CA2078664A1 - Eicosapentaenioc acids and methods for their production - Google Patents

Eicosapentaenioc acids and methods for their production

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Publication number
CA2078664A1
CA2078664A1 CA002078664A CA2078664A CA2078664A1 CA 2078664 A1 CA2078664 A1 CA 2078664A1 CA 002078664 A CA002078664 A CA 002078664A CA 2078664 A CA2078664 A CA 2078664A CA 2078664 A1 CA2078664 A1 CA 2078664A1
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CA
Canada
Prior art keywords
diatoms
epa
nutrient solution
metasilicate
fermentor
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Abandoned
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CA002078664A
Other languages
French (fr)
Inventor
David John Kyle
Raymond Gladue
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Martek Corp
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Individual
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Publication date
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Publication of CA2078664A1 publication Critical patent/CA2078664A1/en
Abandoned legal-status Critical Current

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    • CCHEMISTRY; METALLURGY
    • C12BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12PFERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
    • C12P7/00Preparation of oxygen-containing organic compounds
    • C12P7/64Fats; Fatty oils; Ester-type waxes; Higher fatty acids, i.e. having at least seven carbon atoms in an unbroken chain bound to a carboxyl group; Oxidised oils or fats
    • C12P7/6436Fatty acid esters
    • C12P7/6445Glycerides
    • C12P7/6472Glycerides containing polyunsaturated fatty acid [PUFA] residues, i.e. having two or more double bonds in their backbone
    • AHUMAN NECESSITIES
    • A23FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
    • A23KFODDER
    • A23K20/00Accessory food factors for animal feeding-stuffs
    • A23K20/10Organic substances
    • A23K20/158Fatty acids; Fats; Products containing oils or fats
    • AHUMAN NECESSITIES
    • A23FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
    • A23KFODDER
    • A23K50/00Feeding-stuffs specially adapted for particular animals
    • A23K50/80Feeding-stuffs specially adapted for particular animals for aquatic animals, e.g. fish, crustaceans or molluscs
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61PSPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
    • A61P17/00Drugs for dermatological disorders
    • CCHEMISTRY; METALLURGY
    • C07ORGANIC CHEMISTRY
    • C07CACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C57/00Unsaturated compounds having carboxyl groups bound to acyclic carbon atoms
    • C07C57/02Unsaturated compounds having carboxyl groups bound to acyclic carbon atoms with only carbon-to-carbon double bonds as unsaturation
    • C07C57/03Monocarboxylic acids
    • CCHEMISTRY; METALLURGY
    • C12BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12NMICROORGANISMS OR ENZYMES; COMPOSITIONS THEREOF; PROPAGATING, PRESERVING, OR MAINTAINING MICROORGANISMS; MUTATION OR GENETIC ENGINEERING; CULTURE MEDIA
    • C12N1/00Microorganisms, e.g. protozoa; Compositions thereof; Processes of propagating, maintaining or preserving microorganisms or compositions thereof; Processes of preparing or isolating a composition containing a microorganism; Culture media therefor
    • C12N1/12Unicellular algae; Culture media therefor

Abstract

Abstract of the Invention This invention describes a process for producing single cell edible oils containing eicosapentaenoic acid (EPA) from heterotrophic diatoms. The diatoms are cultivated in a fermentor in a nutrient solution containing nitrogen and silicate. Depletion of the nitrogen followed by depletion of the silicate induces the diatoms to synthesize large quantities of edible oil containing EPA which subsequently is recovered.
The edible oil, and uses for it, also form parts of this invention as do mutant diatoms capable of producing large quantities of EPA.

Description

WOgl/l~27 PCT/US91/02052 207~

EICOSAPENTAENOIC ACIDS AND METHODS FOR THEIR PRODUCTION

Backqround of the Invention This invention relates to edible oils containing omega-3-fatty acids, in particular eicosapentaenoic acid (EPA). The invention also relates to methods of producing EPA in commercially viable yields.
Omega-3-fatty acids are known to be beneficial in reducing the incidence of coronary heart disease. The metabolism of omega-3-fatty acids is not understood.
Thus, although the~e acids are known to have beneficial effects, precise clinical dosages and efficacy are not known.
Omega-3-fatty acids, in~luding EPA, have been found in the oils of cold water marine fish. Indeed, this is the primary source of commercially available EPA. It is believed that the omega-3-fatty acids found in fish originate from phytoplankton which are at the base of the marine food chain. The belief is due to the fact that many phytoplankton species are found to contain reserves of oil containing varying amounts of EPA.
Certain marine microorganisms are known to contain EPA. For example, Yazawa et al., ~._IL~ , 103:5-7 (1988), found 88 strains of gram-negative bacteria which produced EPA. U.S. 4,615,839 (Seto et al.) discloses the cultivation of monocellular green algae in open pools followed by recovery of EPA from those microalgae.

