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.

The production and characteristics of glycogen synthesized by various strains of the thermoacidophilic red microalgae Galdieria grown heterotrophically

AbstractRed microalgae from the Cyanidiophyceae, particularly Galdieria sulphuraria and Cyanidioschyzon merolae, are primitive photosynthetic thermoacidophiles that thrive in acidic hot springs and geysers. Unlike most Cyanidiophyceae, Galdieria strains are metabolically flexible as they can switch from photoautotrophic growth in the light to heterotrophic growth in complete darkness. Galdieria sulphuraria is especially noteworthy for its accumulation of various commercially valuable, functional compounds such as glycogen and phycocyanin. Glycogen, a branched fractal-like polysaccharide composed of several thousands of anhydroglucopyranose units, can be added to cosmetic products and sports drinks as a moisturizer or slow-digestible carbohydrate. While the production and structural characteristics of the glycogen of G. sulphuraria 108.79, isolated from Yellowstone National Park, have been previously described, our investigation aimed to explore glycogen production and properties across various Galdieria strains from different locations. Our findings reveal that all examined strains produce substantial amounts of highly branched glycogen when grown heterotrophically on glycerol in the dark. Notably, the structural characteristics of Galdieria glycogen distinguish it from both eukaryotic and prokaryotic glycogen, exhibiting a significantly higher degree of branching, substantially shorter side chains, and a considerable extent of indigestibility. These findings support the hypothesis that this highly branched, small glycogen is a long-term energy store, enabling survival during extended periods of complete darkness.

Xylose, glucose and acetate as feedstock for three microalgal species cultivated in heterotrophy

Microalgae are known as good producers of high-added value bioproducts useful in many applications such as pharmaceuticals, nutrition or biofuel production. In contrast to phototrophy, heterotrophy emerges as a promising strategy for algal biomass production due to high cell densities, controlled conditions and reduced space requirement. Hemicellulose is the second most abundant material in land plants. Its hydrolysis liberates xylose, glucose, acetate. Our study focuses on three microalgal species, Galdieria sulphuraria, Euglena gracilis, and Auxenochlorella protothecoides, cultivated under heterotrophy with the above-mentioned carbon sources, supplemented alone or in combination. Growth parameters and biomass analysis revealed distinctive characteristics. G. sulphuraria, despite a modest fatty acid content (5–15 % w/w), displayed potential for hemicellulose valorization, demonstrating high biomass yield using xylose as a sole carbon source (approx. 0.5 gDW gxylose−1) and high saturated fatty acid (SFA) content (45–63 %). In our cultivation conditions, E. gracilis only assimilated acetate with low fatty acid content (approx. 6 % w/w), but high SFA content (60–77 %) and high paramylon content (47 % w/w), convertible to wax-esters under anaerobiosis. A. protothecoides exhibited biomass yields of 0.42–0.54 gDW gsubstrate−1 depending on the carbon substrate supplied but maintained constant fatty acid content (16–18 % w/w) in the presence of all substrates except xylose. Surprisingly, despite an inability to grow with xylose alone, sugar depletion analysis indicated decreasing xylose concentration when other carbon sources were present in the cultivation medium for this alga. This comparative study discusses the strengths and weaknesses of each strain, providing insights into their potential when grown on hemicellulose carbon sources.

Model-driven design and validation of glucose supply control in a tubular photobioreactor operated under oxygen-balanced mixotrophy

Scaling up bioprocesses remains challenging due to the partially unpredictable and suboptimal behavior of microbes during scale transition. Mathematical modelling serves as a valuable tool in navigating these challenges. In this study, we developed and validated a kinetic model based on the tank-in-series approach for a novel bioprocess known as oxygen-balanced mixotrophy with the microalga Galdieria sulphuraria. This model aims to facilitate the design of an effective glucose feeding control strategy tailored for two-phase tubular photobioreactors (TPBRs). The residence time distribution of our reference reactor was investigated by means of a tracer experiment. Qualitative analysis of the results indicated that our system was optimally represented by simulations with a 100 stirred-tank reactors (STRs).The controlled variable, oxygen concentration in the gas phase, showed a downward trend in simulations with simplified conditions: fixed oxygen production and balanced glucose supply. The decrease was caused by dominant net heterotrophic activity and accumulation of CO2 in the gas phase. Different configurations of a proportional-integral-derivative (PID) controller were designed by means of the ultimate gain method and compared under these simplified conditions. The most effective PID controller was implemented and refined in simulations with outdoor weather conditions. The model was validated successfully by simulating over time in a lab-scale STR the spatial fluctuations happening in a TPBR. The empirical oxygen consumption and production were faster and steeper than in the model, probably due to inaccuracies in parameter estimation or biomass adaptation.

