| Sulfate-reducing bacteria (SRB) and yeasts are two important microbial groups in deep-sea environment. SRB are the major pulse driver of the carbon and sulfur cycles in deep-sea and play an important role in the deep-sea ecosystem. The study on the SRB diversity and its relationship to the environment could provide helpful information in understanding the characteristics of deep-sea carbon and sulfur cycles and the interaction between deep-sea biogeochemical cycle and the global climate. Yeasts are an important deep-sea microbial resource, and until now, the information about deep-sea yeasts is still scarce. The research on the diversity, distribution, physiological and ecological characteristics of deep-sea yeasts would have important meaning in the industrial exploration and application on deep-sea yeasts.The SRB diversity and community structures in deep layers of deep-sea sediments (more than 2 mbsf (meters below sea floor)) of two sites (WP01-3 (142°30'14"E, 8°31'20"N), WP01-4 (142°59'51"E, 8°53'08"N)) in tropical West Pacific Warm Pool region, as well as the interaction between SRB community and environment, were analyzed based on molecular methods. The results demonstrated that the dominant clones from both sites were related to Gram-positive spore forming genus, Desulfotomaculum. However, the other SRB group which is generally reported to be predominant in deep-sea sediments of other regions, 5 - subclass of the proteobacteria was found to be in very low percentages in this study. Therefore, it can be speculated that there exists a unique chemical environment in deep-sea sediment of this warm pool region. When comparing the Desulfotomaculum sp. related sequences from both sites, it was revealed that though the Desulfotomaculum-like sequences from Site WP01-3 were more diverse than those from Site WP01-4, all these sequences from both sites showed high similarity and formed a new phylogenetically homogeneous cluster in the Desulfotomaculum genus which had never been reported before. So we speculated that these Desulfotomaculum-related sequences belong to new species in the genus. Though no culture was enriched from sediment of Site WP01-3, sequence analysis of enrichment culture further confirmed the dominance of Desulfotomaculum genus in Site WP01-4. But Desulfotomaculum-related sequences from culture-dependent and -independent samples belonged to two different clusters respectively. This difference showed the choice ofcultivation to the microorganisms. Besides SRB, some other microbial groups such as sulfur-oxidizing bacteria (SOB), Addobacterium, and so on, were also detected in the sediment samples. The detection of SOB in the samples suggested that in the deep sediment layer of West Pacific "Warm Pool", there maybe exist a complete sulfur cycle progress driven by the SRB and SOB. And because there existed active sulfate reduction process with a great of concomitant production of H2S in deep sediment layer of West Pacific "Warm pool", it was reasonable that Addobacterium were detected in our samples.With a focus on the collection and exploitation of deep-sea microorganisms, 55 deep-sea yeast strains were isolated from tropical Pacific Ocean. These strains were identified by sequence analysis of the D1/D2 region of the 26S rDNA. The results demonstrated that this method was suitable for the identification of deep-sea yeasts. All the strains could get specific names by this sequence analysis, and there were 3 strains in the collection which belonged to new isolates that had never been collected in the database. Among all the yeast isolates, the most dominant genus was Rhodotorula, which accounted for 36.4% of the isolates. The second dominant was Candida, which represented 21.8% of all isolates. Moreover, Rhodosporidium, Debaryomyces, Pichia, Leucosporidium and Cryptococcus also occupied 7%-ll% in the collection, respectively. Sporidiobolus were detected in very low proportion, which only represented 1.8% of the isolates. The distribution of deep-sea yeasts was analyzed, and it was found that the species distribution was great dependent on the sample sources. In the strains from organism samples, the ascomycetous yeasts were predominant, which accounted for 91.7% of the isolates. While the basidomycetous yeasts were dominant in the strains from sea water samples, which represented 87.5% of the isolates. And for the strains from sediment and over-laid water samples, there were great difference in the isolates from different sea areas. 88.9% of the isolates from East Pacific Ocean belonged to ascomycetous yeasts, while the isolates from West Pacific Ocean all belonged to basidomycetous yeasts. This difference in the yeast distribution was due to the difference in nutrition supply of samples. The adaptability of the yeast strains for temperature factor was studied and it was found that all tested strains showed eurytropic adaption to change in temperature. They could survive in a wide temperature amplitude which spaned from 5 to 30 °C. But the strains from different samples had great difference in the optimal temperature. The optimal temperature of the strains from sea water samples were between 20 and 30 "C, they couldn't growwell in the low temperature (5-10°C). While, many isolates from over-laid water and sediment samples had a wide amplitude of optimal temperature, they could grow well in the low temperature under 10°C. This result incarnated the response of microorganisms to their living environments. At the same time, 6 strains were selected to be identified by BIOLOG Microstation System and their carbon-utilizing patterns were analysed. The identification results were similar with the molecular identification. Among the carbon sources of BIOLOG system, 8 types of carbon sources could be utilized by at least 5 strains. These 8 carbon sources were the familiar saccharide in several sorts of metabolic pathway for microorganisms. While, there were 13 types of carbon sources which could only be used by at most 1 strain. These 13 carbon sources include ramification of glucose, organic acid and several sorts of disaccharide and amylose. Moreover, the strains isolated from different niches had great different carbon-utilizing spectrum. The strains from sharks had the most diverse carbon-utilizing spectrum. Then the second were the strains from sediment and blue-green algae samples, the last were from the cheek of tetraodonts. This difference embodied the diversity of nutrition types in deep-sea yeasts. All these 55 strains of deep-sea yeasts were screened for antimicrobial and antitumor activity. The results showed that only 1 strain was detected to have antimicrobial activity and no strain had antitumor activity. It demonstrated that the screening models we selected were restricted in the antibiotic activity exploitation of deep-sea yeasts. And we need continue to search for new screening models and enlarge screening amounts.
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