Factors affecting light harvesting in the red alga Cyanidioschyzon merolae

The phycobilisome antennas, which contain phycobilin pigments instead of chlorophyll, are crucial for the photosynthetic activity of Cyanidioschyzon merolae cells, which thrive in an acidic and hot water environment. The accessible light intensity and quality, temperature, acidity, and other factors in this environment are quite different from those in the air available for terrestrial plants. Under these conditions, adaptation to the intensity and quality of light, as well as temperature, which are key factors in photosynthesis of higher plants, also affects this process in Cyanidioschyzon merolae cells. Adaptation to varying light conditions requires fast remodeling and re-tuning of their light-harvesting antennas (phycobilisomes) at multiple levels, from regulation of gene expression to structural reorganization of protein-pigment complexes. This review presents selected data on the structure of phycobilisomes, the genetic engineering of the constituent proteins, and the latest results and opinions on the adaptation of phycobilisomes to light intensity and quality, and temperature to photosynthetic activities. We pay special attention to the latest results of the C. merolae research.

Changes in glycosyl inositol phosphoceramides during the cell cycle of the red alga Galdieria sulphuraria

Sphingolipids are significant component of plant-cell plasma membranes, as well as algal membranes, and mediate various biological processes. One of these processes is the change in lipid content during the cell cycle. This change is key to understanding cell viability and proliferation. There are relatively few papers describing highly glycosylated glycosyl inositol phosphorylceramide (GIPC) due to problems associated with the extractability of GIPCs and their analysis, especially in algae. After alkaline hydrolysis of total lipids from the red alga Galdieria sulphuraria, GIPCs were measured by high-resolution tandem mass spectrometry and fragmentation of precursor ions in an Orbitrap mass spectrometer in order to elucidate the structures of molecular species. Fragmentation experiments such as tandem mass spectrometry in the negative ion mode were performed to determine both the ceramide group and polar head structures. Measurement of mass spectra in the negative regime was possible because the phosphate group stabilizes negative molecular ions [M-H]^-. ANALYSIS: of GIPCs at various stages of the cell cycle provided information on their abundance. It was found that, depending on the phases of the cell cycle, in particular during division, the uptake of all three components of GIPC, i.e., long-chain amino alcohols, fatty acids, and polar heads, changes. Structural modifications of the polar headgroup significantly increased the number of molecular species. Analysis demonstrated a convex characteristic for molecular species with only one saccharide (hexose or hexuronic acid) as the polar head. For two carbohydrates, the course of Hex-HexA was linear, while for HexA-HexA it was concave. The same was true for GIPC with three and four monosaccharides.

Condensation derivatives of 4-isopropylbenzaldehyde with acetophenone from the red alga Laurencia tristicha

Seven undescribed condensation derivatives of 4-isopropylbenzaldehyde with acetophenone, including one 1,3,5-trisubstituted pentane-1,5-dione, two 1,3,4,5,7-pentasubstituted heptane-1,7-diones and four 1,2,3,4,5-pentasubstituted cyclohexanols, together with two known flavonoids, were obtained from the red alga Laurencia tristicha. The relative configurations were elucidated by extensive spectroscopic data analysis of MS, 1D and 2D NMR, while the absolute configurations were determined by comparing the experimental and calculated electronic circular dichroism spectra. All the isolates were proven to be naturally occurring in the red alga by LC-MS analysis, and these 1,3,5-trisubstituted-pentane-1,5-dione, 1,3,4,5,7-pentasubstituted-heptane-1,7-diones and 1,2,3,4,5-pentasubstituted-cyclohexanols were reported from natural sources for the first time. The proposed biogenetic pathway of the isolates was also discussed.