Towards sustainable water management for Galdieria sulphuraria cultivation

The red microalga Galdieria sulphuraria has emerged as a promising biotechnological platform for large-scale cultivation and production of high-value compounds, such as the blue pigment phycocyanin. However, a large amount of freshwater and a substantial supply of nutrients challenge both the environmental and the economic sustainability of algal cultivation. Additionally, the extremophilic nature of Galdieria sulphuraria requires cultivation in an acidic culture medium that directly leads to strongly acidic wastewater, which in turn generally exceeds legal limits for industrial wastewater discharge. This research aims to address these challenges, by investigating cultivation water reuse as a strategy to reduce the impacts of Galdieria sulphuraria management. The results indicated that a 25 % water reuse may be easily implemented and showed to be effective at the pilot scale, providing no significant changes in microalgae growth (biomass productivity ~0.21 g L−1 d−1) or in phycocyanin accumulation (~ 10.8 % w/w) after three consecutive cultivation cycles in reused water. Moreover, a single cultivation cycle with water reuse percentages of 71 and 98 %, achieved with membrane filtration and with centrifugation, respectively, was also successful (biomass productivity ~0.24 g L−1 d−1). These findings encourage freshwater reuse implementations in the microalgae sector and support further investigations focusing on coupling cultivation and harvesting in continuous, real-scale configurations. Centrifugation and membrane filtration required substantially different specific electrical energy consumption for water reuse and biomass concentration: in real applications, the former technique would roughly span from 1 to 10 kWh m−3 while the latter is expected to fall within the ample range 0.1–100 kWh m−3, strongly dependent on system size. For this reason, the most suitable separation train should be chosen on a case-by-case basis, considering the prevailing flow rate and the target biomass concentration factor targeted by the separation process.

Removal of Cadmium (II) from Aqueous Solution Using Galdieria sulphuraria CCMEE 5587.1.

The release of cadmium into the environment is a significant global concern due to its toxicity, non-biodegradability, and persistence in nature. There is an urgent need for effective, eco-friendly, and cost-effective systems for removing Cd because of the many drawbacks of conventional physicochemical techniques. This study investigated the ability of the extremophile red microalgal strain Galdieria sulphuraria CCMEE 5587.1 to tolerate and remove Cd (II) ions at acidic pH in a controlled laboratory environment. Three distinct concentrations of Cd (1.5 mg L-1, 3 mg L-1, and 6 mg L-1) were introduced to the cyanidium medium, and G. sulphuraria cells were introduced in the medium and grown for ten days. Four distinct aspects were identified regarding Cd removal: time course Cd removal, total Cd removal, extracellular Cd removal, and intracellular Cd removal. The inhibitory effects of Cd on G. sulphuraria growth were observed using a daily growth profile. Initial incubation days showed an inhibition of G. sulphuraria growth. In addition, increasing the Cd concentration in the medium decreased the growth rate of G. sulphuraria. Rapid Cd removal occurred on the first day of the experiment, followed by a steady removal of Cd until the last day. The highest total removal efficiency occurred in a medium containing 3 mg L-1 of Cd ions, which was 30%. In contrast, the highest sorption capacity occurred in a medium containing 6 mg L-1 of Cd ions, which was 1.59 mg g-1 of dry biomass. In all media compositions, a major fraction (>80%) of Cd removal occurred via adsorption on the cell surface (extracellular). These results showed that G. sulphuraria cells can remove Cd ions from aqueous solution, which makes them a potential bioremediation option for heavy metal removal.

Significance and Applications of the Thermo-Acidophilic Microalga Galdieria sulphuraria (Cyanidiophytina, Rhodophyta).

Galdieria sulphuraria is a thermo-acidophilic microalga belonging to the Cyanidiophyceae (Rhodophyta) class. It thrives in extreme environments, such as geothermal sulphuric springs, with low pH, high temperatures, and high salinity. This microalga utilises various growth modes, including autotrophic, heterotrophic, and mixotrophic, enabling it to exploit diverse organic carbon sources. Remarkably, G. sulphuraria survives and produces a range of bioactive compounds in these harsh conditions. Moreover, it plays a significant role in environmental remediation by removing nutrients, pathogens, and heavy metals from various wastewater sources. It can also recover rare earth elements from mining wastewater and electronic waste. This review article explores the diverse applications and significant contributions of G. sulphuraria.

