Isolation and characterization of a novel thraustochytrid-like microorganism that efficiently produces docosahexaenoic acid

Sustainable and biotechnological production of docosahexaenoic acid from marine protists and slaughterhouse waste

Docosahexaenoic acid (DHA, 22:6n-3) is an essential omega-3 polyunsaturated fatty acid, abundant in the brain and eyes. DHA is crucial for maintaining the structural integrity and physiological functions of these vital organs. Within the brain, DHA is concentrated in the gray matter, synaptic membranes, and hippocampus. Likewise, in the eyes, substantial quantities can be found in the retina, with lower levels in the cornea and lens. Previous studies have outlined the potential for culturing marine heterotrophic protists in ways that provide cost-effective and sustainable DHA biosynthesis. Similarly, our previous work on repurposing slaughterhouse waste has highlighted this underutilized source of brain and ocular tissue, which can support the extraction of valuable nutrients such as DHA. In this review, we will examine the current state of the art related to DHA production from these two sources, explore potential applications, and outline the possible benefits that may be generated from our approaches, with an emphasis on ocular diseases.

Isolation and Characterization of Thraustochytrium Trk-23 Producing Docosahexaenoic Acid from North Kalimantan, Indonesia

<b>Background and Objective:</b> The mangrove forest located in Tarakan Bay, North Kalimantan Province, Indonesia is geographically distant from human settlement and industrial activities. Thus, it remains unaffected by the presence of human-generated waste and industrial pollutants. This study aims to isolate and characterize the microalgae Thraustochytrids from this location, which can produce docosahexaenoic acid (DHA, C22:6, n-3). It is anticipated that these microalgae possess the potential for commercial production of DHA. <b>Materials and Methods:</b> The fallen leaf sample was collected from the mangrove forest, then isolated and purified by scratching technique until a single colony state. The pure isolate then be identified by 18S rDNA. The sequences were then analyzed for similarities using the Basic Local Alignment Search Tool (BLAST). The phylogenetic trees were carried out using the MEGA 6 program. The choice of phylogenetic trees was based on maximum likelihood. <b>Results:</b> The identification 18S rDNA gene, a strain namely Trk-23, was identified as <i>Thraustochytrium</i> sp. In the optimization of the cell growth of this strain, it was found that <i>Thraustochytrium</i> Trk-23 has maximum growth at 6.0% glucose, 1.0% yeast extract and 50% natural seawater, at a pH of 5.0 and a temperature of 30°C. The maximum lipid content is 6.0 g and the DHA proportion is 41.6% of the total fatty acid content with a DHA yield is 2.5 g L¹. <b>Conclusion:</b> Some places in North Kalimantan are still free from industrial pollution and rich with <i>Thraustochytrium</i> sp., which is why it can find <i>Thraustochytrium</i> Trk-23. Due to its potency, <i>Thraustochytrium</i> Trk-23 is the promising candidate microalgae strain for producing DHA commercially.

Draft genome sequence of a docosahexaenoic-acid-producing marine protist, thraustochytrid strain 12B

We sequenced the draft genome of thraustochytrid strain 12B. This strain shows a high production of polyunsaturated fatty acids, such as docosahexaenoic acid. The draft genome sequence of approximately 65 Mbp will provide insights into metabolic engineering to improve the production of polyunsaturated fatty acids in the microorganism.

Chemical and Physical Culture Conditions Significantly Influence the Cell Mass and Docosahexaenoic Acid Content of Aurantiochytrium limacinum Strain PKU#SW8

Thraustochytrids are well-known unicellular heterotrophic marine protists because of their promising ability to accumulate docosahexaenoic acid (DHA). However, the implications of their unique genomic and metabolic features on DHA production remain poorly understood. Here, the effects of chemical and physical culture conditions on the cell mass and DHA production were investigated for a unique thraustochytrid strain, PKU#SW8, isolated from the seawater of Pearl River Estuary. All the tested fermentation parameters showed a significant influence on the cell mass and concentration and yield of DHA. The addition of monosaccharides (fructose, mannose, glucose, or galactose) or glycerol to the culture medium yielded much higher cell mass and DHA concentrations than that of disaccharides and starch. Similarly, organic nitrogen sources (peptone, yeast extract, tryptone, and sodium glutamate) proved to be beneficial in achieving a higher cell mass and DHA concentration. PKU#SW8 was found to grow and accumulate a considerable amount of DHA over wide ranges of KH2PO4 (0.125-1.0 g/L), salinity (0-140% seawater), pH (3-9), temperature (16-36 °C), and agitation (140-230 rpm). With the optimal culture conditions (glycerol, 20 g/L; peptone, 2.5 g/L; 80% seawater; pH 4.0; 28 °C; and 200 rpm) determined based on the shake-flask experiments, the cell mass and concentration and yield of DHA were improved up to 7.5 ± 0.05 g/L, 2.14 ± 0.03 g/L, and 282.9 ± 3.0 mg/g, respectively, on a 5-L scale fermentation. This study provides valuable information about the fermentation conditions of the PKU#SW8 strain and its unique physiological features, which could be beneficial for strain development and large-scale DHA production.

