Red Alga Galdieria Sulphuraria Research Articles

Online determination of phycocyanin in vivo in Galdieria sulphuraria

ABSTRACT The extremophilic red alga Galdieria sulphuraria is well known for its metabolic capabilities with respect to organic carbon sources as well as its ability to produce the blue pigment phycocyanin (PC). The interest in PC as natural food colourant as well as nutraceutical is growing steadily. Therefore, a reliable quantification of PC accumulated by G. sulphuraria is crucial for establishing a production process. PC can be quantified through photometry but only after a laborious extraction procedure, which reduces the amount of data that can be gained from a cultivation. Hence, a faster PC determination method, with the potential to become an online method, is needed. In this study, we present a fast method for estimating the specific PC concentration based on in vivo absorbance spectra from cells of G. sulphuraria. A correlation with the PC concentration in the raw extract could be obtained, resulting in a 10-fold cross-validated coefficient of determination cR2 = 0.951. This makes extraction unnecessary in most cases. Especially in small-scale cultivation, where usually the available amount of biomass limits the number of measurements, this method presents a viable alternative to the extraction of PC.

High-efficient removal of ammonium and co-production of protein-rich biomass from ultrahigh-NH4+ industrial wastewater by mixotrophic Galdieria sulphuraria

Microalgal cultivation system is regarded as an effective bioremediation system for NH4+-containing wastewater. However, ultrahigh NH4+ concentration in wastewater impeded the normal growth of most microalgal species leading to low NH4+ removal efficiency or even algal death, while indigenous bacteria and other biological contaminants in wastewater are negative for algal growth and eventually crash the microalgal-based wastewater treatment system. If maintaining sterile condition throughout the treatment process, the high consumption of energy must result in a high cost of operation with less valuable output. Aiming to achieve the goal of cost-effective NH4+ removal and protein-rich biomass co-production, a novel strategy of NH4+ reutilization from ultrahigh-NH4+ industrial wastewater was developed through photo-fermentation of the thermoacidophilic red alga Galdieria sulphuraria (G. sulphuraria) as cell factory. Results indicated that the highest protein content (71.66 % DW) was attained under optimal conditions with inoculum density of 1 × 108 cells mL−1, pH 3.5, 3380 mg NH4+ L−1 and light intensity of 230 μmol m−2 s−1 in shake flasks system for 4-day culture. Subsequently, repeated fed-batch culture under sterile and non-sterile mode was performed in ca. 5000 mg NH4+ L−1 wastewater medium in 5 L photo-fermenters, achieving a 98 % of NH4+ removal efficiency with a higher NH4+ removal rate (1705.67 mg L−1 d−1), biomass concentration (64.65 g L−1) and protein productivity (8.75 g L−1 d−1) under non-sterile culture mode. This work provided a new solution for high-efficient NH4+ removal coupled with protein-rich biomass production by a lower cost, high-value biomass output and environment-friendly way.

Bio-removal of rare earth elements from hazardous industrial waste of CFL bulbs by the extremophile red alga Galdieria sulphuraria.

In recent decades, a shift has been seen in the use of light-emitting diodes over incandescent lights and compact fluorescent lamps (CFL), which eventually led to an increase in wastes of electrical equipment (WEE), especially fluorescent lamps (FLs) and CFL light bulbs. These widely used CFL lights, and their wastes are good sources of rare earth elements (REEs), which are desirable in almost every modern technology. Increased demand for REEs and their irregular supply have exerted pressure on us to seek alternative sources that may fulfill this demand in an eco-friendly manner. Bio-removal of wastes containing REEs, and their recycling may be a solution to this problem and could balance environmental and economic benefits. To address this problem, the current study focuses on the use of the extremophilic red alga, Galdieria sulphuraria, for bioaccumulation/removal of REEs from hazardous industrial wastes of CFL bulbs and the physiological response of a synchronized culture of G. sulphuraria. A CFL acid extract significantly affected growth, photosynthetic pigments, quantum yield, and cell cycle progression of this alga. A synchronous culture was able to efficiently accumulate REEs from a CFL acid extract and efficiency was increased by including two phytohormones, i.e., 6-Benzylaminopurine (BAP - Cytokinin family) and 1-Naphthaleneacetic acid (NAA - Auxin family).

Reversible adsorption of iridium in lyophilized cells of the unicellular red alga Galdieria sulphuraria.

