Abundant and Rare Taxa of Planktonic Fungal Community Exhibit Distinct Assembly Patterns Along Coastal Eutrophication Gradient.

Revealing planktonic fungal ecology under coastal eutrophication is crucial to our understanding of microbial community shift in marine pollution background. We investigated the diversity, putative interspecies interactions, assembly processes and environmental responses of abundant and rare planktonic fungal communities along a eutrophication gradient present in the Beibu Gulf. The results showed that Dothideomycetes and Agaricomycetes were the predominant classes of abundant and rare fungi, respectively. We found that eutrophication significantly altered the planktonic fungal communities and affected the abundant taxa more than the rare taxa. The abundant and rare taxa were keystone members in the co-occurrence networks, and their interaction was enhanced with increasing nutrient concentrations. Stochastic processes dominated the community assembly of both abundant and rare planktonic fungi across the eutrophication gradient. Heterogeneous selection affected abundant taxa more than rare taxa, whereas homogenizing dispersal had a greater influence on rare taxa. Influences of environmental factors involving selection processes were detected, we found that abundant fungi were mainly influenced by carbon compounds, whereas rare taxa were simultaneously affected by carbon, nitrogen and phosphorus compounds in the Beibu Gulf. Overall, these findings highlight the distinct ecological adaptations of abundant and rare fungal communities to marine eutrophication.

Iron availability is a key factor for freshwater cyanobacterial survival against saline stress.

Estuaries are among the most productive ecosystems and dynamic environments on Earth. Varying salinity is the most important challenge for phytoplankton survival in estuaries. In order to investigate the role of iron nutrition on phytoplankton survival under salinity stress, a freshwater cyanobacterial strain was cultivated in media added with different proportions of seawater (measured with siderophore activities), and supplied with gel-immobilized ferrihydrite as iron source. Results showed that the strain grew well in media with 0% seawater supplied with ferrihydrite as iron source. Surprisingly, the biomasses in media with 50% seawater, with more newly excreted siderophore, were similar to those with 0% seawater, but better than those with 6.25%, 12.5% and 25% seawater. Smaller iron isotopic discriminations between the cyanobacterial cells associated iron and dissolved iron were observed in media with 0% and 50% seawater suggested that higher fractions of iron uptake from aqueous dissolved iron reservoir by these comparatively larger biomasses. In summary, this study proved that iron availability plays a key role in cyanobacterial survival under varying salinity stress, and suggested that siderophores introduced by seawater may accelerate iron dissolution, increase iron availability, and make cyanobacterial cells overcome the adverse effects of high-salinity, and indicated that siderophore excretion is a kind of survival strategy for phytoplankton in face of salinity stress.

Microbial diversity accumulates in a downstream direction in the Three Gorges Reservoir.

Organic and inorganic materials migrate downstream and have important roles in regulating environmental health in the river networks. However, it remains unclear whether and how a mixture of materials (i.e., microbial species) from various upstream habitats contribute to microbial community coalescence upstream of a dam. Here we track the spatial variation in microbial abundance and diversity in the Three Gorges Reservoir based on quantitative PCR and 16S rRNA gene high-throughput sequencing data. We further quantitatively assess the relative contributions of microbial species from mainstem, its tributaries, and the surrounding riverbank soils to the area immediately upstream of the Three Gorges Dam (TGD). We found an increase of microbial diversity and the convergent microbial distribution pattern in areas immediately upstream of TGD, suggesting this area become a new confluence for microbial diversity immigrating from upstream. Indeed, the number of shared species increased from upstream to TGD but unique species decreased, indicating immigration of various sources of microbial species overwhelms local environmental conditions in structuring microbial community close to TGD. By quantifying the sources of microbial species close to TGD, we found little contribution from soils as compared to tributaries, especially for sites closer to TGD, suggesting tributary microbes have greater influence on microbial diversity and environmental health in the Three Gorges Reservoir. Collectively, our results suggest that tracking microbial geographic origin and evaluating accumulating effects of microbial diversity shed light on the ecological processes in microbial communities and provide information for regulating aquatic ecological health.