Cultivation and diversity analysis of novel marine thraustochytrids

Thraustochytrids are a group of unicellular marine heterotrophic protists, and have long been known for their biotechnological potentials in producing squalene, polyunsaturated fatty acids (PUFAs) and other bioactive products. There are less than a hundred known strains from diverse marine habitats. Therefore, the discovery of new strains from natural environments is still one of the major limitations for fully exploring this interesting group of marine protists. At present, numerous attempts have been made to study thraustochytrids, mainly focusing on isolating new strains, analyzing the diversity in specific marine habitats, and increasing the yield of bioactive substances. There is a lack of a systematic study of the culturable diversity, and cultivation strategies. This paper reviews the distribution and diversity of culturable thraustochytrids from a range of marine environments, and describes in detail the most commonly used isolation methods and the control of culture parameters. Furthermore, the perspective approaches of isolation and cultivation for the discovery of new strains are discussed. Finally, the future directions of novel marine thraustochytrid research are proposed. The ultimate goal is to promote the awareness of biotechnological potentials of culturable thraustochytrid strains in industrial and biomedical applications.

Isolation and optimization of a novel thraustochytrid strain for DHA rich and astaxanthin comprising biomass as aquafeed supplement

A marine organism, belonging to the Thraustochytrids family was isolated from mangroves of Mumbai, India. The isolated strain was identified as Aurantiochytrium limacinum by internal transcribed spacer sequence analysis. Optimization of process parameters yielded 14.47 g/L dry cell weight containing 55-58% oil in 3.5 days' cultivation on glucose, yeast extract, and peptone in the bioreactor. Docosahexaenoic acid (DHA) was found to be the dominant long-chain polyunsaturated fatty acid, accounting for 32-35% of total fatty acid content. The process parameter was tweaked to simultaneously synthesize astaxanthin along with DHA. The concurrent synthesis of DHA and astaxanthin-containing biomass establishes the isolated strain as a perfect choice for aquafeed. Accession number: NCBI accession number MN046792.

Isolation, Characterization and Biotechnological Potentials of Thraustochytrids from Icelandic Waters

The following study reports on the first thraustochytrid isolates identified from Iceland. They were collected from three different locations off the northern coast of the country (Location A, Skagaströnd; Location B, Hveravík; and Location C, Eyjafjör&eth;ur). Using 18S rDNA sequence analysis, isolates from Locations A and B were identified within the Thraustochytrium kinnei species while other isolates within the Sicyoidochytrium minutum species when compared to other known strains. Cells isolated from Locations A ( 2 . 10 ± 0 . 70 g/L) and B ( 1 . 54 ± 0 . 17 g/L) produced more biomass than the ones isolated from Location C ( 0 . 43 ± 0 . 02 g/L). This study offers the first-time examination of the utility of byproducts from fisheries as a nitrogen source in media formulation for thraustochytrids. Experiments showed that isolates produced more biomass (per unit of substrate) when cultured on nitrogen of marine ( 2 . 55 ± 0 . 74 g/L) as compared to of commercial origin (&nbsp; 1 . 06 ± 0 . 57 g/L). Glycerol ( 2 . 43 ± 0 . 56 g/L) was a better carbon source than glucose ( 1 . 84 ± 0 . 57 g/L) in growth studies. Fatty acid (FA) profiles showed that the isolates from Location C (S. minutum) had low ratios of monounsaturated ( 4 . 21 ± 2 . 96 % ) and omega-6 ( 0 . 68 ± 0 . 59 % ) FAs. However, the isolates also had high ratios of docosahexaenoic acid (DHA; 35 . 65 ± 1 . 73 % ) and total omega-3 FAs ( 40 . 39 ± 2 . 39 % ), indicating that they could serve as a source of marine oils for human consumption and in aquaculture feeds. The T. kinnei isolates from Location A could be used in biodiesel production due to their high ratios of monounsaturated ( 18 . 38 ± 6 . 27 % ) long chain ( 57 . 43 ± 8 . 27 % ) FAs.

