METHOD FOR THE OBTENTION AND MASS PRODUCTION OF AN ISOLATED CYANOBACTERIA SPECIES PRODUCING PARALYSING PHYCOTOXINS

FIELD OF THE INVENTION

This invention is related to a method to produce cyanobacteria (photosynthetic blue-green algae), specifically to the development of a massive artificial process operating under controlled conditions that is useful to generate desired metabolites, such as paralyzing toxins, at industrial levels. The method is characterized by its high efficiency, high yield, simplicity and high profitability.

DESCRIPTION OF THE PREVIOUS ART

Neosaxitoxin and saxitoxin are components of the paralyzing poison produced by dinoflagellate species of the genera Alexandrium sp., Piridinium sp. and Gimnodinium sp., and therefore they are sometimes present in filter-feeding bivalves and carnivore gastropods contaminated by harmful algal blooms, commonly known as red tides (Lagos, N. (1998) Microalgal blooms: a global issue with negative impact in Chile. Biol. Res. 31: 375-386). These phycotoxins are produced not only by marine dinoflagellates, but also by fresh-water cyanobacteria (photosynthetic blue-green algae).

There are only 5 cyanobacteria described in the literature able to produce shellfish paralyzing phycotoxins, each of them having a characteristic composition regarding the amount and type of produced phycotoxins (profile of paralyzing phycotoxins):

• Cylindrospermopsis raciborskii, isolated from Brazil (Lagos, N., Onodera, H., Zagatto, P.A., Andrinolo, D., Azevedo, S.M.F.Q., and Oshima, Y., 1999, The first evidence of paralytic shellfish toxins in the freshwater cyanobacterium Cylindrospermopsis raciborskii, isolated from Brazil. TOXICON, 37: 1359 - 1373; Molica, R., Onodera, H., Garcia, C., Rivas, M., Andrinolo, D., Nascimento, S., Meguro, H., Oshima, Y., Azevedo, S., and Lagos, N., 2002, Toxins in the freshwater cyanobacterium Cylindrospermopsis raciborskii, isolated from Tabocas reservoir in Caruaru, Pernambuco, Brazil, Phycologia, 41 (6): 606 - 611).
• Aphanizomenon flos-aquae, isolated from Portugal (Pereira, P., Onodera, H., Andrinolo, D., Franca, S., Araujo, F., Lagos, N., and Oshima, Y., 2000, Paralytic shellfish toxins in the freshwater cyanobacteria Aphanizomenon flos-aquae, isolated from Montargil reservoir, Portugal. Toxicon, 38: 1689 - 1702).
• Anabaena circinalis, isolated from Australia (Lagos, 1999).
• Lyngbya wollei, isolated from North America (Lagos, 1999).
• Aphanizomenon(Aph) gracile (Lemm) Lemm (Pereira P LMECYA40). This photosynthetic unicellular blue-green alga is the only cyanobacteria of this type that only produces tetrahydropurines: neosaxitoxin and saxitoxin, in a proportion of 78 to 82% neosaxitoxin and 22 to 18% saxitoxin.

The method proposed in the present application is a continuous culture operating under controlled conditions of a cyanobacterium that produces a simple profile of paralyzing phycotoxins. This profile depends on the cultured species, and includes neosaxitoxin and saxitoxin or gonyaulatoxins 2 and 3. Furthermore, this culture method includes micronutrient addition that allows higher production rates of these pharmacologically active compounds per wet weight of the algae than those previously described.

Neosaxitoxin, saxitoxin and gonyaulatoxins are compounds that have a tetrahydropurine basic structure and are produced by the abovementioned cyanobacteria as secondary metabolites. These compounds, as all secondary metabolites, are inside the cells but are also released into the culture medium. In this way, two sources of these products are generated: in the cell pellet fraction and in the medium where cyanobacteria are cultured.

The massive continuous culture of these cyanobacteria, both in open or naturally-illuminated reactors and in closed illuminated reactors where light is provided by artificial means such as fluorescent tubes or similar means, including white light LEDs, allows permanent and continuous production of the cyanobacteria, which is strictly necessary for industrial level production of neosaxitoxin, the main compound to be purified from these cyanobacteria. However, depending on the cultured cyanobacteria and the culture conditions, not only neosaxitoxin can be purified later on, but also saxitoxin and other saxitoxin analogs, such as gonyaulatoxins and others. All these compounds belong to the group of the paralyzing phycotoxins.