Photosynthesis of the Cyanidioschyzon merolae cells in blue, red, and white light

Photosynthesis and respiration rates, pigment contents, CO2 compensation point, and carbonic anhydrase activity in Cyanidioschizon merolae cultivated in blue, red, and white light were measured. At the same light quality as during the growth, the photosynthesis of cells in blue light was significantly lowered, while under red light only slightly decreased as compared with white control. In white light, the quality of light during growth had no effect on the rate of photosynthesis at low O2 and high CO2 concentration, whereas their atmospheric level caused only slight decrease. Blue light reduced markedly photosynthesis rate of cells grown in white and red light, whereas the effect of red light was not so great. Only cells grown in the blue light showed increased respiration rate following the period of both the darkness and illumination. Cells grown in red light had the greatest amount of chlorophyll a, zeaxanthin, and β-carotene, while those in blue light had more phycocyanin. The dependence on O2 concentration of the CO2 compensation point and the rate of photosynthesis indicate that this alga possessed photorespiration. Differences in the rate of photosynthesis at different light qualities are discussed in relation to the content of pigments and transferred light energy together with the possible influence of related processes. Our data showed that blue and red light regulate photosynthesis in C. merolae for adjusting its metabolism to unfavorable for photosynthesis light conditions.

Agarose degradation for utilization: Enzymes, pathways, metabolic engineering methods and products

Red algae are important renewable bioresources with very large annual outputs. Agarose is the major carbohydrate component of many red algae and has potential to be of value in the production of agaro-oligosaccharides, biofuels and other chemicals. In this review, we summarize the degradation pathway of agarose, which includes an upstream part involving transformation of agarose into its two monomers, D-galactose (D-Gal) and 3,6-anhydro-α-L-galactose (L-AHG), and a downstream part involving monosaccharide degradation pathways. The upstream part involves agarolytic enzymes such as α-agarase, β-agarase, α-neoagarobiose hydrolase, and agarolytic β-galactosidase. The downstream part includes the degradation pathways of D-Gal and L-AHG. In addition, the production of functional agaro-oligosaccharides such as neoagarobiose and monosaccharides such as L-AHG with different agarolytic enzymes is reviewed. Third, techniques for the setup, regulation and optimization of agarose degradation to increase utilization efficiency of agarose are summarized. Although heterologous construction of the whole agarose degradation pathway in an engineered strain has not been reported, biotechnologies applied to improve D-Gal utilization efficiency and construct L-AHG catalytic routes are reviewed. Finally, critical aspects that may aid in the construction of engineered microorganisms that can fully utilize agarose to produce agaro-oligosaccharides or as carbon sources for production of biofuels or other value-adding chemicals are discussed.

In Silico Analysis of ACE Inhibitory Peptides from Chloroplast Proteins of Red Alga Grateloupia asiatica

Inhibition of angiotensin I-converting enzyme (ACE) is one of the key factors to repress high blood pressure. Although many studies have been reported that seaweed protein hydrolysates showed the ACE inhibitory activity, the comprehensive understanding of the relationship was still unclear. In this study, we employed chloroplast genome for in silico analysis and compared it with in vitro experiments. We first extracted water-soluble proteins (WSP) from red alga Grateloupia asiatica, which contained mainly PE, PC, APC, and Rbc, and prepared WSP hydrolysate by thermolysin, resulting that the hydrolysate showed ACE inhibitory activity. Then, we determined the complete chloroplast genome of G. asiatica (187,518 bp: 206 protein-coding genes, 29 tRNA, and 3 rRNA) and clarified the amino acid sequences of main WSP, i.e., phycobiliproteins and Rubisco, to perform in silico analysis. Consequently, 190 potential ACE inhibitory peptides existed in the main WSP sequences, and 21 peptides were obtained by in silico thermolysin digestion. By comparing in vitro and in silico analyses, in vitro ACE inhibitory activity was correlated to the IC₅₀ value from in silico digestion. Therefore, in silico approach provides insight into the comprehensive understanding of the potential bioactive peptides from seaweed proteins.