~'-~ 91/1~27 PCT/US91/020~2 2 2 0 7~ fi g~

While omega-3-fatty acids are known to have medicinal utility, there are problems associated with their use. Because of their association with fi h oils, there is often a fishy odor and unpleasant taste associated with these acids. Additionally, although fish oils do contain EPA, many of these oils cannot be consumed by humans due to the presence of attendant contaminants, such as PCB, as well as a high concentration of oxidation-sensitive polyunsaturated fatty acids, some of which exhibit bioactivities which are different from, and even antagonistic to, EPA.
Furthermore, oils from many fish, particularly fish from tropical zone waters, also contain significant quantities of arachidonic acid which exhibits a biological effect antagonistic to EPA. While production of omega-3-fatty acids in microorganisms would eliminate the contaminant problem~, no commercially acceptable ~nd economically feasible method of producing large quantities of these acids in microorganisms ha6 been available.
Isotopically labelled EPA would be of great benefit in elucidating the pathway of omega-3-fatty acid metaboli~m. However, labelled EPA in sufficient quantities to perform such research has not heretofore been obtainable.
Accordingly, it i~ an object of the present invention to produce EPA in microorganisms by a commercially feasible method to obtain commercially acceptable yields.
Further, it is an ob~ect of the present invention to produce isotopically labelled EPA from this cultivation proce~s in amounts sufficient to study omega-3-fatty acid metabolism.

w091/1~27 PCT/VS91/02052 2 0 ~

The present invention relates to the cultivation of microorganisms in a bioreactor, inducing the generation of edible oils containing omega-3-fatty acids in those microorganisms and recovering those oils and/or fatty acids. The invention also is directed to novel oils which contain omega-3-fatty acids but lack the additional polyunsaturated fatty acids associated with fish oils, to diatoms having increased amounts of omega-3-fatty acids as compared to wild type diatoms growing in the wild, and to mutant diatoms. Typically, these oils are further characterized as exhibi~ing biphasic melting patterns. Furthermore, isotopically labelled omega-3-fatty acids and their production are disclosed.
The present invention provides an economical method of obtaining edible oils havin~ favorable organoleptic characteristics containing EPA without significant amounts of other polyunsaturated fatty acids. Additionally, the method permits cultivation of diatoms to greater cell densities than those typically achieved by prior art processes. The edible oils produced by this method are free of environmental contaminants often found in EPA-containing oils from other sources.

Brief DescriPtion of the Drawinqs Figure 1 is a graphic representation of the biomass accumulation in Nitzschia, alba during its growth and oleogenic phases.
Figure 2 illustrates the process of labelling EPA
with either 13C or deuterium.

WO91/1~27 PCT/US91/02052 2~786~t~

Detailed De~cription of the Best ,Mode of Practicinq the Invention In accordance with the preqent invention, diatoms capable of producing EPA are cultivated in a fermentor containing a nutrient solution capable of supporting the growth of such microorganisms. In their native environment, heterotrophic diatoms are found growing epiphitically on seaweed. Accordingly, sea water is an acceptable medium for the nutrient solution. The sea water can be either natural, filtered or an artificial mix, each of which can be diluted down to ~ strength or concentrated to 2x. Micronutrients can be added and may be required, especially if the sea water is an artificial mix. Such micronutrient are known to those of skill in the art and are readily available from commercial suppliers. ~dditionally, a growth medium specifically designed for growing diatoms is added. A
preferred growth medium is presented in Table l. It is to be understood that variations in this growth medium are well within the ability of skilled workers in this art.

