Microbial lipid production from xylose by Mortierella isabellina

Influence of Borassus flabellifer Endocarps Hydrolysate on Fungal Biomass and Fatty Acids Production by the Marine Fungus Aspergillus sp

Polyunsaturated Fatty Acids (PUFAs) are important nutrients for human health. We aimed to evaluate the efficiency of marine water fungus Aspergillus sp. (Accession no: MZ505709) for lipid biosynthesis. The Yeast Extract Glucose (YEG) medium was supplemented with different concentration of Borassus flabellifer Endocarps Hydrolysate (BFEH; 1-5%) to evaluate the fungal biomass and its lipid accumulation. The combination of glucose and BFEH as carbon source increased the fresh weight (25.43 ± 0.33 g/L), dry weight (21.39 ± 0.77 g/L) and lipid yield (3.14 ± 0.09 g/L) of fungal biomass. The lipid content of dried fungal biomass has shown 91.08 ± 5.07 mg cod liver oil equivalents/g and 125.98 ± 5.96 mg groundnut oil equivalents/g biomass. GC-MS and NMR spectrometry analysis revealed the compounds involved in fatty acid metabolism and lipid signaling pathways along with the presence of linolenic acid. Interestingly, fungus grown in BFEH enriched medium has recorded the maximum amount of lipids with major fatty acid derivatives. Increase in the growth rate of Artemia franciscana was observed, when the extracted fungal lipid was supplemented as a food supplement. Therefore, this study suggests that marine fungal lipid may serve as potential natural compound as nutraceuticals and aquafeeds.

Evaluation of cell disruption methods in the oleaginous yeasts Yarrowia lipolytica QU21 and Meyerozyma guilliermondii BI281A for microbial oil extraction

The interest for oleaginous yeasts has grown significantly in the last three decades, mainly due to their potential use as a renewable source of microbial oil or single cell oils (SCOs). However, the methodologies for cell disruption to obtain the microbial oil are considered critical and determinant for a large-scale production. Therefore, this work aimed to evaluate different methods for cell wall disruption for the lipid extraction of Yarrowia lipolytica QU21 and Meyerozyma guilliermondii BI281A. The two strains were separately cultivated in 5 L batch fermenters for 120 hours, at 26 ºC and 400 rpm. Three different lipid extraction processes using Turrax homogenizer, Ultrasonicator and Braun homogenizer combined with bead milling were applied in wet, oven-dried, and freeze-dried biomass of both strains. The treatment with the highest percentage of disrupted cells and highest oil yield was the ultrasonication of oven-dried biomass (37-40% lipid content for both strains). The fact that our results point to one best extraction strategy for two different yeast strains, belonging to different species, is a great news towards the development of a unified technique that could be applied at industrial plants.

Metabolic Regulation of Sugar Assimilation for Lipid Production in Aspergillus oryzae BCC7051 through Comparative Transcriptome Perspective

Simple Summary

Oleaginous fungi are a promising candidate to produce microbial lipids as alternative sources for industrial applications. As lipids are intracellular metabolites with dynamic traits, the fungal ability in utilizing carbon sources for biomass and lipid production is significant in terms of production yield and economic feasibility. This study aimed to explore the metabolic regulation in lipogenesis of oleaginous Aspergillus oryzae BCC7051 at the transcriptional level. Through comparative transcriptome analysis, a set of differentially expressed genes (DEGs) between the xylose- and glucose-grown cultures (C5 and C6 cultures) at fast-growing and lipid-accumulating stages were identified and functionally categorized into transporter proteins and cellular processes. Combining with the growth and lipid phenotypes, the transcriptome results pointed to a crucial link between sugar assimilation, energy, lipid, and other metabolisms in A. oryzae for leveraging the metabolic flux from xylose to fatty acid and lipid biosynthesis in render the oleaginous features. This study provides a remarkable insight in guiding strain optimization and bioprocess development using renewable feedstocks from agroindustrial residues.