Culturable Diversity and Lipid Production Profile of Labyrinthulomycete Protists Isolated from Coastal Mangrove Habitats of China

Labyrinthulomycete protists have gained significant attention in the recent past for their biotechnological importance. Yet, their lipid profiles are poorly described because only a few large-scale isolation attempts have been made so far. Here, we isolated more than 200 strains from mangrove habitats of China and characterized the molecular phylogeny and lipid accumulation potential of 71 strains. These strains were the closest relatives of six genera namely Aurantiochytrium, Botryochytrium, Parietichytrium, Schizochytrium, Thraustochytrium, and Labyrinthula. Docosahexaenoic acid (DHA) production of the top 15 strains ranged from 0.23 g/L to 1.14 g/L. Two labyrinthulid strains, GXBH-107 and GXBH-215, exhibited unprecedented high DHA production potential with content >10% of biomass. Among all strains, ZJWZ-7, identified as an Aurantiochytrium strain, exhibited the highest DHA production. Further optimization of culture conditions for strain ZJWZ-7 showed improved lipid production (1.66 g/L DHA and 1.68 g/L saturated fatty acids (SFAs)) with glycerol-malic-acid, peptone-yeast-extract, initial pH 7, 28 °C, and rotation rate 150 rpm. Besides, nitrogen source, initial pH, temperature, and rotation rate had significant effects on the cell biomass, DHA, and SFAs production. This study provides the identification and characterization of nearly six dozen thraustochytrids and labyrinthulids with high potential for lipid accumulation.

Improved production of docosahexaenoic acid in batch fermentation by newly-isolated strains of Schizochytrium sp. and Thraustochytriidae sp. through bioprocess optimization

Thraustochytrids, rich in docosahexaenoic acid (DHA, C22:6ω3), represent a potential source of dietary fatty acids. Yet, the effect of culture conditions on growth and fatty acid composition vary widely among different thraustochytrid strains. Two different thraustochytrid strains, Schizochytrium sp. PKU#Mn4 and Thraustochytriidae sp. PKU#Mn16 were studied for their growth and DHA production characteristics under various culture conditions. Although they exhibited similar fatty acid profiles, PKU#Mn4 seemed a good candidate for industrial DHA fermentation while PKU#Mn16 displayed growth tolerance to a wide range of process conditions. Relative DHA content of 48.5% and 49.2% (relative to total fatty acids), respectively, were achieved on glycerol under their optimal flask culture conditions. Maximum DHA yield (Yp/x) of 21.0% and 18.9% and productivity of 27.6 mg/L-h and 31.9 mg/L-h were obtained, respectively, in 5-L bioreactor fermentation operated with optimal conditions and dual oxygen control strategy. A 3.4- and 2.8-fold improvement of DHA production (g/L), respectively, was achieved in this study. Overall, our study provides the potential of two thraustochytrid strains and their culture conditions for efficient production of DHA-rich oil.

Technical difficulties and solutions of direct transesterification process of microbial oil for biodiesel synthesis

Microbial oils are considered as alternative to vegetable oils or animal fats as biodiesel feedstock. Microalgae and oleaginous yeast are the main candidates of microbial oil producers' community. However, biodiesel synthesis from these sources is associated with high cost and process complexity. The traditional transesterification method includes several steps such as biomass drying, cell disruption, oil extraction and solvent recovery. Therefore, direct transesterification or in situ transesterification, which combines all the steps in a single reactor, has been suggested to make the process cost effective. Nevertheless, the process is not applicable for large-scale biodiesel production having some difficulties such as high water content of biomass that makes the reaction rate slower and hurdles of cell disruption makes the efficiency of oil extraction lower. Additionally, it requires high heating energy in the solvent extraction and recovery stage. To resolve these difficulties, this review suggests the application of antimicrobial peptides and high electric fields to foster the microbial cell wall disruption.