Two new pyrrolidine alkaloids from the red alga Acanthophora spicifera

Two new pyrrolidine alkaloids, acanthophoraines B (1) and C (2), together with five known ones (3-7) were isolated from the red alga Acanthophora spicifera. Their structures were elucidated by extensive spectroscopic methods and single-crystal X-ray diffraction analysis. The absolute configuration of 2 was established by ECD calculation. The antibacterial activities of 1-7 were also evaluated.

Solieritide A, a new polyketide from the red alga Solieria sp

A new polyketide, solieritide A (1), along with six known ones (2-7), had been isolated from the red alga Solieria sp. The structures of these compounds were elucidated by spectroscopic analysis. The absolute configuration of 1 was determined by the method of X-ray diffraction. Compound 1 was a rare polyketide bearing benzopyrone ring fused with γ-butyrolactone. Compounds 2-7 were isolated from the red algae of genus Solieria for the first time. The antibacterial activities of 1-7 were also discussed.

Selective loss of photosystem I and formation of tubular thylakoids in heterotrophically grown red alga Cyanidioschyzon merolae

We previously found that glycerol is required for heterotrophic growth in the unicellular red alga Cyanidioschyzon merolae. Here, we analyzed heterotrophically grown cells in more detail. Sugars or other organic substances did not support the growth in the dark. The growth rate was 0.4 divisions day^-1 in the presence of 400 mM glycerol, in contrast with 0.5 divisions day^-1 in the phototrophic growth. The growth continued until the sixth division. Unlimited heterotrophic growth was possible in the medium containing DCMU and glycerol in the light. Light-activated heterotrophic culture in which cells were irradiated by intermittent light also continued without an apparent limit. In the heterotrophic culture in the dark, chlorophyll content drastically decreased, as a result of inability of dark chlorophyll synthesis. Photosynthetic activity gradually decreased over 10 days, and finally lost after 19 days. Low-temperature fluorescence measurement and immunoblot analysis showed that this decline in photosynthetic activity was mainly due to the loss of Photosystem I, while the levels of Photosystem II and phycobilisomes were maintained. Accumulated triacylglycerol was lost during the heterotrophic growth, while keeping the overall lipid composition. Observation by transmission electron microscopy revealed that a part of thylakoid membranes turned into pentagonal tubular structures, on which five rows of phycobilisomes were aligned. This might be a structure that compactly conserve phycobilisomes and Photosystem II in an inactive state, probably as a stock of carbon and nitrogen. These results suggest that C. merolae has a unique strategy of heterotrophic growth, distinct from those found in other red algae.

Bromocatechol conjugates from a Chinese marine red alga, Symphyocladia latiuscula

This study describes an investigation into polybromocatechol conjugates isolated from a marine red alga, Symphyocladia latiuscula (Harvey) Yamada, collected from coastal waters off Qingdao, China. We report on the isolation and characterisation of eight undescribed aconitic acid conjugates, symphyocladins R-X, including a likely solvolysis artifact of symphyocladin S, and an undescribed furanoyl conjugate, symphyocladin Y. Structure elucidation was achieved by detailed spectroscopic analysis. A plausible biosynthetic pathway linking all these co-metabolites through a cascade of quinone methide additions is proposed.

Multiple effects of a Gracilaria vermiculophylla invasion on estuarine mudflat functioning and diversity

