| Summary: | 碩士 === 國立臺灣大學 === 海洋研究所 === 96 === Coral diseases are one of the major natural disturbances that threat the survival
of coral reefs worldwide. However, the characterization and mechanism of infection
have been difficult in understanding the outbreak of coral diseases due to the
limitation of applying classical microbiological assays. In this thesis, the bacteria
consortium of the “black disease” caused by a black mat-like sponge, Terpios
hoshinota, was characterized by electronic microscopy, denaturing gradient gel
electrophoresis (DGGE), and 16S ribosomal DNA library construction. In order to
understand the possible pathogenic bacteria in “black disease”, the specificity of T.
hoshinota associated bacterial community and the variation between sponge-infected
(SI) and non-sponge-infected (NSI) Porites lutea associated bacterial community
were investigated in the fringing reef of the Green Island (Lutao), where outbreak of
Terpios sponge was first reported in 2006.
Result shows that the bacterial communities from seawater, sponge, and coral
were specific. T. hoshinota associated bacterial community was specific and the
dominant bacteria group was autotrophic Cyanobacteria. The Cyanobacteria
associated with T. hoshinota were supposedly a new Cyanobacteria species as
demonstrated by 16S rDNA sequence with a unique morphology. Furthermore, the
high abundance of cyanobacteria in T. hoshinota may contribute positively to T.
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hoshinota outbreak. On the other hand, the diversity and composition similarity of
bacterial community associated with SI and NSI P. lutea were analyzed using
DOTUR and LIBSHUFF. In NSI P. lutea, the dominant bacterial groups were
Gammaproteobacteria, Cyanobacteria, and unclassified bacteria; however, in SI P.
lutea, Gammaproteobacteria and Alphaproteobacteria were major groups and the
abundance of Cyanobacteria and unclassified bacteria were low. In previous studies,
there were diverse coral holobiont on a coral. The natural coral holobiont changed to
dominant bacteria group with abundance of opportunistic bacteria when corals
experience environmental stress; similar situation was observed in SI P. lutea. The
increase of the abundance of Gammaproteobacteria is probably related to
environmental stress (sponge or seawater pollution). In addition, the unexpected
emergence of alphaproteobacteria could be opportunistic bacteria because of
disturbance of natural bacterial community. Disturbance of coral holobiont possible
loss the normal symbiont function for coral and it directly or indirectly supposed to
result in coral disease. Coral associated microbes were variable in different
environment and may be a good bioindicator for environmental stress; therefore,
building up a bioindicator, a long term investigation is apparently essential.
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