Breeding of high biomass and lipid producing Desmodesmus sp. by Ethylmethane sulfonate-induced mutation

Isolation and Whole-genome analysis of Desmodesmus sp. SZ-1: Novel acid-tolerant carbon-fixing microalga

Utilizing microalgae to capture flue gas pollutants is an effective strategy for mitigating greenhouse gas emissions. However, existing carbon-fixing microalgae exhibit poor tolerance towards acidic flue gas. In this study, the Desmodesmus sp. SZ-1, which can thrive in acidic environments and efficiently sequester CO2, was isolated. Desmodesmus sp. SZ-1 exhibited strong acid tolerance ability, with an average carbon fixation rate of 497.6 mg/L/d under 10 % CO2 and pH 3.5. Physiological analysis revealed that SZ-1 responded to high CO2 by increasing chlorophyll levels while coping with acidic stress by activating antioxidant enzymes. Genome analysis revealed a large number of carbon fixation and acid adaptation genes, involved in membrane lipid biosynthesis, H+ pumps, molecular chaperones, peroxidase system, amino acid synthesis, and carbonic anhydrase. This study provides a novel algal resource for mitigating acid gas emissions and a comprehensive genetic database for genetically modifying microalgae.

Screening of antibiotics to obtain axenic cell cultures of a marine microalga Chrysotila roscoffensis

Due to high growth rate, outstanding abiotic stress tolerance, and rich value-added substances, Chrysotila roscoffensis, belonging to the phylum of Haptophyta, can be considered as a versatile resource for industrial exploitation of bioactive compounds. However, the application potential of C. roscoffensis has drawn attention until just recently, and the understanding related to the biological properties of this species is still scarce. For example, the sensitivities of C. roscoffensis to antibiotics, which is essential for the verification of heterotrophic capacity and the establishment of efficient genetic manipulation system is still unavailable. Aiming to provide fundamental information for future exploitation, the sensitivities of C. roscoffensis to nine types of antibiotics were tested in this study. The results demonstrated that C. roscoffensis exhibited relatively high resistances to ampicillin, kanamycin, streptomycin, gentamicin, and geneticin, while was sensitive to bleomycin, hygromycin B, paromomycin, and chloramphenicol. Using the former five types of antibiotics, a bacteria removal strategy was established tentatively. Finally, the axenicity of treated C. roscoffensis was confirmed based on a multi-strategy method including solid plate, 16S rDNA amplification, and nuclear acid staining. This report can provide valuable information for the development of optimal selection markers, which are meaningful for more extensive transgenic studies in C. roscoffensis. Moreover, our study also paves the way for the establishment of heterotrophic/mixotrophic cultivation modes of C. roscoffensis.

Developing algae as a sustainable food source

Current agricultural and food production practices are facing extreme stress, posed by climate change and an ever-increasing human population. The pressure to feed nearly 8 billion people while maintaining a minimal impact on the environment has prompted a movement toward new, more sustainable food sources. For thousands of years, both the macro (seaweed and kelp) and micro (unicellular) forms of algae have been cultivated as a food source. Algae have evolved to be highly efficient at resource utilization and have proven to be a viable source of nutritious biomass that could address many of the current food production issues. Particularly for microalgae, studies of their large-scale growth and cultivation come from the biofuel industry; however, this knowledge can be reasonably translated into the production of algae-based food products. The ability of algae to sequester CO₂ lends to its sustainability by helping to reduce the carbon footprint of its production. Additionally, algae can be produced on non-arable land using non-potable water (including brackish or seawater), which allows them to complement rather than compete with traditional agriculture. Algae inherently have the desired qualities of a sustainable food source because they produce highly digestible proteins, lipids, and carbohydrates, and are rich in essential fatty acids, vitamins, and minerals. Although algae have yet to be fully domesticated as food sources, a variety of cultivation and breeding tools exist that can be built upon to allow for the increased productivity and enhanced nutritional and organoleptic qualities that will be required to bring algae to mainstream utilization. Here we will focus on microalgae and cyanobacteria to highlight the current advancements that will expand the variety of algae-based nutritional sources, as well as outline various challenges between current biomass production and large-scale economic algae production for the food market.

Advances in engineering algae for biofuel production

While algae demonstrate potential as a sustainable fuel source, low productivities limit the economic realization of algal biofuels. High-throughput strain engineering, omics-informed genome-scale modeling, and microbiome engineering are key technologies for enabling algal biofuels. High-throughput strain engineering efforts generate improved traits, including high biomass productivity and lipid content, in diverse algal species. Genome-scale models, constructed with the aid of omics data, provide insight into metabolic limitations and guide rational algal strain engineering efforts. As outdoor cultivation systems introduce exogenous organisms, microbiome engineering seeks to eliminate harmful organisms and introduce beneficial species. Optimizing algal biomass production and lipid content using these technologies may overcome the productivity barrier for the commercialization of algal biofuels.

