To determine the optimum light intensity per cell required for rapid growth regardless of cell density, continuous cultures of the microalga Chlorella zofingiensis were grown with a sufficient supply of nutrients and CO2 and were subjected to different light intensities in the range of 75-1000 μE m(-2) s(-1). The cell density of culture increased over time for all light conditions except for the early stage of the high light condition of 1000 μE m(-2) s(-1). The light intensity per cell required for the high specific growth rate of 0.5 day(-1) was determined to be 28-45 μE g-ds(-1) s(-1). The specific growth rate was significantly correlated to light intensity (y=0.721×x/(66.98+x), r(2)=0.85, p<0.05). A high specific growth rate was maintained over a range of light intensities (250-1000 μE m(-2) s(-1)). This range of light intensities suggested that effective production of C. zofingiensis can be maintained outdoors under strong light by using the optimum specific light intensity.
Influence of the labile organic fraction (LOF) on anaerobic digestion of food waste was investigated in different S/I ratio of 0.33, 0.5, 1.0, 2.0 and 4.0g-VSsubstrate/g-VSinoculum. Two types of substrate, standard food waste (Substrate 1) and standard food waste with the supernatant (containing LOF) removed (Substrate 2) were used. Highest methane yield of 435ml-CH4g-VS(-1) in Substrate 1 was observed in the lowest S/I ratio, while the methane yield of the other S/I ratios were 38-73% lower than the highest yield due to acidification. The methane yields in Substrate 2 were relatively stable in all S/I conditions, although the maximum methane yield was low compared with Substrate 1. These results showed that LOF in food waste causes acidification, but also contributes to high methane yields, suggesting that low S/I ratio (<0.33) is required to obtain a reliable methane yield from food waste compared to other organic substrates.
The recalcitrant landfill leachate was anaerobically digested at various mixing ratios with labile synthetic wastewater to evaluate the degradation properties of recalcitrant wastewater. The proportion of leachate to the digestion system was increased in three equal steps, starting from 0% to 100%, and later decreased back to 0% with the same steps. The chemical oxygen demand (COD) for organic carbon and other components were calculated by analyzing the COD and dissolved organic carbon (DOC), and the removal efficiencies of COD carbon and COD others were evaluated separately. The degradation properties of COD carbon and COD others shifted owing to changing of substrate degradability, and the removal efficiencies of COD carbon and COD others were improved after supplying 100% recalcitrant wastewater. The UV absorptive property and total organic carbon (TOC) of each molecular size using high performance liquid chromatography (HPLC)-size exclusion chromatography (SEC) with UVA and TOC detectors were also investigated, and the degradability of different molecular sizes was determined. Although the SEC system detected extracellular polymeric substances (EPS), which are produced by microbes in stressful environments, during early stages of the experiment, EPS were not detected after feeding 100% recalcitrant wastewater. These results suggest that the microbes had acclimatized to the recalcitrant wastewater degradation. The high removal rates of both COD carbon and COD others were sustained when the proportion of labile wastewater in the substrate was 33%, indicating that the effective removal of recalcitrant COD might be controlled by changing the substrate's degradability.
This review investigates the performance and the feasibility of the integration of an algal reactor in recirculating aquaculture systems (RAS). The number of studies related to this topic is limited, despite the apparent benefit of algae that can assimilate part of the inorganic waste in RAS. We identified two major challenges related to algal integration in RAS: first, the practical feasibility for improving nitrogen removal performance by algae in RAS; second, the economic feasibility of integrating an algal reactor in RAS. The main factors that determine high algal nitrogen removal rates are light and hydraulic retention time (HRT). Besides these factors, nitrogen-loading rates and RAS configuration could be important to ensure algal performance in nitrogen removal. Since nitrogen removal rate by algae is determined by HRT, this will affect the size (area or volume) of the algal reactor due to the time required for nutrient uptake by algae and large surface area needed to capture enough light. Constraints related to design, space, light capture, and reactor management could incur additional cost for aquaculture production. However, the increased purification of RAS wastewater could reduce the cost of water discharge in places where this is subject to levees. We believe that an improved understanding of how to manage the algal reactor and technological advancement of culturing algae, such as improved algal reactor design and low-cost artificial light, will increase the practical and economic feasibility of algal integration in RAS, thus improving the potential of mass cultivation of algae in RAS.