Diversity and Distribution of Methanogenic Community Between Two Typical Alpine Ecosystems on the Qinghai-Tibetan Plateau.

Alpine permafrost regions are important sources of biogenic CH4 and methanogens play an important role in the methane-producing process. The alpine permafrost on the Qinghai-Tibetan plateau comprises about one-sixth of China's land area, and there are various types of alpine ecosystems. However, the methanogenic communities in the typical alpine ecosystems are poorly understood. In this study, the active layers and permafrost layers of the natural ecosystem of alpine grassland (DZ2-1) and alpine swamp meadow (DZ2-5) were selected to investigate the diversity and abundance of methanogenic communities. Methanobacterium (63.65%) are overwhelmingly dominant in the active layer of the alpine grassland (DZ2-1A). ZC-I cluster (26.13%), RC-I cluster (19.56%), and Methanobacterium (15.02%) are the dominant groups in the permafrost layer of the alpine grassland (DZ2-1P). Methanosaeta (32.92%), Fen cluster (29.59%), Methanosarcina (16.33%), and Methanobacterium (13.95%) are the dominant groups in the active layer of the alpine swamp meadow (DZ2-5A), whereas the Fen cluster (50.85%), ZC-I cluster (27.63%), and RC-I cluster (14.15%) are relatively abundant in the permafrost layer of the alpine swamp meadow (DZ2-5P). qPCR data showed that the abundance of methanogens was higher in the natural ecosystem of alpine swamp meadow than in alpine grassland. We found that the community characteristics of methanogens were related to environmental factors. Pearson correlation analyses indicated that the relative abundance of Methanobacterium had a significantly positive correlation with hydrogen concentration (P < 0.01), while the relative abundances of Methanosaeta and Methanosarcina were positively correlated with acetate concentration (P < 0.05). This study will help us to understand the methanogenic communities and their surrounding environments in alpine ecosystems.

Pseudorhodobacter sinensis sp. nov. and Pseudorhodobacter aquaticus sp. nov., isolated from crater lakes.

Three Gram-stain negative, aerobic, non-motile, rod-shaped bacterial strains, Y1R2-4T, Y3R2-3 and DC2N1-10T, isolated from two crater lakes of the Daxinganling Mountains, northern China, were studied to determine their taxonomic position. They grew at 4-30 °C (optimally at 20-25 °C), at pH 6.0-7.5 (optimally at pH 7.0) and in the presence of 0-0.5 % (w/v) NaCl. On the basis of 16S rRNA gene sequence analysis, these strains showed 95.3-96.6 % similarity to members of the genus Pseudorhodobacter, including Pseudorhodobacter ferrugineus DSM 5888T, Pseudorhodobacter wandonensis WT-MW11T, Pseudorhodobacter antarcticus ZS3-33T and Pseudorhodobacter aquimaris HDW-19T. All strains contained Q-10 as the predominant ubiquinone and C18 : 1ω7c as the major fatty acid. The main polar lipids for strains Y1R2-4T and Y3R2-3 were phosphatidylglycerol, phosphatidylcholine, one unidentified aminophospholipid, one unidentified aminolipid, three unidentified phospholipids and two unidentified lipids, and those for strain DC2N1-10T were phosphatidylglycerol, phosphatidylcholine, one unidentified aminophospholipid, one unidentified aminolipid, one unidentified phospholipid and several unidentified lipids. The DNA G+C contents of strains Y1R2-4T, Y3R2-3 and DC2N1-10T were 61.9, 61.0 and 60.0 mol%, respectively. In addition, strain Y1R2-4T shared less than 50 % DNA-DNA relatedness to strain DC2N1-10T. Based on these differences in genetic, physiological and chemotaxonomic properties, strains Y1R2-4T, Y3R2-3 and DC2N1-10T were considered to represent two novel species of the genus Pseudorhodobacter, for which the names Pseudorhodobacter sinensis sp. nov. (type strain Y1R2-4T=CGMCC1.14435T=KCTC 52039T) and Pseudorhodobacter aquaticus sp. nov. (type strain DC2N1-10T=CGMCC1.14433T=KCTC 52040T) are proposed.