Random Mutagenesis as a Promising Tool for Microalgal Strain Improvement towards Industrial Production

Microalgae have become a promising novel and sustainable feedstock for meeting the rising demand for food and feed. However, microalgae-based products are currently hindered by high production costs. One major reason for this is that commonly cultivated wildtype strains do not possess the robustness and productivity required for successful industrial production. Several strain improvement technologies have been developed towards creating more stress tolerant and productive strains. While classical methods of forward genetics have been extensively used to determine gene function of randomly generated mutants, reverse genetics has been explored to generate specific mutations and target phenotypes. Site-directed mutagenesis can be accomplished by employing different gene editing tools, which enable the generation of tailor-made genotypes. Nevertheless, strategies promoting the selection of randomly generated mutants avoid the introduction of foreign genetic material. In this paper, we review different microalgal strain improvement approaches and their applications, with a primary focus on random mutagenesis. Current challenges hampering strain improvement, selection, and commercialization will be discussed. The combination of these approaches with high-throughput technologies, such as fluorescence-activated cell sorting, as tools to select the most promising mutants, will also be discussed.

ARTP and NTG compound mutations improved Cry protein production and virulence of Bacillus thuringiensis X023

A high production mutated strain Bacillus thuringiensis X023PN (BtX023PN) was screened from the wild strain Bacillus thuringiensis X023 (BtX023) after atmospheric and room temperature plasma (ARTP) and nitrosoguanidine (NTG) mutation. BtX023PN grows faster than the wild strain, and its lysis of mother cell was 6 h ahead BtX023, but the ability of sporulation was significantly reduced. Bioassay indicated that compared with the wild type strain, the virulence of BtX023PN against Plutella xylostella (P. xylostella) and Mythimna seperata (M. seperata) increased to 2.33-fold and 2.13-fold respectively. qRT-PCR and SDS-PAGE demonstrated that the production of Cry1Ac increased by 61%. Resequence indicated that the mutated sites enriched on the key carbohydrate metabolism and amino acid metabolism. This study provides a new strain resource for the development of Bt insecticides and a feasible technical strategy for the breeding of Bt. KEY POINTS: • Atmospheric and room temperature plasma used in breeding of Bacillus thuringiensis. • Less stationary phase time with more ICP production. • Semi-lethal concentration against Plutella xylostella reduced by about 57.

Optimization of Lipid Production by Schizochytrium limacinum Biomass Modified with Ethyl Methane Sulfonate and Grown on Waste Glycerol

One of the most promising avenues of biofuel research relates to using waste as a starting feedstock to produce liquid or gaseous energy carriers. The global production of waste glycerol by the refinery industry is rising year after year. The aim of the present study was to examine the effect of ethyl methane sulfonate (EMS) on the growth rates and intracellular lipid accumulation in heterotrophically-cultured Schizochytrium limacinum microalgae, grown on waste glycerol as the carbon source. The strain S. limacinum E20, produced by incubating a reference strain in EMS for 20 min, was found to perform the best in terms of producing biomass (0.054 g_DW/dm³·h) and accumulating intracellular bio-oil (0.021 g/dm³·h). The selected parameters proved to be optimal for S. limacinum E20 biomass growth at the following values: temperature 27.3 °C, glycerol level 249.0 g/dm³, oxygen in the culture 26%, and yeast extract concentration 45.0 g/dm³. In turn, the optimal values for lipid production in an S. limacinum E20 culture were: temperature 24.2 °C, glycerol level 223.0 g/dm³, oxygen in the culture 10%, and yeast extract concentration 10.0 g/dm³. As the process conditions are different for biomass growth and for intracellular lipid accumulation, it is recommended to use a two-step culture process, which resulted in a lipid synthesis rate of 0.41 g/dm³·h.

