysaccharide components of walls. We investigate the origins and evolution of the HRGP superfamily, which is commonly divided into three major multigene families: the arabinogalactan proteins (AGPs), extensins (EXTs), and proline-rich proteins. Using motif and amino acid bias, a newly developed bioinformatics pipeline, we identified HRGPs in sequences from the 1000 Plants transcriptome project (www.onekp.com). Our analyses provide new insights into the evolution of HRGPs across major evolutionary milestones, including the transition to land and the early radiation of angiosperms. Significantly, data mining reveals the origin of glycosylphosphatidylinositol (GPI)-anchored AGPs in green algae and a 3- to 4-fold increase in GPI-AGPs in liverworts and mosses. The first detection of cross-linking (CL)-EXTs is observed in bryophytes, which suggests that CL-EXTs arose though the juxtaposition of preexisting SPn EXT glycomotifs with refined Y-based motifs. We also detected the loss of CL-EXT in a few lineages, including the grass family (Poaceae), that have a cell wall composition distinct from other monocots and eudicots. A key challenge in HRGP research is tracking individual HRGPs throughout evolution. Using the 1000 Plants output, we were able to find putative orthologs of Arabidopsis pollen-specific GPI-AGPs in basal eudicots.

Solar light-driven photocatalytic destruction of cyanobacteria by F-Ce-TiO2/expanded perlite floating composites

A series of efficient solar light-driven F-Ce-TiO2/expanded perlite (EP) floating photocatalysts were successfully synthesized using a facile sol-gel method and applied as algaecides in eutrophic waters. The as-synthesized photocatalysts were characterized by means of XRD, FESEM/EDX, TEM, N2 adsorption/desorption, XPS, UV–vis DRS and PL spectrum. The results show that F-Ce-TiO2/EP has a honeycomb-like structure with F-Ce co-doped TiO2 particles distributed on EP surface. Calcination temperature can greatly affect the doping status, specific surface area and photoelectric properties of F-Ce-TiO2/EP. Among the synthesized photocatalysts, those calcined at 450°C (i.e., F-Ce-TiO2/EP450) exhibited the highest photocatalytic activity. The photocatalytic destruction process could be described by the modified Chick–Watson kinetic model and Hom kinetic model. F-Ce-TiO2/EP450 can achieve the algal cells removal rate of 98.1% within 9h. The algal cell walls obviously damaged in this process. Following the damages, the electron transfer in water-water cycle was also inhibited, thereby accelerating the death of algal cells with the accumulation of the reactive oxygen species (ROS). In addition, microcystin-LR (MC-LR) and metabolic products proved to be effectively removed by photocatalytic oxidation during the algal destruction process. After three consecutive cycles, the removal rate of algal cells can still achieve 88.7% by F-Ce-TiO2/EP450, indicating the F-Ce-TiO2/EP photocatalyst has good reusability and stability.

Enzymes produced by biomass-degrading bacteria can efficiently hydrolyze algal cell walls and facilitate lipid extraction

The toughness of microalgal cell walls makes lipid extraction and large-scale biodiesel production difficult. This study investigated the enzymatic hydrolysis of algal cell walls, in which the enzymes were produced by eight biomass-degrading bacterial strains. The bacteria were first cultured in mineral salt medium containing 5% (w/v) wheat bran and various lignocellulolytic enzymes, including carboxymethyl cellulase (CMCase), filter paper activity (FPase), xylanase, and laccase were monitored in order to obtain an enzymatic extract. All the strains showed marked CMCase activity, with a range of 3.0–6.9 U ml−1 after incubation for 2–5 d. Some strains also produced FPase, xylanase, and laccase. The enzymatic extract was directly added to fresh algae culture at a ratio of 1:3 (v/v) for 48 h. All the bacterial enzymatic extracts significantly disrupted algal cell walls, according to the enhancement of reducing sugar content in the culture. The lipid extraction yield was markedly increased by 10.4–43.9%, depending on the bacteria strains used. Due to its high reducing sugar production and lipid extraction efficiency, Bacillus sp. K1 was selected for a time-course experiment. Maximum lipid yield was obtained after 24 h of incubation at the room temperature, with about 40% of the cells were disrupted. These results showed that enzymes produced by biomass-degrading bacteria can weaken and disrupt cell walls and components of algae and facilitate the release of lipids from algae.

