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Hot springs are some of the most special environments on Earth. Many prokaryotic and eukaryotic microbes have been found to live in this environment. The Himalayan geothermal belt (HGB) has numerous hot springs spread across the area. Comprehensive research using molecular techniques to investigate eukaryotic microorganisms is still lacking; investigating the composition and diversity of eukaryotic microorganisms such as protists in the hot spring ecosystems will not only provide critical information on the adaptations of protists to extreme conditions, but could also give valuable contributions to the global knowledge of biogeographic diversity. In this study, we used high-throughput sequencing to illuminate the diversity and composition pattern of protist communities in 41 geothermal springs across the HGB on the Tibetan Plateau. A total of 1238 amplicon sequence variants (ASVs) of protists were identified in the hot springs of the HGB. In general, Cercozoa was the phylum with the highest richness, and Bacillariophyta was the phylum with the highest relative abundance in protists. Based on the occurrence of protist ASVs, most of them are rare. A high variation in protist diversity was found in the hot springs of the HGB. The high variation in protist diversity may be due to the different in environmental conditions of these hot springs. Temperature, salinity, and pH are the most important environmental factors that affect the protist communities in the surface sediments of the hot springs in the HGB. In summary, this study provides the first comprehensive study of the composition and diversity of protists in the hot springs of the HGB and facilitates our understanding of the adaptation of protists in these extreme habitats.

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Aims: As a high-altitude water area, the Lhasa River's aquatic ecosystem has a high research value due to its special environmental conditions. In recent years, studies on the high-altitude water area have gradually increased, but there are few studies on the community structure of ciliates in the Lhasa River. We conducted this study to explore the composition pattern, spatial and temporal diversity pattern, and maintenance mechanism of ciliate communities in the midstream and downstream reaches of the Lhasa River. Methods: Seventeen samples were collected from the middle and lower reaches of the Lhasa River in May 2015 and August 2015, and October 2016. In-vivo observation, Rugo's iodine solution fixation staining, and Wilbert's protein silver method were utilized for species identification. The spatial and temporal differences of community structure were analyzed by the Shannon diversity index, Margalef index, and richness. The interactions between ciliate groups were analyzed through co-occurrence network. The effects of physical and chemical factors on ciliate community structures were investigated using redundancy analysis (RDA).

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