The invasive Japanese seaweed Gracilaria vermiculophylla has become established over the past several years in numerous European estuaries, from Portugal to Norway. In the Faou estuary (48.295°N-4.179°W, Brittany, France), it forms a dense population at the mud's surface. The effects of G. vermiculophylla on metabolism, diversity, and the food web were studied. Community gross primary production (GPP) and respiration (CR) during emersion, chlorophyll-a content, macrofaunal and meiofaunal diversity and abundance, and stable isotopes (δ¹³C and δ¹⁵N) of representative macrofaunal species and main food sources were measured at low tide in winter, spring, summer 2014, and winter 2015. Results show significant seasonal variation in GPP and CR. Moreover, GPP was significantly higher in areas where G. vermiculophylla was present than in the control area (bare mud). However, this high GPP appeared to be linked to the increase in biomass in primary producers, with their efficiency (primary productivity, i.e. assimilation number) remaining relatively stable compared with the control area. Significant variation in abundance of meiofauna and macrofauna was also detected and new epifaunal species were collected, mainly in Gracilaria-colonized areas. Isotopic food-web Bayesian mixing models strongly suggested that G. vermiculophylla plays a major role in the diet of some dominant species. Mechanisms interacting with the functioning and diversity of the mudflat are discussed. Finally, the invasive seaweed G. vermiculophylla affected the mudflat ecosystem in three ways: as a new primary producer (increase in metabolism), as a habitat-forming species (changes in diversity and abundance of macrofauna and meiofauna), and as a new abundant food source, likely through the detrital pathway.

Expression of Cyanobacterial Acyl-ACP Reductase Elevates the Triacylglycerol Level in the Red Alga Cyanidioschyzon merolae

Nitrogen starvation is known to induce the accumulation of triacylglycerol (TAG) in many microalgae, and potential use of microalgae as a source of biofuel has been explored. However, nitrogen starvation also stops cellular growth. The expression of cyanobacterial acyl-acyl carrier protein (ACP) reductase in the unicellular red alga Cyanidioschyzon merolae chloroplasts resulted in an accumulation of TAG, which led to an increase in the number and size of lipid droplets while maintaining cellular growth. Transcriptome and metabolome analyses showed that the expression of acyl-ACP reductase altered the activities of several metabolic pathways. The activities of enzymes involved in fatty acid synthesis in chloroplasts, such as acetyl-CoA carboxylase and pyruvate dehydrogenase, were up-regulated, while pyruvate decarboxylation in mitochondria and the subsequent consumption of acetyl-CoA by the tricarboxylic acid (TCA) cycle were down-regulated. Aldehyde dehydrogenase, which oxidizes fatty aldehydes to fatty acids, was also up-regulated in the acyl-ACP reductase expresser. This activation was required for the lipid droplet accumulation and metabolic changes observed in the acyl-ACP reductase expresser. Nitrogen starvation also resulted in lipid droplet accumulation in C. merolae, while cell growth ceased as in the case of other algal species. The metabolic changes that occur upon the expression of acyl-ACP reductase are quite different from those caused by nitrogen starvation. Therefore, there should be a method for further increasing the storage lipid level while still maintaining cell growth that is different from the metabolic response to nitrogen starvation.

Treatment with sulphated galactan inhibits macrophage chemotaxis and reduces intraplaque macrophage content in atherosclerotic mice

Experimental data from animal models and clinical studies support connections between the haemostasis and inflammation in atherogenesis. These interfaces among inflammation and thrombogenesis have been suggested as targets for pharmacological intervention to reduce disease progression. We hypothesize that the recently discovered antithrombotic drug Sulphated Galactan (SG) (isolated from the red marine alga Acanthophora muscoides) might reduce atherosclerotic plaque vulnerability and inflammatory gene expression in 10-week aged apolipoprotein E deficient (ApoE-/-) mice under high-cholesterol diet for additional 11weeks. Then, the underlying cellular mechanisms were investigated in vitro. SG (10mg/kg) or Vehicle was subcutaneously injected from week 6 until week 11 of the diet. Treatment with SG reduced intraplaque macrophage and Tissue Factor (TF) content as compared to Vehicle-treated animals. Intraplaque TF co-localized and positively correlated with macrophage rich-areas. No changes on atherosclerotic plaque size, and other intraplaque features of vulnerability (such as lipid, neutrophil, MMP-9 and collagen contents) were observed. Moreover, mRNA expression of MMPs, chemokines and genetic markers of Th1/2/reg/17 lymphocyte polarization within mouse aortic arches and spleens was not affected by SG treatment. In vitro, treatment with SG dose-dependently reduced macrophage chemotaxis without affecting TF production. Overall, the chronic SG treatment was well tolerated. In conclusion, our results indicate that SG treatment reduced intraplaque macrophage content (by impacting on cell recruitment) and, concomitantly, intraplaque TF content of potential macrophage origin in atherosclerotic mice.