Iridium (Ir) is one of the rarest elements in the Earth's crust and is valuable in industry due to its high corrosion resistance. In this study, we used lyophilized cells of a unicellular red alga, Galdieria sulphuraria for the selective recovery of small amounts of Ir from hydrochloric acid (HCl) solutions. The Ir recovery efficiency of the lyophilized cells was higher than that of activated carbon and comparable to that of an ion-exchange resin in up to 0.2 M acid. Lyophilized G. sulphuraria cells showed different selectivity from the ion-exchange resin, adsorbing Ir and Fe in 0.2 M HCl solution while the ion-exchange resin adsorbed Ir and Cd. The adsorbed Ir could be eluted with more than 90% efficiency using HCl, ethylenediaminetetraacetic acid, and potassium hydroxide solutions, but could not be eluted using a thiourea-HCl solution. After the elution of Ir with a 6 M HCl solution, lyophilized cells could be reused up to five times for Ir recovery with over 60% efficiency. Scanning electron-assisted dielectric microscopy and scanning electron microscopy revealed that Ir accumulated in the cytosol of the lyophilized cells. X-ray absorption fine structure analysis demonstrated the formation of an outer-sphere complex between Ir and the cellular residues, suggesting the adsorption via ion exchange, and explaining the ability to elute the Ir and reuse the cells. Our results provide a scientific basis for inexpensive and environmentally friendly biosorbents as an alternative to ion-exchange resins for the recovery of Ir.

Growth of the Red Alga Galdieria sulphuraria in Red Mud-Containing Medium and Accumulation of Rare Earth Elements

Growth of the Red Alga Galdieria sulphuraria in Red Mud-Containing Medium and Accumulation of Rare Earth Elements

The thermoacidophilic red alga Galdieria sulphuraria is a highly efficient cell factory for ammonium recovery from ultrahigh-NH4+ industrial effluent with co-production of high-protein biomass by photo-fermentation

The thermoacidophilic red alga Galdieria sulphuraria is well-suited for nutrient recovery and pathogenic bacteria reduction from urban wastewater, but few investigations were reported for high-NH4+ industrial effluent treatment. The present study evaluated the capacity of NH4+ recovery, bacteria reduction, and high-protein biomass co-production by photo-fermentation of G. sulphuraria. As inoculum, acclimated and non-acclimated seed cultures were applied for non-sterile and sterile cultures in ultrahigh-NH4+ (3,000 ∼ 6,000 mg L-1) wastewater medium prepared from industrial effluent. The acclimated inoculum showed a higher cell growth rate (0.48 d-1) and NH4+ recovery rate (0.34 g L-1 d-1) than the non-acclimated inoculum in shake flasks. The relative abundance of dominant bacteria (Proteobacteria, Actinobacteria, and Acidobacteria) in the associated microbial community declined sharply in non-sterile cultures due to the extremely low pH value. In repeated fed-batch cultures in 5-L photo-fermenters, the maximum NH4+ recovery rate (2.19 g L-1 d-1), biomass production (55.0 g L-1) and productivity (12.0 g L-1 d-1) were achieved with high contents of protein (47.6 %DW) and essential amino acids (18.9 %DW) in sterile culture. Attractively, the maximum NH4+ recovery rate (1.79 g L-1 d-1), biomass production (49.5 g L-1), and productivity (10.8 g L-1 d-1) were achieved with the highest protein production (25.3 g L-1) in non-sterile cultures. This study demonstrates the feasibility of G. sulphuraria as a high-efficient cell factory for recovering NH4+ by photo-fermentation. We developed a novel approach of non-sterile repeated fed-batch culture for cost-effective wastewater treatment and co-production of high-protein biomass, which facilitates algae-based “waste-to-treasure” bioconversion for green manufacturing.

Cell population behavior of the unicellular red alga Galdieria sulphuraria during precious metal biosorption

This study investigates the biosorption mechanism, including cell population behavior, of trace amounts of precious metals (gold, palladium, and platinum) in a unicellular red alga, Galdieria sulphuraria. Single-cell inductively coupled plasma mass spectrometry showed that the number of adsorbing cells and the concentration of adsorbed metal per cell varied depending on solution acidity and metal species. The X-ray absorption fine structure in 5 mM HCl solution indicated that the adsorbed Au formed inner-sphere complexes with S, whereas the adsorbed Pd and Pt formed an inner-sphere complexes with N and/or S. In 500 mM HCl solution, the adsorbed Au and Pd formed inner-sphere complexes only with S, and the Au formed a structure similar to Au2S. At higher acidity, Au and Pd were recovered by interacting with residues that formed more stable complexes, which was accompanied by changes in the behavior of cell populations adsorbing the metals. This is the first study to demonstrate the relationship between changes in the behavior of cell populations and chemical interactions that occur between substrate elements and biomaterial residues during biosorption. The findings of this study provide deeper insights into the biosorption mechanism and a background for the design of an environmentally friendly biosorbent.