Stimulation of Fe(II) Oxidation, Biogenic Lepidocrocite Formation, and Arsenic Immobilization by Pseudogulbenkiania Sp. Strain 2002.

An anaerobic nitrate-reducing Fe(II)-oxidizing bacterium, Pseudogulbenkiania sp. strain 2002, was used to investigate As immobilization by biogenic Fe oxyhydroxides under different initial molar ratios of Fe/As in solutions. Results showed that Fe(II) was effectively oxidized, mainly forming lepidocrocite, which immobilized more As(III) than As(V) without changing the redox state of As. When the initial Fe/As ratios were kept constant, higher initial Fe(II) concentrations immobilized more As with higher Asimmobilized/Feprecipitated in biogenic lepidocrocite. EXAFS analysis showed that variations of initial Fe(II) concentrations did not change the As-Fe complexes (bidentate binuclear complexes ((2)C)) with a fixed As(III) or As(V) initial concentration of 13.3 µM. On the other hand, variations in initial As concentrations but fixed Fe(II) initial concentration induced the co-occurrence of bidentate binuclear and bidentate mononuclear complexes ((2)E) and bidentate binuclear and monodentate mononuclear complexes ((1)V) for As(III) and As(V)-treated series, respectively. The coexistence of (2)C and (2)E complexes (or (2)C and (1)V complexes) could contribute to higher As removal in experimental series with higher initial Fe(II) concentrations at the same initial Fe/As ratio. Simultaneous removal of soluble As and nitrate by anaerobic nitrate-reducing Fe(II)-oxidizing bacteria provides a feasible approach for in situ remediation of As-nitrate cocontaminated groundwater.

Seasonal patterns in microbial communities inhabiting the hot springs of Tengchong, Yunnan Province, China.

Studies focusing on seasonal dynamics of microbial communities in terrestrial and marine environments are common; however, little is known about seasonal dynamics in high-temperature environments. Thus, our objective was to document the seasonal dynamics of both the physicochemical conditions and the microbial communities inhabiting hot springs in Tengchong County, Yunnan Province, China. The PhyloChip microarray detected 4882 operational taxonomic units (OTUs) within 79 bacterial phylum-level groups and 113 OTUs within 20 archaeal phylum-level groups, which are additional 54 bacterial phyla and 11 archaeal phyla to those that were previously described using pyrosequencing. Monsoon samples (June 2011) showed increased concentrations of potassium, total organic carbon, ammonium, calcium, sodium and total nitrogen, and decreased ferrous iron relative to the dry season (January 2011). At the same time, the highly ordered microbial communities present in January gave way to poorly ordered communities in June, characterized by higher richness of Bacteria, including microbes related to mesophiles. These seasonal changes in geochemistry and community structure are likely due to high rainfall influx during the monsoon season and indicate that seasonal dynamics occurs in high-temperature environments experiencing significant changes in seasonal recharge. Thus, geothermal environments are not isolated from the surrounding environment and seasonality affects microbial ecology.

[The research on xiaochalhu decoction improving the inflammation of chronic glomerulonephritis patients and relieving the proteinuria].