Bacterial Long-Chain Polyunsaturated Fatty Acids: Their Biosynthetic Genes, Functions, and Practical Use

The nutritional and pharmaceutical values of long-chain polyunsaturated fatty acids (LC-PUFAs) such as arachidonic, eicosapentaenoic and docosahexaenoic acids have been well recognized. These LC-PUFAs are physiologically important compounds in bacteria and eukaryotes. Although little is known about the biosynthetic mechanisms and functions of LC-PUFAs in bacteria compared to those in higher organisms, a combination of genetic, bioinformatic, and molecular biological approaches to LC-PUFA-producing bacteria and some eukaryotes have revealed the notably diverse organization of the pfa genes encoding a polyunsaturated fatty acid synthase complex (PUFA synthase), the LC-PUFA biosynthetic processes, and tertiary structures of the domains of this enzyme. In bacteria, LC-PUFAs appear to take part in specific functions facilitating individual membrane proteins rather than in the adjustment of the physical fluidity of the whole cell membrane. Very long chain polyunsaturated hydrocarbons (LC-HCs) such as hentriacontanonaene are considered to be closely related to LC-PUFAs in their biosynthesis and function. The possible role of LC-HCs in strictly anaerobic bacteria under aerobic and anaerobic environments and the evolutionary relationships of anaerobic and aerobic bacteria carrying pfa-like genes are also discussed.

Recycling of lipid-extracted hydrolysate as nitrogen supplementation for production of thraustochytrid biomass

Efficient resource usage is important for cost-effective microalgae production, where the incorporation of waste streams and recycled water into the process has great potential. This study builds upon emerging research on nutrient recycling in thraustochytrid production, where waste streams are recovered after lipid extraction and recycled into future cultures. This research investigates the nitrogen flux of recycled hydrolysate derived from enzymatic lipid extraction of thraustochytrid biomass. Results indicated the proteinaceous content of the recycled hydrolysate can offset the need to supply fresh nitrogen in a secondary culture, without detrimental impact upon the produced biomass. The treatment employing the recycled hydrolysate with no nitrogen addition accumulated 14.86 g L(-1) of biomass in 141 h with 43.3 % (w/w) lipid content compared to the control which had 9.26 g L(-1) and 46.9 % (w/w), respectively. This improved nutrient efficiency and wastewater recovery represents considerable potential for enhanced resource efficiency of commercial thraustochytrid production.

Ubiquitous distribution of helmchrome in phototactic swarmers of the stramenopiles

Most swarmers (swimming cells) of the stramenopile group, ranging from unicellular protist to giant kelps (brown algae), have two heterogeneous flagella: a long anterior flagellum (AF) and a relatively shorter posterior flagellum (PF). These flagellated cells often exhibit phototaxis upon light stimulation, although the mechanism by which how the phototactic response is regulated remains largely unknown. A flavoprotein concentrating at the paraflagellar body (PFB) on the basal part of the PF, which can emit green autofluorescence under blue light irradiance, has been proposed as a possible blue light photoreceptor for brown algal phototaxis although the nature of the flavoprotein still remains elusive. Recently, we identified helmchrome as a PF-specific flavoprotein protein in a LC-MS/MS-based proteomics study of brown algal flagella (Fu et al. 2014). To verify the conservation of helmchrome, in the present study, the absence or presence and the localization of helmchrome in swarmers of various algal species were investigated. The results showed that helmchrome was only detected in phototactic swarmers but not the non-phototactic ones of the stramenopile group. Electron microscopy further revealed that the helmchrome detectable swarmers bear a conserved PFB-eyespot complex, which may serve as structural basis for light sensing. It is speculated that all three conserved properties: helmchrome, the PFB structure, and the eyespot apparatus, will be essential parts for phototaxis of stramenopile swarmers.

Exploring omega-3 fatty acids, enzymes and biodiesel producing thraustochytrids from Australian and Indian marine biodiversity

The marine environment harbours a vast diversity of microorganisms, many of which are unique, and have potential to produce commercially useful materials. Therefore, marine biodiversity from Australian and Indian habitat has been explored to produce novel bioactives, and enzymes. Among these, thraustochytrids collected from Indian habitats were shown to be rich in saturated fatty acids (SFAs) and monounsaturated fatty acids (MUFAs), together constituting 51-76% of total fatty acids (TFA). Indian and Australian thraustochytrids occupy separate positions in the dendrogram, showing significant differences exist in the fatty acid profiles in these two sets of thraustochytrid strains. In general, Australian strains had a higher docosahexaenoic acid (DHA) content than Indian strains with DHA at 17-31% of TFA. A range of enzyme activities were observed in the strains, with Australian strains showing overall higher levels of enzyme activity, with the exception of one Indian strain (DBTIOC-1). Comparative analysis of the fatty acid profile of 34 strains revealed that Indian thraustochytrids are more suitable for biodiesel production since these strains have higher fatty acids content for biodiesel (FAB, 76%) production than Australian thraustochytrids, while the Australian strains are more suitable for omega-3 (40%) production.