A comparative study on biochemical methane potential of algal substrates: Implications of biomass pre-treatment and product extraction

Dried powdered algae (SDPA), heat treated algae (MHTA), lipid extracted algae (LEA) and protein extracted algae (PEA) were digested to determine biomethane potential. The average CH4 production rate was ∼2.5-times higher for protein and lipid extracted algae than for whole algae (SDPA and MHTA) whilst the cumulative CH4 production was higher for pre-treated algae. Highest cumulative CH4 production (318.7mlCH4g−1VS) was observed for MHTA followed by SDPA (307.4mlCH4g−1VS). CH4/CO2 ratios of 1.5 and 0.7 were observed for MHTA and LEA respectively. Pre-treatment processes disrupted the algal cell wall, exposing intracellular material which remained intact as opposed to product extraction processes which broke down the intracellular compounds resulting in changes in elemental composition and decreases the cumulative gas yield and CH4/CO2 ratio. Comparative analysis determined that the most profitable route of biomass utilisation was protein extraction followed by biogas production giving ∼2.5-times higher return on investment.

Interaction of silver nanoparticles with algae and fish cells: a side by side comparison

BackgroundSilver nanoparticles (AgNP) are widely applied and can, upon use, be released into the aquatic environment. This raises concerns about potential impacts of AgNP on aquatic organisms. We here present a side by side comparison of the interaction of AgNP with two contrasting cell types: algal cells, using the algae Euglena gracilis as model, and fish cells, a cell line originating from rainbow trout (Oncorhynchus mykiss) gill (RTgill-W1). The comparison is based on the AgNP behavior in exposure media, toxicity, uptake and interaction with proteins.Results(1) The composition of exposure media affected AgNP behavior and toxicity to algae and fish cells. (2) The toxicity of AgNP to algae was mediated by dissolved silver while nanoparticle specific effects in addition to dissolved silver contributed to the toxicity of AgNP to fish cells. (3) AgNP did not enter into algal cells; they only adsorbed onto the cell surface. In contrast, AgNP were taken up by fish cells via endocytic pathways. (4) AgNP can bind to both extracellular and intracellular proteins and inhibit enzyme activity.ConclusionOur results showed that fish cells take up AgNP in contrast to algal cells, where AgNP sorbed onto the cell surface, which indicates that the cell wall of algae is a barrier to particle uptake. This particle behaviour results in different responses to AgNP exposure in algae and fish cells. Yet, proteins from both cell types can be affected by AgNP exposure: for algae, extracellular proteins secreted from cells for, e.g., nutrient acquisition. For fish cells, intracellular and/or membrane-bound proteins, such as the Na+/K+-ATPase, are susceptible to AgNP binding and functional impairment.

Microalgal biomass dewatering using forward osmosis membrane: Influence of microalgae species and carbohydrates composition

The potential application of forward osmosis (FO) in microalgae dewatering requires an improved understanding of the factors that control membrane fouling which can reduce dewatering performance in terms of water flux through membrane and algae recovery. The aim of this study was to elucidate the influence of algae cell wall carbohydrate composition on the FO dewatering performance using three types of draw solutions (sea salts, MgCl2 and CaCl2). Experimental results suggest that the interaction between microalgae and back diffused draw solutes plays a key role. Scenedesmus obliquus with fructose and abundant glucose and mannose in its cell wall showed strong response to the back diffusion of calcium ions which encouraged S. obliquus to produce more extracellular carbohydrates and formed a stable gel network between algal biomass and extracellular carbohydrates, leading to algae aggregation and severe loss in both water flux and algae biomass during FO dewatering with Ca2+-containing draw solution. Chlamydomonas reinhardtii without fructose but great galactose showed a similar response to the calcium back diffusion but to a lower extent. Both S. obliquus and C. reinhardtii did not cause obvious membrane fouling but dramatic algae biomass loss at the end of FO filtration with MgCl2 draw solution due to their interaction with back diffused Mg2+ ions which led to the deposition of algae flocs onto membrane surface and/or feed spacer. Chlorella vulgaris without fructose was the most suitable microalgae species to be dewatered by FO with algae recovery over 81% and negligible flux decline regardless of which draw solution was applied. The findings improve mechanical understanding of FO membrane fouling by microalgae; have significant implications for the algae species selection; and are critical for the development and optimization of FO dewatering processes.

Particulate beta-glucan induces early and late phagosomal maturation in murine macrophages.

Beta-glucans are carbohydrates (glucose polymers) found in the cell walls of fungi, yeast, algae, lichens, and plants such as oats and barley. Beta-glucans bind to glucan receptor on phagocytic cells and modify these cells to become "immunologically active" by generating a variety of innate immune responses. Particulate beta-glucan has been specifically shown to engage dectin-1 receptor, which leads to the recruitment and activation of nicotinamide adenine dinucleotide phosphate oxidase-2 (NOX-2) and release of antimicrobial reactive oxygen species (ROS). Here, we report that yeast-derived beta-glucan particles (YDGP) of a specific size are easily phagocytosed by macrophages and induce the production of ROS. Furthermore, the present work also demonstrates that phagosomal maturation, appearance of acidic vesicular compartments (AVO), and light chain protein-3 (LC3) accumulation within murine macrophages, occur at early and delayed time points after the phagocytic uptake of YDGP. These data suggest that particulate glucans can be exploited to trigger autophagy within phagocytes and, thereby, have implications in antimicrobial therapy.

