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Given that vanadium is a valuable material, the implementation of vanadium recycling processes is thus necessary to enhance the element's value chain as well as minimize its undesirable environmental consequences. Among various remediation methods available, a biological method based on microalgal adsorption is known to be eco-friendly and calls for further investigations. Herein, we evaluated V2O5 adsorption efficiencies of four different microalgal strains: Nannochloropsis oculata, Heterocapsa circularisquama, Chattonella marina, and Chattonella antiqua. Inductively coupled plasma mass spectrometry (ICP-MS) data indicated that vanadium concentration in the culture medium of Nannochloropsis oculata was reduced from 4.61 ± 0.11 mg L−1 to 1.85 ± 0.21 mg L−1 after being exposed to V2O5 solution for 24 h, whereas the supernatants of the other three strains displayed no change in vanadium ion concentration. Therefore, our results indicated a strong potential of Nannochloropsis oculata for recycling vanadium with approximately 59.9% of vanadium ion removal efficiency. Furthermore, morphological observation of Nannochloropsis oculata using scanning electron microscopy (SEM) indicated that the cells were able to maintain their intact morphology even under the presence of high concentrations of heavy metals. Due to the high adsorption efficiency and robustness of Nannochloropsis oculata, the results collectively support it as a potential strain for V2O5 recovery. [ABSTRACT FROM AUTHOR]

In response to ambient hypertonicity, TonEBP (tonicity-responsive enhancer binding protein) stimulates certain genes including those encoding cytokines, transporters for organic solutes, and a molecular chaperone. TonEBP is regulated in a bidirectional manner, upregulated by an increase in ambient tonicity while downregulated by a decrease. To investigate the role of intracellular ionic strength in the activity of TonEBP, we subjected Madin-Darby canine kidney cells to a variety of conditions. Electron microprobe analysis was performed to measure intracellular electrolytes. Under conditions in which changes in cell volume were similar, TonEBP activity correlated with the intracellular ionic strength regardless of the external tonicity. On the other hand, inhibition of the [Na.sup.+]/[K.sup.+]-ATPase and high external [K.sup.+] concentration led to a decreased activity of TonEBP despite a marked increase in the intracellular ionic strength. Because isotonic swelling is known to occur under these conditions, these data suggest that dilution of the cytoplasmic constituents inhibits the activity of TonEBP. We conclude that intracellular ionic strength and water content are major factors that determine the activity of TonEBP. cell ionic strength; cell volume; organic osmolytes; heat shock protein 70; Madin-Darby canine kidney cells

Sugar refinery washing water (SRWW) contains abundant levels of carbon sources and lower levels of contaminants than other types of wastewater, which makes it ideal for heterotrophic cultivation of microalgae. Here, carbon sources in SRWW were utilized for conversion into the form of value-added docosahexaenoic acid (DHA) using Aurantiochytrium sp. KRS101. Since SRWW is not a defined medium, serial optimizations were performed to maximize the biomass, lipid, and DHA yields by adjusting the nutrient (carbon, nitrogen, and phosphorus) concentrations as well as the application of salt stress. Optimum growth performance was achieved with 30% dilution of SRWW containing a total organic carbon of 95,488 mg L−1. Increasing the nutrient level in the medium by supplementation of 9 g L−1 KH2PO4 and 20 g L−1 yeast extract further improved the biomass yield by an additional 14%, albeit at the expense of a decrease in the lipid content. Maximum biomass, lipid, and DHA yields (22.9, 6.33, and 2.03 g L−1, respectively) were achieved when 35 g L−1 sea salt was applied on a stationary phase for osmotic stress. These results demonstrate the potential of carbon-rich sugar refinery washing water for DHA production using Aurantiochytrium sp. KRS101 and proper cultivation strategy. [ABSTRACT FROM AUTHOR]

Ecological studies of microalgae have revealed their potential to co-exist in the natural environment. It provides an evidence of the symbiotic relationship of microalgae with other microorganisms. The symbiosis potential of microalgae is inherited with distinct advantages, providing a venue for their scale-up applications. The deployment of large-scale microalgae applications is limited due to the technical challenges such as slow growth rate, low metabolites yield, and high risk of biomass contamination by unwanted bacteria. However, these challenges can be overcome by exploring symbiotic potential of microalgae. In a symbiotic system, photosynthetic microalgae co-exist with bacteria, fungi, as well as heterotrophic microalgae. In this consortium, they can exchange nutrients and metabolites, transfer gene, and interact with each other through complex metabolic mechanism. Microalgae in this system, termed as a binary culture, are reported to exhibit high growth rate, enhanced bio-flocculation, and biochemical productivity without experiencing contamination. Binary culture also offers interesting applications in other biotechnological processes including bioremediation, wastewater treatment, and production of high-value metabolites. The focus of the study is to provide a perspective to enhance the understanding about microalgae binary culture. In this review, the mechanism of binary culture, its potential, and limitations are briefly discussed. A number of queries are evolved through this study, which needs to be answered by executing future research to assess the real potential of binary culture. [ABSTRACT FROM AUTHOR]

