| Summary: | 博士 === 慈濟大學 === 醫學科學研究所 === 103 === ABSTRACT
Chapter 1
Among antioxidant enzymes, catalases protect microorganisms by degrading hydrogen peroxide under oxidative stress. In the first project of this dissertation, the activities of at least four Vibrio parahaemolyticus catalases (Kat1 to Kat4) are differentially detected using cells that are grown at different stages and under various stress conditions by using zymographic analysis. The results show that only Kat2 is stable at 55°C. Kat1 and Kat2 respond to hydrogen peroxide during the exponential growth phase, and the response decreases upon entering the stationary phase. Kat3 and Kat4 are bifunctional, exhibiting both catalase and peroxidase activities, and are only expressed during the stationary phase, under starvation, or at pH 5.5. The expression of Kat3 and Kat4 depends on RpoS. We confirm that both monofunctional and bifunctional catalases are expressed and function differentially under various stresses to contribute total catalase activities for the survival of V. parahaemolyticus. A comparative genomic study among Vibrio species reveals that only V. parahaemolyticus contains two copies of genes that encode monofunctional and bifunctional catalases. We propose that both types of catalases, either evolved or acquired horizontally through long-term evolution, may play crucial protective roles in V. parahaemolyticus in response to environmental fluctuations.
ABSTRACT
Chapter 2
Vibrio owensii GRA50-12 was isolated from green algae in the intertidal zone at Shitiping in Haulien. The draft genome of GRA50-12 consists of 6,006,497 bps, with a GC content of 45%. The two longest contigs in the draft genome are 1300324 bps and 1129439 bps long. The number of coding sequences is 4,891. Noncoding RNAs contain 120 tRNAs, 1 transfer-messenger RNA (tmRNA), and 22 rRNAs. These results show that the contigs are of high quality for deep genome analysis. The studies using genomic analysis and polyphasic approach show that V. owensii GRA50-12 is closely related to Vibrio owensii OCN002. Genomic analysis also finds a number of stress response genes involving in many abiotic stresses. The genome contains genes encoding toxin production, virulence regulation, type-II, IV, and VI secretion systems, although the type-III secretion system is absent. Taken together, the study shows that V. owensii GRA50-12 is potentially a pathogen and has genes to allow the strain to survive in the ocean.
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