Chlorella can produce an unusually wide range of metabolites under various nutrient availability, carbon source, and light availability. Glucose, an essential molecule for the growth of microorganisms, also contributes significantly to the metabolism of various metabolic compounds produced by Chlorella. In addition, manipulation of light intensity also induces the formation of secondary metabolites such as pigments, and carotenoids in Chlorella. This study will focus on the effect of glucose addition, and moderate light on the regulation of carotenoid, lipid, starch, and other key metabolic pathways in Chlorella sorokiniana. To gain knowledge about this, we performed transcriptome profiling on C. sorokiniana strain NIES-2168 in response to moderate light stress supplemented with glucose under mixotrophic conditions. A total of 60,982,352 raw paired-end (PE) reads 100 bp in length was obtained from both normal, and mixotrophic samples of C. sorokiniana. After pre-processing, 93.63% high-quality PE reads were obtained, and 18,310 predicted full-length transcripts were assembled. Differential gene expression showed that a total of 937, and 1124 genes were upregulated, and downregulated in mixotrophic samples, respectively. Transcriptome analysis revealed that the mixotrophic condition caused upregulation of genes involved in carotenoids production (specifically lutein biosynthesis), fatty acid biosynthesis, TAG accumulation, and the majority of the carbon fixation pathways. Conversely, starch biosynthesis, sucrose biosynthesis, and isoprenoid biosynthesis were downregulated. Novel insights into the pathways that link the enhanced production of valuable metabolites (such as carotenoids in C. sorokiniana) grown under mixotrophic conditions is presented.
The primary biological treatment method for organic sludge is composting and/or anaerobic digestion, but their product (compost or biogas) is of little economic benefit; therefore, an improved process to produce a high-value product is required to make sludge management more sustainable. Maximizing NH3 gas recovery during composting processes has the potential benefit of producing high-value microalgal biomass. However, the majority of produced ammonia does not evaporate as NH3 gas but retains as NH4+-N in the compost after fermentation. The present study investigates the effects of the timing of Ca(OH)2 dosing (on days 2, 5, and 9), and the Ca(OH)2 dose (1.1-2.6 mmol/batch), on lab-scale thermophilic composting of anaerobic sludge. The effects on NH3 recovery, organic matter degradability, and microbial activity are evaluated. Ca(OH)2 dosing immediately improved the emission of NH3, with yields 50-69% higher than those under control conditions. The timing of the dosing did not influence NH3 recovery or organic matter degradability. Higher Ca(OH)2 doses resulted in higher NH3 recovery, while microbial activity was temporarily and marginally inhibited. The pH of the compost reached 10-11.5 but quickly dropped to 8-8.5 within a day, probably because of neutralization of Ca(OH)2 by the emitted CO2 and release of NH3, which maintained the microbial activity. The present study indicated that Ca(OH)2 dosing would be useful to apply during thermophilic composting for NH3 recovery to cultivate high-value microalgal biomass, which enables this process to obtain a more economic benefit.
Chlorella is a popular microalga with robust physiological and biochemical characteristics, which can be cultured under various conditions. The exploration of the small RNA content of Chlorella could improve strategies for the enhancement of metabolite production from this microalga. In this study, stress was introduced to the Chlorella sorokiniana culture to produce high-value metabolites such as carotenoids and phenolic content. The small RNA transcriptome of C. sorokiniana was sequenced, focusing on microRNA (miRNA) content. From the analysis, 98 miRNAs were identified in cultures subjected to normal and stress conditions. The functional analysis result showed that the miRNA targets found were most often involved in the biosynthesis of secondary metabolites, followed by protein metabolism, cell cycle, and porphyrin and chlorophyll metabolism. Furthermore, the biosynthesis of secondary metabolites such as carotenoids, terpenoids, and lipids was found mostly in stress conditions. These results may help to improve our understanding of regulatory mechanisms of miRNA in the biological and metabolic process of Chlorella species. It is important and timely to determine the true potential of this microalga species and to support the potential for genetic engineering of microalgae as they receive increasing focus for their development as an alternative source of biofuel, food, and health supplements.