The toxicity of plastic nanoparticles to green algae as influenced by surface modification, medium hardness and cellular adsorption

To investigate processes possibly underlying accumulation and ecological effects of plastic nano-particles we have characterized their interaction with the cell wall of green algae. More specifically, we have investigated the influence of particle surface functionality and water hardness (Ca2+ concentration) on particle adsorption to algae cell walls. Polystyrene nanoparticles with different functional groups (non-functionalized, −COOH and −NH2) as well as coated (starch and PEG) gold nanoparticles were applied in these studies. Depletion measurements and atomic force microscopy (AFM) showed that adsorption of neutral and positively charged plastic nanoparticles onto the cell wall of P. subcapitata was stronger than that of negatively charged plastic particles. Results indicated that binding affinity is a function of both inter-particle and particle-cell wall interactions which are in turn influenced by the medium hardness and particle concentration. Physicochemical modelling using DLVO theory was used to interpret the experimental data, using also values for interfacial surface free energies. Our study shows that material properties and medium conditions play a crucial role in the rate and state of nanoparticle bio-adsorption for green algae. The results show that the toxicity of nanoparticles can be better described and assessed by using appropriate dose metrics including material properties, complexation/agglomeration behavior and cellular attachment and adsorption. The applied methodology provides an efficient and feasible approach for evaluating potential accumulation and hazardous effects of nanoparticles to algae caused by particle interactions with the algae cell walls.

1-Butyl-3-methylimidazolium hydrogen sulfate catalyzed in-situ transesterification of Nannochloropsis to fatty acid methyl esters

1-Butyl-3-methylimidazolium hydrogen sulfate ([Bmim][HSO4]) is used as a solvent and an acid catalyst for in-situ extractive transesterification of wet Nannochloropsis with methanol. The reaction is supposed to be a five-step process: (1) wet algae cell wall dissolves in ionic liquid at reaction temperatures; (2) hydrogen ions and sulfate ions release from the ionization of HSO4−. The hydrogen ions (H+) act as catalysts for accelerating the reactive extraction of triglyceride from wet Nannochloropsis; (3) hydrogen ions and methanol molecules transfer from bulk to active site of cells without passing through cell wall that is dissolved by ionic liquid; (4) in-situ transesterification of lipid (mainly triglycerides) with methanol; and (5) products transfer from inside of algae cells to outside of cells. The crude biodiesel yield of [Bmim][HSO4] catalyzed in-situ transesterification is about 95.28% at reaction temperature of 200°C, reaction time of 30min, mass ratio of [Bmim][HSO4] to wet Nannochloropsis of 0.9:1, and a mass ratio of methanol to wet algae of 3:1. It decreases to 81.23% after [Bmim][HSO4] is recycled for 4 times, which indicates that [Bmim][HSO4] catalyzed in-situ transesterification is an economic approach for biodiesel production from wet algae.

The Cytoskeleton Architecture of Algivorous Protoplast Feeders (Viridiraptoridae, Rhizaria) Indicates Actin-Guided Perforation of Prey Cell Walls

Several distantly related, phagotrophic microeukaryotes share the remarkable ability to perforate foreign cell walls in a well-defined pattern to acquire protoplast material as food. The underlying cellular processes, especially the local application of cell wall degrading agents, are still unexplored. We examined the distribution of F-actin and alpha-tubulin in the algivorous, viridiraptorid amoeboflagellates Orciraptor agilis and Viridiraptor invadens over their life histories using phalloidin conjugates and immunolocalization. During attack, both species form distinctive, F-actin-rich structures at the contact zone to the algal prey cell, which exactly match the species-specific cell wall perforations and resemble invadopodia and podosome rosettes of mammalian cells to a certain extent. Furthermore, F-actin is involved in the extraction of plastid material by Orciraptor and in prey cell invasion by Viridiraptor (here, F-actin localizes to a characteristic hyaline channel, which surrounds the streaming cytoplasm). The digestive-reproductive stages of viridiraptorids display a highly ordered microtubular cytoskeleton, whereas distinct phalloidin-positive actin structures could not be detected. We discuss the presumed function of F-actin during perforation and penetration of the algal cell wall by viridiraptorids, and compare the cytoskeleton architecture of these protoplast feeders to amoeboflagellates from different eukaryotic supergroups.

Dynamics of cell wall assembly during early embryogenesis in the brown alga Fucus.