The process of continuous industrial production with high cyanobacteria yields has not been carried out previously. Until now, no development of an artificial procedure for cyanobacteria having a characteristic and unique phycotoxin profile has been described; for example, a unique composition containing only neosaxitoxin and saxitoxin in a predefined 5 to 1 ratio respectively, or only gonyaulatoxins without any other paralyzing phycotoxins.

Another advantageous characteristic is the very high production of phycotoxins obtained when using the selected culture conditions and procedures that are described in the present invention, which allows cyanobacteria to be defined as the best source of these phycotoxins, especially neosaxitoxin in the case of Aphanizo menon(Aph) gracile (Lemm) Lemm, which is the major component and the most interesting one to be massively produced.

This species of cyanobacteria, Aphanizomenon(Aph) gracile (Lemm) Lemm, a producer of saxitoxin and mainly neosaxitoxin, was collected from Crato Lake, a water reservoir in Portugal, isolated and codified as LMECYA 41 and was identified as Aphanizomenon (Aph) gracile (Lemm) Lemm, firstly taking into account its morphology and later based on its 16S rRNA gene sequence (Paulo Pereira, et al., 2001. 5th International conference on toxic cyanobacteria, July 15-20 2001, Queensland, Australia).

Initially, this strain was collected in a crude water sample collected from the reservoir, which had a high predominance of Aphanizomenon (Aph) gracile (Lemm) Lemm filaments, the second predominating species, with 32 to 40% of the total mass of species found in the original sample. Later, in the laboratory, conventional routine techniques were used to repetitively and successively wash and isolate trichomas individually in cloning droplets taken with clamps (small sterile isolation rings), all in sterile culture media and being observed with the help of an inverted microscope, to obtain a single trachoma that was transferred to a sterile 10-milliliter flask containing 5 milliliters of medium. The culture of this single cyanobacterium (unialgal culture) was grown at 25°C for 2 to 4 weeks, until reaching a suitable development state for subsequent production. From this original isolate, massive expansion and production of this unialgal cyanobacterium was started by doing continuous replications as required, using always the count of filaments maintained as a guide, and always in the exponential growing phase. During this growth and development stage of the unialgal culture, the strain was kept under light-darkness cycles of 16:8 hours. The filaments were counted using lugol stain in Sedgewick Rafter and Palmer-Maloney counting cells, thereby controlling the development of the culture.

This method to isolate a cyanobacterium to get a pure culture can be applied to any of the cyanobacteria able to produce paralyzing phycotoxins mentioned above.

Once the pure culture is obtained, it is used as an inoculum for massive production of cyanobacteria according to the present invention.

The advantages of the present invention to massively produce cyanobacteria that are able to produce paralyzing phycotoxins under controlled conditions are:

• Continuous and permanent production under controlled conditions of cyanobacteria that are able to produce paralyzing phycotoxins.
• Low production costs because the culture medium is very elemental, since it does not include highly-valued nutrients and only requires light control, which means that handling of cyanobacteria is relatively easy.
• Providing a continuous source of paralyzing phycotoxins (saxitoxin, neosaxitoxin and gonyaulatoxins) independent from environmental conditions and changes.
• Very favorable cost-production-yield relationship that has not been achieved previously and has not been described in any industrial process until now.

OBJECT OF THE INVENTION

The general object of the present invention is the massive continuous industrial production of a cyanobacterium that produces mainly paralyzing phycotoxins, such as saxitoxin, neosaxitoxin and/or gonyaulatoxins, under controlled conditions and at low cost.

A specific object of the present invention is the development of a procedure for optimized production of a cyanobacterial monoculture at low cost and commercially competitive.

Another specific objective of the invention is the achievement of continuous industrial procedure using a cyanobacteria strain in perpetuity as a source of high added value compounds that are not commercially available and have applications as clinical therapies for several pathologies.

Another specific object of the invention is the achievement of a continuous culture of this cyanobacterial strain directed to produce mainly neosaxitoxin, with a small proportion of saxitoxin (one fifth saxitoxin), or mainly gonyaulatoxins 2/3 as major and main components.

Another specific objective of the invention is to achieve a high production of neosaxitoxin and/or gonyaulatoxins per cyanobacterial cell.

BRIEF DESCRIPTION OF THE DRAWINGS

• FIGURA 1: Production of filaments in one culture day using the culture medium of the present invention (MLA Medium modified with methionine, arginine and allantoic acid) in continuous light conditions and the unmodified medium (simple MLA Medium) with light:darkness cycling.

