Molecular Determination of Organic Adsorption Sites on Smectite during Fe Redox Processes Using ToF-SIMS Analysis.

Turnover of soil organic carbon (SOC) is strongly affected by a balance between mineral protection and microbial degradation. However, the mechanisms controlling the heterogeneous and preferential adsorption of different types of SOC remain elusive. In this work, the heterogeneous adsorption of humic substances (HSs) and microbial carbon (MC) on a clay mineral (nontronite NAu-2) during microbial-mediated Fe redox cycling was determined using time-of-flight secondary ion mass spectrometry (ToF-SIMS). The results revealed that HSs pre-adsorbed on NAu-2 would partially inhibit structural modification of NAu-2 by microbial Fe(III) reduction, thus retarding the subsequent adsorption of MC. In contrast, NAu-2 without precoated HSs adsorbed a significant amount of MC from microbial polysaccharides as a result of Fe(III) reduction. This was attributed to the deposition of a thin Al-rich layer on the clay surface, which provided active sites for MC adsorption. This study provides direct and detailed molecular evidence for the first time to explain the preferential adsorption of MC over HSs on the surface of clay minerals in iron redox processes, which could be critical for the preservation of MC in soil. The results also indicate that ToF-SIMS is a unique tool for understanding complex organic-mineral-microbe interactions.

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.

Correlative surface imaging reveals chemical signatures for bacterial hotspots on plant roots.

The rhizosphere is arguably the most complex microbial habitat on Earth, comprising an integrated network of plant roots, soil and a highly diverse microbial community (the rhizosphere microbiome). Understanding, predicting and controlling plant-microbe interactions in the rhizosphere will allow us to harness the plant microbiome as a means to increase or restore plant ecosystem productivity, improve plant responses to a wide range of environmental perturbations, and mitigate the effects of climate change by designing ecosystems for long-term soil carbon storage. To this end, it is imperative to develop new molecular approaches with high spatial resolution to capture interactions at the plant-microbe, microbe-microbe, and plant-plant interfaces. In this work, we designed an imaging sample holder that allows integrated surface imaging tools to map the same locations of a plant root-microbe interface with submicron lateral resolutions, providing novel in vivo analysis of root-microbe interactions. Specifically, confocal fluorescence microscopy, time-of-flight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) were used for the first time for the correlative imaging of the Brachypodium distachyon root and its interaction with Pseudomonas SW25, a typical plant growth-promoting soil bacterium. Imaging data suggest that the root surface is inhomogeneous and that the interaction between Pseudomonas and Brachypodium roots was confined to only a few spots along the sampled root segments and that the bacterial attachment spots were enriched in Na- and S-related and high-mass organic species. We conclude that the attachment of the Pseudomonas cells to the root surface is outcompeted by strong root-soil mineral interactions but facilitated by the formation of extracellular polymeric substances (EPS).

Mutual Interactions between Reduced Fe-Bearing Clay Minerals and Humic Acids under Dark, Oxygenated Conditions: Hydroxyl Radical Generation and Humic Acid Transformation.

Hydroxyl radicals (·OH) exert a strong impact on the carbon cycle due to their nonselective and highly oxidizing nature. Reduced iron-containing clay minerals (RIC) are one of the major contributors to the formation of ·OH in dark environments, but their interactions with humic acids (HA) are poorly known. Here, we investigate the mutual interactions between RIC and HA under dark and oxygenated conditions. HA decreased the oxidation rate of structural Fe(II) in RIC but significantly promoted the ·OH yield. HA dissolved a fraction of Fe(II) from RIC to form an aqueous Fe(II)-HA complex. ·OH were generated through both heterogeneous (through oxidation of structural Fe(II)) and homogeneous pathways (through oxidation of aqueous Fe(II)-HA species). RIC-mediated ·OH production by providing H2O2 to react with Fe(II)-HA and electrons to regenerate Fe(II)-HA. This highly efficient homogeneous pathway was responsible for increased ·OH yield. Abundant ·OH significantly decreased the molecular size, bleached chromophores, and increased the oxygen-containing functional groups of HA. These molecular changes of HA resembled photochemical transformation of HA. The mutual interaction between RIC and HA in dark and redox-fluctuating environments provides a new pathway for fast turnover of recalcitrant organic matters in clay- and HA-rich ecosystems such as tropical forest soils and tidal marsh sediments.