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]-. Analysisof 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.

Effect of lyophilization on the acid resistance of a unicellular red alga Galdieria sulphuraria during platinum recovery

The widespread use of platinum (Pt) in medical treatments and the industry has led to the increasing presence of low amounts of Pt in various wastewaters, and the sustainable recycling of Pt has garnered attention because of the associated economic and environmental advantages. Herein, we report that the lyophilization of the cells of a unicellular red alga, Galdieria sulphuraria, enabled the recovery of Pt with an efficiency over 90% from a 2 M hydrochloric acid (HCl) solution containing 10 mg/L Pt—comparable to the acid and Pt concentrations found in metal wastewater. Moreover, the lyophilized cells recovered only Pt, with 80% efficiency, from a 2 M HCl solution containing 10 mg/L concentrations of seven metals, and the selectivity of this method for Pt was higher than those of ion-exchange resins and activated carbons. Scanning electron-assisted dielectric microscopy showed that Pt was accumulated inside the cells, especially in chloroplasts. X-ray absorption near-edge structure revealed that Pt(IV) was reduced to Pt(II), forming an inner-sphere complex with S in the thiol residues in the lyophilized cells. The formation of an inner-sphere complex with S appears to increase the acid tolerance while retaining the high selectivity of lyophilized G. sulphuraria cells toward Pt.

Untargeted Metabolomics Unveil Changes in Autotrophic and Mixotrophic Galdieria sulphuraria Exposed to High-Light Intensity.

The thermoacidophilic red alga Galdieria sulphuraria has been optimizing a photosynthetic system for low-light conditions over billions of years, thriving in hot and acidic endolithic habitats. The growth of G. sulphuraria in the laboratory is very much dependent on light and substrate supply. Here, higher cell densities in G. sulphuraria under high-light conditions were obtained, although reductions in photosynthetic pigments were observed, which indicated this alga might be able to relieve the effects caused by photoinhibition. We further describe an extensive untargeted metabolomics study to reveal metabolic changes in autotrophic and mixotrophic G. sulphuraria grown under high and low light intensities. The up-modulation of bilayer lipids, that help generate better-ordered lipid domains (e.g., ergosterol) and keep optimal membrane thickness and fluidity, were observed under high-light exposure. Moreover, high-light conditions induced changes in amino acids, amines, and amide metabolism. Compared with the autotrophic algae, higher accumulations of osmoprotectant sugars and sugar alcohols were recorded in the mixotrophic G. sulphuraria. This response can be interpreted as a measure to cope with stress due to the high concentration of organic carbon sources. Our results indicate how G. sulphuraria can modulate its metabolome to maintain energetic balance and minimize harmful effects under changing environments.

Removal of sugars in wastewater from food production through heterotrophic growth of Galdieria sulphuraria.

The unicellular extremophilic red alga Galdieria sulphuraria is capable of chemoheterotrophy and its growth has been investigated on some defined and undefined substrates. In this study, the removal of sugars in wastewater from fruit‐salad production with G. sulphuraria strain SAG 21.92 was analyzed. Growth and sugar consumption were determined under variation of temperature, pH‐value and concentration of a model substrate, containing sucrose, glucose and fructose. In shake flask cultivation maximum specific growth rate and specific substrate consumption rate of 1.53±0.09 day−1 and 2.41±0.14 gSub·gDW −1·day−1 were measured at pH 2 and 42°C. A scale‐up of this process was conducted in a 3 L stirred tank reactor (STR). Wastewater from fruit‐salad production was diluted to 15 g·L−1 total sugar concentration, supplemented with micronutrients and ammonia and pH was set to 3. Determined growth rate and substrate consumption were 1.21 day−1 and 1.88 gSub·gDW −1·day−1, respectively. It was demonstrated, that high sugar concentrations in wastewater streams from food production processes can be significantly reduced with G. sulphuraria SAG 21.92. This strain could achieve substrate consumption rates in wastewater, equal to the more common strain 074G, but at higher pH values. Generated biomass can be used for production of phycocyanin, a valuable nutraceutical.