Microalgae are promising candidate resources from marine ecology for health-improving effects. Metabolite profiling of the microalgal diatom, Chaetoceros calcitrans was conducted by using robust metabolomics tools, namely ¹H nuclear magnetic resonance (NMR) spectroscopy coupled with multivariate data analysis (MVDA). The unsupervised data analysis, using principal component analysis (PCA), resolved the five types of extracts made by solvents ranging from polar to non-polar into five different clusters. Collectively, with various extraction solvents, 11 amino acids, cholesterol, 6 fatty acids, 2 sugars, 1 osmolyte, 6 carotenoids and 2 chlorophyll pigments were identified. The fatty acids and both carotenoid pigments as well as chlorophyll, were observed in the extracts made from medium polar (acetone, chloroform) and non-polar (hexane) solvents. It is suggested that the compounds were the characteristic markers that influenced the separation between the clusters. Based on partial least square (PLS) analysis, fucoxanthin, astaxanthin, violaxanthin, zeaxanthin, canthaxanthin, and lutein displayed strong correlation to 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging and nitric oxide (NO) inhibitory activity. This metabolomics study showed that solvent extractions are one of the main bottlenecks for the maximum recovery of bioactive microalgal compounds and could be a better source of natural antioxidants due to a high value of metabolites.
Development of thermophilic composting for maximizing NH3 gas recovery would enable the production of a nitrogen source which is free from pathogen/heavy metal, for the cultivation of high-value microalgae. The present study examined the effect of NH3 recovery, nitrogen mass balance, and microbial community dynamics on thermophilic composting of shrimp aquaculture sludge. The emission of NH3 gas at 60 and 70 °C was 14.7% and 15.6%, respectively, which was higher than that at 50 °C (9.0%). The nitrogen mass balance analysis revealed that higher temperatures enhanced the solubilization of non-dissolved nitrogen and liberation of NH3 gas from the produced NH4+-N. High-throughput microbial community analysis revealed the shift of the dominant bacterial group from Bacillus to Geobacillus with the rise of composting temperature. In conclusion, thermophilic composting of shrimp aquaculture sludge at 60-70 °C was the most favorable condition for enhancing NH3 gas recovery.
The responses of two species of microalgae, Chlorella sorokiniana and Chlorella zofingiensis, were compared regarding their morphological and biochemical properties under photoautotrophic and mixotrophic conditions. These microalgae were cultured under both conditions, and their crude ethanolic extracts were examined for their pigment and total phenolic contents. In addition, the microalgae's antioxidant activities were determined using a DPPH radical scavenging assay and a ferric reducing antioxidant power (FRAP) assay. Both strains showed increases in cell size due to the accumulation of lipid bodies and other cell contents, especially carotenoids, under the mixotrophic condition. Notably, reductions in phenolic and chlorophyll contents were observed to be associated with lower antioxidant activity. C. zofingiensis compared with C. sorokiniana, demonstrated higher antioxidant activity and carotenoid content. This study showed that different species of microalgae responded differently to varying conditions by producing different types of metabolites, as evidenced by the production of higher levels of phenolic compounds under the photoautotrophic condition and the production of the same levels of carotenoids under both photoautotrophic and mixotrophic conditions.
Significantly high eicosapentaenoic acid (EPA) and fucoxanthin contents with high production rate were achieved in semi continuous culture of marine diatom. Effects of dilution rate on the production of biomass and high value biocompounds such as EPA and fucoxanthin were evaluated in semi-continuous cultures of Chaetoceros gracilis under high light condition. Cellular dry weight increased at lower dilution rate and higher light intensity conditions, and cell size strongly affected EPA and fucoxanthin contents. The smaller microalgae cells showed significantly higher (p < 0.05) value of 17.1 mg g-dw-1 fucoxanthin and 41.5% EPA content per total fatty acid compared to those observed in the larger cells. Chaetoceros gracilis can accumulate relatively higher EPA and fucoxanthin than those reported previously. In addition, maintenance of small cell size by supplying sufficient nutrients and light energy can be the key for the increase production of valuable biocompounds in C. gracilis.