Abstract

Microbial lipid production with cost effectiveness is a prerequisite for the oleochemical sector. In this work, genome-wide transcriptional responses on the utilization of xylose and glucose in oleaginous Aspergillus oryzae were studied with relation to growth and lipid phenotypic traits. Comparative analysis of the active growth (t1) and lipid-accumulating (t2) stages showed that the C5 cultures efficiently consumed carbon sources for biomass and lipid production comparable to the C6 cultures. By pairwise comparison, 599 and 917 differentially expressed genes (DEGs) were identified in the t1 and t2 groups, respectively, in which the consensus DEGs were categorized into polysaccharide-degrading enzymes, membrane transports, and cellular processes. A discrimination in transcriptional responses of DEGs set was also found in various metabolic genes, mostly in carbohydrate, amino acid, lipid, cofactors, and vitamin metabolisms. Although central carbohydrate metabolism was shared among the C5 and C6 cultures, the metabolic functions in acetyl-CoA and NADPH generation, and biosynthesis of terpenoid backbone, fatty acid, sterol, and amino acids were allocated for leveraging biomass and lipid production through at least transcriptional control. This study revealed robust metabolic networks in the oleaginicity of A. oryzae governing glucose/xylose flux toward lipid biosynthesis that provides meaningful hints for further process developments of microbial lipid production using cellulosic sugar feedstocks.

Enhancement of lipid productivity from a promising oleaginous fungus

Oleaginous fungi have recently gained increasing attention among different microorganisms due to their ability for lipid production for the preparation of biofuel. In the present study, a locally isolated fungus E45, identified genetically as Aspergillus sp. strain EM2018, was found to produce 25.2% of the total lipids content of its dry cell weight (DCW). Optimization of culture conditions was performed and lipid accumula­tion increased by about 2.4 fold (from 25.2% to 60.1% of DCW) when the fungus was grown for seven days in the potato dextrose (50 g/L) liquid medium at pH 5.0, incubation temperature at 30 ºC and inoculum size of 2 × 106 spore/mL. Supplementation of the medium with yeast extract and NaNO3 at a concentration of 0.05% as organic and inorganic nitrogen sources, respectively, increased lipid production (53.3% lipid/dry biomass). Gas chromatography analysis of fungal lipids revealed the presence of saturated (mainly palmitic acid C16:0 (33%) and lignoceric acid C24:0 (15%)) and unsaturated fatty acids in different proportions (mainly linoleic acid C18:2 (24.4%), oleica cid C18:1 (14%) and arachidonic C20:4 (7.4%). These findings suggest this new oleaginous fungus as a promising feedstock for various industrial applications and for the preparation of biodiesel.

Single-cell oil production by Mortierella isabellina DSM 1414 using different sugars as carbon source

Pure carbon sources, especially carbohydrates which are raw materials deriving from agro-industrial processes, are often used for small-scale single-cell oil production by fermentation. The aim of this study was to investigate the effects of different pure carbon sources on cell growth, lipid accumulation, and γ-linolenic acid (GLA) production by the filamentous fungus Mortierella isabellina DSM 1414 (Deutsche Sammlung von Mikroorganismen). The sugars utilized in this study are found extensively and abundantly in nature, especially in food raw materials and, in consequence, in agro-food industry wastes or surpluses. Thus, the potential of many waste materials containing these sugars to be used in the production of single-cell oil by fermentation could also be evaluated. The effects of the sugars utilized on cell growth, biomass production, and lipid production were investigated. Fatty acids were also analysed in the lipids produced at the end of the fermentations. Results showed that the maximum biomass production was 10.80 g/L in lactose-based media, while the maximum oil production was 5.44 g/L in maltose-based media. Oleic (20.42%-42.94%), palmitic (14.96%-22.19%), and stearic (9.00%-26.92%) acids were the major fatty acids along with linoleic acid (11.35%-18.67%) and GLA (3.56%-8.04%). The production of GLA as the target fatty acid was remarkable. This study indicates that agro-industrial waste including most of the sugars utilized (except for arabinose and sucrose with lipid production of 0.81 and 0.28 g/L, respectively) can be employed for production of single-cell oil by M. isabellina DSM 1414 which contains a high amount of GLA.

Non-conventional hosts for the production of fuels and chemicals

Biotechnology offers a green alternative for the production of fuels and chemicals using microbes. Although traditional model hosts such as Escherichia coli and Saccharomyces cerevisiae have been widely studied and used, they may not be the best hosts for industrial application. In this review, we explore recent advances in the use of nonconventional hosts for the production of a variety of fuel, cosmetics, perfumes, food, and pharmaceuticals. Specifically, we highlight twenty-seven popular molecules with a special focus on recent progress and metabolic engineering strategies to enable improved production of fuels and chemicals. These examples demonstrate the promise of nonconventional host engineering.