Biotechnological Production of Docosahexaenoic Acid Using Aurantiochytrium limacinum: Carbon Sources Comparison And Growth Characterization

Aurantiochytrium limacinum, a marine heterotrophic protist/microalga has shown interesting yields of docosahexaenoic acid (DHA) when cultured with different carbon sources: glucose, pure and crude glycerol. A complete study in a lab-scale fermenter allowed for the characterization and comparison of the growth kinetic parameters corresponding to each carbon source. Artificial Marine Medium (AMM) with glucose, pure and crude glycerol offered similar biomass yields. The net growth rates (0.10–0.12 h⁻¹), biomass (0.7–0.8 g cells/g Substrate) and product (0.14–0.15 g DHA/g cells) yields, as well as DHA productivity were similar using the three carbon sources. Viable potential applications to valorize crude glycerol are envisioned to avoid an environmental problem due to the excess of byproduct.

Impact of carbon and nitrogen feeding strategy on high production of biomass and docosahexaenoic acid (DHA) by Schizochytrium sp. LU310

A new isolated Schizochytrium sp. LU310 from the mangrove forest of Wenzhou, China, was found as a high producing microalga of docosahexaenoic acid (DHA). In this study, the significant improvements for DHA fermentation by the batch mode in the baffled flasks (i.e. higher oxygen supply) were achieved. By applied the nitrogen-feeding strategy in 1000 mL baffled flasks, the biomass, DHA concentration and DHA productivity were increased by 110.4%, 117.9% and 110.4%, respectively. Moreover, DHA concentration of 21.06 g/L was obtained by feeding 15 g/L of glucose intermittently, which was an increase of 41.25% over that of the batch mode. Finally, an innovative strategy was carried out by intermittent feeding carbon and simultaneously feeding nitrogen. The maximum DHA concentration and DHA productivity in the fed-batch cultivation reached to 24.74 g/L and 241.5 mg/L/h, respectively.

Long-chain polyunsaturated fatty acid sources and evaluation of their nutritional and functional properties

Recent studies have clearly shown the importance of polyunsaturated fatty acids (as essential fatty acids) and their nutritional value for human health. In this review, various sources, nutritional properties, and metabolism routes of long-chain polyunsaturated fatty acids (LC-PUFA) are introduced. Since the conversion efficiency of linoleic acid (LA) to arachidonic acid (AA) and also α-linolenic acid (ALA) to docosahexaenoic acid (DHA) and eicosatetraenoic acid (EPA) is low in humans, looking for the numerous sources of AA, EPA and EPA fatty acids. The sources include aquatic (fish, crustaceans, and mollusks), animal sources (meat, egg, and milk), plant sources including 20 plants, most of which were weeds having a good amount of LC-PUFA, fruits, herbs, and seeds; cyanobacteria; and microorganisms (bacteria, fungi, microalgae, and diatoms).

Pollen baiting facilitates the isolation of marine thraustochytrids with potential in omega-3 and biodiesel production

Marine heterotrophic microbes are capable of accumulating large amounts of lipids, omega-3 fatty acids, carotenoids, and have potential for biodiesel production. Pollen baiting using Pinus radiata pollen grain along with direct plating techniques were used in this study as techniques for the isolation of oil-producing marine thraustochytrid species from Queenscliff, Victoria, Australia. Thirteen isolates were obtained using either direct plating or using pine pollen, with pine pollen acting as a specific substrate for the surface attachment of thraustochytrids. The isolates obtained from the pollen baiting technique showed a wide range of docosahexaenoic acid (DHA) accumulation, from 11 to 41 % of total fatty acid content (TFA). Direct plating isolates showed a moderate range of DHA accumulation, from 19 to 25 % of TFA. Seven isolates were identified on the basis of 18S rRNA sequencing technique as Thraustochytrium species, Schizochytrium species, and Ulkenia species. Although both methods appear to result in the isolation of similar strains, pollen baiting proved to be a simpler method for the isolation of these relatively slow-growing organisms.