Investigation of the carbon footprint of the cultivation of the heterotrophic microalga Galdieria sulphuraria on hydrolyzed straw and digestate

The purpose of this study was to assess the carbon footprint of a production process for 1 kg of dry algal biomass powder (Galdieria sulphuraria) cultivated on straw and digestate as carbon and nitrogen sources, respectively, for further optimization. It was examined whether and to what extent the use of straw and digestate can reduce the environmental impact (global warming and resource efficiency) and how this can result in a more sustainable use of resources. The investigated process was compared to a process where conventional glucose serves as a carbon source. The findings demonstrate that the hydrolysis of straw results in a worst environmental impact compared to the conventional process. Hydrolysis alone releases approx. 8 kg CO2-eq., which is predominantly caused by the energy demand. The results of this study therefore clearly revealed that the hydrolysis of straw needs to be optimized to foster a sustainable use of agriculture residues.

Productivity, amino acid profile, and protein bioaccessibility in heterotrophic batch cultivation of Galdieria sulphuraria

The polyextremophilic Galdieria sulphuraria is emerging as a promising microalgal species for food applications. This work explores the potential of heterotrophically cultivated G. sulphuraria as a protein producer for human consumption. To this end, the performances of four G. sulphuraria strains grown under the same conditions were compared. Amino acid profiles varied among strains and growth phases, but all samples met FAO dietary requirements for adults. The specific growth rates were between 1.01 and 1.48 day−1. After glucose depletion, all strains showed an increase of 38–49 % in nitrogen content within 48 h, reaching 7.8–12.0 % w/w. An opposite trend was observed in protein bioaccessibility, which decreased on average from 69 % during the exponential phase to a minimum of 32 % 48 h after stationary phase, with significant differences among the strains. Therefore, selecting the appropriate strain and harvesting time is crucial for successful single-cell protein production.

Biotreatment of swine wastewater by mixotrophic Galdieria sulphuraria

Biotreatment of swine wastewater via microalgae is an environmentally sustainable and economical efficient strategy capable to transform nitrogen, phosphorous, and organic/inorganic carbons into value added products as lipids, carbohydrates, and proteins, while high ammonium tolerant microalgal species with efficient COD and ammonium removal efficiency is lacking, limiting its practical application. Thermophilic and acidophilic Galdieria sulphuraria (G. sulphuraria) are reported to have high ammonium removal efficiency, while its application in ammonium rich swine wastewater treatment without dilution is rarely reported. Accordingly, mixotrophic cultivation of G. sulphuraria has been tested for biotreatment of swine wastewater. The results indicate that G. sulphuraria can grow well in swine wastewater with maximum growth rate of 0.72 g/(L.d) when 15 g/L of glucose is added. Simultaneously, a maximum COD removal efficiency of 94.8% and ammonium removal rate of 550.5 mg/(L.d) are observed. The addition of glucose leads to decreases of lipid, protein and ash contents, and simultaneous increase of carbohydrates owing to the varied C/N ratios. The final microalgal biomass has relatively lower carbon content of 48.5% with 20 g/L glucose than 49.3% of control, consequently leads to a relatively lower HHV value of 20.64 MJ.kg−1. Above all, mixotrophic cultivation of G. sulphuraria are promising strategy for swine wastewater treatment with high energy recovery, potentially providing an economical strategy for swine wastewater treatment.

Development of dual strain microalgae cultivation system for the direct carbon dioxide utilization of power plant flue gas

This study aims to propose a biological system that allows for direct utilization of flue gas for carbon dioxide capture and utilization by microalgae. The strain Chlorella sp. ABC-001 is employed for its high growth rate as well as lipid and carbohydrate content. Toxicity tests showed that cell growth was unaffected by NO, but the presence of SO2 showed critical damage on cell growth. Hence, an extremophile alga, Galdieria sulphuraria 5587.1 was applied to build a dual-strain cultivation system to mitigate the effect of SO2 toxicity and increase CO2 capture efficiency. All SO2 was removed by Galdieria culture and the system exhibited stable growth from a simulated flue gas stream containing CO2, NO and SO2. Combined CO2 biofixation rate of 793 mg/L/d and lipid productivity of 113 mg/L/d was achieved. The results showed that this new cultivation system is a promising alternative for reducing CO2 emissions from power plants.