Overexpression of fatty acid synthesis genes in Synechocystis sp. PCC 6803 with disrupted glycogen synthesis increases lipid production with further enhancement under copper induced oxidative stress

In the present study, fatty acid synthesis genes such as alpha and beta subunits of acetyl CoA carboxylase (accA and accD) were overexpressed in the glgC (Glucose-1-phosphate adenylyltransferase) knockout Synechocystis sp. PCC 6803. The biomass and lipid contents were evaluated in both the wild type and the engineered strains after copper treatment. The maximum lipid production of 0.981 g/L with the productivity of 81.75 mg/L/d was obtained from the copper treated ΔglgC + A-OX strain, which showed a 3.3-fold increase compared to the untreated wild type with satisfactory biodiesel properties. After copper treatment the knockout strain improved the unsaturated fatty acids level contributing to the increase of the saturated and mono-unsaturated ratio with improvement of the fuel quality. Copper induced oxidative stress also improved the photosynthetic pigments in engineered strains leading to increased tolerance against oxidative stress in the engineered strains. The copper treatment increased the antioxidant enzyme activities in the engineered strains especially in ΔglgC + A-OX strain. The carbon flux to lipid synthesis was enhanced by the engineered strains particularly with the knockout-overexpression strains. The Synechocystis sp. PCC 6803 engineered with ΔglgC + A-OX showed high potential for fuel production after the copper treatment.

Improving microalgae for biotechnology - From genetics to synthetic biology - Moving forward but not there yet

Microalgae are a diverse group of photosynthetic organisms that can be exploited for the production of different compounds, ranging from crude biomass and biofuels to high value-added biochemicals and synthetic proteins. Traditionally, algal biotechnology relies on bioprospecting to identify new highly productive strains and more recently, on forward genetics to further enhance productivity. However, it has become clear that further improvements in algal productivity for biotechnology is impossible without combining traditional tools with the arising molecular genetics toolkit. We review recent advantages in developing high throughput screening methods, preparing genome-wide mutant libraries, and establishing genome editing techniques. We discuss how algae can be improved in terms of photosynthetic efficiency, biofuel and high value-added compound production. Finally, we critically evaluate developments over recent years and explore future potential in the field.

Fourth generation biofuel from genetically modified algal biomass: Challenges and future directions

Genetic engineering applications in the field of biofuel are rapidly expanding due to their potential to boost biomass productivity while lowering its cost and enhancing its quality. Recently, fourth-generation biofuel (FGB), which is biofuel obtained from genetically modified (GM) algae biomass, has gained considerable attention from academic and industrial communities. However, replacing fossil resources with FGB is still beset with many challenges. Most notably, technical aspects of genetic modification operations need to be more fully articulated and elaborated. However, relatively little attention has been paid to GM algal biomass. There is a limited number of reviews on the progress and challenges faced in the algal genetics of FGB. Therefore, the present review aims to fill this gap in the literature by recapitulating the findings of recent studies and achievements on safe and efficient genetic manipulation in the production of FGB. Then, the essential issues and parameters related to genome editing in algal strains are highlighted. Finally, the main challenges to FGB pertaining to the diffusion risk and regulatory frameworks are addressed. This review concluded that the technical and biosafety aspects of FGB, as well as the complexity and diversity of the related regulations, legitimacy concerns, and health and environmental risks, are among the most important challenges that require a strong commitment at the national/international levels to reach a global consensus.

Synthesis, characterization and application of intracellular Ag/AgCl nanohybrids biosynthesized in Scenedesmus sp. as neutral lipid inducer and antibacterial agent

The current research focuses on the Intracellular biosynthesis of Ag/AgCl nanohybrids in microalgae, Scenedesmus sp. The effect of biosynthesis process on growth and lipid profile of cells is key element of this study. Ag/AgCl nanohybrids synthesized intracellularly were characterized by UV-Vis spectrophotometer, Powder X-Ray Diffraction (P-XRD), Scanning Electron Microscopy (SEM), High Resolution Transmission Electron Microscopy (HRTEM). 10-20 nm and 10-50 nm sized spherical shaped nanoparticles of polycrystalline nature were grown using 0.5 and 1 mM of AgNO₃ precursor, respectively and Scenedesmus sp. as reducing agent. Total lipid content of the cells treated with 0.5 mM and 1 mM AgNO₃ was static and found to be 43.2 ± 0.01 μg/mL and 48.2 ± 0.02 μg/mL respectively at 120 h of Ag/AgCl nanoparticles biosynthesis. FAME (Fatty Acid Methyl Ester) profile was improved due to intracellular nanoparticles biosynthesis with maximum C16:0 (palmitic acid) (35.7%) in cells treated with 0.5 mM AgNO₃ used for Ag/AgCl nanohybrids synthesis. Palmitic acid in cells exposed to 0.5 mM concentration of metallic precursor increased by 75.86%. Synthesized nanoparticles were tested on four bacterial strains to establish its antibacterial efficiency showing appropriate zone of inhibition at varying concentrations. Present study efficiently demonstrates the utility of microalgae integrating nanoparticles biosynthesis and lipid accumulation.

