Genomics-based identification of a cold adapted clade in Deinococcus.

BACKGROUND: Microbes in the cold polar and alpine environments play a critical role in feedbacks that amplify the effects of climate change. Defining the cold adapted ecotype is one of the prerequisites for understanding the response of polar and alpine microbes to climate change. RESULTS: Here, we analysed 85 high-quality, de-duplicated genomes of Deinococcus, which can survive in a variety of harsh environments. By leveraging genomic and phenotypic traits with reverse ecology, we defined a cold adapted clade from eight Deinococcus strains isolated from Arctic, Antarctic and high alpine environments. Genome-wide optimization in amino acid composition and regulation and signalling enable the cold adapted clade to produce CO2 from organic matter and boost the bioavailability of mineral nitrogen. CONCLUSIONS: Based primarily on in silico genomic analysis, we defined a potential cold adapted clade in Deinococcus and provided an updated view of the genomic traits and metabolic potential of Deinococcus. Our study would facilitate the understanding of microbial processes in the cold polar and alpine environments.

The distribution and drivers of microbial pigments in the cryoconite of four Tibetan glaciers.

Microbial pigments play a significant role in glacier albedo reduction, thereby contributing to accelerated glacier retreat. The Tibetan Plateau has experienced rapid glacier retreat in recent decades due to global warming, yet there is limited understanding of microbial pigment distribution in the region. Here, we investigated the pigment concentration and composition in cryoconite from four glaciers. Our results showed that chlorophylls were the dominant pigments in Palong No. 4 (PL) and Jiemayangzong (JMYZ) glaciers located in the south of the Tibetan Plateau, while carotenoids were dominant in Qiangyong (QY) and Tanggula (TGL) glaciers located in the central region. Additionally, the chlorophyll b to chlorophyll a ratio, which is an indicator of the algae-to-cyanobacteria ratio, was higher in PL and JMYZ compared to QY and TGL. By using Random Forest Regression and Structural Equation Modelling, we determined that the concentrations of chlorophyll a, chlorophyll b, and carotenoids were associated with autotrophic bacteria relative abundance, climatic factors, and a combination of bacterial and climatic factors, respectively. This study is the first to describe the distribution of microbial pigments in cryoconite from Tibetan glaciers, providing additional support on the influence of algal pigment on glacier retreat.

The unique salt bridge network in GlacPETase: a key to its stability.

The extensive accumulation of polyethylene terephthalate (PET) has become a critical environmental issue. PET hydrolases can break down PET into its building blocks. Recently, we identified a glacial PET hydrolase GlacPETase sharing less than 31% amino acid identity with any known PET hydrolases. In this study, the crystal structure of GlacPETase was determined at 1.8 Å resolution, revealing unique structural features including a distinctive N-terminal disulfide bond and a specific salt bridge network. Site-directed mutagenesis demonstrated that the disruption of the N-terminal disulfide bond did not reduce GlacPETase's thermostability or its catalytic activity on PET. However, mutations in the salt bridges resulted in changes in melting temperature ranging from -8°C to +2°C and the activity on PET ranging from 17.5% to 145.5% compared to the wild type. Molecular dynamics simulations revealed that these salt bridges stabilized the GlacPETase's structure by maintaining their surrounding structure. Phylogenetic analysis indicated that GlacPETase represented a distinct branch within PET hydrolases-like proteins, with the salt bridges and disulfide bonds in this branch being relatively conserved. This research contributed to the improvement of our comprehension of the structural mechanisms that dictate the thermostability of PET hydrolases, highlighting the diverse characteristics and adaptability observed within PET hydrolases.IMPORTANCEThe pervasive problem of polyethylene terephthalate (PET) pollution in various terrestrial and marine environments is widely acknowledged and continues to escalate. PET hydrolases, such as GlacPETase in this study, offered a solution for breaking down PET. Its unique origin and less than 31% identity with any known PET hydrolases have driven us to resolve its structure. Here, we report the correlation between its unique structure and biochemical properties, focusing on an N-terminal disulfide bond and specific salt bridges. Through site-directed mutagenesis experiments and molecular dynamics simulations, the roles of the N-terminal disulfide bond and salt bridges were elucidated in GlacPETase. This research enhanced our understanding of the role of salt bridges in the thermostability of PET hydrolases, providing a valuable reference for the future engineering of PET hydrolases.

Genomic analyses reveal a low-temperature adapted clade in Halorubrum, a widespread haloarchaeon across global hypersaline environments.