WO91/1~27 PCr/US9l/02052 2~78~

~L , GROWTH MEDIUM COMPOSITION
Ingredients needed for 2x30L Fermentors and 2x350L
Fermentors.
Total Recipe 30L-Ba~ch 350L-Batch l9g/L I~O. (Instant Ocean~) 570g 6.65Kg 3g/L NaNO3 90g 1.05Kg 0.5g/L NaH2PO4HH2O l5g 175g 0.2g/L Na2SiO3H5H2O 6g 70g 6ml/L f/2 TM (trace metals) 180ml 2.lL
60mg~L H3B03 1.8g 21g 6mg/L Na2SeO3 180mg 2.lg 10mg/L NaF 300mg 3.5g 40mg/L SrCl2H6H2O 1.2g 14g 150mg/L XBr 4.5g 52.5g 0.5g/L KCl l5g 175g 2ml/L B6 TM (trace metals) 60ml 700ml After Sterilization O.lml/L of 0.lmg/ml B12 3ml 35ml O.lml/L of 0.lmq/ml Biotin 3ml 35ml 2ml/L of lmg/ml Thiamine HCl 60ml 700ml Glucose: (1) Start with 80g/L 6L 70L
(40~ stock solution) (2) Add another 40g/1 31 35L
1 and 2 (additional 6 liters on day 2) Silicate: Add 60ml/liter of 1.8L 21L
100g/liter stock solutLon add additional amounts of stock solution over 48 hours WO91/1~2~ PCT/US91/020s2 2 0 7 ~

Any diatom~ capable of producing EPA can be used in the present invention. Moreover, it is preferred to use heterotrophic diatoms. For the purposes of this specification, the term llheterotrophic diatoms~ means those diatoms capable of growing in the dark on a particular carbon substrate. Different carbon substrates can be used with different species and such substrates can easily be determined by persons of skill in the art. Preferred genera of diatoms include 10 Nitzschia, CYclotella and Navicula. Within Nitzschia, the colorless species are especially preferred. In particular, Nitzschia alba is especially suitable for use in the present invention. Intended to be utilized in this invention are wild strains, mutants or recombinantly constructed microorganisms which produce increased amounts of EPA when cultured in accordance with the present invention. Suitable diatom~ can be isolated from the surfaces of seaweed where they grow epiphitically. A szmple of a ~train of Nitzschia alba, an especially preferred species, has been deposited with the American Type Culture Collection, Rockville, Md., and been assigned Accession No. 40775.
The present invention provides for the culturing of diatom~ at a much higher cell density than has heretofore been obtainable. Cell density refers to the amount of biomass present in the fermentator.
Typically, cell density accumulations in open pond cultivation of diatoms is from about 0.2-l grams dry weight/liter. In contrast, by applying the method of the present invention, and cultivating the diatoms in a fermentor, biomass densities of from 40-50 grams dry weight/liter have been obtained. Such a high cell density contributes to the enhanced production of edible oils containing EPA.

WO91/1~27 PCT/~'S91/OZ052 7 2~6~

Together with sea water, the growth medium hereafter will be referred to as a nutrient solution.
The nutrient solution typically includes available nitrogen. By available n.itrogen is meant nitrogen in a form suitable for diatom use in the biosynthesis of nitrogen containing molecules. Examples of suitable forms of such nitrogen include sodium nitrate or pota~sium nitrate. Sodium nitxate is preferred. To obtain an amount of diatom biomass equal to about 50 g/
per liter of solution ~ about 3 to about 4 grams of sodium nitrate per liter of solution should be provided. The nitrate can be included in the initial medium sterilization and need not be added thereafter.
Also added to the medium, after sterilization, is lS a quantity of diatom~ sufficient to inoculate the fermentor. These initial diatoms are referred to herein as the "~eed diatoms. Generally seed diatoms are obtained by culturing diatoms on agar plate6 and transferring cells from the agar plates to tubes containing 2-5 ml of culture medium. After a period of growth, the cells in the tubes are in turn used to inoculate 50 ml of medium in a 250 ml shake flask. The contents of the inoculated shake flask are used as the seed for a 2 liter fermentor. In production run~ it is preferred ~o use seed culture medium in volumes of from about 5 to lO~ of the volume o~ the fermentor. For example, in a 300 liter fermentor from about 15 to 30 liters of s2ed culture medium preferably would be added.
As the diatoms are being cultivated they are fed botn silicate and carbon. A preferred form of silicate is metasilicate, Na2SiO3. Metasilicate has both a 5 and a 9 hydrate form. Either form is acceptable for use in the present invention. In a nutrient solution having a typical pH and salinity permitting the growth of wos1/~27 PCTtUS91/~2052 8 2Q7~6~

