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Sulfated polysaccharides of red marine microalgae have recently gained much attention for biomedical applications due to their anti-inflammatory and antioxidant properties. However, their low mechanical properties limit their use in tissue engineering. Herein, to enhance the mechanical properties of the sulfated polysaccharide produced by the red marine microalga, Porphyridium sp. (PS), it was integrated with the fluorenylmethoxycarbonyl diphenylalanine (FmocFF) peptide hydrogelator. Transparent, stable hydrogels were formed when mixing the two components at a 1:1 ratio in three different concentrations. Electron microscopy showed that all hydrogels exhibited a nanofibrous structure, mimicking the extracellular matrix. Furthermore, the hydrogels were injectable, and tunable mechanical properties were obtained by changing the hydrogel concentration. The composite hydrogels allowed the sustained release of curcumin which was controlled by the change in the hydrogel concentration. Finally, the hydrogels supported MC3T3-E1 preosteoblasts viability and calcium deposition. The synergy between the sulfated polysaccharide, with its unique bioactivities, and FmocFF peptide, with its structural and mechanical properties, bears a promising potential for developing novel tunable scaffolds for tissue engineering that may allow cell differentiation into various lineages.

The cells of the red microalga Porphyridium UTEX 637 are encapsulated within a sulfated polysaccharide whose external part (i.e., the soluble fraction) dissolves into the medium. It is thought that the main function of the polysaccharide is to protect the algal cells from the extreme environmental conditions, such as drought and high light, prevailing in their native sea-sand habitat. In this study, we evaluated the antioxidant properties of the water-soluble polysaccharide of Porphyridium sp. by determining the ability of a polysaccharide solution to inhibit: (1) autooxidation of linoleic acid, as determined by the standard thiobarbituric acid (TBA) and ferrous oxidation (FOX) assays; and (2) oxidative damage to 3T3 cells as determined by the dichlorofluorescein (DCFH) assay. In all three assays, the polysaccharide inhibited oxidative damage in a dose-dependent manner. Antioxidant activity was also exhibited by fractions of the polysaccharide obtained by sonication followed by separation on a reverse-phase HPLC with a C sub(8) semi-preparative column. It is suggested that the antioxidant activity of the sulfated polysaccharide protects the alga against reactive oxygen species produced under high solar irradiation, possibly by scavenging the free radicals produced in the cell under stress conditions and transporting them from the cell to the medium.

The molecular phylogeny of red algal actin genes, with emphasis on the paraphyletic \"Bangiophyceae,\" was examined and compared to the rhodophyte SSU rDNA phylogeny. Nineteen new genomic actin sequences and seven SSU rDNA sequences were obtained and subjected to diverse phylogenetic analyses (maximum likelihood, distance/neighbor-joining, maximum parsimony, Bayesian analyses, and, with respect to protein sequences, also quartet puzzling). The actin trees confirmed most of the major clades found in the SSU rDNA phylogenies, although with a lower resolution. An actin gene duplication in the florideophycean lineage is reported, presumably related to an increased complexity of sexual reproduction. In addition, the distribution and characteristics of spliceosomal introns found in some of the actin sequences were examined. Introns were found in almost all florideophycean actin genes, whereas only two bangiophyte sequences contained introns. One intron in the florideophycean actin genes was also found in metazoan, and, shifted by one or two nucleotides, in a glaucocystophyte, a cryptophyte, and two fungal actin genes, and thus may be an ancient intron.

M. Keidan, H. Broshy, D. van Moppes and S. (Malis) Arad. 2006. Assimilation of sulphur into the cell-wall polysaccharide of the red microalga Porphyridium sp. (Rhodophyta). Phycologia 45: 505-511. DOI: 10.2216/05-57.1 The cell walls of red algae contain sulphated polysaccharides. It is believed that the bioactivity of such natural sulphated polysaccharides may be attributed to the sulphate groups. Knowledge of the mode of sulphation of these polysaccharides is, however, very limited. The current study forms part of our efforts to elucidate the mode of sulphation of the cell-wall polysaccharide of the red microalga Porphyridium sp. Although this microalga is an obligatory photoautotroph, under conditions of sulphate starvation it can assimilate the sulphur-containing amino acid cysteine (but not methionine) and incorporate sulphur from [ 35 S]cysteine into the cell-wall polysaccharide. The ratio between 35 S uptake to the soluble polysaccharide complex and to the cells was threefold higher from [ 35 S]cysteine than that from Na 2 35 SO 4 , although the uptake of 35 S to the cells was higher when Na 2 35 SO 4 was used as the sulphur source. Pulse-chase experiments demonstrated that differences in the incorporation of 35 S from the two sulphur sources were greater for the soluble polysaccharide complex (45.1% from [ 35 S]cysteine vs. 13.9% from Na 2 35 SO 4 ) than for the cellular fractions (bound polysaccharide, protein and low-molecular-weight fraction). SDS-PAGE analysis showed that the 35 S label resided predominantly in the polysaccharide of the soluble complex and not in the glycoprotein. The effect of sodium chlorate, a sulphation inhibitor, on 35 S incorporation into the soluble polysaccharide complex and the different cellular fractions depended on the 35 S source: significant inhibition of sulphation of the soluble polysaccharide complex was found for [ 35 S]cysteine as the source of sulphate, i.e. 87% vs.36.4% for Na2 35 SO4. This study suggests that in addition to the commonly accepted sulphate pathway, there is another sulphation pathway in which cysteine serves as the sulphur source.