Biomass composition, lipid characterization, and metabolic profile analysis of the fed-batch fermentation process of two different docosahexanoic acid producing Schizochytrium sp. strains

Growth and fermentation characteristics, biomass composition, lipid characterization and metabolic profiling analysis of two different Schizochytrium sp. strains, the original strain and the industrial adaptive strain, were investigated in the fed-batch fermentation process. The final cell biomass, total lipids content, docosahexanoic acid (DHA) content and DHA productivity of the adaptive strain were much higher than those of the original strain. The metabolic distinctions which extensively existed between these two strains were revealed by the score plot of principal component analysis. In addition, potential biomarkers responsible for discriminating different strains were identified as myo-inositol, histidine, alanine, asparagine, cysteine, and oxalic acid. These findings provided new insights into the industrial strain screening and further improvement of DHA production by Schizochytrium sp.

Improvement of docosahexaenoic acid production on glycerol by Schizochytrium sp. S31 with constantly high oxygen transfer coefficient

Volumetric mass transfer coefficient (kLa) is a key fermentation parameter for the production of docosahexaenoic acid (DHA) from glycerol by Schizochytrium sp. S31. In order to elucidate the effects of kLa on the fermentations, both baffled and unbaffled flask cultures and fed-batch cultures were developed in present work. The results showed that high kLa could effectively increase the DHA concentration, DHA productivity and conversion yield (Yx/s, g/g). When kLa was set at 1802 ± 105 h(-1) in the fed-batch culture, DHA concentration was achieved at 28.93 g/L, DHA productivity at 301 mg/L/h and Yx/s at 0.44 ± 0.02 g/g, all of which were significantly higher than those in the previous similar studies.

Structural Confirmation of a Unique Carotenoid Lactoside, P457, in Symbiodinium sp. Strain nbrc 104787 Isolated from a Sea Anemone and its Distribution in Dinoflagellates and Various Marine Organisms

The molecular structure of the carotenoid lactoside P457, (3S,5R,6R,3'S,5'R,6'S)-13'-cis-5,6-epoxy-3',5'-dihydroxy-3-(β-d-galactosyl-(1→4)-β-d-glucosyl)oxy-6',7'-didehydro-5,6,7,8,5',6'-hexahydro-β,β-caroten-20-al, was confirmed by spectroscopic methods using Symbiodinium sp. strain NBRC 104787 cells isolated from a sea anemone. Among various algae, cyanobacteria, land plants, and marine invertebrates, the distribution of this unique diglycosyl carotenoid was restricted to free-living peridinin-containing dinoflagellates and marine invertebrates that harbor peridinin-containing zooxanthellae. Neoxanthin appeared to be a common precursor for biosynthesis of peridinin and P457, although neoxanthin was not found in peridinin-containing dinoflagellates. Fucoxanthin-containing dinoflagellates did not possess peridinin or P457; green dinoflagellates, which contain chlorophyll a and b, did not contain peridinin, fucoxanthin, or P457; and no unicellular algae containing both peridinin and P457, other than peridinin-containing dinoflagellates, have been observed. Therefore, the biosynthetic pathways for peridinin and P457 may have been coestablished during the evolution of dinoflagellates after the host heterotrophic eukaryotic microorganism formed a symbiotic association with red alga that does not contain peridinin or P457.

A fermentation strategy for producing docosahexaenoic acid in Aurantiochytrium limacinum SR21 and increasing C22:6 proportions in total fatty acid

During the fermentation process, dissolved oxygen values and carbon-to-nitrogen ratios are critical factors influencing DHA productivity. This study employed an intermittent oxygen feeding method to maintain a 50% dissolved oxygen level and produced a dissolved oxygen fluctuation environment to facilitate both Aurantiochytrium limacinum SR21 growth and lipid accumulation. Study results indicated that at a 1.25 C:N ratio and medium composition of 100gL(-1) glycerol, 40gL(-1) yeast extract, and 40gL(-1) peptone, A. limacinum SR21 achieved biomass at 61.76gL(-1), lipid content at 65.2%, DHA concentration at 20.3gL(-1), and DHA productivity at 122.62mgL(-1)h(-1), this result were better than most similar researches. Dissolved oxygen fluctuation environment also altered the fatty acid composition of A. limacinum SR21. In the late period of the fermentation process, C16:0 fatty acid ratios decreased significantly to below 5%, and C22:6 fatty acid ratios increased to 70%.

Development of a novel technique for axenic isolation and culture of thraustochytrids from New Zealand marine environments

AIMS

To maintain axenic cultures of commercially important thraustochytrids, a novel procedure was developed for the isolation of zoospores and sporangium from heterotrophic seawater samples and axenic culture on solid media.