diatoms, metasilicates irreversibly form a polymeric precipitate at concentrations in excess of about 250mg/l. Such precipitates are unacceptable as they make the silica~es unavailable for use by the diatoms.
This previously unsolved problem is overcome in ~he present invention where from about 5 to about 7 grams of metasilicate per liter of nutrient solution desirably is added to the fermentor. The undesirable precipitation is avoided by feeding the metasilicate into the fermentor at a controlled rate. The metasilicate can added incrementally in a fed batch mode. Preferably it is added in a continuous gradient feed. A continuous gradient feed is a slower rate of addition than a fed batch mode, as will be understood by those of skill in the art. Those of skill in the art, in po session of this invention, can easily determine without undue experimentation suitable rates of silicate addition.
During the growth phase of the diatoms the ratio of silicate to carbon preferably is kept constant.
Therefore, the~e two nutrients can be fed to the batch togethar at interval~ throughout the cultivation.
Using glucose as an example of a carbon source, the ratio of glucose to metasilicate desirably i5 from about lO grams to 35 grams of glucose per gram of metasilicate. A particularly preferred ratio is about 20 gr~ms of glucose per gram of metasilicate. Those of skill in the art can easily calculate acceptable ratios using other carbon sources, such as hydrolyzed whey, or starch.
Alternatively, the carbon source can be added batch-wise, i.e. enough carbon source for a complete batch is added at the beginning of the fermentation.
If this alternative is chosen, the metasilicate is added slowly to the fermentation, effectively WO91/1~27 PCT/VS91/02052 207~

controlling the rate of growth of the diatoms. Typical growth rates will comprise a doubling of the biomass every 4-8 hours.
While any type of fermentor can be used with the present invention, stirred~pot fermentors with conventional Rushton turbine-agitation are a preferred embodiment. Such turbines agitate by rotating a shaft having protruding flat blades for maximum aeration.
Preferably the speed of rotation is kept to a speed of less than 250cm/sec at the tip of the shaft.
Maintaining the speed at less than 250cm/sec reduces the likelihood of shearing, or otherwise damaging, the diatoms. An especially preferred fermentor for large-scale cultivation is an air-lift fermentor. Such fer,mentors are well known to those of skill in the art and eliminate potential shear damage.
According to the process of the present invention, heterotrophic diatoms are cultivated in fermentors as described above. While phototrophic microorganisms typically produce some EPA when cultivated in, for example, open ponds, it unexpectedly has been found that heterotrophic diatoms can be induced to enter an oleogenic phase wherein they produce a single cell oil containing EPA. Figure 1 demonstrate~ the increased production of biomas~ during oleogenesis. From about 40 to 50~ of this biomass can be attributed to oil production. Induction of oleogenesis can be triggered by depriving the microorganism of certain nutrients.
In particular, it is known that limiting the availability of nitrogen triggers oleogenesis in many oil producing microbes. Moreover, limiting the availability of silicon to diatoms is known to trigger oleogenesis. Borowitzka, ~Micro-Algal Biotechnologyll, Cambridge University Press (1988). However, in the present invention it has been discovered that the WOgl/l~27 PCT/US91/02052 ~7g~61~
timing of the impo~ition of a s.ilicon deficiency substantially increases the production of edible oil containing EPA by the diatom.
After about 24 to 48 hours of cultivation, the diatoms have depleted the available nitrogen in the growth medium. At this time, they typically have achieved a biomass density of 20 to 30 g/l which can be measured as the mass of the freeze dried pellet of cells from a known volume of culture. Of course, this time period is somewhat flexible as it depends in part on the amount of nitrogen initially added and on the rate of silicon feed. For several hours after nitrogen depletion occurs, silicate and glucose continue to be fed to the diatoms. While these additional nutrients can be added either continuously or incrementally, it i8 preferable to add the nutrients incrementally. Generally, the time period of this subsequent silicate feeding will be from about 12 to about 24 hours and is terminated when about 5 g/l of metasilicate, in total, has been added to the culture.
The diatoms then enter an oleogenic phase wherein enhanced amounts of edible oils containing EPA are more rapidly synthesized. The oleogenic phase can be continued for varying amounts of time but preferably is from about 1~ hours to about 36 hour~ duration.
Preferably the oleogenic phase will be permitted to continue for about 24 hours. During thi~ phase EPA is produced as a ~ingle cell oil. For the purpo~es of this specification, single cell oil means a triglyceride product of a unicellular microorganism.
The particular length of time of the oleogenic pha~e will depend upon the type of microorganism cultivated and the available nutrient supply and can be determined by those of skill in the art. In the case of Nitzschia alba the yields begin to decrease if this stage is W091/l~27 PC~/US91/02052 11 207~6~