BACKGROUND: Cold-adapted archaea have diverse ecological roles in a wide range of low-temperature environments. Improving our knowledge of the genomic features that enable psychrophiles to grow in cold environments helps us to understand their adaptive responses. However, samples from typical cold regions such as the remote Arctic and Antarctic are rare, and the limited number of high-quality genomes available leaves us with little data on genomic traits that are statistically associated with cold environmental conditions. RESULTS: In this study, we examined the haloarchaeal genus Halorubrum and defined a new clade that represents six isolates from polar and deep earth environments ('PD group' hereafter). The genomic G + C content and amino acid composition of this group distinguishes it from other Halorubrum and the trends are consistent with the established genomic optimization of psychrophiles. The cold adaptation of the PD group was further supported by observations of increased flexibility of proteins encoded across the genome and the findings of a growth test. CONCLUSIONS: The PD group Halorubrum exhibited denser genome packing, which confers higher metabolic potential with constant genome size, relative to the reference group, resulting in significant differences in carbon, nitrogen and sulfur metabolic patterns. The most marked feature was the enrichment of genes involved in sulfur cycling, especially the production of sulfite from organic sulfur-containing compounds. Our study provides an updated view of the genomic traits and metabolic potential of Halorubrum and expands the range of sources of cold-adapted haloarchaea.

Glacier as a source of novel polyethylene terephthalate hydrolases.

Polyethylene terephthalate (PET) is a major component of microplastic contamination globally, which is now detected in pristine environments including Polar and mountain glaciers. As a carbon-rich molecule, PET could be a carbon source for microorganisms dwelling in glacier habitats. Thus, glacial microorganisms may be potential PET degraders with novel PET hydrolases. Here, we obtained 414 putative PET hydrolase sequences by searching a global glacier metagenome dataset. Metagenomes from the Alps and Tibetan glaciers exhibited a higher relative abundance of putative PET hydrolases than those from the Arctic and Antarctic. Twelve putative PET hydrolase sequences were cloned and expressed, with one sequence (designated as GlacPETase) proven to degrade amorphous PET film with a similar performance as IsPETase, but with a higher thermostability. GlacPETase exhibited only 30% sequence identity to known active PET hydrolases with a novel disulphide bridge location and, therefore may represent a novel PET hydrolases class. The present work suggests that extreme carbon-poor environments may harbour a diverse range of known and novel PET hydrolases for carbon acquisition as an environmental adaptation mechanism.

Distinct strategies of the habitat generalists and specialists in sediment of Tibetan lakes.

Microbial metacommunities normally comprise generalists and specialists. Uncovering the mechanisms underlying the diversity patterns of these two sub-communities is crucial for aquatic biodiversity maintenance. However, little is known about the ecological assembly processes and co-occurrence patterns of the habitat generalists and specialists across large spatial scales in plateau lake sediments, particularly regarding their environmental adaptations. Here, we investigated assembly processes of the habitat generalists and specialists in sediment of Tibetan lakes and their role in the stability of metacommunity co-occurrence network. Our results showed that the habitat generalists exhibited broader environmental thresholds and closer phylogenetic clustering than specialist counterparts. In contrast, the specialists exhibited stronger phylogenetic signals of ecological preferences compared with the habitat generalists. Stochastic processes dominated the habitat generalist (63.2%) and specialist (81.3%) community assembly. Sediment pH was the major factor mediating the balance between stochastic and deterministic processes in the habitat generalists and specialists. In addition, as revealed by network analysis, the habitat specialists played a greater role in maintaining the stability of metacommunity co-occurrence network. The insights gained from this study can be helpful to understand the mechanisms underlying maintenance of sediment microbial diversity in plateau lakes.

Interfacial Electron Engineering of Palladium and Molybdenum Carbide for Highly Efficient Oxygen Reduction.

Interfacial electron engineering between noble metal and transition metal carbide is identified as a powerful strategy to improve the intrinsic activity of electrocatalytic oxygen reduction reaction (ORR). However, this short-range effect and the huge structural differences make it a significant challenge to obtain the desired electrocatalyst with atomically thin noble metal layers. Here, we demonstrated the combinatorial strategies to fabricate the heterostructure electrocatalyst of Mo2C-coupled Pd atomic layers (AL-Pd/Mo2C) by precise control of metal-organic framework confinement and covalent interaction. Both atomic characterizations and density functional theory calculations uncovered that the strong electron effect imposed on Pd atomic layers has intensively regulated the electronic structures and d-band center and then optimized the reaction kinetics. Remarkably, AL-Pd/Mo2C showed the highest ORR electrochemical activity and stability, which delivered a mass activity of 2.055 A mgPd-1 at 0.9 V, which is 22.1, 36.1, and 80.3 times higher than Pt/C, Pd/C, and Pd nanoparticles, respectively. The present work has developed a novel approach for atomically noble metal catalysts and provides new insights into interfacial electron regulation.