The commercial production of microalgae-derived docosahexaenoic acid (DHA) has been expanding due to several advantages of algal over fish oil produced DHA. While the DHA production technology from microalgae is already economically competitive, alternatives to pure glucose and yeast extract still need to be explored to reduce the costs and increase the profits further. In the present study, orange peel waste (OPW) and various nitrogen sources were investigated as alternative nutrient sources for the economic cultivation of Aurantiochytrium sp. KRS101. The utilization of orange peel extract (OPE) supplemented with NaNO 3 showed a higher DHA yield than that supplemented with NH 4 Cl or urea, and pH 5.5 was found to be the optimum initial condition for Aurantiochytrium sp. KRS101. OPE optimized with supplemental NaNO 3 (1.2 g/L) resulted in a DHA yield of 0.63 g/L, which was 2.5 fold greater than the yield obtained using a conventional basal medium containing a similar amount of total nitrogen and 67% greater total carbon sources. This result implied not only that the conventional use of glucose and yeast extract have lower efficiency levels during nutrient metabolism but also that the types of carbon and nutrient sources have a significant effect on the DHA yield. The addition of supplemental glucose further enhanced the biomass, fatty acid methyl esters (FAME), and DHA yields, which unveiled the high C:N ratio requirement of Aurantiochytrium sp. KRS101. These results suggest that the development and optimization of microalgae fermentation using OPE and NaNO 3 is a possible route for the economical production of DHA and for the additional utilization of food waste. [ABSTRACT FROM AUTHOR]

Algal biofuel feedstocks are excellent candidates for sustainable and eco-friendly fuels for the next generation, which can be improved by genetic modifications for their maximal production of biomaterials. However, currently available genetic modifications involve the introduction of foreign DNA into the algal genome, and this may face legal and public conflicts due to the risk of environmental, economic, and/or health problems. In this regard, we employed an old concept of crop improvement that has been accepted in the long history of agriculture, i.e. polyploidization. Polyploidization of crop plants has been selected fortuitously or intentionally not only for increased quality and/or quantity of products, but also for enhanced stress tolerance. We induced diploidy in the model algae Chlamydomonas by treating haploid cells with the microtubule inhibitor colcemid, and the resulting diploids were selected for increased colony size and neutral lipid contents. Two of the isolated diploid strains containing doubled DNA contents, named CMD ex1 and CMD ex4, were increased in their cell size and cellular weight. These diploids were excellent in coping with abiotic stresses, including nutritional, oxidative, and cold stresses. Under these conditions, the diploids accumulated two times more biomass and FAME yield compared to the control. To understand underlying mechanisms, we performed RNA-Seq analyses for the diploid under the cold stress. Transcriptomic analyses revealed that the diploids showed enhanced expression of genes involved in photosynthesis, energy metabolism, and translation as well as reduced starch metabolism. Overall, diploids of Chlamydomonas showed improvements including increased yields of biomass and FAME and enhanced stress tolerance compared to wild-type organisms. The results demonstrate that polyploidization can be utilized in industrial microalgae for the production of biofuels and other biomaterials not only on a laboratory scale but also in outdoor cultivation, where stress conditions are inevitable. [ABSTRACT FROM AUTHOR]

Abstract: We measured the growth of and lipid production by the model microalga Chlamydomonas reinhardtii under different phototrophic, heterotrophic, and mixotrophic conditions to determine the optimal conditions for growth and biodiesel production. In particular, we examined cell growth and yield of fatty acid methyl esters (FAMEs) when C. reinhardtii was cultured in the presence of different organic carbon sources (acetate, glucose, glycerol, and sucrose). C. reinhardtii grew under various conditions, but mixotrophic cultivation was best. The greatest biomass production (2.15gL−1 in 5days) and FAME yield (16.41% of biomass) were observed under mixotrophic cultivation with acetate (10gL−1). As an alternative to acetate, we additionally tested the use of volatile fatty acids (VFAs; acetic, propionic, and butyric acids), which can be inexpensively produced through fermentation of food waste. The highest FAME yield (19.02% of biomass) and biomass production (2.05gL−1 in 5days) were obtained with 5gL−1 of VFAs. This result indicates that VFAs can serve as an inexpensive alternative carbon source for maximizing lipid production in mixotrophic cultivation of C. reinhardtii. [Copyright &y& Elsevier]

Abstract: High-cost downstream process is a major bottleneck for producing microalgal biodiesel at reasonable price. Conventional lipid extraction process necessitates biomass drying process, which requires substantial amount of energy. In this regard, lipid extraction from wet biomass must be an attractive solution. However, it is almost impossible to recover lipid directly from wet microalgae with current technology. In this study, we conceived osmotic shock treatment as a novel method to extract lipid efficiently. Osmotic shock treatment was applied directly to wet Chlamydomonas reinhardtii biomass with water content >99%, along with both polar and non-polar organic solvents. Our results demonstrated that osmotic shock could increase lipid recovery approximately 2 times. We also investigated whether the presence of cell wall or different cell stages could have any impact on lipid recovery. Cell wall-less mutant stains and senescent cell phase could display significantly increased lipid recovery. Taken together, our results suggested that osmotic shock is a promising technique for wet lipid extraction from microalgal biomass and successfully determined that specific manipulation of biomass in certain cell phase could enhance lipid recovery further. [Copyright &y& Elsevier]