Biodiesels from microbial oils: Opportunity and challenges

Although biodiesel has been extensively explored as an important renewable energy source, the raw materials-associated cost poses a serious challenge on its large-scale commercial production. The first and second generations of biodiesel are mainly produced from usable raw materials, e.g. edible oils, crops etc. Such a situation inevitably imposes higher demands on land and water usage, which in turn compromise future food and water supply. Obviously, there is an urgent need to explore alternative feedstock, e.g. microbial oils which can be produced by many types of microorganisms including microalgae, fungi and bacteria with the advantages of small footprint, high lipid content and efficient uptake of carbon dioxide. Therefore, this review offers a comprehensive picture of microbial oil-based technology for biodiesel production. The perspectives and directions forward are also outlined for future biodiesel production and commercialization.

Microbial conversion of xylose into useful bioproducts

Microorganisms can produce a number of different bioproducts from the sugars in plant biomass. One challenge is devising processes that utilize all of the sugars in lignocellulosic hydrolysates. D-xylose is the second most abundant sugar in these hydrolysates. The microbial conversion of D-xylose to ethanol has been studied extensively; only recently, however, has conversion to bioproducts other than ethanol been explored. Moreover, in the case of yeast, D-xylose may provide a better feedstock for the production of bioproducts other than ethanol, because the relevant pathways are not subject to glucose-dependent repression. In this review, we discuss how different microorganisms are being used to produce novel bioproducts from D-xylose. We also discuss how D-xylose could be potentially used instead of glucose for the production of value-added bioproducts.

The isolation of pentose-assimilating yeasts and their xylose fermentation potential

For the implementation of cellulosic ethanol technology, the maximum use of lignocellulosic materials is important to increase efficiency and to reduce costs. In this context, appropriate use of the pentose released by hemicellulose hydrolysis could improve de economic viability of this process. Since the Saccharomyces cerevisiae is unable to ferment the pentose, the search for pentose-fermenting microorganisms could be an alternative. In this work, the isolation of yeast strains from decaying vegetal materials, flowers, fruits and insects and their application for assimilation and alcoholic fermentation of xylose were carried out. From a total of 30 isolated strains, 12 were able to assimilate 30 g L⁻¹ of xylose in 120 h. The strain Candida tropicalis S4 produced 6 g L⁻¹ of ethanol from 56 g L⁻¹ of xylose, while the strain C. tropicalis E2 produced 22 g L⁻¹ of xylitol. The strains Candida oleophila G10.1 and Metschnikowia koreensis G18 consumed significant amount of xylose in aerobic cultivation releasing non-identified metabolites. The different materials in environment were source for pentose-assimilating yeast with variable metabolic profile.

Single cell oil production by Trichosporon cutaneum from steam-exploded corn stover and its upgradation for production of long-chain α,ω-dicarboxylic acids

BACKGROUND

Single cell oil (SCO) production from lignocelluloses by oleaginous microorganisms is still high in production cost, making the subsequent production of biofuels inviable economically in such an era of low oil prices. Therefore, how to upgrade the final products of lignocellulose-based bioprocess to more valuable ones is becoming a more and more important issue.

RESULTS

Differently sourced cellulases were compared in the enzymatic hydrolysis of the steam-exploded corn stover (SECS) and the cellulase from the mixed culture of Trichoderma reesei and Aspergillus niger was found to have the highest enzymatic hydrolysis yield 86.67 ± 4.06%. Three-stage enzymatic hydrolysis could greatly improve the efficiency of the enzymatic hydrolysis of SECS, achieving a yield of 74.24 ± 2.69% within 30 h. Different bioprocesses from SECS to SCO were compared and the bioprocess C with the three-stage enzymatic hydrolysis was the most efficient, producing 57.15 g dry cell biomass containing 31.80 g SCO from 327.63 g SECS. An efficient and comprehensive process from corn stover to long-chain α,ω-dicarboxylic acids (DCAs) was established by employing self-metathesis, capable of producing 6.02 g long-chain DCAs from 409.54 g corn stover and 6.02 g alkenes as byproducts.