longer than about 24 to 36 hours. Harvesting ~o obtain the oil containing EPA can occur immediately following the oleogenic phase.
An oxygen concentration greater than that required by aerobic respiration of the cells enhances diatom growth and EPA synthesis. The elevated level of oxygen is provided by high aeration rates, direct 2 sparging or fermentor pressurization. There is a direct corrçlation between dissolved oxygen concentration and EPA synthssis because 2 iS a ~ubstrate for EPA synthesis. At a dis~olved oxygen concentration of 30% of air saturation, typical EPA
levels in the oil are from about 2 to about 3%. At a dissolved oxygen concentration of 50% of air saturation, the EPA content of the oil increases to about 4-5~.
The cultivation can be carried out at any temperature at which diatoms can be grown. A preferred temperature range i8 from about 15C to about 40C. A
convenient, and economical, temperature to carry out the cultivation is 30C. Herein lies another advantage of the present invention over, for example, cultivation in open pondR which are sub~ected to extremes of weather. Temperatures at the lower end of the above range tend to improve the level of EPA with respect to unsatur~ted fatty acids but such temperatures also decrease the overall productivity rate. The highest productivity rates, as mea6ured by the rate of biomass doubling, occur at about 30C.
The cultivation can be carried out over a broad pH
range. A preferred pH is from about 7.0 to about 8.5.
This pH range can be maintained by the addition of concentrated silicate solution at a pH of about 12. If pH adjustment is required above and beyond what the addition of silicate effects, either sodium or WO9l/1~27 PCT/US91/02052 2~7~
potassium hydroxide can be added in an amount effective to adjust the pH.
Also encompassed by this invention are mutant strains of diatoms having increased amounts of EPA, S lower amounts of saturated fatty acids or both.
Techniques for obtaining mutant strains, such as treating with a mutagen and screening for progeny having the desired characteristics, are known to those of skill in the art. As used herein, ''increased'l or ~'lower" means an amount greater or lesser, respectively, than the amount ordinarily found in wild type diatoms.
Diatoms comprising about 40% triglycerides as their biomass are a portion of this invention.
Typically, wild type diatoms are found to comprise from about 5 to about 20% triglycerides as their biomas6.
Because a portion o f thi8 invention lie6 in the recognition that diatoms succes~fully can be economically cultivated to produce large quantities of single cell oil, the cultivation of such diatoms to obtain any single cell oil is contemplated to be within the scope of this invention. For example, wild type diatoms of the species Nitzschia alba typically have less th~n about 3% EPA and 40-60% of saturated fatty acids. The same species in the present invention typically has from about 3-5% EPA and 50% of saturated fatty acids. This increased percentage of EPA is desirable.
Additionally, the triglycerides of the present invention exhibit a biphasic melting pattern. As diatoms are not animals such an effect is unexpected, as will be appreciated by those of skill in the art.
Such a melting pattern is exhibited by dairy fats, such as butter, but has not heretofore been reported in a single cell oil from any other primary producer.

WO91/1~27 PCT/US91/U2052 13 ~ 0 7 ~

Accordingly, single cell oils produced by the method of the present invention containing triglycerides exhibiting a biphasic melting pattern also form a portion of this invention.
A preferred oil produced by the process of this invention has the following fatty acid composition.

