CC BY
53
2004
Известия ТИНРО
Том 137
УДК 576.8(26)
T.Misonou, K.Tsuda, R.Kaji (University of Yamanashi, Kofu, Japan)
CULTURE OF CYANOBACTERIA USING DEEP SEAWATER
Мисоноу Т., Цуда К., Кадзи Р. Культивирование цианобактерий с использованием глубинной морской воды // Изв. ТИНРО. — 2004. — Т. 137. — С. 285-288.
Морская вода с глубин свыше 200-300 м является биологически и химически чистой. В то же время она содержит высокие природные концентрации различных неорганических элементов, кроме того, обладает постоянной низкой температурой. Поэтому в последнее время в Японии такая вода широко применяется в промышленности, сельском хозяйстве и рыболовстве. Рассматриваются возможности применения морской воды, добытой с глубины 615 м у о. Окинава, в качестве среды для культивирования цианобактерий Spirulina sp. Результаты эксперимента признаны удовлетворительными. Полученная биомасса может быть использована в водородном производстве и для других целей.
The seawater under 200 to 300 m depth of the sea is named "Deep Seawater" (DSW). DSW is continuously formed by horizontal and vertical circulation of seawater in various scales in the world. The organic carbon concentration of DSW is very low since there are few photoautotrophic cells of phytoplankton and/or other organisms. DSW is biologically, chemically clean, containing plenty of various inorganic elements and keeping stable low temperature. In Japan, the application of DSW is widely spread recently in the field of agriculture, fishery and industry.
We attempted to apply DSW to the culture of cyanobacteria. Using enriched DSW from 615 m depth at Okinawa Island as a culture medium, Spirulina sp. grows satisfactorily. The obtained cells are possibly used as a bio-resource for hydrogen production and other purposes.
What is deep seawater?
The seawater beyond a continental shelf, under 200-300 m depth is especially named "deep seawater" (DSW). Since water absorbs a visible light, the sunlight almost not penetrates to such depth. DSW contains few photoautotrophic cells of phytoplankton and heterotrophic organisms. As photosynthesis is impossible there, the supply of organic carbon is strongly restricted to DSW. Though the concentration of organic carbon in DSW is very low, inorganic nutrients are abundant since the organic compounds from sea surface are fully degraded unless reaching to this depth and various inorganic compounds are accumulated to DSW.
Moreover, as DSW is under a thermocline which is formed ca. 200 m depth, there is no exchange of water between DSW and the surface layer of the sea. It means that a variety of pollutants are unlikely to contaminate DSW. Namely, DSW is biologically and chemically clean, containing plenty of various inorganic ions, and it keeps a stable low temperature throughout the year.
DSW does not stay in the same place. In the sea near Greenland or in Antarctic Seas, the cooled seawater settles to the seabed especially in winter and
flows as deep sea circulation (Fig. 1). This flux of the North Pacific Deep Water (NPDW) flows very slowly through the Atlantic Ocean — Antarctic Seas — Indian Ocean — Pacific Ocean and rises to the sea surface by mixing with warm surface water in the North Pacific Ocean after 1500 to 2000 years. The stability of this deep-sea flux is assumed to be an important stabilizing factor of the global climate.
Fig. 1. Global conveyor (Schmitz, 1995)
In the rising point of such deep-sea flux , various aquatic resources are abundant due to the constant supply of inorganic nutrients of DSW. Moreover, a progressive use of DSW in various fields is developed in Japan at the present time.
Near the coastal zone of islands of Japan, there are two fluxes other than NPDW, the North Pacific Intermediate Water (NPIW) from the Okhotsk Sea circulating for ca. 50 years in the Pacific Ocean, and the Japan Sea Proper Water (JSPW) originated in the area off Vladivostok. NPDW, NPIW and JSPW flow under 1500, 500-1500, and 200-500 m depth, respectively. DSW drawn in Japan is mostly NPIW or JSPW (Fig. 2).