CONCLUSIONS

On-site cellulase production by the mixed culture of T. reesei and A. niger is proven the most efficient in providing cellulase to the lignocellulose-based bioprocess. Three-stage enzymatic hydrolysis was found to have very good application value in SCO production by Trichosporon cutaneum from SECS. A whole process from corn stover to long-chain DCAs via a combination of biological and chemical approaches was successfully established and it is an enlightening example of the comprehensive utilization of agricultural wastes.

Microbial oil - A plausible alternate resource for food and fuel application

Microbes have recourse to low-priced substrates like agricultural wastes and industrial efflux. A pragmatic approach towards an emerging field- the exploitation of microbial oils for biodiesel production, pharmaceutical and cosmetic applications, food additives, biopolymer production will be of immense remunerative significance in the near future. Due to high free fatty acid, nutritive content and simpler solvent extraction processes of microbial oils with plant oil, microbial oils can back plant oils in food applications. The purpose of this review is to evaluate the opulence of lipid production in native and standard micro-organisms and also to emphasize the vast array of applications including food and fuel by obtaining maximum yield.

Utilization of xylose by engineered strains of Ashbya gossypii for the production of microbial oils

BACKGROUND

Ashbya gossypii is a filamentous fungus that is currently exploited for the industrial production of riboflavin. The utilization of A. gossypii as a microbial biocatalyst is further supported by its ability to grow in low-cost feedstocks, inexpensive downstream processing and the availability of an ease to use molecular toolbox for genetic and genomic modifications. Consequently, A. gossypii has been also introduced as an ideal biotechnological chassis for the production of inosine, folic acid, and microbial oils. However, A. gossypii cannot use xylose, the most common pentose in hydrolysates of plant biomass.

RESULTS

In this work, we aimed at designing A. gossypii strains able to utilize xylose as the carbon source for the production of biolipids. An endogenous xylose utilization pathway was identified and overexpressed, resulting in an A. gossypii xylose-metabolizing strain showing prominent conversion rates of xylose to xylitol (up to 97% after 48 h). In addition, metabolic flux channeling from xylulose-5-phosphate to acetyl-CoA, using aheterologous phosphoketolase pathway, increased the lipid content in the xylose-metabolizing strain a 54% over the parental strain growing in glucose-based media. This increase raised to 69% when lipid accumulation was further boosted by blocking the beta-oxidation pathway.

CONCLUSIONS

Ashbya gossypii has been engineered for the utilization of xylose. We present here a proof-of-concept study for the production of microbial oils from xylose in A. gossypii, thus introducing a novel biocatalyst with very promising properties in developing consolidated bioprocessing to produce fine chemicals and biofuels from xylose-rich hydrolysates of plant biomass.

Microbial oil production byMortierella isabellinafrom corn stover under different pretreatments

Mixed culture ofTrichoderma reeseiandAspergillus nigerwas employed to accomplish on-site cellulase production where cellulases were applied directly to the enzymatic hydrolysis of pretreated corn stover.

Ultrasound assisted extraction of food and natural products. Mechanisms, techniques, combinations, protocols and applications. A review

This review presents a complete picture of current knowledge on ultrasound-assisted extraction (UAE) in food ingredients and products, nutraceutics, cosmetic, pharmaceutical and bioenergy applications. It provides the necessary theoretical background and some details about extraction by ultrasound, the techniques and their combinations, the mechanisms (fragmentation, erosion, capillarity, detexturation, and sonoporation), applications from laboratory to industry, security, and environmental impacts. In addition, the ultrasound extraction procedures and the important parameters influencing its performance are also included, together with the advantages and the drawbacks of each UAE techniques. Ultrasound-assisted extraction is a research topic, which affects several fields of modern plant-based chemistry. All the reported applications have shown that ultrasound-assisted extraction is a green and economically viable alternative to conventional techniques for food and natural products. The main benefits are decrease of extraction and processing time, the amount of energy and solvents used, unit operations, and CO₂ emissions.

