Archaea have multiple roles in global biogeochemical cycles. However, we still have limited knowledge about how environmental factors affect the diversity and function of different archaeal lineages. The goal of this study was to examine the change in the abundance and community structure of Archaea in the sediments collected from the lower Pearl River (mainly North River tributary), its estuary, and coastal South China Sea (SCS) in order to evaluate how archaeal ecological function might change along the salinity gradient. Pyrosequencing of the 16S rDNA gene of Archaea was performed on sediment samples from Feilaixia Dam on the North River tributary to Wanshan islands, which have a salinity range of 0.1 to 31.2‰. Consistent with the salt tolerance of cultivated representatives, methanogens in the genera Methanoregula, Methanosaeta, and Methanosarcina and Nitrososphaera within Thaumarchaeota of the ammonia-oxidizing Archaea (AOA) were abundant in freshwater sediments of the North River tributary, whereas the marine-associated genera Methanococcoides and Nitrosopumilus were the most abundant methanogens and AOA, respectively, in the estuary and coastal SCS. However, the percentages of total methanogens decreased and Thaumarchaeota increased with salinity, respectively. The phylum Crenarchaeota was largely represented by class-level lineages with no cultivated representatives, which collectively were more abundant in the estuary and coastal SCS in comparison to freshwater sites. This study indicates that salinity is the dominating factor affecting archaeal community structure and ecological function from the North River tributary of the Pearl River, its estuary, and coastal SCS, which is consistent with salinity control on microbial diversity in other regions of the world.
Using RNA-based techniques and hot spring samples collected from Yunnan Province, China, we show that the amoA gene of aerobic ammonia-oxidizing archaea can be transcribed at temperatures higher than 74°C and up to 94°C, suggesting that archaeal nitrification can potentially occur at near boiling temperatures.Aerobic ammonia-oxidizing archaea (AOA) are one major group of microorganisms mediating the autotrophic ammonia oxidation (2) which is central to the global nitrogen cycle (9). AOA possess an ammonia monooxygenase (AMO) which is the enzyme responsible for catalyzing aerobic ammonia oxidation, and its ␣ subunit is encoded by the amoA gene (15). Multiple amoA gene-based molecular studies have demonstrated that AOA can be adapted to a large gradient of environmental variables with respect to temperature (0.2 to 97°C) and pH (2.5 to 9.0) (see the review by Erguder et al.[2] and the references therein). However, so far, only moderately thermophilic "Candidatus Nitrososphaera gargensis" and thermophilic "Candidatus Nitrosocaldus yellowstonii" have been obtained in culture and show the capability of oxidizing ammonia at high temperatures; they can produce nitrite at 46°C and 60 to 74°C at pHs 7 to 8, respectively (1, 4). In addition, Reigstad et al. (12) demonstrated biological ex situ nitrification at 85°C and pH 3.0, using terrestrial hot-spring samples. This indicated that the AMO enzyme is active at temperatures of up to 85°C. In the meantime, with the use of DNA-based molecular techniques, Reigstad et al. (12) and Zhang et al. (16) retrieved AOA amoA gene clone sequences from global terrestrial hot springs with a large gradient of pHs (2.5 to 9.0) and temperatures (38 to 97°C). However, the AOA amoA gene has never been transcribed from environments with temperatures higher than 74°C. In the present study, we performed RNA-based studies investigating the abundance and diversity in hot springs (temperature, 44.5 to 94.0°C; pH, 2.4 to 9.0) of Yunnan Province in southwestern China.
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