FattY Acid 14:0 16:0 18:1 18:2 18:3 20:4 20:5 Others % Com~osition 23 33 33 2 l l 4 3 As discussed above, the present invention provides a method for reliably and consistently obtaining iarge quantities of an EPA-containing oil. Typically, in one embodiment of the invention the diatoms are synthesizing at least about 203 of their biomass as edible oil. Because the edible oil is a single cell oil, its recove~y is greatly facilitated. After the oleogenic phase, the diatoms can be extracted wet or dry, according to techniques known to those of skill in the art, to produce a complex containing lipids. After extraction, this complex of lipids can be further ~eparated to obtain EPA using known technigues. The preferred dry extraction method uses hexane as the extracting ~olvent. The cells are first centrifuged, and the cell pellet frozen and lyophilized prior to extraction with hexane. Such an extraction requires little or no physical disruption of the cells.
Extraction with the hexane at 40C in a ~olume to mass ratio of hexane to dry biomass of about 4:1 obtains greater than about 95~ of the oil within about 0.5 hour. If a wet cell paste rather than dried cells is used, then a mixture of ethanol and hexane is the preferred extraction medium.
The edible oil of the present in~ention contains fatty acids in addition to EPA. Predominantly, these Wo91/1~27 PCT/US91/02052 1~ 2~78fifi 1 other lipids are of only three types, palmitic (16:0), oleic (18:l) and myristic (14:0), thereby simplifying the purification proce-qs. In contrast, fi~h oils contain a wide variety of fatty acids in addition to EPA.
~ uantities of EPA of su~ficient purity and amount to perform re~earch on EPA metabolism can be obtained by the method of the present i.nvention. Accordingly, by including an isotope in the nutrient solution, labelled EPA will be 6ynthesized by the diatoms and can be recovered. If the labels are of the type known as stable isotope~ such as deuterium or carbon l3 or radioisotopes such as tritium or carbon 14, the EPA
will incorporate those labels and can be used in tracer lS studies in animals or humans or other research. It is to be under~tood that in addition to providing a labelled carbon substrate such as 13C-glucose or 14C-glucose to a heterotrophic diatom grown in the absence of light ~ources, 13co2, or '4Co2 can be provided to an autotrophic photosynthetic diatom. In both instances D20 or 3H20 c~n be supplied. Autotrophic dîatoms also must be exposed to a light source of sufficient intensity to facilitate photosynthesis. Suitable photo~ynthetic specie~ include those from the genus Cvclotella, NHvicula, PhaeodactYlum and Monodus. These organisms are preferred for the production of labelled EPA as they are autotrophic and contain higher levels of EPA than Nitzqchia alba.
The present invention also includes food and feed products, die~ary supplements and cosmetics which contain EPA produced by the methods disclosed herein.
For example, due to the high protein content and elevated levels of EPA, the EPA-producing microorganisms, taken as a whole cel~ biomass paste, can be used as feeds for aquaculture, includin~ fish, WO91/1~27 PCT~US91/02052 lS ~07~6~

shellfish and zoo plankton. In addition foods or dietary supplements containing EPA are believed to be effective in reducing coronary di~ease.
The oil produced by the methods of this invention, and the EPA recovered therefrom, al80 has beneficial effects, at least in part, in the treatment of ~kin disorders such as p60ria8i8. The u5e of EPA from fish oil has been reported to have a beneficial effect on skin lesion~ caused by psoriasi~. Accordingly, cosmetics containing the single cell oil of this invention or the EPA recovered therefrom are included within the scope of this invention. In particular, skin treatments, lotions or creams containing the single cell oil are contemplated. Such would have an olfactory advantage over fish oils containing EPA and al~o would not pos~ess the other contaminant~ found in fish oil.
The present invention having been generally described, reference is had to the following non-2n limiting specific example.
Exam~le Into a conventional 30 liter stirred tankfermentor (STF) is added the nutrient medium of Table 1, e~clusive of th~ vitamins, gluco~e and silicate.
The fermentor is equipped with a Rushton-type turbine agitator. The STF and the medium are sterilized.
After cooling the medium to about 30C, the vitamins are added, followed by the addition of sufficient amounts of 40% glucose syrup to provide a glucose concentration of about 80 g/l. Concentrated sodium metasilicate pentahydrate (lO0 g/l) is then added to provide a total silicate concentration of about 200 mg/l. Next, the inoculating amount of culture is added ` in an amount approximately equal to 5~ of the total volume of the fermentor, e.g. 1.5 liters/30 liters.

