| Budget Amount *help |
¥3,830,000 (Direct Cost: ¥3,500,000、Indirect Cost: ¥330,000)
Fiscal Year 2007: ¥1,430,000 (Direct Cost: ¥1,100,000、Indirect Cost: ¥330,000)
Fiscal Year 2006: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 2005: ¥1,700,000 (Direct Cost: ¥1,700,000)
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| Research Abstract |
Biofilms on submarine substrata can act as efficient inducers for settlement and metamorphosis of Acropora larvae. Indeed, bacteria that induce metamorphosis have been identified from biofilms; one strain of Pseudoalteromonas and three of Alteromonas. Since micro-environments on substrata are very diverse, there could be more bacteria species capable of inducing metamorphosis. Such bacteria were screened by a new method in this study. Each bacteria source was swabbed from a 1 cm^2 surface of tiles submerged in a reef for 3 months, and suspended in sterilized seawater (SSW). Membrane filters were soaked in each suspension and incubated on agar media. For passage, the bacteria-grown filter (mixed culture filter; MCF) was broken into pieces in SSW. We tested each MCF for the activity to induce metamorphosis. Out of 32 MCF lineages from 16 sources, metamorphosis-inducing batches were obtained in 11 from 8. Although individual batches varied in their activities, every lineage contained one or more batches giving 100% metamorphosis. Some lineages retained their activities through passages. Next, a total of 230 independent strains were isolated from 12 active MCFs, and 19 isolates turned out to induce metamorphosis, including 17 giving 100% metamorphosis. According to 16SrDNA sequencing analyses, 17 isolates, except 2 that failed to be identified, fell into 7 species in 4 genera; Pseudoalteromonas, Alteromonas, Vibrio and one in alpha-proteobacteria. Our original culture method using MCFs enabled us to get metamorphosis-inducing bacteria very efficiently, compared with the conventional isolation method (1/80 and 3/500 isolates). This study reveals that inducer bacteria spread over in wide taxa. In addition, we found two Pseudoalteromonas species that inhibit metamorphosis. These findings may suggest very high diversity of bacteria concerned with the metamorphosis decision of Acropora larvae.
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