BRIEF DESCRIPTION OF THE INVENTION

In the present application, a method to massively obtain and produce cyanobacteria in a continuous culture is presented. The examples of cyanobacteria that can be cultured continuously are:

• Cylindrospermopsis raciborskii, Aphanizomenon flos-aquae;
• Aphanizomenon(Aph) issatschenkoi (Usacev) Proskina-Lavrenco;
• Anabaena circinalis, Lyngbya wollei and Aphanizomenon gracile (Lemm) Lemm.

The knowledge about cyanobacteria that produce paralyzing phycotoxins is associated to a public health issue, wherein shellfish contamination with these phycotoxins, related to blooms of phycotoxin-producing dinoflagellates, has a serious impact on public health and the shellfish canning industry in regions where red tides are present, i.e. where phycotoxin-producing dinoflagellates blooms appear (Lagos 1998).

These cyanobacteria species, when described for the first time, were characterized only according to anatomy and classical taxonomical characteristics. These species were not initially studied or characterized according to the compounds they produce, and when the study of the produced phycotoxins was carried out, the objective was to understand and solve the toxicity levels and public health problems. However, until the presentation of this application, a massive production of paralyzing phycotoxins (all saxitoxin analogs) derived from cyanobacteria or the culture of cyanobacteria as a continuous and perpetual source of paralyzing phycotoxins have never been proposed.

In the present application, a method to massively obtain and produce cyanobacteria in a continuous culture is presented, taking as an example the culture of (Aph) gracile (Lemm) Lemm. However, the continuous culture method is applicable to the cyanobacteria genera mentioned previously> Cylindrospermopsis raciborskii, Aphanizomenon flos-aquae, Aphanizomenon(Aph) issatschenkoi (Usacev) Proskina-Lavrenco, Anabaena circinalis, Lyngbya wollei, and Aphanizomenon gracile (Lemm) Lemm.

The availability of these isolated cyanobacteria has allowed the development of continuous studies and the invention of the present massive production process

To culture and develop a cyanobacterium, serial open or closed reactors are required, and direct illumination is needed to coat all the reactors.

The culture only requires fresh water, mineral salts and micronutrients in low amounts, all of them with low costs and readily prepared.

Another preferred requirement is a permanent light cycle with no darkness period, which also constitutes an innovation of this massive culture procedure, since cyanobacteria are photosynthetic organisms that require light and reach maximal development always in the exponential growth phase. In relation to this, it is worth highlighting that light and darkness cycles with different hourly regimes can also be used during the development of this continuous culture, even natural light cycles. Another innovation of the process described in this application is the permanent maintenance of the culture in the exponential growth phase and in a permanent state of production of phycotoxins, which is achieved by carrying out selective quantified harvests, depending on the quantitative development of the culture in each reactor.

The culture of cyanobacteria requires sterile media to keep the cultures in the best conditions; however these cultures do not require extreme sterility conditions as in the case of the culture of eukaryotic cells such as mammal cells.

These cyanobacteria are very resistant to contamination and since their development requirements are minimal and therefore the culture media used in the present invention are too "poor" for the development of other microorganisms, these are natural selection media where only these photosynthetic organisms can grow.

The optimal range of temperature for the growth of these cyanobacteria is comprised between the usual ranges of variation of the environmental temperature variations in a Mediterranean climate such as Central Chile (from Arica to Temuco).

When cyanobacteria have developed, a volume suitable to be used, for example, for purification of a metabolite produced by the cyanobacteria, is removed and the volume removed from the cell culture is restituted by adding an equivalent volume of sterilized medium. According to the filament counting in time, once a determined development has been reached, another suitable volume of cyanobacteria can be collected, always keeping the same final volume of the culture medium by replacing the harvested volume of cells by an equivalent refill volume.

In this way, a system of cultured cyanobacteria is obtained as a continuous source for production of cyanobacteria.

DETAILED DESCRIPTION OF THE INVENTION

To start a culture of a cyanobacterium able to produce paralyzing phycotoxins at industrial levels, an isolated and characterized cyanobacterium is required, which can be selected from Cylindrospermopsis sp., Aphanizomenon sp., Anabaena sp., and Lyngbya sp., and the like.