WO91/1~27 PCT/US91/02052 16 2~7~

Agitation is commenced with the tip speed set to 85-90 cm/sec and air sparging at 1 VVM started. Over about 16 hours an additional charge of concentrated metasilicate (0.53 liters) is added and the agitation speed increased to 126 cm/sec. Over about the next 24 hours, more concentrated silicate (0.83 liters) is added. Agitation speed again is increased to about 180~185 cm/sec. Over about the next 3 hours an additional 0.15 liters of concentrated metasilicate is added. Thus, the total amount of metasilicate added is about 156 grams or about 1.6 liters of concentrated solution. At about 4a hours additional glucoRe (about 5 liters) is added, for a total glucose addi~ion of about 4. a Kg or about 12 liters of 40% glucose syrup.
The culture ic permitted to grow for an additional 16 hours, maintaining the agitation speed and aeration rate. Then, the fermentor is harvested using a Sharples continuous flow centrifuge producing a biomass density of app~oximately 45-48 grams dry weight per liter. The re~ulting pellet, about 20-38% solids, is removed and frozen to about -20C. A vacuum tray drier is used to remove water from the pellet. The single cell oil pellet then i~ extracted with hexane. The hexane subsequently i~ removed by distillation leaving the extracted single cell oil.

Claims (56)