Enhancing carbohydrate repartitioning into lipid and carotenoid by disruption of microalgae starch debranching enzyme

Light/dark cycling is an inherent condition of outdoor microalgae cultivation, but is often unfavorable for lipid accumulation. This study aims to identify promising targets for metabolic engineering of improved lipid accumulation under outdoor conditions. Consequently, the lipid-rich mutant Chlamydomonas sp. KOR1 was developed through light/dark-conditioned screening. During dark periods with depressed CO₂ fixation, KOR1 shows rapid carbohydrate degradation together with increased lipid and carotenoid contents. KOR1 was subsequently characterized with extensive mutation of the ISA1 gene encoding a starch debranching enzyme (DBE). Dynamic time-course profiling and metabolomics reveal dramatic changes in KOR1 metabolism throughout light/dark cycles. During light periods, increased flux from CO₂ through glycolytic intermediates is directly observed to accompany enhanced formation of small starch-like particles, which are then efficiently repartitioned in the next dark cycle. This study demonstrates that disruption of DBE can improve biofuel production under light/dark conditions, through accelerated carbohydrate repartitioning into lipid and carotenoid.

Metabolic Engineering for Carotenoid Production Using Eukaryotic Microalgae and Prokaryotic Cyanobacteria

Eukaryotic microalgae and prokaryotic cyanobacteria are diverse photosynthetic organisms that produce various useful compounds. Due to their rapid growth and efficient biomass production from carbon dioxide and solar energy, microalgae and cyanobacteria are expected to become cost-effective, sustainable bioresources in the future. These organisms also abundantly produce various carotenoids, but further improvement in carotenoid productivity is needed for a successful commercialization. Metabolic engineering via genetic manipulation and mutational breeding is a powerful tool for generating carotenoid-rich strains. This chapter focuses on carotenoid production in microalgae and cyanobacteria, as well as strategies and potential target genes for metabolic engineering. Recent achievements in metabolic engineering that improved carotenoid production in microalgae and cyanobacteria are also reviewed.

Harnessing the Power of Mutagenesis and Adaptive Laboratory Evolution for High Lipid Production by Oleaginous Microalgae and Yeasts

Oleaginous microalgae and yeasts represent promising candidates for large-scale production of lipids, which can be utilized for production of drop-in biofuels, nutraceuticals, pigments, and cosmetics. However, low lipid productivity and costly downstream processing continue to hamper the commercial deployment of oleaginous microorganisms. Strain improvement can play an essential role in the development of such industrial microorganisms by increasing lipid production and hence reducing production costs. The main means of strain improvement are random mutagenesis, adaptive laboratory evolution (ALE), and rational genetic engineering. Among these, random mutagenesis and ALE are straight forward, low-cost, and do not require thorough knowledge of the microorganism’s genetic composition. This paper reviews available mutagenesis and ALE techniques and screening methods to effectively select for oleaginous microalgae and yeasts with enhanced lipid yield and understand the alterations caused to metabolic pathways, which could subsequently serve as the basis for further targeted genetic engineering.

The Use of Urea and Kelp Waste Extract is A Promising Strategy for Maximizing the Biomass Productivity and Lipid Content in Chlorella sorokiniana

The decline in fossil fuel reserves has forced researchers to seek out alternatives to fossil fuels. Microalgae are considered to be a promising feedstock for sustainable biofuel production. Previous studies have shown that urea is an important nitrogen source for cell growth and the lipid production of microalgae. The present study investigated the effect of different concentrations of urea combined with kelp waste extract on the biomass and lipid content of Chlorella sorokiniana. The results revealed that the highest cell density, 20.36 × 107 cells-1, and maximal dry biomass, 1.70 g/L, were achieved in the presence of 0.5 g/L of urea combined with 8% kelp waste extract. Similarly, the maximum chlorophyll a, b and beta carotenoid were 10.36 mg/L, 7.05, and 3.01 mg/L, respectively. The highest quantity of carbohydrate content, 290.51 µg/mL, was achieved in the presence of 0.2 g/L of urea and 8% kelp waste extract. The highest fluorescence intensity, 40.05 × 107 cells-1, and maximum total lipid content (30%) were achieved in the presence of 0.1 g/L of urea and 8% kelp waste extract. The current study suggests that the combination of urea and kelp waste extract is the best strategy to enhance the biomass and lipid content in Chlorella sorokiniana.