Fate of glacier surface snow-originating bacteria in the glacier-fed hydrologic continuums.

Glaciers represent important biomes of Earth and are recognized as key species pools for downstream aquatic environments. Worldwide, rapidly receding glaciers are driving shifts in hydrology, species distributions and threatening microbial diversity in glacier-fed aquatic ecosystems. However, the impact of glacier surface snow-originating taxa on the microbial diversity in downstream aquatic environments has been little explored. To elucidate the contribution of glacier surface snow-originating taxa to bacterial diversity in downstream aquatic environments, we collected samples from glacier surface snows, downstream streams and lakes along three glacier-fed hydrologic continuums on the Tibetan Plateau. Our results showed that glacier stream acts as recipients and vectors of bacteria originating from the glacier environments. The contributions of glacier surface snow-originating taxa to downstream bacterial communities decrease from the streams to lakes, which was consistently observed in three geographically separated glacier-fed ecosystems. Our results also revealed that some rare snow-originating bacteria can thrive along the hydrologic continuums and become dominant in downstream habitats. Finally, our results indicated that the dispersal patterns of bacterial communities are largely determined by mass effects and increasingly subjected to local sorting of species along the glacier-fed hydrologic continuums. Collectively, this study provides insights into the fate of bacterial assemblages in glacier surface snow following snow melt and how bacterial communities in aquatic environments are affected by the influx of glacier snow-originating bacteria.

Horizontal and vertical gene transfer drive sediment antibiotic resistome in an urban lagoon system.

Rapid urbanization has resulted in pervasive occurrence of antibiotic resistance genes (ARGs) in urban aquatic ecosystems. However, limited information is available concerning the ARG profiles and the forces responsible for their assembly in urban landscape lagoon systems. Here, we employed high-throughput quantitative PCR (HT-qPCR) to characterize the spatial variations of ARGs in surface and core sediments of Yundang Lagoon, China. The results indicated that the average richness and absolute abundance of ARGs were 11 and 53 times higher in the lagoon sediments as compared to pristine reference Tibetan lake sediments, highlighting the role of anthropogenic activities in ARG pollution. Co-occurrence network analysis indicated that various anaerobic prokaryotic genera belonging to Alpha-, Deltaproteobacteria, Bacteroidetes, Euryarchaeota, Firmicutes and Synergistetes were the potential hosts of ARGs. The partial least squares-path modeling (PLS-PM) analysis revealed positive and negative indirect effects of physicochemical factors and heavy metals on the lagoon ARG profiles, via biotic factors, respectively. The horizontal (mediated by mobile genetic elements) and vertical (mediated by prokaryotic communities) gene transfer may directly contribute the most to drive the abundance and composition of ARGs, respectively. Furthermore, the neutral community model demonstrated that the assembly of sediment ARG communities was jointly governed by deterministic and stochastic processes. Overall, this study provides novel insights into the diversity and distribution of ARGs in the benthic habitat of urban lagoon systems and underlying mechanisms for the spread and proliferation of ARGs.

Haloactinobacterium glacieicola sp. nov., isolated from an ice core.

A Gram-stain-positive, rod-shaped and motile bacterium with lateral flagellum, designated T3246-1T, was isolated from an ice core, which was drilled from Hariqin Glacier on the Tibetan Plateau, PR China. It grew optimally at 20 °C, pH 7-8 and in the presence of 3 % (w/v) NaCl. The major fatty acid of strain T3246-1T was anteiso-C15 : 0. Major polar lipids were diphosphatidylglycerol, phosphatidylglycerol and phosphatidylinositol. MK-8 was the dominant isoprenoid quinone. The whole-cell sugars were rhamnose, xylose and mannose. The major cell-wall peptidoglycan was lysine. The genomic DNA G+C content of the strain was 71.4 mol%. Results of phylogenetic analysis based on 16S rRNA gene sequences showed that strain T3246-1T formed a lineage within the genus Haloactinobacterium and was closely related to Haloactinobacterium album YIM 93306T with 95.99 % similarity. The average nucleotide identity value between strain T3246-1T and Haloactinobacterium album YIM 93306T was 76.65 %. Based on phenotypic and chemotaxonomic characteristics, strain T3246-1T was considered to represent a novel species of the genus Haloactinobacterium, for which the name Haloactinobacterium glacieicola sp. nov. is proposed. The type strain is T3246-1T (=CGMCC 1.13535T=JCM 32923T).