METHODS AND RESULTS

Thraustochytrid cultures were isolated from Whangapoua Harbour in North East New Zealand and subjected to two antibiotic and antifungal treatment regimes designed to eliminate bacteria and fungi. Antibiotic trial 1 was designed to determine the appropriate combination of antibiotics (including streptomycin/penicillin, ampicillin, rifampicin, nalidixic acid, tetracycline, gentamicin and the antifungal agent nystatin). Antibiotic trial 2 determined the optimal dosing frequency and concentration of the antibiotics, and antifungal found to be the most promising in trial 1. Axenic cultures were then spread plated onto nutrient agar containing the optimal antibiotic cocktail, and pure thraustochytrid colonies were purified on solid media using standard microbiological techniques.

CONCLUSIONS

Removal of bacteria and fungi was best accomplished using a mixture of three antibiotics and one antifungal; rifampicin (300 mg l(-1)), streptomycin/penicillin (25 mg l(-1)) and nystatin (10 mg l(-1)) were incorporated in seawater samples and incorporated into cultures every 24 h for a minimum of 2 days.

SIGNIFICANCE AND IMPACT OF THE STUDY

The axenic isolation and culture of marine thraustochytrids from a marine habitat in New Zealand have significant implications for the biotechnological development of these potentially valuable protists. This method has global significance as it is reasonable to assume it could be used throughout the world to obtain axenic thraustochytrid cultures.

Production of lipids containing high levels of docosahexaenoic acid by a newly isolated microalga, Aurantiochytrium sp. KRS101

In the present study, a novel oleaginous Thraustochytrid containing a high content of docosahexaenoic acid (DHA) was isolated from a mangrove ecosystem in Malaysia. The strain identified as an Aurantiochytrium sp. by 18S rRNA sequencing and named KRS101 used various carbon and nitrogen sources, indicating metabolic versatility. Optimal culture conditions, thus maximizing cell growth, and high levels of lipid and DHA production, were attained using glucose (60 g l⁻¹) as carbon source, corn steep solid (10 g l⁻¹) as nitrogen source, and sea salt (15 g l⁻¹). The highest biomass, lipid, and DHA production of KRS101 upon fed-batch fermentation were 50.2 g l⁻¹ (16.7 g l⁻¹ day⁻¹), 21.8 g l⁻¹ (44% DCW), and 8.8 g l⁻¹ (40% TFA), respectively. Similar values were obtained when a cheap substrate like molasses, rather than glucose, was used as the carbon source (DCW of 52.44 g l⁻¹, lipid and DHA levels of 20.2 and 8.83 g l⁻¹, respectively), indicating that production of microbial oils containing high levels of DHA can be produced economically when the novel strain is used.

Enhancement of docosahexaenoic acid production by Schizochytrium sp. using a two-stage oxygen supply control strategy based on oxygen transfer coefficient

AIMS

To improve the yield and productivity of docosahexaenoic acid (DHA) by Schizochytrium sp. in terms of the analysis of microbial physiology.

METHODS AND RESULTS

A two-stage oxygen supply control strategy, aimed at achieving high concentration and high productivity of DHA, was proposed. At the first 40 h, K(L) a was controlled at 150·1 h(-1) to obtain high μ for cell growth, subsequently K(L) a was controlled at 88·5 h(-1) to maintain high q(p) for high DHA accumulation. Finally, the maximum lipid, DHA content and DHA productivity reached 46·6, 17·7 g l(-1) and 111 mg l(-1) h(-1), which were 43·83%, 63·88% and 32·14% over the best results controlled by constant K(L) a.

CONCLUSIONS

This paper described a two-stage oxygen supply control strategy based on the kinetic analysis for efficient DHA fermentation by Schizochytrium sp.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study showed the advantage of two-stage control strategy in terms of microbial physiology. As K(L) a is a scaling-up parameter, the idea developed in this paper could be scaled-up to industrial process and applied to other industrial biotechnological processes to achieve both high product concentration and high productivity.

Possible biosynthetic pathways for all cis-3,6,9,12,15,19,22, 25,28-hentriacontanonaene in bacteria