OBJECTIVE: To observe the balance of T help cell1/2 (Th1/Th2), the changes of correlated proinflammatory cytokines (IFN-gamma and IL-4), and regulated on activation normal T cell expressed and secreted (RANTES), and the abnormal expression of IL-17, the effector of T help cell17 (Th17) in chronic glomerulonephritis (CGN)patients with Shaoyang disease, thus revealing the mechanisms of Xiaochaihu Decoction (XD) for treating proteinuria of CGN patients according to the theory of mediating Shaoyang meridian. METHODS: Totally 70 CGN patients with Shaoyang disease were randomly assigned to two groups, the treatment group (treated by XD) and the control group [treated by Shenyan Kangfu Tablet (SKT)], 35 in each group. Besides, 20 healthy volunteers were recruited as the healthy control group. Besides, routine therapy of chronic kidney disease (CKD), patients in the treatment group and the control group were treated with XD and SKT respectively for 4 weeks. The changes of Chinese medical syndrome, the effectiveness, 24-h urinary protein, renal functions, the peripheral blood IFN-gamma, IL-4, Th1/Th2, IL-17, and RANTES were compared. RESULTS: Before treatment the Th1/Th2, IL-17, and RANTES of the two treated groups were higher, and the IL-4 level was lower than those of the healthy control group (P < 0.05). After treatment the improvement of Chinese medical syndrome, main symptoms, the effectiveness was better in the XD group than in the SKT group (P < 0.05, P < 0.01). The proteinuria obviously decreased in the treatment group, with the efficacy superior to the SKT group (P < 0.05). The Th1/Th2, IL-17, and RANTES decreased to various degrees when compared with the SKT group (P < 0.05, P < 0.01). The IL-4 level increased more obviously in the treatment group than in the control group (P < 0.05). There was no statistical difference in the improvement of the renal function (P > 0.05). CONCLUSIONS: The immune disorder of the CGN patients with Shaoyang disease was correlated with Th1/Th2 imbalance, and abnormal changes of Th17 cell functions and RANTES. XD could improve the inflammation by regulating the immune disorder of CGN patients with Shaoyang disease, which proved that the theory of mediating Shaoyang meridian could be used to improve the inflammation of CGN patients, thus relieving the proteinuria.

Effects of Mineral on Taxonomic and Functional Structures of Microbial Community in Tengchong Hot Springs via in-situ cultivation.

Diverse mineralogical compositions occur in hot spring sediments, but the impact of minerals on the diversity and structure of microbial communities remains poorly elucidated. In this study, different mineral particles with various chemistries (i.e., hematite, biotite, K-feldspar, quartz, muscovite, aragonite, serpentine, olivine, barite, apatite, and pyrite) were incubated for ten days in two Tengchong hot springs, one alkaline (pH ~ 8.34) with a high temperature (~ 82.8 °C) (Gumingquan, short as GMQ) and one acidic (pH ~ 3.63) with a relatively low temperature (~ 43.3 °C) (Wenguangting, short as WGT), to determine the impacts of minerals on the microbial communities taxonomic and functional diversities. Results showed that the mineral-associated bacterial taxa differed from those of the bulk sediment samples in the two hot springs. The relative abundance of Proteobacteria, Euryarchaeota, and Acidobacteria increased in all minerals, indicating that these microorganisms are apt to colonize on solid surfaces. The α-diversity indices of the microbial communities on the mineral surfaces in the WGT were higher than those from the bulk sediment samples (p < 0.05), which may be caused by the stochastically adhering process on the mineral surface during 10-day incubation, different from the microbial community in sediment which has experienced long-term environmental and ecological screening. Chemoheterotrophy increased with minerals incubation, which was high in most cultured minerals (the relative contents were 5.8 - 21.4%). Most notably, the sulfate respiration bacteria (mainly related to Desulfobulbaceae and Syntrophaceae) associated with aragonite in the acidic hot spring significantly differed from other minerals, possibly due to the pH buffering effect of aragonite providing more favorable conditions for their survival and proliferation. By comparison, aragonite cultured in the alkaline hot spring highly enriched denitrifying bacteria and may have promoted the nitrogen cycle within the system. Collectively, we speculated that diverse microbes stochastically adhered on the surface of minerals in the water flows, and the physicochemical properties of minerals drove the enrichment of certain microbial communities and functional groups during the short-term incubation. Taken together, these findings thereby provide novel insights into mechanisms of community assembly and element cycling in the terrestrial hydrothermal system associated with hot springs.

Distribution of heavy metals in coastal sediments under the influence of multiple factors: A case study from the south coast of an industrialized harbor city (Tangshan, China).