A comprehensive review on cultivation and harvesting of microalgae for biodiesel production: Environmental pollution control and future directions

Biodiesel is one of the best promising candidates in response to the energy crisis, since it has the capability to minimize most of the environmental problems. Microalgae, as the feedstock of third-generation biodiesel, are considered as one of the most sustainable resources. However, microalgae production for biodiesel feedstock on a large scale is still limited, because of the influences of lipid contents, biomass productivities, lipid extraction technologies, the water used in microalgae cultivation and processes of biomass harvesting. This paper firstly reviews the recent advances in microalgae cultivation and growth processes. Subsequently, current microalgae harvesting technologies are summarized and flocculation mechanisms are analyzed, while the characteristics that the ideal harvesting methods should have are summarized. This review also summarizes the environmental pollution control performances and the key challenges in future. The key suggestions and conclusions in the paper can offer a promising roadmap for the cost-effective biodiesel production.

Development and characterization of a Nannochloropsis mutant with simultaneously enhanced growth and lipid production

BACKGROUND

The necessity to develop high lipid-producing microalgae is emphasized for the commercialization of microalgal biomass, which is environmentally friendly and sustainable. Nannochloropsis are one of the best industrial microalgae and have been widely studied for their lipids, including high-value polyunsaturated fatty acids (PUFAs). Many reports on the genetic and biological engineering of Nannochloropsis to improve their growth and lipid contents have been published.

RESULTS

We performed insertional mutagenesis in Nannochloropsis salina, and screened mutants with high lipid contents using fluorescence-activated cell sorting (FACS). We isolated a mutant, Mut68, which showed improved growth and a concomitant increase in lipid contents. Mut68 exhibited 53% faster growth rate and 34% higher fatty acid methyl ester (FAME) contents after incubation for 8 days, resulting in a 75% increase in FAME productivity compared to that in the wild type (WT). By sequencing the whole genome, we identified the disrupted gene in Mut68 that encoded trehalose-6-phosphate (T6P) synthase (TPS). TPS is composed of two domains: TPS domain and T6P phosphatase (TPP) domain, which catalyze the initial formation of T6P and dephosphorylation to trehalose, respectively. Mut68 was disrupted at the TPP domain in the C-terminal half, which was confirmed by metabolic analyses revealing a great reduction in the trehalose content in Mut68. Consistent with the unaffected N-terminal TPS domain, Mut68 showed moderate increase in T6P that is known for regulation of sugar metabolism, growth, and lipid biosynthesis. Interestingly, the metabolic analyses also revealed a significant increase in stress-related amino acids, including proline and glutamine, which may further contribute to the Mut68 phenotypes.

CONCLUSION

We have successfully isolated an insertional mutant showing improved growth and lipid production. Moreover, we identified the disrupted gene encoding TPS. Consistent with the disrupted TPP domain, metabolic analyses revealed a moderate increase in T6P and greatly reduced trehalose. Herein, we provide an excellent proof of concept that the selection of insertional mutations via FACS can be employed for the isolation of mutants with improved growth and lipid production. In addition, trehalose and genes encoding TPS will provide novel targets for chemical and genetic engineering, in other microalgae and organisms as well as Nannochloropsis.

Isolation and Characterization of Two Microalgal Isolates from Vietnam with Potential for Food, Feed, and Biodiesel Production

Microalgae are promising feedstock for the production of biodiesel and diverse medium- and high-value products such as pigments and polyunsaturated fatty acids. The importance of strain selection adapted to specific environments is important for economical purposes. We characterize here two microalgal strains, isolated from wastewater of shrimp cultivation ponds in Vietnam. Based on the 18S rDNA-ITS region, one strain belongs to the Eustigmatophyceae class and is identical to the Nannochloropsis salina isolate D12 (JX185299.1), while the other is a Chlorophyceae belonging to the Desmodesmus genus, which possesses a S516 group I intron in its 18S rDNA gene. The N. salina strain is a marine and oleaginous microalga (40% of dry weight (DW) at stationary phase) whole oil is rich in saturated fatty acids (around 45% of C16:0) suitable for biodiesel and contains a few percent of eicosapentaenoic acid (C20:5). The Desmodesmus isolate can assimilate acetate and ammonium and is rich in lutein. Its oil contains around 40%–50% α-linolenic acid (C18:3), an essential fatty acid. Since they tolerate various salinities (10% to 35‰), both strains are thus interesting for biodiesel or aquaculture valorization in coastal and tropical climate where water, nutrient, and salinity availability vary greatly depending on the season.