Variation with depth of the abundance, diversity and pigmentation of culturable bacteria in a deep ice core from the Yuzhufeng Glacier, Tibetan Plateau.

It has been suggested that the cryosphere is a new biome uniquely dominated by microorganisms, although the ecological characteristics of these cold-adapted bacteria are not well understood. We investigated the vertical variation with depth of the proportion of pigmented bacteria recovered from an ice core drilled in the Yuzhufeng Glacier, Tibetan Plateau. A total of 25,449 colonies were obtained from 1250 ice core sections. Colonies grew on only one-third of the inoculated Petri dishes, indicating that although the ice core harbored abundant culturable bacteria, bacteria could not be isolated from every section. Four phyla and 19 genera were obtained; Proteobacteria formed the dominant cluster, followed by Actinobacteria, Bacteroidetes and Firmicutes. The proportion of pigmented bacteria increased with depth from 79 to 95% and yellow-colored colonies predominated throughout the ice core, making up 47% of all the colonies. Pigments including α- and ß-carotene, diatoxanthin, peridinin, zea/lutein, butanoyloxy, fucoxanthin and fucoxanthin were detected in representative colonies with α-carotene being the dominant carotenoid. To the best of our knowledge, this is the highest resolution study of culturable bacteria in a deep ice core reported to date.

Mucilaginibacterpsychrotolerans sp. nov., isolated from peatlands.

A Gram-stain-negative, rod-shaped, non-flagellated, pink, cold-tolerant bacterial strain, NH7-4T, was isolated from the Riganqiao peatlands on the Tibetan Plateau. The 16S rRNA gene sequence of the novel isolate shared a pairwise similarity ranging from 96.84 to 93.02 % with type strains of species of the genus Mucilaginibacter. Growth of strain NH7-4T occurred between 0 and 30 °C and at pH 5.0-9.0, with an optimum growth temperature at 20 °C and an optimum pH for growth of approximately 7.0. The major isoprenoid quinone was MK-7. The major cellular fatty acids were summed feature 3 (C16 : 1ω7c and/or iso-C15 : 0 2-OH), iso-C15 : 0, iso-C17 : 0 3-OH, C16 : 0, iso-C15 : 0 3-OH and C16 : 1ω5c. The major polar lipid of strain NH7-4T was phosphatidylethanolamine. Strain NH7-4T did not assimilate any substrates in API 20NE strips without low concentrations of yeast extract being present and had a lower optimal growth temperature, which distinguished it from other type strains of species of the genus Mucilaginibacter. The DNA G+C content of strain NH7-4T was 48.6 mol%. Based on phylogenetic, phenotypic and chemotaxonomic data, strain NH7-4T (=JCM 30607T=CGMCC1.14937T) represents a novel species of the genus Mucilaginibacter for which the name Mucilaginibacter psychrotolerans sp. nov. is proposed.

Erythrobacter arachoides sp. nov., isolated from ice core.

A Gram-stain-negative, rod-shaped bacterial strain, designed RC4-10-4T, belonging to the genus Erythrobacter, was isolated from the East Rongbuk Glacier on the Tibetan Plateau. Strain RC4-10-4T grew optimally at pH 7.0, at 25 °C and in the presence of 2 % (w/v) NaCl. Summed feature 3 (C16 : 1 ω6c and/or iso-C15 : 0 2-OH), summed feature 8 (C18 : 1 ω7c and/or C18 : 1 ω6c) and C16 : 0 were the major fatty acids. The major polar lipids were phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, sphingoglycolipid and phosphatidylcholine. Carotenoid was detected in the cells. The DNA G+C content of the novel strain was 66.4 mol%. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain RC4-10-4T formed a distinct phylogenetic lineage within the cluster comprising Erythrobacter strains. Similarities between the 16S rRNA gene sequences of strain RC4-10-4T and the closely related strains Erythrobacter luteus KCTC 42179T, Erythrobacter gangjinensis KCTC 22330T, Erythrobacter odishensis KCTC 23981T and Erythrobacter atlanticuls KCTC 42697T were 98.0, 97.6, 97.5 and 97.2 %. The DNA-DNA hybridization values were 37.6, 15.4, 29.8 and 35.8 %, respectively. Based on the phenotypic and phylogenetic characteristics, strain RC4-10-4T represents a novel species of the genus Erythrobacter, for which the name Erythrobacter arachoides sp. nov. is proposed, with the type strain RC4-10-4T (=CGMCC 1.15507T=JCM 31277T).