This research investigated the spatial distribution of heavy metals, including mercury (Hg), cadmium (Cd), copper (Cu), arsenic (As), nickel (Ni), lead (Pb), chromium (Cr), and zinc (Zn), in surface sediments from a coastal area near to an industrial harbor (Tangshan Harbor, China) using 161 sediment samples. According to the geo-accumulation index (Igeo), 11 samples were classified as unpolluted (Igeo≤0). Notably, 41.0 % of the research samples were moderately or strongly polluted (2 < Igeo≤3) with Hg and 60.2 % of the samples were moderately polluted (1 < Igeo≤2) in Cd. The ecological effect evaluation showed that the metals Zn, Cd, and Pb were at the effect range low level, and 51.6 % of the samples for Cu, 60.9 % for Cr, 90.7 % for As, 41.0 % for Hg, and 64.0 % for Ni fell in the range between the effect range-low and the effect range-mean levels, respectively. The correlation analysis showed that the distribution patterns of Cr, Cu, Zn, Ni, and Pb were similar to each other, high in the northwest, southeast, and southwest regions of the study area and low in the northeast region, which corresponded well with sediment size components. Based on principal component analysis (PCA) and positive matrix factorization (PMF), four distinct sources of pollution were quantitatively attributed, including agricultural activities (22.08 %), fossil fuel consumption (24.14 %), steel production (29.78 %), and natural sources (24.00 %). Hg (80.29 %), Cd (82.31 %) and As (65.33 %) in the region's coastal sediments were predominantly contributed by fossil fuel, steel production and agricultural sources, respectively. Cr (40.00 %), Cu (43.63 %), Ni (47.54 %), and Zn (38.98 %) were primarily of natural lithogenic origin, while Pb mainly came from the mixed sources of agricultural activities (36.63 %), fossil fuel (36.86 %), and steel production (34.35 %). Multiple factors played important roles in the selective transportation of sedimentary heavy metals, particularly sediment properties, and hydrodynamic sorting processes in the study area.

Response of methanogenic community and their activity to temperature rise in alpine swamp meadow at different water level of the permafrost wetland on Qinghai-Tibet Plateau.

Wetlands are an important source of atmospheric methane (CH4) and are sensitive to global climate change. Alpine swamp meadows, accounting for ~50% of the natural wetlands on the Qinghai-Tibet Plateau, were considered one of the most important ecosystems. Methanogens are important functional microbes that perform the methane producing process. However, the response of methanogenic community and the main pathways of CH4 production to temperature rise remains unknown in alpine swamp meadow at different water level in permafrost wetlands. In this study, we investigated the response of soil CH4 production and the shift of methanogenic community to temperature rise in the alpine swamp meadow soil samples with different water levels collected from the Qinghai-Tibet Plateau through anaerobic incubation at 5°C, 15°C and 25°C. The results showed that the CH4 contents increased with increasing incubation temperature, and were 5-10 times higher at the high water level sites (GHM1 and GHM2) than that at the low water level site (GHM3). For the high water level sites (GHM1 and GHM2), the change of incubation temperatures had little effect on the methanogenic community structure. Methanotrichaceae (32.44-65.46%), Methanobacteriaceae (19.30-58.86%) and Methanosarcinaceae (3.22-21.24%) were the dominant methanogen groups, with the abundance of Methanotrichaceae and Methanosarcinaceae having a significant positive correlation with CH4 production (p < 0.01). For the low water level site (GHM3), the methanogenic community structure changed greatly at 25°C. The Methanobacteriaceae (59.65-77.33%) was the dominant methanogen group at 5°C and 15°C; In contrast, the Methanosarcinaceae (69.29%) dominated at 25°C, and its abundance showed a significant positive correlation with CH4 production (p < 0.05). Collectively, these findings enhance the understanding of methanogenic community structures and CH4 production in permafrost wetlands with different water levels during the warming process.

High speciation rate of niche specialists in hot springs.