Biosorption of rare earth elements from luminophores by G. sulphuraria (Cyanidiophytina, Rhodophyta)

Lanthanides are indispensable constituents of modern technologies and are often challenging to acquire from natural resources. The demand for REEs is so high that there is a clear need to develop efficient and eco-friendly recycling methods. In the present study, freeze-dried biomass of the polyextremophile Galdieria sulphuraria was employed to recover REEs from spent fluorescent lamps (FL) luminophores by pretreating the freeze-dried biomass with an acid solution to favour ion exchange and enhance the binding sites on the cell surface available for the metal ions. Lanthanides were extracted from the luminophores using sulfuric acid solutions according to standardised procedures, and the effect of biosorbent dosage (0.5–5 mg/ml) and biosorption time (5–60 min) were evaluated. The content of individual REEs in the luminophores and the resulting algal biomass were determined using inductively coupled plasma mass spectrometry (ICP-MS). The most abundant REE in the luminophores was yttrium (287.42 mg/g dm, 91.60% of all REEs), followed by europium (20.98 mg/g, 6.69%); cerium, gadolinium, terbium and lanthanum was in trace. The best biosorption performances were achieved after 5 min and at the lowest biosorbent dosage (0.5 mg/mL). The highest total metal amount corresponded to 41.61 mg/g dried mass, and yttrium was the most adsorbed metal (34.59 mg/g dm, 82.88%), followed by cerium (4.01 mg/g); all other metals were less than 2 mg/g. The rapidity of the biosorption process and the low biosorbent dosage required confirmed this microalga as a promising material for creating an eco-sustainable protocol for recycling REEs.

Removal of Cadmium and Lead from Synthetic Wastewater Using Galdieria sulphuraria

The strain of red microalgae Galdieria sulphuraria CCMEE 5587.1 was evaluated in a controlled laboratory environment for its ability to tolerate and remove two heavy metal (HM) ions: cadmium [Cd(II)] and lead [Pb(II)] in aqueous solutions as a single metal species. Various concentrations (0 mg L−1 to 5 mg L−1) of Cd and Pb ions were added to the Cyanidium medium in which the chosen microalgae strain G. sulphuraria CCMEE 5587.1 was grown at an acidic pH of 2.5. The effectiveness of G. sulphuraria CCMEE 5587.1 in tolerating and removing these two metal ions was measured by analyzing its growth profile, growth rate, nutrient removal, and metal ion removal efficiency. The growth of G. sulphuraria CCMEE 5587.1 was inhibited during the initial days of incubation, and the growth rate decreased when the HM concentration in the media was increased. Nutrient removal in the HM-containing media is comparable to that in the control media at low metal concentrations but decreases as the metal concentration rises. G. sulphuraria CCMEE 5587.1 has the highest removal efficiency for Cd and Pb in a medium containing 2.5 mg L−1 of metal ions, which is 49.80% and 25.10%, and the corresponding sorption capacity is 1.45 mg g−1 and 0.53 mg g−1 of dry biomass, respectively. These findings suggest that G. sulphuraria CCMEE 5587.1 holds potential as a viable bioremediation solution for extracting Cd and Pb from wastewater, alongside its capacity to remove nutrients concurrently. The study underscores the dual advantage of G. sulphuraria CCMEE 5587.1, making it a promising candidate for addressing heavy metal pollution in wastewater treatment processes.

Algae Cultivation as Measure for the Sanitation of Organic Waste—A Case Study Based on the Alga Galdieria sulphuraria Grown on Food Waste Hydrolysate in a Continuous Flow Culture

Due to its growth under harsh acidic conditions, the microalga Galdieria sulphuraria may offer the opportunity to combine sanitation and the utilization of organic waste streams. To further deepen the knowledge of alternative waste treatment strategies that allow for holistic utilization, the control and removal of microbial contaminants via non-sterile heterotrophic G. sulphuraria on food waste hydrolysate were investigated in a continuous flow bioreactor culture. Furthermore, a substrate reservoir and harvested biomass were stored under non-sterile conditions over a period of 12 days. Despite the non-sterile conditions, the microbial load of the biomass could be kept under control. Neither the pathogen Salmonella sp. nor the coliform bacteria Escherichia coli could be found. Only nine counts per g of biomass were found for species belonging to Enterococcus spp., Enterobacteriacae, and moulds. Aerobic spore formers were counted with 2700 counts per g of biomass. Most of the aerobic mesophilic counts were formed by yeasts (1.5 × 106 vs. 1.3 × 106 counts per g biomass). The results revealed that, when using acidic growth conditions, contamination will not take over the culture; thus, the sterilization of waste materials can be skipped. It is assumed that such an approach can result in efficient processes for future waste-based bioeconomy strategies.