Red algae are extremely attractive for biotechnology because they synthesize accessory photosynthetic pigments (phycobilins and carotenoids), unsaturated fatty acids, and unique cell wall sulfated polysaccharides. We report a high-efficiency chloroplast transformation system for the unicellular red microalga Porphyridium sp. This is the first genetic transformation system for Rhodophytes and is based on use of a mutant form of the gene encoding acetohydroxyacid synthase [AHAS(W492S)] as a dominant selectable marker. AHAS is the target enzyme of the herbicide sulfometuron methyl, which effectively inhibits growth of bacteria, fungi, plants, and algae. Biolistic transformation of synchronized Porphyridium sp. cells with the mutant AHAS(W492S) gene that confers herbicide resistance gave a high frequency of sulfomethuron methyl-resistant colonies. The mutant AHAS gene integrated into the chloroplast genome by homologous recombination. This system paves the way for expression of foreign genes in red algae and has important biotechnological implications.

N-glycosylation is one of the most important post-translational modifications that influence protein polymorphism, including protein structures and their functions. Although this important biological process has been extensively studied in mammals, only limited knowledge exists regarding glycosylation in algae. The current research is focused on the red microalga Porphyridium sp., which is a potentially valuable source for various applications, such as skin therapy, food, and pharmaceuticals. The enzymes involved in the biosynthesis and processing of N-glycans remain undefined in this species, and the mechanism(s) of their genetic regulation is completely unknown. In this study, we describe our pioneering attempt to understand the endoplasmic reticulum N-Glycosylation pathway in Porphyridium sp., using a bioinformatic approach. Homology searches, based on sequence similarities with genes encoding proteins involved in the ER N-glycosylation pathway (including their conserved parts) were conducted using the TBLASTN function on the algae DNA scaffold contigs database. This approach led to the identification of 24 encoded-genes implicated with the ER N-glycosylation pathway in Porphyridium sp. Homologs were found for almost all known N-glycosylation protein sequences in the ER pathway of Porphyridium sp.; thus, suggesting that the ER-pathway is conserved; as it is in other organisms (animals, plants, yeasts, etc.).

Red microalgae contain functional sulfated polysaccharides (containing dietary fibers), polyunsaturated fatty acids, zeaxanthin, vitamins, minerals, and proteins. Studies in rat models support the therapeutic properties of algal biomass and isolated polysaccharides. Algal products incorporated into rat diets were found to significantly improve total serum cholesterol, serum triglycerides, hepatic cholesterol levels, HDL/LDL ratios and increased fecal excretion of neutral sterols and bile acids. Morphological and metabolic changes were induced by consumption of algal products. These results suggest that red microalgae can be used as potent hypocholesterolemic agents, and they support the potential use of red microalgae as novel nutraceuticals.

The cell-wall sulphated polysaccharide of the red microalga Porphyridium sp. has impressive antiviral activity against Herpessimplex viruses types 1 and 2 (HSV 1, 2) and Varicella zoster virus(VZV). Treatment of cells with 1 μg mL-1 polysaccharideresulted in 50% inhibition of HSV-infection as measured by the plaqueassay. Inhibition of the production of new virus particles was also shownwhen pre-infected cell cultures were treated with the polysaccharide. Inaddition, there was indirect evidence for a strong interaction between thepolysaccharide and HSV and a weak interaction with the cell surface.Depending on the concentration, the polysaccharide completely inhibitedor slowed down the development of the cytopathic effect in HSV or VZVpreinfected cells, but did not show any cytotoxic effects on Vero cells evenwhen a concentration as high as 250 μg mL-1 was used. Itseems therefore that the polysaccharide is able to inhibit viral infection bypreventing adsorption of virus into the host cells and/or by inhibiting theproduction of new viral particles inside the host cells. Thus, this alga seems tobe a good candidate for the development of an antiviral drug.

During the life cycle of Chlorella vulgaris Beijerinck var vulgaris fa. vulgaris growing synchronously, the specific activity of ornithine decarboxylase peaked at the 2nd hour of the cycle, whereas that of arginine decarboxylase changed only slightly, increasing towards the end of the cycle. The endogenous level of putrescine and spermidine on a per cell basis increased gradually up to the 8th hour of the cycle, and declined thereafter. Thus, the peak of ornithine decarboxylase activity and the polyamine increase preceded both DNA replication (which took place between the 6th and 8th hours of the cycle) and autospore release (which started at the 8th hour). A 2-fold increase in the light intensity caused doubling of the DNA content, resulting in doubling of the number of autospores per mother cell. It also brought about a 2-fold increase in the specific activity of ornithine decarboxylase and polyamine content, the peaks being at the same hour of the cycle under high and low light intensities. The increase in cell number and polyamine content in a Chlorella culture grown under high light intensity was inhibited by α-difluoromethyl ornithine, a specific inhibitor of ornithine decarboxylase, this inhibition being partially reversed by putrescine. It is suggested that in C. vulgaris the sequence of events which relates polyamine biosynthesis to cell division is as follows: increased ornithine decarboxylase activity, accumulation of polyamines, DNA replication, and autospore release.

The development of the biotechnology for red microalgae polysaccharides requires an interdisciplinary approach and concerted efforts involving large‐scale cultivation of the algae, chemical characterization of the polysaccharide, an environmental understanding, and molecular–genetic developments. Due to concerted efforts in these directions, the sulfated polysaccharides of the red microalgae have already found applications in the cosmetics industry, and the development of pharmaceutical applications is underway. Future R&D directions are likely to be focused on bringing to fruition the vast potential of red microalgae as “cell factories,” for protein production and delivery.