Ecological and evolutionary processes simultaneously regulate microbial diversity, but the evolutionary processes and their driving forces remain largely unexplored. Here we investigated the ecological and evolutionary characteristics of microbiota in hot springs spanning a broad temperature range (54.8-80 °C) by sequencing the 16S rRNA genes. Our results demonstrated that niche specialists and niche generalists are embedded in a complex interaction of ecological and evolutionary dynamics. On the thermal tolerance niche axis, thermal (T) sensitive (at a specific temperature) versus T-resistant (at least in five temperatures) species were characterized by different niche breadth, community abundance and dispersal potential, consequently differing in potential evolutionary trajectory. The niche-specialized T-sensitive species experienced strong temperature barriers, leading to completely species shift and high fitness but low abundant communities at each temperature ("home niche"), and such trade-offs thus reinforced peak performance, as evidenced by high speciation across temperatures and increasing diversification potential with temperature. In contrast, T-resistant species are advantageous of niche expansion but with poor local performance, as shown by wide niche breadth with high extinction, indicating these niche generalists are "jack-of-all-trades, master-of-none". Despite of such differences, the T-sensitive and T-resistant species are evolutionarily interacted. Specifically, the continuous transition from T-sensitive to T-resistant species insured the exclusion probability of T-resistant species at a relatively constant level across temperatures. The co-evolution and co-adaptation of T-sensitive and T-resistant species were in line with the red queen theory. Collectively, our findings demonstrate that high speciation of niche specialists could alleviate the environmental-filtering-induced negative effect on diversity.

High Abundance of Thaumarchaeota Found in Deep Metamorphic Subsurface in Eastern China.

Members of the Thaumarchaeota phylum play a key role in nitrogen cycling and are prevalent in a variety of environments including soil, sediment, and seawater. However, few studies have shown the presence of Thaumarchaeota in the terrestrial deep subsurface. Using high-throughput 16S rRNA gene sequencing, this study presents evidence for the high relative abundance of Thaumarchaeota in a biofilm sample collected from the well of Chinese Continental Scientific Drilling at a depth of 2000 m. Phylogenetic analysis showed a close relationship of these thaumarchaeotal sequences with known ammonia-oxidizing archaea (AOA) isolates, suggesting the presence of AOA in the deep metamorphic environment of eastern China which is believed to be oxic. Based on fluid geochemistry and FAProTax functional prediction, a pathway of nitrogen cycling is proposed. Firstly, heterotrophic nitrogen fixation is executed by diazotrophic bacteria coupled with methane oxidation. Then, ammonia is oxidized to nitrite by AOA, and nitrite is further oxidized to nitrate by bacteria within the phylum Nitrospirae. Denitrification and anaerobic ammonia oxidation occur slowly, leading to nitrate accumulation in the subsurface. With respect to biogeochemistry, the reaction between downward diffusing O2 and upward diffusing CH4 potentially fuels the ecosystem with a high relative abundance of Thaumarchaeota.

A critical review of mineral-microbe interaction and co-evolution: mechanisms and applications.

Mineral-microbe interactions play important roles in environmental change, biogeochemical cycling of elements and formation of ore deposits. Minerals provide both beneficial (physical and chemical protection, nutrients, and energy) and detrimental (toxic substances and oxidative pressure) effects to microbes, resulting in mineral-specific microbial colonization. Microbes impact dissolution, transformation and precipitation of minerals through their activity, resulting in either genetically controlled or metabolism-induced biomineralization. Through these interactions, minerals and microbes co-evolve through Earth history. Mineral-microbe interactions typically occur at microscopic scale but the effect is often manifested at global scale. Despite advances achieved through decades of research, major questions remain. Four areas are identified for future research: integrating mineral and microbial ecology, establishing mineral biosignatures, linking laboratory mechanistic investigation to field observation, and manipulating mineral-microbe interactions for the benefit of humankind.

Trophic states regulate assembly processes and network structures of small chromophytic phytoplankton communities in estuarine and coastal ecosystem.

Small chromophytic phytoplankton (SCP) are anticipated to be more important for a significant proportion of primary production in estuarine-coastal ecosystems. However, responses of SCP community to coastal eutrophication are still unclear. In this study, we investigated diversity, co-occurrence and assembly features of SCP communities, as well as relationship with environmental factors in subtropical Beibu Gulf. The results exhibited that the alpha diversity and beta diversity of SCP communities were significantly different among eutrophic states. Co-occurrence network revealed a complex interaction that most amplicon sequence variants (ASVs) in modules of the network were specific to trophic states. Further, phylogenetic based ß-nearest taxon distance analyses revealed that stochastic processes mainly provided 69.26% contribution to SCP community assembly, whereas deterministic processes dominated community assembly in heavy eutrophic state. Overall, our findings elucidate the mechanism of diversity and assembly in SCP community and promote the understanding of SCP ecology related to subtropical coastal eutrophication.

