Bacterial and Archaeal Communities within an Ultraoligotrophic, High-altitude Lake in the Pre-Himalayas of the Qinghai-Tibet Plateau

Archaeal and Bacterial Communities Within the Wetland Alkaline Har Lake of the Qinghai-Xizang Plateau

Har Lake (HL) is in the northeastern basin of the Qinghai-Xizang Plateau (QTP), sits at an altitude of 4379 m, and is classified as a soda lake within a wetland ecosystem. Evaluating the archaeal and bacterial communities in HL could offer valuable insights into the biogeochemical cycling within plateau wetland lakes. Consequently, high-throughput sequencing of 16S rRNA genes was conducted in this study to assess the composition of HL microbial communities and their association with environmental factors. The HL archaeal communities comprised 5 phyla, 5 classes, and 30 genera, while the bacterial communities comprised 28 phyla, 52 classes, and 542 genera. The dominant archaeal phylum was Thaumarchaeota (30.30-93.07% relative abundances), followed by Woesearchaeota (6.79-67.78%), while the most abundant genus was Nitrososphaera (30.30-93.07%). The distribution of Nitrososphaera was significantly correlated with TN, Mg2+, and Ca2+ concentrations. Bacterial communities predominantly comprised the Proteobacteria phylum (59.33-74.70%), followed by Bacteroidetes (13.92-19.19%) and Firmicutes (0.69-9.60%). Dominant bacterial genera included halophilic hydrocarbon-degrading bacteria like Oleibacter (1.90-18.69%), Perlucidibaca (5.19-17.46%), and Thalassolituus (0.80-11.98%). The results suggest Nitrososphaera and Woesearchaeota may be key taxa involved in carbon and nitrogen biogeochemical cycling within HL. Additionally, the high abundances of halophilic hydrocarbon-degrading bacteria suggests that potential contamination of HL may have occurred due to frequent animal and human activities. Overall, this study provides valuable insights into the archaeal and bacterial community structures in high-altitude soda lake wetlands and their interactions with their unique environments.

Isolation optimization and screening of halophilic enzymes and antimicrobial activities of halophilic archaea from the high-altitude, hypersaline Da Qaidam Salt Lake, China

AIM

The aim of this study is to increase the diversity of culturable halophilic archaea by comparing various isolation conditions and to explore the application of halophilic archaea for enzyme-producing activities and antimicrobial properties.

METHODS AND RESULTS

We systematically compared the isolation performance of various archaeal and bacterial media by isolating halophilic archaea from the Da Qaidam Salt Lake, a magnesium sulfate subtype hypersaline lake on the Qinghai-Tibet Plateau, China, using multiple enrichment culture and gradient dilution conditions. A total of 490 strains of halophilic archaea were isolated, which belonged to five families and 11 genera within the order Halobacteriales of the class Halobacteria of the phylum Euryarchaeota. The 11 genera consisted of nine known genera and two potentially new genera, the former including Halorubrum, Natranaeroarchaeum, Haloplanus, Haloarcula, Halorhabdus, Halomicrobium, Halobacterium, Natrinema, and Haloterrigene. Halorubrum was the dominant genus with a relative abundance of 78.98%. By comparing different culture conditions, we found that bacterial media 2216E and R2A showed much better isolation performance than all archaeal media, and enrichment culture after 60 d and dilution gradients of 10-1 and 10-2 were best fitted for halophilic archaea cultivation. The screening of 40 halophilic archaeal strains of different species indicated that these halophilic archaea had great extracellular enzyme activities, including amylase (62.5%), esterase (50.0%), protease (27.5%), and cellulase (15.0%), and possessed great antimicrobial activities against human pathogens. A total of 34 strains exhibited antimicrobial activity against four or more pathogens, and 19 strains exhibited antimicrobial activity against all six pathogens.

CONCLUSIONS

The diversity of culturable halophilic archaea was significantly increased by enrichment culture and selection of bacterial media, and screening of representative strains showed that halophilic archaea have multiple extracellular enzyme activities and broad-spectrum antimicrobial activity against human pathogens.

Planktonic/benthic Bathyarchaeota as a "gatekeeper" enhance archaeal nonrandom co-existence and deterministic assembling in the Yangtze River

Archaea, the third proposed domain of life, mediate carbon and nutrient cycling in global natural habitats. Compared with bacteria, our knowledge about archaeal ecological modes in large freshwater environments subject to varying natural and human factors is limited. By metabarcoding analysis of 303 samples, we provided the first integrate biogeography about archaeal compositions, co-existence networks, and assembling processes within a 6000 km continuum of the Yangtze River. Our study revealed that, among the major phyla, water samples owned a higher proportion of Thaumarchaeota (62.8%), while sediments had higher proportions of Euryarchaeota (33.4%) and Bathyarchaeota (18.8%). A decline of polarization in phylum abundance profile was observed from plateau/mountain/hill to basin/plain areas, which was attributed to the increase of nutrients and metals. Planktonic and benthic Bathyarchaeota tended to co-occur with both major (e.g., methanogens or Thermoplasmata) and minor (e.g., Asgard or DPANN) taxa in the non-random networks, harboring the highest richness and abundances of keystone species and contributing the most positively to edge number, node degree, and nearest neighbor degree. Furthermore, we noted significantly positive contributions of Bathyarchaeota abundance and network complexity to the dominance of deterministic process in archaeal assembly (water: 65.3%; sediments: 92.6%), since higher carbon metabolic versatility of Bathyarchaeota would benefit archaeal symbiotic relations. Stronger deterministic assembling was identified at the lower-reach plain, and higher concentrations of ammonium and aluminum separately functioning as nutrition and agglomerator were the main environmental drivers. We lastly found that the Three Gorges Dam caused a simultaneous drop of benthic Bathyarchaeota abundance, network co-existence, and deterministic effects immediately downstream due to riverbed erosion as a local interference. These findings highlight that Bathyarchaeota are a "gatekeeper" to promote fluvial archaeal diversity, stability, and predictability under varying macroscopic and microscopic factors, expanding our knowledge about microbial ecology in freshwater biogeochemical cycling globally.