Production Strategies and Applications of Microbial Single Cell Oils

Polyunsaturated fatty acids (PUFAs) of the ω-3 and ω-6 class (e.g., α-linolenic acid, linoleic acid) are essential for maintaining biofunctions in mammalians like humans. Due to the fact that humans cannot synthesize these essential fatty acids, they must be taken up from different food sources. Classical sources for these fatty acids are porcine liver and fish oil. However, microbial lipids or single cell oils, produced by oleaginous microorganisms such as algae, fungi and bacteria, are a promising source as well. These single cell oils can be used for many valuable chemicals with applications not only for nutrition but also for fuels and are therefore an ideal basis for a bio-based economy. A crucial point for the establishment of microbial lipids utilization is the cost-effective production and purification of fuels or products of higher value. The fermentative production can be realized by submerged (SmF) or solid state fermentation (SSF). The yield and the composition of the obtained microbial lipids depend on the type of fermentation and the particular conditions (e.g., medium, pH-value, temperature, aeration, nitrogen source). From an economical point of view, waste or by-product streams can be used as cheap and renewable carbon and nitrogen sources. In general, downstream processing costs are one of the major obstacles to be solved for full economic efficiency of microbial lipids. For the extraction of lipids from microbial biomass cell disruption is most important, because efficiency of cell disruption directly influences subsequent downstream operations and overall extraction efficiencies. A multitude of cell disruption and lipid extraction methods are available, conventional as well as newly emerging methods, which will be described and discussed in terms of large scale applicability, their potential in a modern biorefinery and their influence on product quality. Furthermore, an overview is given about applications of microbial lipids or derived fatty acids with emphasis on food applications.

Single cell oil production by Mortierella isabellina from steam exploded corn stover degraded by three-stage enzymatic hydrolysis in the context of on-site enzyme production

Single cell oil (SCO), promising as alternative oil source, was produced from steam exploded corn stover (SECS) by Mortierella isabellina. Different bioprocesses from SECS to SCO were compared and the bioprocess C using the three-stage enzymatic hydrolysis was found to be the most efficient one. The bioprocess C used the lowest enzyme input 20FPIU cellulase/g glucan and the shortest time 222h, but produced 44.94g dry cell biomass and 25.77g lipid from 327.63g dry SECS. It had the highest lipid content 57.34%, and its productivities and yields were much higher than those of the bioprocess B and comparable to the bioprocess A, indicating that the three-stage enzymatic hydrolysis could greatly improve the efficiency of the bioprocess from high solid loading SECS to SCO by Mortierella isabellina. This work testified the application value of three-stage enzymatic hydrolysis in lignocellulose-based bioprocesses.

Microwave, ultrasound, thermal treatments, and bead milling as intensification techniques for extraction of lipids from oleaginous Yarrowia lipolytica yeast for a biojetfuel application

In the present work, two different ways of lipids extraction from Yarrowia lipolytica yeast were investigated in order to maximize the extraction yield. Firstly, various modern techniques of extraction including ultrasound, microwave, and bead milling were tested to intensify the efficiency of lipid recovery. Secondly, several pretreatments such as freezing/defrosting, cold drying, bead milling, and microwave prior two washing of mixture solvent of chloroform:methanol (1:2, v/v) were study to evaluate the impact on lipid recovery. All these treatments were compared to conventional maceration, in terms of lipids extraction yield and lipid composition analysis. The main result of this study is the large difference of lipid recovery among treatments and the alteration of lipids profile after microwave and ultrasound techniques.

Effect of media compositions on α-glucosidase inhibitory activity, growth and fatty acid content in mycelium extracts of Colletotrichum sp. TSC13 from Taxus Sumatrana (Miq.) de Laub

The active α-glucosidase inhibitor compounds in the endophytic fungus Colletotrichum sp. TSC13 were found to be the unsaturated fatty acids (oleic, linoleic and linolenic acids). These compounds have potential as antidiabetic agents. The aim of the present study is to investigate the effects of various media composition on growth (mycelium dry weight) and the fatty acids content (μg mg(-1) mycelium DW) of Colletotrichum sp. TSC13 in relation to its α-glucosidase inhibitory activity. For that purpose, the experiments were set up by varying the carbon and nitrogen sources, metal ions and desaturase and fatty acid synthase inhibitors in the media. Colletotrichum sp. TSC13 grown on potato dextrose broth (PDB) was used as control. The α-glucosidase inhibitory activities were (range from 43.9 ± 2.5 to 88.6 ± 5.2%) at 10 μg mL(-1). This activity seemed to correlate with the unsaturated fatty acids content of the samples. Different sugars as carbon source experiment showed that xylose gave the highest growth (938.7 ± 141.6 mg). However, the highest fatty acids content was obtained from fructose medium which containing linoleic acid (38.8 ± 4.9 μ g mg(-1) DW). Soluble starch gave better growth (672.5 ± 62.3 mg) but very low fatty acids content (2.8 ± 0.1 μg mg(-1) DW) was obtained. Yeast extract was the best nitrogen source. Fatty acids production was better as compared to beef extract and soytone. This is the first report of various media compositions on fatty acids content in Colletotrichum sp. TSC13 in relation to its α-glucosidase inhibitory activity.