In Situ Liquid Secondary Ion Mass Spectrometry: A Surprisingly Soft Ionization Process for Investigation of Halide Ion Hydration.

The understanding of ion solvation phenomena is of significance due to their influences on many important chemical, biological, and environmental processes. Mass spectrometry (MS)-based methods have been used to investigate this topic with molecular insights. As ion-solvent interactions are weak, ionization processes should be as soft as possible in order to retain solvation structures. An in situ liquid secondary ion MS (SIMS) approach developed in our group has been recently utilized in investigations of Li ion solvation in nonaqueous solution, and it detected a series of solvated Li ions. As traditionally SIMS has long been recognized as a hard ionization process with strong damage occurring at the sputtering interface, it is very interesting to study further how soft in situ liquid SIMS can be. In this work, we used halide ion hydration as an example to compare the ionization performance of the in situ liquid SIMS approach with regular electrospray ionization MS (ESI-MS). Results show that, although ESI has been recognized as a soft ionization method, nearly no solvated halide ions were detected by ESI-MS analysis, which acquired only strong signals of salt ion clusters. In contrast, in liquid SIMS spectra, a series of obvious hydrated halide ion compositions could be observed. We further evaluated the hydration numbers of halide ions and revealed the effects of the ion size, charge density, and polarizability on the hydration phenomenon. Our findings demonstrated that the in situ liquid SIMS approach is surprisingly soft, and it is expected to have very broad applications on investigation of various ion-solvent interactions and many other interesting chemical processes (e.g., the initial nucleation of nanoparticle formation) in liquid environment.

Latitudinal distribution of ammonia-oxidizing bacteria and archaea in the agricultural soils of eastern China.

The response of soil ammonia-oxidizing bacterial (AOB) and archaeal (AOA) communities to individual environmental variables (e.g., pH, temperature, and carbon- and nitrogen-related soil nutrients) has been extensively studied, but how these environmental conditions collectively shape AOB and AOA distributions in unmanaged agricultural soils across a large latitudinal gradient remains poorly known. In this study, the AOB and AOA community structure and diversity in 26 agricultural soils collected from eastern China were investigated by using quantitative PCR and bar-coded 454 pyrosequencing of the amoA gene that encodes the alpha subunit of ammonia monooxygenase. The sampling locations span over a 17° latitude gradient and cover a range of climatic conditions. The Nitrosospira and Nitrososphaera were the dominant clusters of AOB and AOA, respectively; but the subcluster-level composition of Nitrosospira-related AOB and Nitrososphaera-related AOA varied across the latitudinal gradient. Variance partitioning analysis showed that geography and climatic conditions (e.g., mean annual temperature and precipitation), as well as carbon-/nitrogen-related soil nutrients, contributed more to the AOB and AOA community variations (∼50% in total) than soil pH (∼10% in total). These results are important in furthering our understanding of environmental conditions influencing AOB and AOA community structure across a range of environmental gradients.

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.

[Structure of planktonic ammonia-oxidizing community in the waters near the Three Gorges Dam of the Yangtze River].

OBJECTIVE: Investigation of ammonia-oxidizing microorganisms (AOM) in natural environments is of great importance to understand global nitrogen cycling. However, little is known about the effects of dam constructions on the AOM community. We studied the diversity of the free-living and particle-attached AOM populations in the waters behind and in front of the Three Gorges Dam of the Yangtze River, and analyzed the possible correlation between the observed difference in the two fractions of AOM with the environmental parameters. METHODS: Two sampling locations near the Three Gorges Dam were selected: one behind and the other in front of the dam. Physicochemical profiles of waters at each location were measured, and the biomass in the waters was collected by filtration. The diversity of AOM in the collected samples was investigated by using an integrated approach including reverse transcription and clone library construction. RESULTS: The turbidity, dissolved oxygen, and redox potential of the water in front of the dam were higher than those behind the dam. The AOM population behind and in front of the dam was dominated by ammonia-oxidizing archaea, whereas the ammonia-oxidizing bacteria were not detected. The distribution of free-living and particle-attached AOA behind and in front of the dam was different: the particle-attached AOA behind the dam was more diverse than that in front of the dam, whereas the free-living AOA showed the opposite tendency; the difference between the fractions of AOA behind the dam was apparently higher than that in front of the dam. CONCLUSION: The dominant AOA population did not show significant variation in the waters behind and in front of the dam, whereas the altered water dynamics resulted from the TGD construction may change the distribution of free-living and particle-attached AOA fractions in the waters behind and in front of the dam.

