| Summary: | 碩士 === 國立臺灣大學 === 海洋研究所 === 105 === Most of the Earth’s biosphere is permanently cold environment, which temperature is lower than 5 °C, including alpine and polar regions which constitute 25 % of the world’s land surface area, and deep sea, etc. Many psychrotrophs have been isolated from these cold environments. There isn’t any permanently cold environment in Taiwan, for the reason that Taiwan is situated in the subtropical zone. However, the high elevation regions (over 3,000 m) in the Yushan National Park are classified as frigid zones. Therefore, psychrotrophs may abundantly exist in those cold habitats. The purpose of this study was to investigate the compositions and diversity of psychrotrophs in the soil of the high elevation regions of Yushan. Another aim was to find out the novel psychrotrophs existing in the soil of the high elevation regions of Yushan. The soil samples were collected from the different vegetation in the regions of Main, North (3,600 – 3,700 m) and West Peaks (3,402 – 3,518 m) of Yuhsan. This study was conducted using bacterial enumeration and isolation by plate method, detecting the phenotypic characteristics, and the 16S rRNA gene sequences, and constructing the phylogenetic tree by neighbor-joining method. The results revealed that the bacterial abundance of psychrotrophs in the soil of the high elevation regions of Yushan ranged from 2.8 × 106 to 3.5 × 107 (CFU/g wet wt.). About 97 % of isolates were psychrotolerant bacteria. Analysis of the 16S rRNA sequences revealed that 86.7 %, 9.5 %, 1.9 % and 1.9 % of isolates could be divided to four phyla namely Proteobacteria, Firmicutes, Actinobacteria, Bacteroidetes, respectively. The isolates further distributed into 18 genera, Pseudomonas, Janthinobacterium, Rahnella, Rouxiella, Acinetobacter, Duganella, Flavobacterium, Stenotrophomonas, Collimonas, Variovorax, Luteibacter, Dyella, Caballeronia, Serratia, Arthrobacter, Paenibacillus, Rhodococcus, Oerskovia. In this study, Pseudomonas was the predominant genus (45.7%), follwed by Rahnella (11.4 %) and Janthinobacterium (9.5 %). The result of psychrotrophs composition revealed that the diversity of genera in the regions of West Peak (15 genera) was higher than that in the regions of Main and North Peaks. The result also indicated that Pseudomonas widely distributed in the soil of the high elevation regions of Yushan. Additionally, the sequences similarity of strain H2 in this study and its related type species was lower than 97 %. It meant that strain H2 might have the potential to be proposed as a novel species. According to the result of phylogenetic tree, strain H2 might be a novel species of the genus Glaciimonas.
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