The culture of cyanobacteria, considering a particularly selected species, is carried out in suitable aerated stirred reactors with permanent illumination. Light can be artificial, e.g. light emitted by fluorescent tubes.

The culture medium considered for the reproduction of cyanobacteria comprises distilled water, mineral salts and micronutrients, all sterile.

The culture medium is prepared based on the MLA X 40 medium (MLA medium, CSIRO Marine Research, CSIRO Microalgae Research Center, Hobart, Australia) for cyanobacterial culture (microalgae@marine.csiro.au), which comprises, among others, the following components: MgSO₄ × 7H₂O, NaNO₃, K₂HPO₄, H₃BO₃, H₂SeO₄, biotin, vitamin B12 and thiamine-HCl, EDTA-Na, ferric chloride hexahydrate, sodium carbamate and manganese chloride hydrate, NaHCO₃, CaCl₂ × 2H₂O, CuSO₄ × 5H₂O, ZnSO₄ × 7H₂O, CoCl₂ × 6H₂O, NaMoO₄ × 2H₂O. Furthermore, the culture medium of the present invention incorporates arginine, methionine and allantoic acid.

In the following table, concentration ranges useful for the method of the present invention are presented for the components mentioned above.

Compound

Minimal concentration (g/l)

Maximal concentration (g/l)

MgSO₄ × 7H₂O

3.71 E-02

6.18E-02

NaNO₃

1.28E-01

2.13E-01

K₂HPO₄

2.61 E-02

4.35E-02

H₃BO₃

1.85E-03

3.09E-03

H₂SeO₄

9.68E-04

1.61 E-03

Biotin

3.75E-08

6.25E-08

Vitamin B12

3.75E-08

6.25E-08

Thiamine HCl

7.50E-05

1.25E-04

CuSO₄ × 5H₂O

7.50E-06

1.25E-05

ZnSO₄ × 7H₂O

1.65E-05

2.75E-05

CoCl₂ × 6H₂O

7.50E-06

1.25E-05

NaMoO₄ × 2H₂O

4.50E-06

7.50E-06

Na₂EDTA

3.27E-03

5.45E-03

FeCl₃ × 6H₂O

1.19E-03

1.98E-03

NaHCO₃

4.50E-04

7.50E-04

MnCl₂ × H₂O

2.70E-04

4.50E-04

Additionally, the culture medium comprises from 2 to 3.5 mM of arginine, from 1 to 2.2 mM of methionine and from 0.7 to 1.3 mM of allantoic acid in the final composition.

The preparation of the culture medium is carried out using stock solutions that are separately prepared and sterilized by filtration or autoclaving.

The MLA culture medium from CSIRO for cyanobacterial growth is known, however the complete culture medium described in the present invention considers mineral salts, micronutrients and vitamins that are not found in said medium or in any other publication regarding cyanobacterial culture.

Once the medium is prepared, cyanobacteria are inoculated ranging from 20 to 40 million filaments per each 3 liters of the culture medium of the invention.

The culture conditions consider constant illumination provided by fluorescent tubes at a controlled temperature from 15 to 35°C, preferably in a range from 20 to 35°C, with an optimum of 22 ± 2°C.

In particular, depending on the division cycle of the strain used in the culture, it is possible to remove a volume from 20 to 40% of the total volume of the reactor to process cyanobacteria and replace this volume with an equivalent volume of fresh culture medium. For example, if the division cycle is 0.33 per day, it is possible to remove one third of the culture volume and replace it with an equivalent volume of fresh culture medium every 1 to 2 days.

To determine the moment to harvest cyanobacteria, growth is monitored through filament counting and care is taken to restitute an equivalent volume of culture medium each time a removal of cyanobacteria is carried out.

There is a previous publication wherein the culture of the strain Aphanizomenon (Aph) gracile (Lemm) Lemm LMECYA40 is described, but the culture medium described in this publication is totally different from the modified MLA medium described in this invention. This is the first time the use of MLA medium is described as a base for the culture of cyanobacteria. To adapt the culture of cyanobacteria of the present invention, the MLA medium has been modified adding the components arginine, methionine and allantoic acid, all compounds that have surprisingly demonstrated to be highly potent stimulants of the production of the phycotoxins saxitoxin, neosaxitoxin and gonyaulatoxins.

In the first step, the method of the invention comprises generating an inoculum with a number of filaments in the range from 20 to 40 million, cultured in small 250-ml flasks in a culture chamber with a light:darkness cycling of 16:8 hours and temperature controlled at 22 ± 2°C.