Distribution of Hydrogen-Producing Bacteria in Tibetan Hot Springs, China.

Investigating the distribution of hydrogen-producing bacteria (HPB) is of great significance to understanding the source of biological hydrogen production in geothermal environments. Here, we explored the compositions of HPB populations in the sediments of hot springs from the Daggyai, Quzhuomu, Quseyongba, and Moluojiang geothermal zones on the Tibetan Plateau, with the use of Illumina MiSeq high-throughput sequencing of 16S rRNA genes and hydA genes. In the present study, the hydA genes were successfully amplified from the hot springs with a temperature of 46-87°C. The hydA gene phylogenetic analysis showed that the top three phyla of the HPB populations were Bacteroidetes (14.48%), Spirochaetes (14.12%), and Thermotogae (10.45%), while Proteobacteria were absent in the top 10 of the HPB populations, although Proteobacteria were dominant in the 16S rRNA gene sequences. Canonical correspondence analysis results indicate that the HPB community structure in the studied Tibetan hot springs was correlated with various environmental factors, such as temperature, pH, and elevation. The HPB community structure also showed a spatial distribution pattern; samples from the same area showed similar community structures. Furthermore, one HPB isolate affiliated with Firmicutes was obtained and demonstrated the capacity of hydrogen production. These results are important for us to understand the distribution and function of HPB in hot springs.

Unconventional microbial mechanisms for the key factors influencing inorganic nitrogen removal in stormwater bioretention columns.

Bioretention systems are environmentally friendly measures to control the amount of water and pollutants in urban stormwater runoff, and their treatment performance for inorganic N strongly depends on various microbial processes. However, microbial responses to variations of N mass reduction in bioretention systems are complex and poorly understood, which is not conducive to management designs. In the present study, a series of bioretention columns were established to monitor their fate performance for inorganic N (NH4+and NO3-) by using different configurations and by dosing with simulated stormwater events. The results showed that NH4+ was efficiently oxidized to NO3-, mainly by ammonia- and nitrite-oxidizing bacteria in the oxic media, regardless of the configurations of the bioretention systems or stormwater conditions. In contrast, NO3- removal pathways varied greatly in different columns. The presence of vegetation efficiently improved NO3-mass reduction through root assimilation and enhancement of microbial NO3- reduction in the rhizosphere. The construction of an organic-rich saturation zone can make the redox potential too low for heterotrophic denitrification to occur, so as to ensure high NO3- mass reduction mainly via stimulating chemolithotrophic NO3- reduction coupled with oxidation of reductive sulfur compounds derived from the bio-reduction of sulfate. In contrast, in the organic-poor saturation zone, multiple oligotrophic NO3- reduction pathways may be responsible for the high NO3- mass reduction. These findings highlight the necessity of considering the variation of N bio-transformation pathways for inorganic N removal in the configuration of bioretention systems.

Onshore soil microbes and endophytes respond differently to geochemical and mineralogical changes in the Aral Sea.

There is limited knowledge about how microbiome develops along the geochemical and mineralogical change in onshore soils derived from continuous desiccation of lakes. In this study, geochemistry and mineralogy were studied in the Aral Sea onshore soils exposed in different periods (from the 1970s to 2018), followed by microbial analyses on the studied soils and the aboveground organs of dominant plants. The soils exhibited an increasing gradient of total soluble salts (TSS: 0.4-0.5 g/L to 71.3 g/L) and evaporite minerals (e.g., gypsum, halite) from the farshore to the nearshore. In the studied soils, microbial diversity decreased with increasing TSS, and microbial community dissimilarities among samples was positively correlated with the contents of gypsum and calcite minerals. Among the measured environmental variables, minerals contributed most to the observed microbial variation. In contrast, the endophytic microbial communities in the aboveground organs of dominant plants were not related to any of the measured variables, indicating that they differed from their soil counterparts with respect to their responses to geochemical and mineralogical variations in soils. In summary, these results help us understand the response of onshore soil microbiome to the decline of lake water caused by continuous desiccation.

Potential utilization of terrestrially derived dissolved organic matter by aquatic microbial communities in saline lakes.

