Diversity Of Culturable Thermococcales In Guaymas Hydrothermal Vents And The Genome Analysis Of Pyrococcus Yayanossi CH1

The order Thermococcales represents a large group of hyperthermophilic organoheterotrophic anaerobes. It consists of three genera, Thermcococcus, Pyrococcus, Palaeococcus. They are widely distributed in various marine high temperature solfataric environments. Their fast growing character and strong ability to adapt make them as one of the dominant microbial groups in various environments. As a group of sulfur reducers, they played an important role in the carbon and sulfur circulation in various ecosystems. Guaymas Basin is located on the east pacific rise. The surface waters are very productive and are responsible for rapid organic sediment accumulation at the seabed. These organic matters can be pyrolyzed by high temperature vent fluid to petroleum like products. Unique Thermococcales probably harbor this unique environment. This study discussed the diversity of Thermococcales in Guaymas hydrothermal vents using culture dependent method. Totally, 42 isolates were got, including 28 Thermococcus strains and 14 Pyrococcus strains. During the isolation, a super extreme enrichment condition (108℃-30Mpa) was developed and tested efficient for isolating Pyrococcus. As closely related Thermococcales strains are indistinguishable by their 16S rDNA sequence. This study searched for candidate biomarkers using genome comparson method. EF-2, known as elongation factor 2, could be used to distinguish different Thermcococcales. As the phylogenetic relationships among different Thermococcales could also be well indicated by EF-2, EF-2 was considered as an alternative gene marker suitable for Thermococcales.Genomes conceal a vast intricate record of their carriers'descent and evolution. In the second part of this study the genome of Pyrococcus yayanossi CH1 was analyzed. CH1 is the first obligate pizeophilic and hyperthermophilic archaea in the world whose optimal growth pressure is 52Mpa.. As its opt pressure is 11Mpa higher than its isolated environment (depth 4100m, ~41Mpa), CH1 probably come from the hot rock strata 3km beneath the sea floor. This study determined and annotated the complete 1716818bp-genome of CH1, followed by a comparison with other three Pyrococcus genomes. Results indicated that CH1 had the smallest genome size among isolated Pyrococcus but with the highest GC content. Codon usage bias analysis showed CH1 prefer using genetic codes whose third position was G or C. As for the amino acids composition of proteins, five amino aicds were preferred, including glycine, alanine, valine, histidine and arginine, while other three having lower composition percentages, including lysine, isoleucine and asparagines. Analysis also found the gene order of CH1 genome was completely different from other Pyrococcus. But these differences were not caused by IS(insert sequences) or transposases in the genome. Fewer IS(Insert sequence) and transposases contributed to the best conservation of the original genome. Besides, a Zn-dependent alcohol dehydrogenase coming from Staphylothermus was found in CH1 genome. It was the most direct evidence that gene communication exisisted between Thermococcales and other microbes in hydrothermal vents. Such kind gene communication might join all the genes in the microbial community as a gene pool, in which genes which could bring advantages were retained. Such mechanism might help the community to cope with disturbing environments in hydrothermal vents. Gene function analysis indicated CH1 had poor ability in carbohydrate and amino acids metabolim. In contrast, more hydrogenase and membrane bound complexes were precdited from CH1 genome, reflecting stronger ability in respiration. In deep hot biosphere, simple organic matters(such as formate), hydrogen and methane were generated by geological processes. The exsistence of relative more hydrogenases and formate hydrogen lyase system proably got advantages for CH1 in such an extreme envrionment. As CH1 genome still retained these metabolic traints, it was considered that CH1 originally lived in the deep subsurface strata while hot fluid took it to the hydrothermal vent on the sea floor.