Temperature and microbial interactions drive the deterministic assembly processes in sediments of hot springs.

Terrestrial geothermal ecosystems, as a representative of extreme environments, exhibit a variety of geochemical gradients, and their microbes are thought to be under high stress through environmental selection. However, it is still unclear how stochasticity and biotic interactions contribute to the microbial community assembly in hot springs. Here, we investigated the assembly processes and co-occurrence patterns of microbiota (i.e. bacteria and archaea) in both water and sediments sampled from fifteen hot springs in the Tengchong area, Southwestern of China, using 16S rRNA gene sequencing combined with multivariate ecological and statistical methods. These hot springs harbored more specialists than non-geothermal ecosystems, which are well-adapted to the extreme conditions, as shown by extremely high nearest-taxon index (NTI) and narrower niche width. Habitat differentiation led to the differences in microbial diversity, species-interactions, and community assembly between water and sediment communities. The sediment community showed stronger phylogenetic clustering and was primarily governed by heterogeneous selection, while undominated stochastic processes and dispersal limitation were the major assembly processes in the water community. Temperature and ferrous iron were the major factors mediating the balance of stochastic and deterministic assembly processes in sediment communities, as evidenced by how divergences in temperature and ferrous iron increased the proportion of determinism. Microbial interactions in sediments contributed to deterministic community assembly, as indicated by more complex associations and greater responsiveness to environmental change than water community. These findings uncover the ecological processes underlying microbial communities in hot springs, and provide potential insight into understanding the mechanism to maintain microbial diversity in extreme biospheres.

Minerals Determined a Special Ecological Niche and Selectively Enriched Microbial Species from Bulk Water Communities in Hot Springs.

Minerals provide physical niches and supply nutrients or serve as electron donors/acceptors for microorganism survival and growth, and thus minerals and microbes co-evolved. Yet, little is known about how sediment minerals impact microbial community assembly in hot springs and to what extent mineralogical composition influences microbial community composition and diversity. Here the influences of minerals on thermophiles in Tengchong hot springs were revealed by network analysis of field samples, as well as in-situ microcosm experiments with minerals. A molecular ecological network was constructed based on high throughput sequencing data of 16S rRNA gene, with a combination of water geochemistry and sedimentary mineralogical compositions. Six modules were identified and this highly modular network structure represents the microbial preference to different abiotic factors, consequently resulting in niche partitioning in sedimentary communities in hot springs. Diverse mineralogical compositions generated special niches for microbial species. Subsequently, the in-situ microcosm experiments with four minerals (aragonite, albite, K-feldspar, and quartz) and spring water were conducted in a silicate-hosted alkaline spring (i.e., Gmq) and a carbonate-hosted neutral hot spring (i.e., Gxs) for 70 days. Different microbial preferences were observed among different mineral types (carbonate versus silicate). Aragonite microcosms in Gmq spring enriched archaeal genera Sulfophobococcus and Aeropyrum within the order Desulfurococcales by comparison with both in-situ water and silicate microcosms. Sulfophobococcus was also accumulated in Gxs aragonite microcosms, but the contribution to overall dissimilarity is much lower than that in Gmq spring. Besides, Caldimicrobium was a bacterial genus enriched in Gxs aragonite microcosms, in contrast to in-situ water and silicate microcosms, whereas Candidatus Kryptobacter and Thermus were more abundant in silicate microcosms. The differences in microbial accumulations among different mineral types in the same spring implied that mineral chemistry may exert extra deterministic selective pressure in drawing certain species from the bulk water communities, in addition to stochastic absorption on mineral surface. Taken together, our results highlight the special niche partitioning determined by mineralogical compositions and further confirm that minerals could be used as "fishing bait" to enrich certain rare microbial species.