A very long chain polyunsaturated hydrocarbon, hentriacontanonaene (C31:9), was detected in an eicosapentaenoic acid (EPA)-producing marine bacterium, which was isolated from the mid-latitude seashore of Hokkaido, Japan, and was tentatively identified as mesophilic Shewanella sp. strain osh08 from 16S rRNA gene sequencing. The geometry and position of the double bonds in this compound were determined physicochemically to be all cis at positions 3, 6, 9, 12, 15, 19, 22, 25, and 28. Although C31:9 was detected in all of the seven EPA- or/and docosahexaenoic acid-producing bacteria tested, an EPA-deficient mutant (strain IK-1Delta8) of one of these bacteria had no C31:9. Strain IK-1Delta8 had defects in the pfaD gene, one of the five pfa genes responsible for the biosynthesis of EPA. Although Escherichia coli DH5alpha does not produce EPA or DHA inherently, cells transformed with the pfa genes responsible for the biosynthesis of EPA and DHA produced EPA and DHA, respectively, but not C31:9. These results suggest that the Pfa protein complex is involved in the biosynthesis of C31:9 and that pfa genes must not be the only genes responsible for the formation of C31:9. In this report, we determined for the first time the molecular structure of the C31:9 and discuss the possible biosynthetic pathways of this compound.

Thraustochytrid Marine Protists: production of PUFAs and Other Emerging Technologies

Thraustochytrids, the heterotrophic, marine, straminipilan protists, are now established candidates for commercial production of the omega-3 polyunsaturated fatty acid (omega-3 PUFA), docosahexaenoic acid (DHA), that is important in human health and aquaculture. Extensive screening of cultures from a variety of habitats has yielded strains that produce at least 50% of their biomass as lipids, and DHA comprising at least 25% of the total fatty acids, with a yield of at least 5 g L(-1). Most of the lipids occur as triacylglycerols and a lesser amount as phospholipids. Numerous studies have been carried out on salinity, pH, temperature, and media optimization for DHA production. Commercial production is based on a fed batch method, using high C/N ratio that favors lipid accumulation. Schizochytrium DHA is now commercially available as nutritional supplements for adults and as feeds to enhance DHA levels in larvae of aquaculture animals. Thraustochytrids are emerging as a potential source of other PUFAs such as arachidonic acid and oils with a suite of PUFA profiles that can have specific uses. They are potential sources of asataxanthin and carotenoid pigments, as well as other lipids. Genes of the conventional fatty acid synthesis and the polyketide-like PUFA synthesis pathways of thraustochytrids are attracting attention for production of recombinant PUFA-containing plant oils. Future studies on the basic biology of these organisms, including biodiversity, environmental adaptations, and genome research are likely to point out directions for biotechnology explorations. Potential areas include enzymes, polysaccharides, and secondary metabolites.

Accumulation of docosahexaenoic acid-rich lipid in thraustochytrid Aurantiochytrium sp. strain T66: effects of N and P starvation and O2 limitation

Aurantiochytrium sp. strain T66 was grown in batch bioreactor cultures in a defined glutamate- and glycerol-containing growth medium. Exponentially growing cells had a lipid content of 13% (w/w) of dry weight. A fattening of cells fed excess glycerol occurred in the post-exponential growth phase, after the medium was depleted of N or P. Lipid accumulation was also initiated by O2 limitation (below 1% of saturation). N starvation per se, or in combination with O2 limitation, gave the highest lipid content, i.e., 54% to 63% (w/w) of dry weight. The corresponding maximum culture density was 90 to 100 g/l dry biomass. The content of docosahexaenoic acid (22:6n-3) in N starved, well-oxygenated cells reached 29% (w/w) of total fatty acids but increased to 36% to 52% in O2-limited cells, depending on the time span of the limitation. O2-limited cells did not accumulate the monounsaturated fatty acids that were normally present. We inferred that the biological explanation is that O2 limitation hindered the O2-dependent desaturase(s) and favored the O2-independent polyunsaturated fatty acid synthase. The highest overall volumetric productivity of docosahexaenoic acid observed was 93 mg/l/h. Additionally, we present a protocol for quantitative lipid extraction, involving heat and protease treatment of freeze-dried thraustochytrids.

In vivo conversion of triacylglycerol to docosahexaenoic acid-containing phospholipids in a thraustochytrid-like microorganism, strain 12B

The thraustochytrid-like microorganism, strain 12B, cultivated in peptone, yeast extract, and 8% (w/v) glucose in 50% (v/v) seawater, accumulated docosahexaenoic acid (DHA)-rich triacylglycerol (TAG) at 67% of total lipid. When these TAG-accumulated cells were cultivated in glucose-deficient medium, dry cell weight (3 mg per ml culture) increased approximately 3-fold relative to baseline but the TAG/total lipid decreased to 5%. At the same time, the amount of phospholipid (5 mg) per whole culture also increased 3-fold. Hence, phospholipid/total lipid increased from 13% to 67%. High levels of DHA (more than 50% of total) were maintained in phosphatidylcholine.