| Budget Amount *help |
¥3,200,000 (Direct Cost: ¥3,200,000)
Fiscal Year 1998: ¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 1997: ¥2,000,000 (Direct Cost: ¥2,000,000)
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| Research Abstract |
Cyanobacteria play an important role as primary producers in aquatic environment. Carbon dioxide and nitrogen fixed by photosynthetically growing cyanobacteria are further utilized by other heterotrophic organisms. It has been generally accepted that heterotrophic bacteria directly utilize products excreted from algae, including cyanobacteria.
Beside, the biological process for the degradation of environmental pollutants, bioremediation, has been paid significant attention. In order to construct an efficient and stable bioremediation system, microbial consortiums are often utilized, which are composed of several strains of microorganisms capable of the degradation and/or mediating the degradation of pollutants. These microbial consortium is composed of heterotrophic bacteria, therefore, is not suitable for the application in the low-nutrient condition, such as marine environment.
Here, we focused on the application of the cyanobacteria as the producer and doner of nutrient for heterotrop
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hic bacteria, which are capable for the bioremediaton. We designated such a systematic microbial consortium composed of autotrophic bacteria and heterotrophic bacteria as an "Artificial Symbiosis". We aimed the construction of an artificial symbiosis and its application for the bioremediation of insecticide.
First, we have investigated the model artificial symbiosis, which is composed of a nitrogen fixing cyanobacterium, Anabaena sp. PCC7 120 and Escherichia coli as a representative heterotrophic bacterium. E.coli cells were able to grow in the culture supernatant of Anabaena sp., indicating that E.coli cells can metabolite the nutrients excreted by Anabaena sp.. On the basis of this finding, we carried out the pseudo-continuous maintenance of the artificial symbiosis, under both continuous light illumination and light/dark cycle. Both of the system were revealed to be maintained for more than 200 hours without the decrease in both microorganisms, suggesting that our idea of the artificial symbiosis can be constructed and maintained.
Then we have constructed an artificial symbiosis for bioremediation of insecticide, As for the cyanobacterium, Anabaena sp. was used. As for the heterotrophic bacterium, Flavobacterium sp. which produces an enzyme, phosphotriesterase (PTE), thereby degradating organophosphorous insecticides, was used. Flavobacterium sp. Was able to grow in the culture supernatant of Anabeana sp., and also express enough level of PTE for the degradation of phenitrothion, a representative organophosphorous insecticide. Pseudo-continuous cultivation of the artificial symbiosis composed of Anabaena sp. and Flavobacterium sp. was carried out under both continuous light illumination and light/dark cyrcle. The ability of the degradation of phenitrothion has been maintained in the both conditions, by expressing PTE activity of growing Flavobacterium sp. cells.
We also succeeded in the construction of a recombinant marine cyanobacterial strain, which can grow in the presence of heavy metals, such as Zn, Cu or Cd, by the heterogenic expression of metallothionein gene. Such recombinant marine cyanobacterial strains will be further utilized for the construction of an artificial symbiosis for bioremediation. Less
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