Hymenobacter frigidus sp. nov., isolated from a glacier ice core.

A psychrophilic, Gram-stain-negative, rod-shaped, red-pigmented bacterium, designated strain B1789T, was isolated from an ice core of Muztagh Glacier on the Tibetan Plateau in China. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain B1789T was related to members of the genus Hymenobacter and had highest sequence similarity with Hymenobacter antarcticus JCM 17217T (97.9 %). The major menaquinone was MK-7 and the major polar lipid was phosphatidylethanolamine. The predominant fatty acids were iso-C15 : 0, anteiso-C15 : 0 and summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c). The DNA G+C content was 59.4 mol%. In DNA-DNA hybridization tests, strain B1789T shared 42 % relatedness with H. antarcticus JCM 17217T. Based on the results of phenotypic and chemotaxonomic tests, strain B1789T was considered as representing a novel species of the genus Hymenobacter, for which the name Hymenobacter frigidus sp. nov. is proposed. The type strain is B1789T (=JCM 30595T=CGMCC 1.14966T).

Massilia glaciei sp. nov., isolated from the Muztagh Glacier.

A Gram-stain-negative, rod-shaped, bacterial strain, B448-2T, was isolated from an ice core from the Muztagh Glacier, on the Tibetan Plateau. B448-2T grew optimally at pH 7.0 and 20 °C in the presence of 0-1.0 % (w/v) NaCl. The results of 16S rRNA gene sequence similarity analysis indicated that B448-2T was closely related to Massilia eurypsychrophila CGMCC 1.12828T, Rugamonas rubra CCM3730T and Duganella zoogloeoides JCM20729T at levels of 97.8, 97.7  and 97.3 %, respectively. The predominant fatty acids of B448-2T were summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c) and C16 : 0. The predominant isoprenoid quinone was Q-8. The major polar lipids were phosphatidylethanolamine, phosphatidylglycerol and diphosphatidylglycerol. The genomic DNA G+C content of the strain was 66.1 mol%. In DNA-DNA hybridization tests, B448-2T shared 37.6 % DNA-DNA relatedness with Massilia eurypsychrophila CGMCC 1.12828T. On the basis of the results for phenotypic and chemotaxonomic characteristics, B448-2T was considered to represent a novel species of the genus Massilia, for which the name Massiliaglaciei sp. nov. is proposed. The type strain is B448-2T (=JCM 30271T=CGMCC 1.12920T).

Description of Conyzicola nivalis sp. nov., isolated from glacial snow, and emended description of the genus Conyzicola and Conyzicola lurida.

A cold-tolerant, translucent, yellow-pigmented, Gram-stain-positive, non-motile, rod-shaped bacteria was isolated from snow of the Zadang Glacier on the Tibetan Plateau, PR China. 16S rRNA gene sequence similarity analysis indicated that the isolate was closely related to Conyzicola lurida KCTC 29231T and Leifsonia psychrotolerans DSM 22824T at a level of 97.72 and 97.49 %, respectively. Other close relatives had a 16S rRNA gene sequence similarity of less than 97 %. The major cell-wall amino acid was 2,4-diaminobutyric acid. The cell-wall sugars were rhamnose, ribose, glucose, galactose and mannose. The major menaquinones were MK-9, MK-10 and MK-11. The major polar lipids were diphosphatidylglycerol and phosphatidylglycerol. The predominant fatty acids were anteiso-C15 : 0 and iso-C16 : 0. In DNA-DNA hybridization tests, strain ZD5-4T shared 43.6 and 34.2 % relatedness with C. lurida KCTC 29231T and L. psychrotolerans DSM 22824T, respectively. Based on phenotypic and chemotaxonomic characteristics, strain ZD5-4T was considered to represent a novel species of the genus Conyzicola, for which the name Conyzicola nivalis sp. nov. is proposed. The type strain is ZD5-4T (=JCM 30076T=CGMCC 1.12813T). Emended descriptions of the genus Conyzicola and Conyzicola lurida are also provided.