The inoculum obtained is transferred into reactors, which are in kept in sterile and isolated conditions.

The culture temperature of the method of the present invention is controlled to be between 20 - 25°C. For example, if Aphanizomenon (Aph) gracile (Lemm) Lemm is going to be produced, it has to be taken into account that this strain is well cultured in the range from 15 to 30°C, optimally 22 ± 2°C.

Aphanizomenon (Aph) gracile (Lemm) Lemm cells have a previously known division cycle of 0.33 per day. This means that in three days the culture doubles the cell mass. This allows the collection of one liter of culture from each 3-liter reactor every 1 to 2 days maximum.

The volume removed from the cell culture is restituted adding one liter of sterilized medium. The next day or the other, according to the filament counting, another liter of cyanobacterial culture can be collected, always keeping a total volume of 3 liters of culture medium.

In this way, a system of cultured cyanobacteria is obtained as a continuous source for perpetual production of cyanobacteria. The collection of culture medium with cyanobacteria can be conveniently carried out every two days, thereby obtaining a larger number of filaments. Under maximal production conditions, it is not convenient to space harvesting for more than 4 days, since the culture deteriorates and phycotoxin production decrease when filament concentration in the culture increases.

The cell pellet corresponds to filament-forming cyanobacteria. These filaments have from 20 to 100 cells and even more cells linked in a filament. For that reason, they are called filamentous cyanobacteria. When the cyanobacteria are "healthy" and grow well, they form filaments, because they undergo cell division therein. This filamentous characteristic is used as growth control, because it is a positive cyanobacterial development control. The ability to form filaments allows a better control of medium contamination, since when the medium is contaminated and an infection arises, cyanobacteria do not form filaments.

The cell pellet comprises filaments that are quantified in the inverted microscope, since individual cells are very small, difficult to count and are not present in a healthy culture.

Furthermore, cell-free medium is collected as the supernatant of a centrifugation step used to obtain a pellet. This centrifugation is conveniently performed at 10,000 g for 20 minutes. Phycotoxins are also present as soluble species in this supernatant.

This supernatant is the second phycotoxin source. In good culture conditions, with healthy filaments, no contamination and in permanent exponential growth phase, it tends to be less than 5% of the total content obtained in the pellet fraction.

The productivity described in the present invention is between 60-125 times higher than productivities described by Paulo Pereira et al., 2001, (5th International Conference on Toxic Cyanobacteria, July 15-20 2001, Queensland, Australia).

The strain was cultured in conventional conditions (without the reactors developed and used in this invention), with other nutrients and micronutrients, keeping light:darkness cycles of 16:8 hours, and at other temperatures. Certainly, in the present invention a massive industrial production is described that includes not only a new continuous culture method, but also a procedure using a novel infrastructure, which as a whole delivers an innovative proposal with a surprising effect due to the high yields that have never been described or demonstrated before.

Although the previous description contains many specifications, these specifications must not be taken as limiting the scope of the invention, but only as illustrations of some of the modalities of the invention that are actually preferred.

The developed pilot industrial process is a continuous culture comprising 200 reactors that allow the daily collection of 200 liters of cyanobacteria able to produce paralyzing phycotoxins (neosaxitoxin, saxitoxin or gonyaulatoxins).

EXAMPLE 1: Preparation of culture media

To prepare the culture medium, more concentrated stock solutions of micronutrients, mineral salts and vitamins are prepared. All solutions are prepared with distilled water.

The Vitamin Stock (solution A) is prepared according to the directions in the following table:

Concentration (mg/ml)

Volume (ml)

Final concentration (mg/ml)

Biotin

0.1

0.05

0.00005

Vitamin B12

0.1

0.05

0.00005

Thiamine HCl

0.1

In other words, 1 mg of biotin was dissolved in 10 ml of distilled water. Similarly, 1 mg of vitamin B12 was dissolved in 10 ml of distilled water. 0.05 ml from each of these two solutions were taken and mixed with 10 mg of thiamine HCl in a final volume of 100 ml completed with distilled water.

The Micronutrient Stock (solution B) was prepared from primary solutions of CuSO₄ 5H₂O (1 g/l), ZnSO₄. 7H₂O (2.2 g/l), CoCl₂. 6H₂O (1 g/l), NaMoO₄ 2H₂O (0.6 g/l).

To 800 ml of a solution as indicated in the table below, 10 ml of each primary solution were added.