Effects of nitrogen concentration on growth, biomass, and biochemical composition of Desmodesmus communis (E. Hegewald) E. Hegewald

Nitrogen, being one of the building blocks of biomacromolecules, is an important nutrient for microalgae growth. Nitrogen availability alters the growth and biochemical composition of microalgae. We investigated the effects of different nitrogen concentrations on specific growth rate (SGR), biomass productivity (BP), total protein and lipid content and amino acid and fatty acid composition of Desmodesmus communis. Nitrogen deficiency increased algal growth and changed the lipid amount and composition. The maximum growth and BP were detected in 75% N-medium. The highest total protein and lipid amount were detected in 50% N- and 75% N-media, respectively. Amino acid and fatty acid compositions of samples varied widely depending on the nutrient concentrations. The amount of unsaturated fatty acid (USFAs) was higher than saturated fatty acid (SFAs) and Linolenic acid percentage is higher than the limit of European standards in all media. The data reported here provide important contributions how nitrogen scarcity and abundance affect the growth and biochemical content of microalgae and this information can further be utilized in culture optimization in studies aimed at microalgae production for biofuels.

Improving lipid production by strain development in microalgae: Strategies, challenges and perspectives

Over the past decade, the number of original articles and reviews presenting microalgae as a promising feedstock for biodiesel has increased tremendously. Many improvements of microalgae have been achieved through selection and strain development for industrial applications. However, the large-scale production of lipids for commercialization is not yet realistic because the production is still much more expensive than that of agricultural products. This review summarizes recent research on the induction of lipid biosynthesis in microalgae and the various strategies of genetic and metabolic engineering for enhancing lipid production. Strain engineering targets are proposed based on these strategies. To address current limitations of strain engineering for lipid production, this review provides insights on recent engineering strategies based on molecular tools and methods, and also discusses further perspectives.

Modification and improvement of microalgae strains for strengthening CO2 fixation from coal-fired flue gas in power plants

Biological CO₂ capture using microalgae is a promising new method for reducing CO₂ emission of coal-fired flue gas. The strain of microalgae used in this process plays a vital role in determining the rate of CO₂ fixation and characteristics of biomass production. High requirements are put forward for algae strains due to high CO₂ concentration and diverse pollutants in flue gas. CO₂ can directly diffuse into the cytoplasm of cells by extra- and intracellular CO₂ osmotic pressure under high CO₂ concentrations. The flue gas pollutants, such as SO_x, NO_x and fly ashes, have negative effects on the growth of microalgae. This work reviewed the state-of-the-art advances on microalgae strains used for CO₂ fixation, focusing on the modification and improvement of strains that are used for coal-fired flue gas. Methods such as genetic engineering, random mutagenesis, and adaptive evolution have the potential to facilitate photosynthesis, improve growth rate and reduce CO₂ emission.

Species disparity response to mutagenesis of marine yeasts for the potential production of biodiesel

BACKGROUND

Among the third-generation biodiesel feed stock, oleaginous marine yeasts are the least studied microorganisms for such purpose.

RESULTS

Wild strains yeasts were isolated from various Tunisian marine sources including fish waste (Candida tenuis CtTun15, Debaryomyces hansenii DhTun2015, Trichosporon asahii TaTun15 and Yarrowia lipolytica YlTun15) and seawater (Rhodotorula mucilaginosa RmTun15). Following incubation with ethyl methanesulfonate (EMS: 75 mM) for various periods of time (T15, T30, T45, T60 min), the cell viability of these strains responded differentially according to yeast species. For instance, mutated CtTun15 did not survive after 30 min of EMS treatment; higher resistances were observed in DhTun2015 (45 min), in YlTun15, RmTun15 and in TaTun15 (60 min) but with significant decreased cell viabilities (survival rate: 6.02, 3.16, 11.22, 11.58, 7.70%, respectively). For all surviving mutated strains, the optima of biomass and lipid yields were detected after 96 h in YPD culture; but derived from strains submitted to different period of EMS incubation. In most mutated strains, the maximum biomass (BP) and lipid (LP) productivities coincided and were observed after 30 min of EMS incubation. Only CtTun15 showed different optima of BP and LP (after 30 min and 15 min, respectively). The fatty acids (FA) compositions considered essential in the prediction of biodiesel criteria; were highly affected by EMS mutagenesis. Essentially, 30- and 45-min EMS incubation induced the highest levels of PUFA and MUFA in YlTun15, RmTun15 and TaTun15 with non-significant differences in the different times. However, CtTun15 and DhTun2015 mutant strains responded differently, with the highest levels of MUFA observed following 15 and 45 min; and that of PUFA after 30 and 45 min, respectively.

CONCLUSION

The methyl-esterification of FA from the three mutated yeast strains (30 min-YlTun15, RmTun15 and TaTun15) yielded biodiesel with physical proprieties consistent with the International Standard System. However, investigations are needed for up-scaling biodiesel production.