We Claim:
1. A method of producing a single cell edible oil containing eicosapentaenoic acid (EPA) comprising:
cultivating heterotrophic diatoms in a bioreactor containing a nutrient solution including silicate and available nitrogen, inducing said diatoms to enter an oleogenic phase wherein said diatoms are synthesizing at least about 20% of their biomass as edible oil and recovering said edible oil.
2. The method of claim 1, further comprising feeding silica to said microorganisms, said feeding being initiated prior to inducing said oleogenic phase and continuing after said diatoms have depleted said available nitrogen.
3. The method of claim 2 wherein said diatoms comprise Nitzschia sp.
4. The method of claim 3 wherein said diatoms comprise colorless species of Nitzschia.
5. The method of claim 1 further comprising maintaining an oxygen concentration greater than that required by aerobic respiration of the cells in said fermentor at least from the time of said oleogenic phase initiation to harvesting.
6. The method of claim 5 wherein said cultivation is carried out at a temperature of from about 15°C to about 40°C.
7. The method of claim 6 wherein said temperature is about 30°C.
8. The method of claim 5 wherein said cultivation is at a pH of from about 7.0 to about 8.5.
9. The process of claim 5 wherein said induction comprises withholding silicate from said nutrient solution.
10. The process of claim 5 wherein the length of time of said oleogenic phase is from about 12 hours to about 36 hours.
11. The process of claim 5 further comprising causing a nitrogen deficiency in said fermentor from about 12 to about 24 hours prior to withholding silicate from said diatoms.
12. The process of claim 5 wherein said fermentor contains a medium comprising sea water.
13. The process of claim 12 wherein said medium further comprises micronutrients.
14. The process of claim 5, wherein said fermentor comprises a stirred pot fermentor having turbine induced agitation.
15. The process of claim 14, wherein the speed of said turbine at its tip is less than about 250cm/sec.
16. The process of claim 5, wherein said fermentor in an air-lift fermentor.
17. The process of claim 5 wherein said dissolved oxygen comprises about 50% of air saturation.
18. The process of claim 5 wherein said silica comprises metasilicate.
19. The process of claim 18 wherein said metasilicate is added to said fermentor in an amount of from about 5 grams to about 7 grams per liter of culture medium.
20. The process of claim 19 wherein said metasilicate is added to said fermentor in a continuous gradient feed or a fed batch mode.
21. The process of claim 20 wherein said metasilicate is fed to said diatoms in conjunction with a carbon source.
22. The process of claim 21 wherein said carbon source comprises glucose.
23. The process of claim 22 wherein the ratio of said glucose to said metasilicate is from about 10 grams to about 35 grams of glucose per gram of metasilicate.
24. The process of claim 23 wherein said ratio is about 20 grams of glucose per gram of metasilicate.
25. The process of claim 5 wherein said nutrient solution further comprises a carbon source selected from glucose, hydrolyzed whey or hydrolyzed starch.
26. The process of claim 25 wherein said nitrogen is in the form of sodium nitrate or potassium nitrate.
27. The process of claim 26 wherein said nitrogen is of the form of sodium nitrate and said sodium nitrate is present in said nutrient solution at a concentration of from about 3 grams to about 4 grams per liter of solution.
28. Mutant diatoms having elevated levels of EPA, lower levels of saturated fatty acids or both.
29. A diatom comprising about 40% of its biomass as triglycerides.
30. The diatom of claim 29, wherein said triglycerides exhibit a biphasic melting pattern.
31. An edible oil produced by the process of claim 5, containing triglycerides exhibiting a biphasic melting pattern.
32. The triglycerides of claim 31 wherein the fatty acid comprises from about 2 to about 20% EPA.
33. The process of claim 1, further comprising including in said nutrient solution at least one substrate containing an isotope selected from the group of isotopes of 13C, 2H, 14C, 3H.
34. The process of claim 33 wherein said isotope comprises deuterium or carbon-13.
35. The process of claim 33 wherein said substrate comprises D2O or tritiated water.
36. The process of claim 33 wherein said substrate comprises [13C]-glucose, [14C]-glucose; 13CO2 or 14CO2.
37. Isotopically labelled EPA produced by the process of claim 33.
38. A process for producing EPA comprising (a) cultivating colorless diatoms in a fermentor containing a nutrient solution having at least available nitrogen, (b) maintaining in said nutrient solution a dissolved oxygen content of from about 10% to about 70%
of air saturation, (c) adding to said nutrient solution glucose and metasilicate wherein the ratio of glucose to metasilicate is from about 10:1 to about 35:1 and from about 5 to about 7 grams of metasilicate are added per liter of said nutrient solution, said mixture added after said diatoms have depleted the available nitrogen in said nutrient solution, (d) maintaining the temperature of said nutrient solution at from about 15°C to about 40°C, (e) maintaining the pH of said nutrient solution at from about 7.0 to about 8.5, (f) inducing an oleogenic phase in said diatoms by ceasing said addition of metasilicate, and (g) recovering said oil containing said EPA after said oleogenic phase is complete.
39. The process of claim 38 wherein said diatom comprises Nitzschia alba.
40. The process of claim 39 wherein said dissolved oxygen content is at least 50% of air saturation, said ratio of glucose to metasilicate is about 20:1 and is added incrementally throughout about 12 to about 24 hours after said nitrogen-depletion, said temperature is about 30°C, and said oleogenic phase occurs over approximately a 24 hour period.
41. Food products containing EPA produced by the method of claim 1, 5, 38 or 40.
42. Dietary supplements containing EPA produced by the process of claim 1, 5, 38 or 40.
43. Cosmetics containing EPA produced by the process of claim 1, 5, 38 or 40 .
44. The cosmetics of claim 43, wherein said cosmetics comprise skin creams, lotions or treatments.
45. A method for the treatment of psoriasis comprising applying the skin cream, lotion or treatment of claim 44 to the area of skin afflicted with said psoriasis.
46. A method for obtaining increased yields of EPA from cultured diatoms in a fermentor containing a nutrient solution comprising culturing said diatoms to a cell density of from about 40 to about 50 grams per liter of said nutrient solution, inducing an oleogenic phase in said diatoms wherein said EPA is synthesized and recovering said EPA.
47. The method of claim 46 wherein said diatom is an autotrophic diatom.
48. The method of claim 47 wherein said autotrophic diatom is Nitzschia sp. or Cyclotella sp.
49. The method of claim 46 wherein said diatom is a heterotrophic diatom.
50. The method of claim 49 wherein said diatom comprises Nitzschia sp. or Cyclotella sp.
51. The method of claim 50 wherein said Nitzschia is a colorless species.
52. The method of claim 51 wherein said colorless Nitzschia is Nitzschia alba.
53. Feed for aquaculture comprising cells of a diatom capable of producing a single cell oil which contains EPA which have been cultivated under conditions inducing production of said single cell oil.
54. Feed for aquaculture in accordance with claim 53, wherein said aquaculture comprises shrimp, fish or zoo plankton.
55. Feed for aquaculture in accordance with claim 53, wherein said diatoms comprise Nitzschia sp.
56. Feed for aquaculture in accordance with claim 55, wherein said diatoms comprise colorless species of Nitzschia.
CA002078664A 1990-03-21 1991-03-20 Eicosapentaenioc acids and methods for their production Abandoned CA2078664A1 (en)

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WO1991014427A1 (en) 1991-10-03
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US5244921A (en) 1993-09-14
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US5567732A (en) 1996-10-22

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