Different Behaviour between Autotrophic and Heterotrophic Galdieria sulphuraria (Rhodophyta) Cells to Nitrogen Starvation and Restoration. Impact on Pigment and Free Amino Acid Contents

The unicellular red alga Galdieria sulphuraria is a polyextremophilic organism with a metabolic flexibility to grow autotrophically or heterotrophically. Galdieria can also produce and accumulate biotechnologically attractive products such as pigments (phycocyanin) and proteins. In this research we studied the effects of nitrogen starvation and its subsequent restoration on pigment and free amino acid contents both in photoautotrophic and heterotrophic cells. Following the nitrogen starvation, the levels of the primary photosynthetic pigments decreased both in autotrophic and heterotrophic cells, except for the chlorophyll a marginally diminished in heterotrophic cells. Ammonium supply to G. sulphuraria N starved cells caused a significant increase of total chlorophylls both in autotrophic and heterotrophic cells. It was observed how such increase was more rapid and marked in heterotrophic cells than in the autotrophic ones. Under N starvation, phycocyanin contents decreased in both autotrophic and in heterotrophic cells; however, after a time-lapse of 24 hours, they resulted significantly higher in heterotrophic cells. In Galdieria sulphuraria, like in other microalgae, free amino acid contents were profoundly dependent on nitrogen status of the cells but heterotrophic cells maintained much higher levels, especially of glutamate, respect to autotrophic ones. In general, cells grown in the presence and absence of light showed different responses toward N availability; in particular heterotrophic cells seemed to respond quicker to the ammonium restoration compared to autotrophic ones.

Biomass and phycobiliprotein production of Galdieria sulphuraria, immobilized on a twin-layer porous substrate photobioreactor.

The extremophile red alga Galdieria sulphuraria was successfully grown immobilized in a twin-layer porous substrate bioreactor (TL-PSBR). A maximal biomass growth rate of 10g dry weight m-2day-1 was measured at a photon fluence rate of 200μmol photons m-2s-1 with addition of 1% CO2 and a temperature of 34°C. Under these conditions, a maximal biomass value of 232gm-2 was attained after 33days of growth. Phycobilin productivity, however, was highest at a lower photon fluence rate of 100μmol photons m-2s-1 and reached a phycobilin value of 14gm-2, a phycobilin content in the biomass of 63mgg-1 and a phycobilin growth rate of 0.28gm-2day-1 for phycocyanin and 0.23gm-2day-1 for allophycocyanin. Addition of CO2 was essential to enhance growth and phycobilin production in G. sulphuraria and further optimization of the cultivation process in the TL-PSBR appears possible using a multi-phase approach, higher growth temperatures and optimization of nutrient supply. It is concluded that autotrophic cultivation of G. sulphuraria in a TL-PSBR is an attractive alternative to suspension cultivation for phycobilin production and applications in bioremediation.

Comparison of the Dynamic Properties of the Bacterial Tubulin Homolog FtsZ, from Bacteria to Chloroplast

The tubulin homolog FtsZ is the major cytoskeletal protein in the bacterial cell division machinery, conserved in almost all bacteria, archaea, and chloroplasts. Bacterial FtsZ assembles spontaneously into dynamic protofilaments in vitro and forms a dynamic contractile ring or Z-ring in vivo. FtsZ from different species can have different dynamic properties. Here, we compare the dynamic properties of FtsZ from Escherichia coli (EcFtsZ), from the chloroplast of red alga Galdieria sulphuraria (GsFtsZA and GsFtsZB), and from the cyanobacterium Synechocystis sp. PCC 6803 (SyFtsZ). EcFtsZ assembles in vitro into mostly single protofilaments with an average length of 200 nm, which is highly dynamic, turning over with a half time of 5-8 s both in vitro and in vivo. The mechanism of dynamics is now established to be treadmilling, which involves adding subunits at one end and disassembling at the other. Chloroplasts arose in eukaryotes as endosymbionts of a cyanobacterium. The ancestral ftsZ gene was duplicated early in chloroplast evolution, and most express two FtsZ proteins for its division. Our studies on the GsFtsZA and GsFtsZB showed that both FtsZs assembled into large bundles of protofilaments. Random co-assembly of GsFtsZs enhanced their disassembly kinetics, suggesting GsFtsZB mostly as a regulator. In contrast to the two FtsZs in chloroplasts, there is only one FtsZ in cyanobacteria, similar to other bacteria. Our studies showed SyFtsZ assembled into thick bundles either straight or curved as toroids. This bundling is similar to that of chloroplast FtsZ, consistent with its origin in cyanobacteria. The assembly of SyFtsZ occurred in two stages. The first stage consisted of the assembly of single-stranded protofilaments and opened circles; the second stage formed bundles and toroids. The bundling might benefit the cell division of large cells.