New biofuel alternatives: integrating waste management and single cell oil production

Concerns about greenhouse gas emissions have increased research efforts into alternatives in bio-based processes. With regard to transport fuel, bioethanol and biodiesel are still the main biofuels used. It is expected that future production of these biofuels will be based on processes using either non-food competing biomasses, or characterised by low CO₂ emissions. Many microorganisms, such as microalgae, yeast, bacteria and fungi, have the ability to accumulate oils under special culture conditions. Microbial oils might become one of the potential feed-stocks for biodiesel production in the near future. The use of these oils is currently under extensive research in order to reduce production costs associated with the fermentation process, which is a crucial factor to increase economic feasibility. An important way to reduce processing costs is the use of wastes as carbon sources. The aim of the present review is to describe the main aspects related to the use of different oleaginous microorganisms for lipid production and their performance when using bio-wastes. The possibilities for combining hydrogen (H₂) and lipid production are also explored in an attempt for improving the economic feasibility of the process.

Cell mass energetic yields of fed-batch culture by Lipomyces starkeyi

Estimation of the energy capacity of a microbial cell mass on the basis of its lipid content and elemental composition can be used for the comparative evaluation of different microbial sources of biodiesel. Lipomyces starkeyi cell mass concentration reached 94.6 g/L with 37.4% of lipids in a fed-batch process using xylose and urea as substrates. The fatty acid composition of the yeast oil was quite similar to that of palm oil. L. starkeyi converted more than 80% of the energy contained in xylose into cell mass energy yield. The approach used in this study makes it possible to determine the energy of a cell mass by its elemental composition. A heat of combustion (Q c) of 25.7 (kJ/g) was obtained for the cell mass after 142 h of fed-batch cultivation, which represents approximately 56% of the energy content of diesel oil (45.4 kJ/g). The Q c of the triacylglycerols produced was 48.9 (kJ/g), indicating the potential of this oleaginous yeast for biodiesel production. Our work developed here provides a simple and efficient tool for characterization of this cell mass to further our understanding of its use as a feedstock for bioenergy production.

Quantitative assessment of the degree of lipid unsaturation in intact Mortierella by Raman microspectroscopy

Fungi of the genus Mortierella can accumulate large amounts of unusual lipids depending on species, strain, and growth conditions. Fast and easy determination of key parameters of lipid quality for these samples is required. In this contribution, we apply Raman microspectroscopy to determine the degree of unsaturation for fungal lipids directly inside intact hyphae without elaborate sample handling. Six Mortierella species were grown under varying conditions, and Raman spectra of single lipid vesicles were acquired. From the spectra, we calculate a peak intensity ratio I(1270 cm(-1))/I(1445 cm(-1)) from the signals of =CH and -CH2/-CH3 groups, respectively. This ratio is linked to the iodine value (IV) using spectra of reference compounds with known IV. IVs of fungal samples are compared to gas chromatography results. Values from both methods are in good accordance. Lipid composition is found to vary between the investigated species, with Mortierella alpina having the most unsaturated lipid (IV up to 280) and Mortierella exigua the least unsaturated (IV as low as 70). We find Raman microspectroscopy a suitable tool to determine the IV reliably, fast, and easily inside intact hyphae without extensive sample handling or treatment. The method can also be transferred to other microscopic samples.

Batch culture and repeated-batch culture of Cunninghamella bainieri 2A1 for lipid production as a comparative study