Japan
Fig. 2. DSW around islands of
In Okinawa prefecture in the most southern part of Japan, the Okinawa Research Institute of Deep Seawater was established in 2000. This institute draws 13,000 t/day of DSW from 615 m depth. This DSW considered mainly NPIW is utilized in the fields of fisheries, agriculture and industry. For example, the low temperature of DSW is used to regulate the temperature of a greenhouse in the field of agriculture or to many purposes in the field of industry to control temperature. One of the applications of fisheries is an algal cultivation. Various algae may grow well in this clean and inorganic nutrition-rich DSW and the obtained biomass may be used as foods for human, feeds for livestock or materials for extraction or fermentation of various organic compounds having economic value.
Concentration of inorganic elements in DSW and SOT medium, mg/L
Culture of cyanobacteria with DSW
We have started a project to apply DSW to the culture of cyanobacteria. Table shows the content of inorganic elements in DSW from Okinawa Island area. Although total P, N and Fe are insufficient, Mg and Ca are excessive and K is sufficient in comparison with artificial SOT medium.
At first, we tried to culture a cyanobacterium Spir-ulina sp. in DSW. One milliliter of stock culture of Spir-ulina sp. was inoculated into the 150 mL of autoclaved DSW in 200 mL flask and cultured under ca. 2,000 lx of fluorescent light (L: D = 16: 8 hr) at 20 oC with constant rotated shaking. The cell growth is monitored by the absorption of 560 and 750 nm. Since the cells grew slowly with DSW (Fig. 3, A), P, N and Fe were added up to the level of SOT medium (Fig. 3, B). The cells grew fast and densely in this enriched DSW. To avoid the precipitation of the cells, EDTA (ethylene diamine tetra-acetic acid) was added as a chelating agent. Though the cell growth was a little lowered, the flock formation was depressed (Fig. 3, C).
Element DSW SOT
P 0.05 89.0
N 0.47 412.0
K 450.0 673.0
Mg 1450.0 19.7
Ca 562.0 10.9
Fe 0.065 2.0
B 3.81 0.5
Zn 0.002 0.05
Fig. 3. Growth curves of Spir-ulina sp.: A — DSW; B — DSW + + P/N/Fe; C — DSW + P/N/Fe + + EDTA (215 |M)
As the flock formation was assumed to depend on the concentration of the cation and pH of the medium, the chelating effect of EDTA on pH change was analyzed (Fig. 4). The pH change was monitored according to the addition of NaOH to 100 mL DSW with various concentration of EDTA.
For the concentration of EDTA over 0.5 mM, the pH change of DSW by addition of NaOH was strongly inhibited. Thus, we assumed DSW might be available as a culture medium if adding some inorganic nutrients with chelating agent. The most effective concentration of these factors on the cell growth should be determined.
Fig. 4. The effect of EDTA on pH change of DSW
From the biomass of cyanobacteria obtained using DSW, various useful compounds may be extracted for industrial circles and/or cyanobacterial cells may be used to evolve hydrogen or to fix nitrogen, etc.
Perspective of the DSW application
The field of DSW application in Japan is widely spreading not only to agriculture, but also to production of various health supplements or other staffs by food or medical industry in recent years. The application of DSW as a culture medium of various organisms is also hopeful. Since cyanobacteria are expected as a useful bio-resource, the combination of DSW and cyanobacterial culture should be intensively studied.
Ninety-seven percent of the Earth water is in the sea, and DSW accounts for up to 95 % of all seawater. Although the amount of DSW is considered enormous as a natural resource, unrestricted waste of DSW should be rigorously prohibited. While monitoring the effect on the other ecosystems, a method for sustainable application has to be developed.
Reference
Schmitz W.J. On the interbasin-scale thermohaline circulation // Rev. Geophys. — 1995. — № 33. — P. 151-173.
Поступила в редакцию 4.03.04 г.