Cold Acclimation of the Thermoacidophilic Red Alga Galdieria sulphuraria: Changes in Gene Expression and Involvement of Horizontally Acquired Genes.

Galdieria sulphuraria is a unicellular red alga that lives in hot, acidic, toxic metal-rich, volcanic environments, where few other organisms survive. Its genome harbors up to 5% of genes that were most likely acquired through horizontal gene transfer. These genes probably contributed to G.sulphuraria's adaptation to its extreme habitats, resulting in today's polyextremophilic traits. Here, we applied RNA-sequencing to obtain insights into the acclimation of a thermophilic organism towards temperatures below its growth optimum and to study how horizontally acquired genes contribute to cold acclimation. A decrease in growth temperature from 42�C/46�C to 28�C resulted in an upregulation of ribosome biosynthesis, while excreted proteins, probably components of the cell wall, were downregulated. Photosynthesis was suppressed at cold temperatures, and transcript abundances indicated that C-metabolism switched from gluconeogenesis to glycogen degradation. Folate cycle and S-adenosylmethionine cycle (one-carbon metabolism) were transcriptionally upregulated, probably to drive the biosynthesis of betaine. All these cold-induced changes in gene expression were reversible upon return to optimal growth temperature. Numerous genes acquired by horizontal gene transfer displayed temperature-dependent expression changes, indicating that these genes contributed to adaptive evolution in G.sulphuraria.

Cellular accumulation of cesium in the unicellular red alga Galdieria sulphuraria under mixotrophic conditions

As a consequence of the Fukushima Daiichi Nuclear Power Plant accident which occurred in Japan in 2011, huge amounts of radioactive cesium (Cs) spread across a large area at low concentrations. Bioremediation is known as an effective method for the recovery and concentration of metals at low concentrations. In the present study we showed that G. sulphuraria cells recovered 52 ± 15% of the Cs present in a potassium-deficient medium containing 30 μg L−1 Cs in 10 days. Because of the advantages in biotechnological use, G. sulphuraria is a good candidate for the decontamination of radioactive Cs. In G. sulphuraria cells, Cs was accumulated specifically under mixotrophic condition of the three different culture conditions used (autotorophic, mixotrophic, and heterotrophic condition). Cells in the early logarithmic phase of growth did not accumulate Cs, whereas those in the late logarithmic phase did. Cs accumulated in the cell exists mainly in a soluble form (e.g., salt, chelating complex).

Burning coal spoil heaps as a new habitat for the extremophilic red alga Galdieria sulphuraria

Galdieria sulphuraria (Cyanidiales) is a worldwide acclaimed thermoacidophilic red microalga with a limited distribution due to special conditions required for growth and metabolism. Until now, the alga was almost exclusively restricted to acid geothermal environments around the world. However, we have found this species on the surface of a burning coal spoil heap in central Europe. It is the first record of G. sulphuraria in this type of habitat. A rbcL phylogeny confirmed that the population of this extremophile belongs to the continental European lineage and we consider Italian geothermal sites as a potential source of Czech G. sulphuraria. The dispersal of unicellular red microalgae is far from fully understood and the discovery of Galdieria in another region of Europe on a relatively newly established anthropogenic site allows us to understand better the distribution patterns and dispersal abilities of this ecologically important algal group. In addition, we have also analyzed the phylogenetic position of Galdieria strain CCALA 965 isolated from a highly acidic site without geothermal activity in the Czech Republic and confirmed it to belong to the species G. phlegrea, until now known only from Italy.