Concentration (g/l)

Amount (g) in 800ml

Na₂EDTA

5.45

4.36

FeCl₃ · 6H₂O

1.975

1.58

NaHCO₃

0.75

0.6

MnCl₂ · H₂O

0.45

0.36

Finally, the volume was completed up to 1 liter with distilled water to get 1 liter of Micronutrient Stock Solution (solution B).

To prepare 250 ml of a concentrated 40x stock of MLA medium, the volumes indicated for each component in the following table were added to 130 ml of distilled water:

Component

Solution (g/l)

Volume (ml)

MgSO₄ · 7H₂O

49.4

10

NaNO₃

85

20

K₂HPO₄ 6.96

50

H₃BO₃

2.47

10

H₂SeO₄

1.29

10

Vitamin Stock (solution A)

10

Micronutrient Stock (solution B)

10

Finally, to prepare one liter of MLA culture medium to be sterilized by filtration through 0.22 micrometer membranes, the following volumes are combined:

(g/l)

Volume (ml)

Distilled water

964

40x MLA Stock

25'

NaHCO₃

16.9

10

CaCl₂ · 2H₂O

29.4

1

In case of using autoclave sterilization at 121°C for 15 minutes, the amounts indicated below are used, and pH is adjusted to 7.5 - 8.0 with HCl or other suitable acid.

(g/l)

Volume (ml)

Distilled water

973

40× MLA Stock

25

NaHCO₃

16.9

1

CaCl₂ · 2H₂O

29.4

1

The concentrations of the final components are those indicated in the following table:

Compound

Concentration in the ready-to-use medium (g/l)

MgSO₄ · 7H₂O

4.94E-02

NaNO₃

1.70E-01

K₂HPO₄

3.48E-02

H₃BO₃

2.47E-03

H₂SeO₄

1.29E-03

Biotin

5.00E-08

Vitamin B12

5.00E-08

Thiamine HCl

1.00E-04

CuSO₄ · 5H₂O

1.00E-05

ZnSO₄ · 7H₂O

2.20E-05

CoCl₂ · 6H₂O

1.00E-05

NaMoO₄ · 2H₂O

6.00E-06

Na₂EDTA

4.36E-03

FeCl₃ · 6H₂O

1.58E-03

NaHCO₃

6.00E-04

MnCl₂ · H₂O

3.60E-04

NaHCO₂ and CaCl₂ · 2H₂O must be added as needed, since their concentration depends on the type of sterilization (filtration or autoclaving) used for the medium.

All the solutions can be stored refrigerated for no more than 1 month.

Finally, to prepare the culture medium of the present invention, arginine, methionine and allantoic acid were added at final concentrations of 2.8 mM arginine, 1.7 mM methionine and 1 mM allantoic acid.

This final mixture of added components is determinant to obtain the results of this invention and said components are not part of the MLA Medium (CSIRO Marine Research) described above.

EXAMPLE 2: Culture of Aphanizomenon (Aph) gracile (Lemm) Lemm

Each reactor containing 3 liters of the culture medium described in Example 1 was inoculated with 35 million filaments of Aphanizomenon (Aph) gracile (Lemm) Lemm. The reactors were kept at a controlled temperature of 22°C ± 2°C, with permanent illumination from fluorescent tubes. Once the culture reached the exponential phase, one-third of the total reactor volume was collected (1 liter) and replaced with 1 liter of fresh medium. The former culture had a doubling time of 0.33 times per day.

Subsequently, the culture medium with cyanobacteria was centrifuged at 10,000 g for 20 minutes.

The yields obtained in the present invention are always expressed as a function of the number of filaments, since the presence of filaments (association of many individual cells) is an indicator of the quality of the culture and of the permanent reproduction and development of the cells. A filament-rich culture is a "healthy" culture and is in permanent development. The cell pellet is a pellet of filaments and the purification of phycotoxins starts therefrom.

Batch

Culture day

Filaments of cyanobacteria in the pellet per ml

Collected volume (ml)

1

Day 1

590,000

1000

2

Day 2

598,000

1000

3

Day 3

630,000

1000

4

Day 4

596,000

1000

5

Day 5

626,000

1000

6

Day 6

788,000

1000

7

Day 7

534,000

1000

8

Day 8

756,000

1000

9

Day 9

754,000

1000

10

Day 10

614,000

1000

11

Day 11

622,000

1000

12

Day 12

608,000

1000

13

Day 13

770,800

1000

The cell pellet of each batch is the volume obtained from one liter of culture harvested each day from the reactor. This can also be carried out every other day, to achieve a larger number of filaments. Under these maximal production conditions, it is preferable to carry out the harvest no more than 4 days apart, to avoid culture deterioration and phycotoxin production decrease.