Mixotrophic and heterotrophic growth of Galdieria sulphuraria using buttermilk as a carbon source

The growth of the polyextremophile red microalga Galdieria sulphuraria ACUF 064 was evaluated under mixotrophy and heterotrophy in a 13-L lab-scale stirred photobioreactor, using buttermilk as a carbon source. Beforehand, G. sulphuraria ACUF 064 growth on glucose, galactose and lactose was evaluated. No significant differences were observed in terms of growth when lactose, glucose or galactose was used as a carbon source. Overall, the biomass yield on carbon was 70% higher in mixotrophy than heterotrophy for galactose (2.0 gx gC−1) and lactose (2.0 gx gC−1), while it was similar for glucose (1.5 gx gC−1). At the same time, the yield of biomass on nitrogen for cultures grown in lactose was the lowest in comparison to all the other tested substrates. This was also supported by a higher C-phycocyanin content, with 5.9% wC-PC/wx as the highest value in mixotrophy. A preliminary experiment in flasks under mixotrophic conditions with different buttermilk dilutions revealed that a dilution ratio of 40% v/v of buttermilk (corresponding to 2.0 gC L−1) was optimal for biomass production. Finally, G. sulphuraria ACUF 064 was grown in the optimal buttermilk dilution ratio in a 13 L photobioreactor. The highest biomass productivity was also obtained in mixotrophy (0.55 gx L−1 d−1), corresponding to a carbon removal of 61%. Overall, lactose-containing substrates such as buttermilk hold promise as a substrate for the growth of G. sulphuraria while revalorizing an industrial effluent.

Galdieria sulphuraria: An Extremophilic Alga as a Source of Antiviral Bioactive Compounds.

In the last decades, the interest in bioactive compounds derived from natural sources including bacteria, fungi, plants, and algae has significantly increased. It is well-known that aquatic or terrestrial organisms can produce, in special conditions, secondary metabolites with a wide range of biological properties, such as anticancer, antioxidant, anti-inflammatory, and antimicrobial activities. In this study, we focused on the extremophilic microalga Galdieria sulphuraria as a possible producer of bioactive compounds with antiviral activity. The algal culture was subjected to organic extraction with acetone. The cytotoxicity effect of the extract was evaluated by the 2,5-diphenyl-2H-tetrazolium bromide (MTT) assay. The antiviral activity was assessed through a plaque assay against herpesviruses and coronaviruses as enveloped viruses and poliovirus as a naked one. The monolayer was treated with different concentrations of extract, ranging from 1 µg/mL to 200 µg/mL, and infected with viruses. The algal extract displayed strong antiviral activity at non-toxic concentrations against all tested enveloped viruses, in particular in the virus pre-treatment against HSV-2 and HCoV-229E, with IC50 values of 1.7 µg/mL and IC90 of 1.8 µg/mL, respectively. However, no activity against the non-enveloped poliovirus has been detected. The inhibitory effect of the algal extract was confirmed by the quantitative RT-PCR of viral genes. Preliminary chemical profiling of the extract was performed using ultra-high-performance liquid chromatography coupled to high-resolution mass spectrometry (UHPLC-HRMS), revealing the enrichment in primary fatty acid amides (PFAA), such as oleamide, palmitamide, and pheophorbide A. These promising results pave the way for the further purification of the mixture to explore its potential role as an antiviral agent.

Use of an extremophile red microalga (Galdieria sulphuraria) to produce phycocyanin from tangerine peel waste

To enhance the economic feasibility and secure the stable production of algal value-added product, relatively fresh and clean tangerine peel waste was tested as a nutrient source for the production of phycocyanin (a value-added pigment) by an extremophile red microalga, Galdieria sulphuraria. First, tangerine peel extract was compared with conventional growth medium, and then, the adjustments of the pH (3.5) and nutrient balance (1119.30 mg/L NH4-N and 45.53 mg/L PO4-P) were applied to prepare a tangerine peel-based medium for cultivation of G. sulphuraria. Then phototrophic seed culture was adopted to increase the maximized phycocyanin yield up to 2-fold. In the final stage, optimized tangerine peel medium had a 1.7-fold increased phycocyanin yield (159.00 ± 14.55 mg/L) on day 6 compared with the conventional glucose medium (93.67 ± 8.81 mg/L) due to the combination of diverse sugars (glucose, xylose, and fructose) in tangerine peel medium.