The Chloroplast Tubulin Homologs FtsZA and FtsZB from the Red Alga Galdieria sulphuraria Co-assemble into Dynamic Filaments

FtsZ is a homolog of eukaryotic tubulin and is present in almost all bacteria and many archaea, where it is the major cytoskeletal protein in the Z ring, required for cell division. Unlike some other cell organelles of prokaryotic origin, chloroplasts have retained FtsZ as an essential component of the division machinery. However, chloroplast FtsZs have been challenging to study because they are difficult to express and purify. To this end, we have used a FATT tag expression system to produce as soluble proteins the two chloroplast FtsZs from Galdieria sulphuraria, a thermophilic red alga. GsFtsZA and GsFtsZB assembled individually in the presence of GTP, forming large bundles of protofilaments. GsFtsZA also assembled in the presence of GDP, the first member of the FtsZ/tubulin superfamily to do so. Mixtures of GsFtsZA and GsFtsZB assembled protofilament bundles and hydrolyzed GTP at a rate approximately equal to the sum of their individual rates, suggesting a random co-assembly. GsFtsZA assembly by itself in limiting GTP gave polymers that remained stable for a prolonged time. However, when GsFtsZB was added, the co-polymers disassembled with enhanced kinetics, suggesting that the GsFtsZB regulates and enhances disassembly dynamics. GsFtsZA-mts (where mts is a membrane-targeting amphipathic helix) formed Z ring-like helices when expressed in Escherichia coli Co-expression of GsFtsZB (without an mts) gave co-assembly of both into similar helices. In summary, we provide biochemical evidence that GsFtsZA assembles as the primary scaffold of the chloroplast Z ring and that GsFtsZB co-assembly enhances polymer disassembly and dynamics.

Cultivation of Acidophilic Algae Galdieria sulphuraria and Pseudochlorella sp. YKT1 in Media Derived from Acidic Hot Springs.

Microalgae possess a high potential for producing pigments, antioxidants, and lipophilic compounds for industrial applications. However, the cultivation of microalgae comes at a high cost. To reduce the cost, changes from a closed bioreactor to open pond system and from a synthetic medium to environmental or wastewater-based medium are being sought. However, the use of open pond systems is currently limited because of contamination by undesirable organisms. To overcome this issue, one strategy is to combine acidophilic algae and acidic drainage in which other organisms are unable to thrive. Here, we tested waters from sulfuric acidic hot springs (Tamagawa, pH 1.15 and Tsukahara, pH 1.14) in Japan for the cultivation of the red alga Galdieria sulphuraria 074G and the green alga Pseudochlorella sp. YKT1. Both of these spring waters are rich in phosphate (0.043 and 0.145 mM, respectively) compared to other environmental freshwater sources. Neither alga grew in the spring water but they grew very well when the waters were supplemented with an inorganic nitrogen source. The algal yields were ∼2.73 g dry weight/L for G. sulphuraria and ∼2.49 g dry weight/L for P. sp. YKT1, which were comparable to those in an autotrophic synthetic medium. P. sp. YKT1 grew in the spring waters supplemented either of NH4+, NO3- or urea, while G. sulphuraria grew only when NH4+ was supplemented. For P. sp. YKT1, the spring water was adjusted to pH 2.0, while for G. sulphuraria, no pH adjustment was required. In both cases, no additional pH-buffering compound was required. The phycocyanin of the thermophilic G. sulphuraria is known to be more thermostable than that from the Spirulina platensis currently used in phycocyanin production for commercial use. The phycocyanin content in G. sulphuraria in the Tsukahara water supplemented with NH4+ was 107.42 ± 1.81 μg/mg dry weight, which is comparable to the level in S. platensis (148.3 μg/mg dry weight). P. sp. YKT1 cells in the Tamagawa water supplemented with a nitrogen source formed a large amount of lipid droplets while maintaining cellular growth. These results indicate the potential of sulfuric hot spring waters for large-scale algal cultivation at a low cost.

Lipidomic analysis of the extremophilic red alga Galdieria sulphuraria in response to changes in pH

Analysis of polar lipids from the red micro-alga Galdieria sulphuraria by means of the HILIC-LC/high resolution ESI-tandem MS determined 14 classes of lipids including identification of tens of molecular species of lipids and their regioisomers. The extremophilic alga G. sulphuraria uses several mechanisms for adaptation to low pH and high temperature, the major change being a replacement of cellular phospholipids by betaine lipids. We also found a change in the ratio of regioisomers of the polar lipids, i.e. phospho-, glyco- and betaine lipids, in dependence on the culture medium pH. We hypothesize that biosynthesis of polar lipids via the prokaryotic and/or eukaryotic pathway is dependent on ambient pH.