Warming favors subtropical lake cyanobacterial biomass increasing.

Subtropical lakes are increasingly subject to cyanobacterial blooms resulting from climate change and anthropogenic activities, but the lack of long-term historical data limits understanding of how climate changes have affected cyanobacterial growth in deep subtropical lakes. Using high-resolution DNA data derived from a sediment core from a deep lake in southwestern China, together with analysis of other sedimentary hydroclimatic proxies, we investigated cyanobacterial biomass and microbial biodiversity in relation to climate changes during the last millennium. Our results show that both cyanobacterial abundance and microbial biodiversity were higher during warmer periods, including the Medieval Warm Period (930-1350 CE) and the Current Warm Period (1900 CE-present), but lower during cold periods, including the Little Ice Age (1400-1850 CE). The significant increases in cyanobacterial abundance and microbial biodiversity during warmer intervals are probably because warm climate not only favors cyanobacterial growth but also concentrates lake water nutrients through water budgets between evaporation and precipitation. Furthermore, because rising temperatures result in greater vertical stratification in deep lakes, cyanobacteria may have exploited these stratified conditions and accumulated in dense surface blooms. We anticipate that under anthropogenic warming conditions, cyanobacterial biomass may continue to increase in subtropical deep lakes.

Facilitated arsenic immobilization by biogenic ferrihydrite-goethite biphasic Fe(III) minerals (Fh-Gt Bio-bi-minerals).

Biogenic iron(III) minerals (BIM) widely occur in aquatic systems. However, characteristics and mechanisms of As sequestration by biogenic biphasic Fe(III) minerals (Bio-bi-minerals) are not clearly understood. We investigated characteristics of Bio-bi-minerals induced by Pseudogulbenkiania sp. strain 2002 and explored their As sequestration mechanisms by monitoring particle morphology, mineralogical composition, and As binding properties. Results showed that Fe(II) oxidation (about 3 mM) by Pseudogulbenkiania sp. strain 2002 under growth condition produced biogenic ferrihydrite-goethite biphasic Fe(III) minerals (Fh-Gt Bio-bi-minerals), which showed better performance in As immobilization compared to corresponding biogenic monophasic Fe(III) minerals (Bio-mono-minerals). Decreased particle size, increased abundance of ferrihydrite and occurrence of bidentate mononuclear edge-sharing (2E) and monodentate mononuclear edge-sharing As complexes (1V) contributed to enhanced As immobilization by Fh-Gt Bio-bi-minerals. We suggest that the Bio-bi-minerals have the potential to illuminate As biogeochemical cycles in aquatic systems and to remediate As and nitrate co-contaminated groundwater.

Unraveling the diversity of sedimentary sulfate-reducing prokaryotes (SRP) across Tibetan saline lakes using epicPCR.

Sulfate reduction is an important biogeochemical process in the ecosphere; however, the major taxa of sulfate reducers have not been fully identified. Here, we used epicPCR (Emulsion, Paired Isolation, and Concatenation PCR) technology to identify the phylogeny of sulfate-reducing prokaryotes (SRP) in sediments from Tibetan Plateau saline lakes. A total of 12,519 OTUs and 883 SRP-OTUs were detected in ten lakes by sequencing of 16S rRNA gene PCR amplicons and epicPCR products of fused 16S rRNA plus dsrB gene, respectively, with Proteobacteria, Firmicutes, and Bacteroidetes being the dominant phyla in both datasets. The 120 highly abundant SRP-OTUs (> 1% in at least one sample) were affiliated with 17 described phyla, only 7 of which are widely recognized as SRP phyla. The majority of OTUs from both the whole microbial communities and the SRPs were not detected in more than one specific lake, suggesting high levels of endemism. The α-diversity of the entire microbial community and SRP sub-community showed significant positive correlations. The pH value and mean water temperature of the month prior to sampling were the environmental determinants for the whole microbial community, while the mean water temperature and total nitrogen were the major environmental drivers for the SRP sub-community. This study revealed there are still many undocumented SRP in Tibetan saline lakes, many of which could be endemic and adapted to specific environmental conditions.