EXAMPLE 3: Comparison of the culture with simple (unmodified) MLA medium and the modified MLA medium of the present invention.

Figure 1 shows the difference between a culture of Aphanizomenon gracile in the simple (unmodified) MLA medium and a culture of Aphanizomenon gracile with the modified MLA culture medium of the present invention. It is easily appreciable that the modified medium of the present invention, including a final concentration of 2.8 mM arginine, 1.7 mM methionine and 1 mM allantoic acid, is surprisingly superior to the culture using the simple (unmodified) MLA medium.

Table 2 below shows the concentration of the different phycotoxins in the supernatant and the yield of cyanobacterial filaments thereof. The table also indicates the concentration of filaments per ml of culture medium according to the method of the present invention.

Concentration in the supernatant

Concentration of phycotoxin per filament

Cyano. fil./ml*

neoSTX mM

STX mM

neoSTX µg /ml

STX µg /ml

neoSTX pg/fil.

STX pg/fil

8.98

3.5

2.83

1.05

2.42

0.9

1,170,000,00

13.66

4.91

4.3

1.47

3.44

1.18

1,250,000,00

3.42

1.03

1.08

0.31

1.71

0.49

630,000,00

17.82

4.78

5.61

1.43

9.42

2.41

596,000,00

17.81

4.02

5.61

1.21

13.17

2.83

426,000,00

7.66

1.47

2.41

0.44

4.94

0.91

488,000,00

10.87

2.19

3.42

0.66

10.25

1.97

334,000,00

10.52

2.07

3.31

0.62

4.38

0.82

756,000,00

10.77

1.96

3.39

0.59

7.47

1.3

454,000,00

17.24

2.99

5.43

0.9

13.12

2.16

414,000,00

5.31

0.41

1.67

0.12

5.19

0.38

322,000,00

12.26

2.17

3.86

0.65

9.47

1.59

408,000,00

9.84

1.94

3.1

0.58

17.42

3.27

178,000,00

STX: saxitoxin

neoSTX: neosaxitoxin

Cyano. fil.: cyanobacterial filaments

* Cyanobacterial filaments are associations of 20 to 100 cyanobacterial cells. These cyanobacteria form filaments in solution and those filaments are counted using the magnification of an inverted microscope.

Table 3 shows different phycotoxin production batches. It is clearly observed that the mean yield of phycotoxin per filament is much higher when using the modified MLA medium with the growth conditions of the present invention, in comparison with the culture in simple (unmodified) MLA medium representing the previous state of the art.

Production of phycotoxins in modified MLA medium and permanent illumination

Production of phycotoxins in simple MLA medium with light:darkness cycling

neoSTX pg/fil.

STX pg/fil

neoSTX pg/fil.

STX pg/fil

2.42

0.9

0.09

0.03

3.44

1.18

0.13

0.04

1.71

0.49

0.06

0.02

9.42

2.41

0.35

0.09

13.17

2.83

0.49

0.1

4.94

0.91

0.18

0.03

10.25

1.97

0.38

0.07

4.38

0.82

0.16

0.03

7.47

1.3

0.28

0.05

13.12

2.16

0.48

0.08

5.19

0.38

0.19

0.01

9.47

1.59

0.35

0.06

17.42

3.27

0.65

0.12

Average

7.88

1.55

0.29

0.06

The yields obtained in these experiments show a surprising and unexpected production of pure phycotoxins (neosaxitoxin and saxitoxin) per cyanobacterial filament cultured in the modified MLA medium (Table 2), when compared to the production of the cyanobacterial filaments cultured with usual conditions (simple MLA medium) and described in the state of the art in small culture flasks, with no continuous aeration and with light (day): darkness (night) cycles (Table 3).

In the example described herein, cyanobacteria are always in the logarithmic growth phase, with permanent illumination 24 hours a day and with permanent collection of cyanobacteria, inducing permanent growth by adding new nutrients in a volume that is equivalent to the volume collected in each harvest.

As demonstrated' in Table 3, the method of the invention achieves better yields that are approximately 25 times greater than those of known methods.