Microalgae can use either ammonium or nitrate for its growth and vitality. However, at a certain level of concentration, ammonium nitrogen exhibits toxicity which consequently can inhibit microalgae productivity. Therefore, this study is aimed to investigate the tolerance of Tetraselmis tetrathele to high ammonium nitrogen concentrations and its effects on growth rate, photosynthetic efficiency (F v /F m ), pigment contents (chlorophyll a, lutein, neoxanthin, and β-carotene), and fatty acids production. Experiments were performed at different ammonium nitrogen concentrations (0.31-0.87 gL-1) for 6 days under a light source with an intensity of 300 μmol photons m-2 s-1 and nitrate-nitrogen source as the experimental control. The findings indicated no apparent enhancement of photosynthetic efficiency (Fv/Fm) at high levels of ammonium nitrogen (
-N) for T. tetrathele within 24 h. However, after 24 h, the photosynthetic efficiency of T. tetrathele increased significantly (p < 0.05) in high concentration of
-N. Chlorophyll a content in T. tetrathele grown in all of the different
-N levels increased significantly compared to nitrate-nitrogen (NO3-N) treatment (p < 0.05); which supported that this microalgal could grow even in high level of
-N concentrations. The findings also indicated that T. tetrathele is highly resistant to high ammonium nitrogen which suggests T. tetrathele to be used in the aquaculture industry for bioremediation purpose to remove ammonium nitrogen, thus reducing the production cost while improving the water quality.
We isolated fifty-two strains from the marine aquaculture ponds in Malaysia that were evaluated for their lipid production and ammonium tolerance and four isolates were selected as new ammonium tolerant microalgae with high-lipid production: TRG10-p102 Oocystis heteromucosa (Chlorophyceae); TRG10-p103 and TRG10-p105 Thalassiosira weissflogii (Bacillariophyceae); and TRG10-p201 Amphora coffeiformis (Bacillariophyceae). Eicosapentenoic acid (EPA) in three diatom strain was between 2.6 and 18.6 % of total fatty acids, which were higher than in O. heteromucosa. Only A. coffeiformi possessed arachidonic acid. Oocystis heteromucosa naturally grew at high ammonium concentrations (1.4-10 mM), whereas the growth of the other strains, T. weissflogii and A. coffeiformi, were visibly inhibited at high ammonium concentrations (>1.4 mM-NH4). However, two strains of T. weissflogii were able to grow at up to 10 mM-NH4 by gradually acclimating to higher ammonium concentrations. The ammonium tolerant strains, especially T. weissflogii which have high EPA contents, were identified as a valuable candidate for biomass production utilizing NH4-N media, such as ammonium-rich wastewater.
This study was designed to profile the metabolites of Isochrysis galbana, an indigenous and less explored microalgae species. 1H Nuclear Magnetic Resonance (NMR) spectroscopy and Liquid Chromatography-Mass Spectrometry (LCMS) were used to establish the metabolite profiles of five different extracts of this microalga, which are hexane (Hex), ethyl acetate (EtOAc), absolute ethanol (EtOH), EtOH:water 1:1 (AqE), and 100% water (Aq). Partial least square discriminant analysis (PLS-DA) of the generated profiles revealed that EtOAc and Aq extracts contain a diverse range of metabolites as compared to the other extracts with a total of twenty-one metabolites, comprising carotenoids, polyunsaturated fatty acids, and amino acids, that were putatively identified from the NMR spectra. Meanwhile, thirty-two metabolites were successfully annotated from the LCMS/MS data, ten of which (palmitic acid, oleic acid, α-linolenic acid, arachidic acid, cholesterol, DHA, DPA, fucoxanthin, astaxanthin, and pheophytin) were similar to those present in the NMR profile. Another eleven glycerophospholipids were discovered using MS/MS-based molecular network (MN) platform. The results of this study, besides providing a better understanding of I.galbana's chemical make-up, will be of importance in exploring this species potential as a feed ingredient in the aquaculture industry.