EMS-induced mutation followed by quizalofop-screening increased lipid productivity in Chlorella sp

The objective of this study was to enhance biomass and lipid productivity in Chlorella sp. isolate 6-4 by inducing mutagenesis with two growth inhibitors: the herbicide quizalofop-P-ethyl, a known inhibitor of acetyl-CoA carboxylase (ACCase) activity, and chemical mutagen, ethyl methanesulfonate (EMS), at different concentrations and length of times. The induced-mutagenized microalgae were screened on selective medium containing 10-100 µM quizalofop. The biomass yield, biomass productivity, lipid content, and lipid productivity of mutagenized microalgae were determined. The result showed that 100-200 mM EMS concentrations and 30 min incubation time were the most effective. Biomass yield and biomass productivity of the mutagenized microalgae E50-30-40, E100-60-40, and E100-30-60 were statistically significant higher than those of the wild type. The mutagenized microalgae E100-30-60 showed that the highest biomass yield and biomass productivity were 111 and 110% higher than the wild type, respectively (p < 0.01). Lipid content and lipid productivity of the mutagenized microalgae E200-30-40 were 59 and 53% significantly higher than the wild type, respectively. It should be noted that biomass productivity of the mutagenized microalgae E200-30-40 was not significantly different from E100-30-60, meaning that this microalga strain exhibited highest both biomass and lipid productivity. These results indicated that inducing mutagenesis by EMS subsequently screening by herbicide could lead to enhance biomass and lipid accumulation. Therefore, this methodology could be used for improvement microalgae for biofuel production.

Improvement on lipid production by Scenedesmus obliquus triggered by low dose exposure to nanoparticles

Carbon nanotubes (CNTs), α-Fe₂O₃ nanoparticles (nano Fe₂O₃) and MgO nanoparticles (nano MgO) were evaluated for the effects on algae growth and lipid production. Nano Fe₂O₃ promoted cell growth in the range of 0-20 mg·L^-1. CNTs, nano Fe₂O₃ and nano MgO inhibited cell growth of Scenedesmus obliquus at 10, 40 and 0.8 mg·L^-1 respectively. Neutral lipid and total lipid content increased with the increasing concentration of all tested nanoparticles. The maximum lipid productivity of cultures exposed to CNTs, nano Fe₂O₃ and nano MgO was observed at 5 mg·L^-1, 5 mg·L^-1 and 40 mg·L^-1, with the improvement by 8.9%, 39.6% and 18.5%. High dose exposure to nanoparticles limited increase in lipid productivity, possibly due to the repression on cell growth caused by nanoparticles-catalyzed reactive oxygen species (ROS) generation, finally leading to reduction in biomass and lipid production. Reduced accumulation of fatty acids of C18:3n3, C18:3n6 and C20:2 was observed in cells exposed to nanoparticles.

Improving of lipid productivity of the oleaginous microalgae Chlorella pyrenoidosa via atmospheric and room temperature plasma (ARTP)

In this study, an efficient screening program was established with ARTP. Five strains from oleaginous microalgae Chlorella pyrenoidosa were screened from mutant library after mutagenizing by ARTP. Among them, the optimal mutant strain was named as II-H6. In the BG11 medium, the OD₆₈₀ of II-H6 in stationary phase were increased by 32.08% than the original strain. Meanwhile, compared with the original strain, the dry weight and lipid productivity of II-H6 were increased by 22.07% and 16.85%, respectively. II-H6 showed a good genetic stability in BG11 medium and the optimum growth temperature and pH were 33°C and 9.0. 18S gene fragment length of II-H6 strain were 1886bp. Analysis of the gene fragment showed that the II-H6 strain had a close relationship to the original strain, and it belonged to the mutation within the genus Chlorella.

Augmented lipid accumulation in ethyl methyl sulphonate mutants of oleaginous microalga for biodiesel production

The aim of this work was to generate high lipid accumulating mutants of Chlorella minutissima (CM) using ethyl methyl sulphonate (EMS) as a random chemical mutagen. Amid the 5% surviving cells after exposure to EMS (2M), three fast growing mutants (CM2, CM5, CM7) were selected and compared with wild type for lipid productivity and biochemical composition. Among these mutants, CM7 showed the maximum biomass (2.4g/L) and lipid content (42%) as compared to wild type (1.5g/L; 27%). Further, the mutant showed high photosynthetic pigments with low starch content signifying the re-allocation of carbon flux to lipid. The obtained mutant showed no visible morphological changes in comparison to its WT. The fatty acid profile showed increase in monounsaturated fatty acids while decreased saturated and polyunsaturated fatty acids signifying good quality biodiesel. The mutant strain thus obtained can be optimized further and applied for enhanced biodiesel production.