This research was performed based on a comparative study on fungal lipid production by a locally isolated strain Cunninghamella bainieri 2A1 in batch culture and repeated-batch culture using a nitrogen-limited medium. Lipid production in the batch culture was conducted to study the effect of different agitation rates on the simultaneous consumption of ammonium tartrate and glucose sources. Lipid production in the repeated-batch culture was studied by considering the effect of harvesting time and harvesting volume of the culture broth on the lipid accumulation. The batch cultivation was carried out in a 500 ml Erlenmeyer flask containing 200 ml of the fresh nitrogen-limited medium. Microbial culture was incubated at 30 °C under different agitation rates of 120, 180 and 250 rpm for 120 h. The repeated-batch culture was performed at three harvesting times of 12, 24 and 48 h using four harvesting cultures of 60%, 70%, 80% and 90%. Experimental results revealed that nitrogen source (ammonium tartrate) was fully utilized by C. bainieri 2A1 within 24 h in all agitation rates tested. It was also observed that a high amount of glucose in culture medium was consumed by C. bainieri 2A1 at 250 rpm agitation speed during the batch fermentation. Similar results showed that the highest lipid concentration of 2.96 g/L was obtained at an agitation rate of 250 rpm at 120 h cultivation time with the maximum lipid productivity of 7.0 × 10(-2) mg/ml/h. On the other hand, experimental results showed that the highest lipid concentration produced in the repeated-batch culture was 3.30 g/L at the first cycle of 48 h harvesting time using 70% harvesting volume, while 0.23 g/L gamma-linolenic acid (GLA) was produced at the last cycle of 48 h harvesting time using 80% harvesting volume.

Characterization of malic enzyme and the regulation of its activity and metabolic engineering on lipid production

Nowadays, microbial lipids are employed as the feedstock for biodiesel production, which has attracted great attention across the whole world.

Optimization of aeration and agitation rate for lipid and gamma linolenic acid production by Cunninghamella bainieri 2A1 in submerged fermentation using response surface methodology

The locally isolated filamentous fungus Cunninghamella bainieri 2A1 was cultivated in a 5 L bioreactor to produce lipid and gamma-linolenic acid (GLA). The optimization was carried out using response surface methodology based on a central composite design. A statistical model, second-order polynomial model, was adjusted to the experimental data to evaluate the effect of key operating variables, including aeration rate and agitation speed on lipid production. Process analysis showed that linear and quadratic effect of agitation intensity significantly influenced lipid production process (P < 0.01). The quadratic model also indicated that the interaction between aeration rate and agitation speed had a highly significant effect on lipid production (P < 0.01). Experimental results showed that a lipid content of 38.71% was produced in optimum conditions using an airflow rate and agitation speed of 0.32 vvm and 599 rpm, respectively. Similar results revealed that 0.058 (g/g) gamma-linolenic acid was produced in optimum conditions where 1.0 vvm aeration rate and 441.45 rpm agitation rate were used. The regression model confirmed that aeration and agitation were of prime importance for optimum production of lipid in the bioreactor.

Ultrasonication aided in-situ transesterification of microbial lipids to biodiesel

In-situ transesterification of microbial lipid to biodiesel has been paid substantial attention due to the fact that the lipid extraction and transesterification can be conducted in one-stage process. To improve the feasibility of in-situ transesterification, ultrasonication was employed to reduce methanol requirement and reaction time. The results showed that the use of ultrasonication could achieve high conversion of lipid to FAMEs (92.1% w lipid conversion/w total lipids) with methanol to lipid molar ratio 60:1 and NaOH addition 1% w/w lipid in 20 min, while methanol to lipid molar ratio 360:1, NaOH addition 1% w/w lipid, and reaction time 12h was required to obtain similar yield in in-situ transesterification without ultrasonication. The compositions of FAMEs obtained in case of ultrasonication aided in-situ transesterification were similar as that of two-stage extraction followed by transesterification processes.

Ultrasonication assisted lipid extraction from oleaginous microorganisms

Various solvents, including water, hexane, methanol, and chloroform/methanol (1:1 v/v), were tested to identify the efficiency of lipid extraction from Trichosporon oleaginosus and an oleaginous fungal strain SKF-5 under ultrasonication (520 kHz 40 W and 50 Hz 2800 W) and compared with the conventional chloroform methanol (2:1 v/v) extraction method. The highest lipid recovery 10.2% and 9.3% with water, 43.2% and 33.2% with hexane, 75.7% and 65.1% with methanol, 100% and 100% w/w biomass with chloroform/methanol were obtained from T. oleaginosus and SKF-5 strain, respectively, at ultrasonication frequency 50 Hz and power input 2800 W. Ultrasonication chloroform/methanol extraction recovered total lipid in a short time (15 min) and low temperature (25°C). Whereas the conventional chloroform methanol extraction to achieve total lipid recovery required 12h at 60°C. Ultrasonication chloroform/methanol extraction would be a promising method of lipid extraction from the microorganisms.