Strategic Use of Extremophilic Microalgae as a Carbon Source in the Thermo-Chemical Process

Microalgal biomass has a high CO2 fixation and growth rate when using CO2 as a carbon source. Moreover, biomass can also be employed as a carbon resource to produce biofuels and chemicals. As the growth rate of extremophilic microalgae remains unaffected by harsh conditions, the present study proposes that these microalgae (such as Galdieria sulphuraria) are a rapidly growing carbon resource for syngas production. Hence, two different experiments were performed as part of this study: (1) cultivation of G. sulphuraria under outdoor conditions and (2) conversion of G. sulphuraria into syngas. The productivity of G. sulphuraria under mixotrophic condition (0.82 g L–1 d–1) was about 1.6 faster than a widely cultivated Chlorella sp. HS2. Moreover, G. sulphuraria was converted into syngas using CO2 as a co-feedstock. The simultaneous reduction of CO2 and the oxidation of volatile matter (VM) from the thermolysis of G. sulphuraria promoted syngas formation. The chemical reaction was influenced by the molecular size of the VMs. In the presence of the Ni catalyst, low-molecular-weight VMs were formed owing to chemical bond scissions. Syngas formation under CO2 doubled compared with that under inert conditions. The findings suggest that G. sulphuraria is a feasible carbon source for CO2 fixation and chemical production.

Scale-down of oxygen and glucose fluctuations in a tubular photobioreactor operated under oxygen-balanced mixotrophy.

Oxygen-balanced mixotrophy (OBM) is a novel type of microalgal cultivation that improves autotrophic productivity while reducing aeration costs and achieving high biomass yields on substrate. The scale-up of this process is not straightforward, as non-ideal mixing in large photobioreactors might have unwanted effects in cell physiology. We simulated at lab scale dissolved oxygen and glucose fluctuations in a tubular photobioreactor operated under OBM where glucose is injected at the beginning of the tubular section. We ran repeated batch experiments with the strain Galdieria sulphuraria ACUF 064 under glucose pulse feeding of different lengths, representing different retention times: 112, 71 and 21 minutes. During the long and medium tube retention time simulations, dissolved oxygen was depleted 15 to 25 minutes after every glucose pulse. These periods of oxygen limitation resulted in the accumulation of coproporphyrin III in the supernatant, an indication of disruption in the chlorophyll synthesis pathway. Accordingly, the absorption cross section of the cultures decreased steeply, going from values of 150 - 180 m2 ·kg-1 at the end of the first batch down to 50 - 70 m2 ·kg-1 in the last batches of both conditions. In the short tube retention time simulation, dissolved oxygen always stayed above 10% air saturation and no pigment reduction nor coproporphyrin III accumulation were observed. Concerning glucose utilization efficiency, glucose pulse feeding caused a reduction of biomass yield on substrate in the range of 4 to 22% compared to the maximum levels previously obtained with continuous glucose feeding (0.9 C-g·C-g-1 ). The missing carbon was excreted to the supernatant as extracellular polymeric substances constituted by carbohydrates and proteins. Overall, the results point out the importance of studying large-scale conditions in a controlled environment and the need for a highly controlled glucose feeding strategy in the scale-up of mixotrophic cultivation. This article is protected by copyright. All rights reserved.

Low-concentration palladium recovery from diluted aqua regia-based wastewater using lyophilized algal cells

Ion-exchange resins and activated carbons are used in waste refinement in the electronics industry to recover low concentrations of palladium (Pd) dissolved in diluted aqua regia (HCl:HNO3 = 3:1, v/v). However, these techniques are inefficient and have higher costs than benefits. Here, we showed that the lyophilized cells of the microalga Galdieria sulphuraria recovered Pd from 4 M acid-diluted aqua regia with < 135 mg L–1 Pd and 6 M acid solution containing < 50 mg L–1 Pd with greater efficiency than ion-exchange resins and activated carbons. X-ray absorption fine structure, photoemission spectroscopy, and electron microscopy revealed that Pd was adsorbed in the periphery of lyophilized cells by forming an inner-sphere complex with sulfur. Among other metals, G. sulphuraria could recover 97% of Pd from 5 M acid-containing aqua regia-based wastewater generated during the production of printed circuit boards.