Enhancement of lipid production in Scenedesmus sp. by UV mutagenesis and hydrogen peroxide treatment

The high potential UV mutagenized Scenedesmus sp. was obtained in which the cells had a higher biomass and lipid content than the wild type with an increase from 1.9 to 2.4g/L and from 40 to 55% of dry cell weight respectively after 12days. Oxidative stress imposed by H₂O₂ treatment decreased the biomass of both the wild type and the mutant. The H₂O₂ treated mutant when grown in BG11 medium showed an increase in biomass which was in contrast to a decreased biomass observed in the H₂O₂ treated wild type. A 3-fold increase in lipid yield of 1.63g/L was obtained in the oxidative stress-induced mutant compared to the wild type. Overall results indicate that prior treatment of UV-mutagenized Scenedesmus with oxidative stress can increase the total lipid production which, due to its derived methyl ester having acceptable biodiesel properties, can be potentially utilized for biodiesel production.

Development of a Dunaliella tertiolecta Strain with Increased Zeaxanthin Content Using Random Mutagenesis

Zeaxanthin is a xanthophyll pigment that is regarded as one of the best carotenoids for the prevention and treatment of degenerative diseases. In the worldwide natural products market, consumers prefer pigments that have been produced from biological sources. In this study, a Dunaliella tertiolecta strain that has 10–15% higher cellular zeaxanthin content than the parent strain (zea1), was obtained by random mutagenesis using ethyl methanesulfonate (EMS) as a mutagen. This mutant, mp3, was grown under various salinities and light intensities to optimize culture conditions for zeaxanthin production. The highest cellular zeaxanthin content was observed at 1.5 M NaCl and 65–85 μmol photons·m⁻²·s⁻¹, and the highest daily zeaxanthin productivity was observed at 0.6 M NaCl and 140–160 μmol photons·m⁻²·s⁻¹. The maximal yield of zeaxanthin from mp3 in fed-batch culture was 8 mg·L⁻¹, which was obtained at 0.6 M NaCl and 140–160 μmol photons·m⁻²·s⁻¹. These results suggest that random mutagenesis with EMS is useful for generating D. tertiolecta strains with increased zeaxanthin content, and also suggest optimal culture conditions for the enhancement of biomass and zeaxanthin production by the zeaxanthin accumulating mutant strains.

Enhancement of Biomass and Lipid Productivities of Water Surface-Floating Microalgae by Chemical Mutagenesis

Water surface-floating microalgae have great potential for biofuel applications due to the ease of the harvesting process, which is one of the most problematic steps in conventional microalgal biofuel production. We have collected promising water surface-floating microalgae and characterized their capacity for biomass and lipid production. In this study, we performed chemical mutagenesis of two water surface-floating microalgae to elevate productivity. Floating microalgal strains AVFF007 and FFG039 (tentatively identified as Botryosphaerella sp. and Chlorococcum sp., respectively) were exposed to ethyl methane sulfonate (EMS) or 1-methyl-3-nitro-1-nitrosoguanidine (MNNG), and pale green mutants (PMs) were obtained. The most promising FFG039 PM formed robust biofilms on the surface of the culture medium, similar to those formed by wild type strains, and it exhibited 1.7-fold and 1.9-fold higher biomass and lipid productivities than those of the wild type. This study indicates that the chemical mutation strategy improves the lipid productivity of water surface-floating microalgae without inhibiting biofilm formation and floating ability.

Kelp waste extracts combined with acetate enhances the biofuel characteristics of Chlorella sorokiniana

To probe the effect of kelp waste extracts (KWE) combined with acetate on biochemical composition of Chlorella sorokiniana, the cultures were performed under independent/combined treatment of KWE and acetate. The results showed that high cell density and biomass were obtained by KWE combined with acetate treatments, whose biomass productivity increased by 79.69-102.57% and 20.04-35.32% compared with 3.0gL-1 acetate and KWE treatments respectively. The maximal neutral lipid per cell and lipid productivity were gained in KWE combined with 3.0gL-1 acetate treatment, which increased by 16.32% and 129.03% compared with 3.0gL-1 acetate, and 253.35% and 70.74% compared with KWE treatment. Meanwhile, C18:3n3 and C18:2n6c contents were reduced to 4.90% and 11.88%, whereas C16:0 and C18:1n9c were improved to 28.71% and 37.76%. Hence, supplementing appropriate acetate in KWE cultures is supposed to be a great potential method for large-scale cultivation of C. sorokiniana to generate biofuel.