Aureimonas glaciei sp. nov., isolated from an ice core.

A bacterial strain, B5-2T, was isolated from an ice core drilled from Muztagh Glacier, China. Strain B5-2T was a Gram-stain-negative, short rod-shaped, motile by polar flagella, aerobic bacterium. The major fatty acids of strain B5-2T were summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c) and iso-C13 : 0. The G+C content of the DNA from strain B5-2T was 69.3 mol%. The predominant isoprenoid quinone of strain B5-2T was Q-10. The major polar lipids were phosphatidylglycerol, phosphatidylethanolamine, phosphatidylmonomethylethanolamine, phosphatidyldimethylethanolamine, phosphatidylcholine, an unidentified phospholipid and sulfoquinovosyldiacylglycerol. Comparative 16S rRNA gene sequence analysis revealed that the novel strain B5-2T shared highest similarity (96.7 %) with Aureimonas altamirensis S21BT. On the basis of the results of this polyphasic study, strain B5-2T represents a novel species of the genus Aureimonas, for which the name Aureimonas glaciei sp. nov. is proposed. The type strain is B5-2T (=CGMCC 1.15493T=KCTC 52395T).

Polymorphobacter glacialis sp. nov., isolated from ice core.

A Gram-stain-negative, non-spore-forming, rod-shaped bacterium, B555-2T, was isolated from an ice core drilled from Muztagh Glacier on the Tibetan Plateau, China. According to phylogenetic analysis with 16S rRNA gene sequences, the novel strain was most closely related to Polymorphobacter fuscus D40PT and Polymorphobacter multimanifer 262-7T with 98.4 and 96.9 % similarity, respectively. It grew optimally at pH 7 and 15 °C with 0.6 % NaCl (m/v). Carotenoid was detected from the cells. Major polar lipids were phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, sphingoglycolipid, phophatidylmonomethy lethanolamine, phophatidylcholine. The major fatty acids were summed feature 3 (C16 : 1ω7c and/or iso-C15 : 0 2-OH) (42.8 %), summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c) (28.8 %), C14 : 0 2-OH (10.1 %) and C16 : 0 (8.2 %). The predominant ubiquinone was Q-10. The DNA G+C content was 62.1 mol%. In DNA-DNA hybridization tests, strain B555-2T shared 21.9 and 18.6 % DNA-DNA relatedness with P. fuscus D40PT and P.multimanifer 262-7T, respectively. Accordingly, strain B555-2T represents a novel species in the genus Polymorphobacter, for which the name Polymorphobacter glacialis sp. nov. is proposed. The type strain is B555-2T (=CGMCC 1.15519T=KCTC 52396T).

Salinity Affects the Composition of the Aerobic Methanotroph Community in Alkaline Lake Sediments from the Tibetan Plateau.

Lakes are widely distributed on the Tibetan Plateau, which plays an important role in natural methane emission. Aerobic methanotrophs in lake sediments reduce the amount of methane released into the atmosphere. However, no study to date has analyzed the methanotroph community composition and their driving factors in sediments of these high-altitude lakes (>4000 m). To provide new insights on this aspect, the abundance and composition in the sediments of six high-altitude alkaline lakes (including both freshwater and saline lakes) on the Tibetan Plateau were studied. The quantitative PCR, terminal restriction fragment length polymorphism, and 454-pyrosequencing methods were used to target the pmoA genes. The pmoA gene copies ranged 104-106 per gram fresh sediment. Type I methanotrophs predominated in Tibetan lake sediments, with Methylobacter and uncultivated type Ib methanotrophs being dominant in freshwater lakes and Methylomicrobium in saline lakes. Combining the pmoA-pyrosequencing data from Tibetan lakes with other published pmoA-sequencing data from lake sediments of other regions, a significant salinity and alkalinity effect (P = 0.001) was detected, especially salinity, which explained ∼25% of methanotroph community variability. The main effect was Methylomicrobium being dominant (up to 100%) in saline lakes only. In freshwater lakes, however, methanotroph composition was relatively diverse, including Methylobacter, Methylocystis, and uncultured type Ib clusters. This study provides the first methanotroph data for high-altitude lake sediments (>4000 m) and shows that salinity is a driving factor for the community composition of aerobic methanotrophs.