Zygotes from Fucus species have been used extensively to study cell polarization and rhizoid outgrowth, and in this model system cell wall deposition aligns with the establishment of polarity. Monoclonal antibodies are essential tools for the in situ analysis of cell wall glycans, and here we report the characteristics of six monoclonal antibodies to alginates (BAM6-BAM11). The use of these, in conjunction with monoclonal antibodies to brown algal sulfated fucans, has enabled the study of the developmental dynamics of the Fucus zygote cell walls. Young zygotes are spherical and all alginate epitopes are deposited uniformly following cellulose deposition. At germination, sulfated fucans are secreted in the growing rhizoid wall. The redistribution of cell wall epitopes was investigated during treatments that cause reorientation of the growth axis (change in light direction) or disrupt rhizoid development (arabinogalactan-protein-reactive Yariv reagent). Alginate modeling was drastically impaired in the latter, and both treatments cause a redistribution of highly sulfated fucan epitopes. The dynamics of cell wall glycans in this system have been visualized in situ for the first time, leading to an enhanced understanding of the early developmental mechanisms of Fucus species. These sets of monoclonal antibodies significantly extend the available molecular tools for brown algal cell wall studies.

Enhancement of methane production from various microalgae cultures via novel ozonation pretreatment

In this work, the application of ozone, an unexplored pretreatment to improve methane production from three mixed microalgae sources was investigated. Ozonation at various, culture-dependent dosages was employed and its impact on the efficiency of subsequent anaerobic digestion was examined in comparison with untreated biomass. Regardless of the O3 pretreatment conditions, the methane yield in all cases could be increased by various extents (6–66%). The highest methane production (432.7mLCH4g−1VSalgal, equaling to 259.6mLCH4g−1CODin) was attained with the culture composed of 35% Scenedesmus, 30% Dictyosphaerium, 15% Keratococcus, 10% Oscillatoria, 8% Monoraphidium and 2% Nitzchia, using the highest dosage of ozone (382mgO3g−1VSalgal) for pretreatment. Electron microscopic assessment revealed the devastating effect of O3 on algal cell wall structure and integrity, which was thus identified as the key-contributor to the improvement of CH4 fermentation.

Optimization of enzyme-assisted lipid extraction from Nannochloropsis microalgae

Cell wall disruption is one of the most critical and energy-consuming steps in the overall process of lipid extraction from microalgae. In this paper we investigate a multi-enzyme pretreatment based on the use of cellulase (CEL) and mannanase (GMA) for the recovery of lipids from the marine microalga Nannochloropsis sp. A central composite design coupled with response surface methodology was used to optimize the treatment and evaluate the effect of temperature (T=15–75°C), pH (2–8), pretreatment time (P=30–270min), CEL dosage (D1=0–20mg/g) and GMA dosage (D2=0–2mg/g) on lipid extraction. About 90% of lipids were recovered from Nannochloropsis cells pretreated under optimal process conditions (T=53°C, pH=4.4, P=210min, D1=13.8mg/g and D1=1.5mg/g). FTIR spectra and TEM images of Nannochloropsis cells showed that the enzymatic treatment produced significant alterations in the algal cell wall structure, with extensive loss of cell boundaries and release of intracellular material. Overall, the results obtained indicate that the proposed approach can significantly improve the recovery of lipids from Nannochloropsis sp., further supporting the use of enzymes in microalgal processes.

β-1,3-Glucans are components of brown seaweed (Phaeophyceae) cell walls.

LAMP is a cell wall-directed monoclonal antibody (mAb) that recognizes a β-(1,3)-glucan epitope. It has primarily been used in the immunolocalization of callose in vascular plant cell wall research. It was generated against a brown seaweed storage polysaccharide, laminarin, although it has not often been applied in algal research. We conducted in vitro (glycome profiling of cell wall extracts) and in situ (immunolabeling of sections) studies on the brown seaweeds Fucus vesiculosus (Fucales) and Laminaria digitata (Laminariales). Although glycome profiling did not give a positive signal with the LAMP mAb, this antibody clearly detected the presence of the β-(1,3)-glucan in situ, showing that this epitope is a constituent of these brown algal cell walls. In F. vesiculosus, the β-(1,3)-glucan epitope was present throughout the cell walls in all thallus parts; in L. digitata, the epitope was restricted to the sieve plates of the conductive elements. The sieve plate walls also stained with aniline blue, a fluorochrome used as a probe for callose. Enzymatic digestion with an endo-β-(1,3)-glucanase removed the ability of the LAMP mAb to label the cell walls. Thus, β-(1,3)-glucans are structural polysaccharides of F. vesiculosus cell walls and are integral components of the sieve plates in these brown seaweeds, reminiscent of plant callose.