Evaluation of physicochemical properties, proximate and nutritional composition of Gracilaria edulis collected from Palk Bay

Gracilaria edulis, a red alga present in southeast coast of India was evaluated for its nutritional composition. FT-IR analysis of soluble polysaccharides revealed the presence of galactans, 3,6-anhydro-α-L-galactopyranose, sulphated galactose and the gelling agent agar, with the sulphate content estimated as 51.01 μg/mg of polysaccharide. Results of physicochemical properties and nutritional profile reveal the presence of dietary fibre (8.9 ± 0.62% DW), carbohydrate (101.61 ± 1.8 mg/g DW), crude protein (6.68 ± 0.94 mg/g DW) and lipid content (8.3 ± 1.03 mg/g DW). G. edulis contains biologically important fatty acids like palmitic acid (2.06%), linolenic acid (2.56%), and oleic acid (1.98%). The other nutritional components present in high amounts are proline, chlorophyll A and B, all the essential amino acids and vitamin A, E and C. These findings suggest that G. edulis has potent nutritional value which might be used as a source of nutrients for human and animals.

Production of domoic acid by laboratory culture of the red alga Chondria armata

To clarify the production mechanisms and biologic functions of domoic acid (DA) by the red alga Chondria armata, we established a laboratory culture of C. armata. The alga grew better in modified PES medium (mPES) without trace metals or manganese than in unmodified mPES (seawater + nitrate, phosphate, iron, trace metals, vitamins, and 2-[4-(2-hydroxyethyl)-1-piperazinyl]-ethanesulfonic acid), suggesting that C. armata is especially hypersensitive to the toxicity of excessive manganese. C. armata cultured in N·P·Fe medium (seawater + nitrate, phosphate, and iron) grew best (mean growth rate 828.4%) at a relative nutrient concentration of 50%. Liquid chromatography-mass spectrometry analysis of the algal extracts revealed that the DA content of the cultured explants (2273-3308 ppm) was 4-5 fold higher than that of wild specimens. The extract of pooled explants (60 g) was purified by activated charcoal treatment and several types of column chromatography to afford ca. 10 mg DA. The (1)H-nuclear magnetic resonance spectrum of the preparation was indistinguishable from the previously reported spectrum of DA, indicating that C. armata itself has an ability to produce DA.

Expression of budding yeast FKBP12 confers rapamycin susceptibility to the unicellular red alga Cyanidioschyzon merolae

The target of rapamycin (TOR) is serine/threonine protein kinase that is highly conserved among eukaryotes and can be inactivated by the antibiotic rapamycin through the formation of a ternary complex composed of rapamycin and two proteins, TOR and FKBP12. Differing from fungi and animals, plant FKBP12 proteins are unable to form the ternary complex, and thus plant TORs are insensitive to rapamycin. This has led to a poor understanding of TOR functions in plants. As a first step toward the understanding of TOR function in a rapamycin-insensitive unicellular red alga, Cyanidioschyzon merolae, we constructed a rapamycin-susceptible strain in which the Saccharomyces cerevisiae FKBP12 protein (ScFKBP12) was expressed. Treatment with rapamycin resulted in growth inhibition and decreased polysome formation in this strain. Binding of ScFKBP12 with C. merolae TOR in the presence of rapamycin was demonstrated in vivo and in vitro by pull-down experiments. Moreover, in vitro kinase assay showed that inhibition of C. merolae TOR kinase activity was dependent on ScFKBP12 and rapamycin.