Lakes receive large amounts of terrestrially derived dissolved organic matter (tDOM). However, little is known about how aquatic microbial communities interact with tDOM in lakes. Here, by performing microcosm experiments we investigated how microbial community responded to tDOM influx in six Tibetan lakes of different salinities (ranging from 1 to 358 g/l). In response to tDOM addition, microbial biomass increased while dissolved organic carbon (DOC) decreased. The amount of DOC decrease did not show any significant correlation with salinity. However, salinity influenced tDOM transformation, i.e., microbial communities from higher salinity lakes exhibited a stronger ability to utilize tDOM of high carbon numbers than those from lower salinity. Abundant taxa and copiotrophs were actively involved in tDOM transformation, suggesting their vital roles in lacustrine carbon cycle. Network analysis indicated that 66 operational taxonomic units (OTUs, affiliated with Alphaproteobacteria, Actinobacteria, Bacteroidia, Bacilli,  Gammaproteobacteria, Halobacteria, Planctomycetacia, Rhodothermia, and Verrucomicrobiae) were associated with degradation of CHO compounds, while four bacterial OTUs (affiliated with Actinobacteria, Alphaproteobacteria, Bacteroidia and Gammaproteobacteria) were highly associated with the degradation of CHOS compounds. Network analysis further revealed that tDOM transformation may be a synergestic process, involving cooperation among multiple species. In summary, our study provides new insights into a microbial role in transforming tDOM in saline lakes and has important implications for understanding the carbon cycle in aquatic environments.

Role of clay-associated humic substances in catalyzing bioreduction of structural Fe(III) in nontronite by Shewanella putrefaciens CN32.

Previous studies have shown that humic substances can serve as electron shuttle to catalyze bioreduction of structural Fe(III) in clay minerals, but it is unclear if clay-sorbed humic substances can serve the same function. It is unknown if the electron shuttling function is dependent on electron donor type and if humic substances undergo change as a result. In this study, humic acid (HA) and fulvic acid (FA) were sorbed onto nontronite (NAu-2) surface. Structural Fe(III) in HA- and FA-coated NAu-2 samples was bioreduced by Shewanella putrefaciens CN32 using H2 and lactate as electron donors. The results showed a contrasting effect of humic substances on bioreduction of structural Fe(III), depending on the electron donor type. With H2 as electron donor, humic substances had little effect on bioreduction of Fe(III) (the reduction extent: 26.2%, 27.4%, 29.3% for HA-coated, FA-coated, and uncoated NAu-2, respectively). In contrast, these substances significantly enhanced bioreduction of Fe(III) with lactate as electron donor (the reduction extent: 20.2%, 20.7%, 11.5% for HA-coated, FA-coated, and uncoated NAu-2, respectively). This contrasting behavior is likely caused by the difference in reaction free energy and electron transport process between H2 and lactate. When H2 served as electron donor, more energy was released than when lactate served as electron donor. In addition, because of different cellular locations of lactate dehydrogenase (inner membrane) and H2 hydrogenase (the periplasm), electrons generated by H2 hydrogenase may pass through the electron transport chain more rapidly than those generated from lactate dehydrogenase. Through their functions as electron shuttle and/or carbon source, clay-sorbed HA/FA underwent partial transformation to amino acids and other compounds. The availability of external carbon source played an important role in the amount and type of secondary product generation. These results have important implications for coupled iron and carbon biogeochemical cycles in clay- and humic substance-rich environments.

Thioarsenate Formation Coupled with Anaerobic Arsenite Oxidation by a Sulfate-Reducing Bacterium Isolated from a Hot Spring.

Thioarsenates are common arsenic species in sulfidic geothermal waters, yet little is known about their biogeochemical traits. In the present study, a novel sulfate-reducing bacterial strain Desulfotomaculum TC-1 was isolated from a sulfidic hot spring in Tengchong geothermal area, Yunnan Province, China. The arxA gene, encoding anaerobic arsenite oxidase, was successfully amplified from the genome of strain TC-1, indicating it has a potential ability to oxidize arsenite under anaerobic condition. In anaerobic arsenite oxidation experiments inoculated with strain TC-1, a small amount of arsenate was detected in the beginning but became undetectable over longer time. Thioarsenates (AsO4-xSx2- with x = 1-4) formed with mono-, di- and tri-thioarsenates being dominant forms. Tetrathioarsenate was only detectable at the end of the experiment. These results suggest that thermophilic microbes might be involved in the formation of thioarsenates and provide a possible explanation for the widespread distribution of thioarsenates in terrestrial geothermal environments.

Relative importance of advective flow versus environmental gradient in shaping aquatic ammonium oxidizers near the Three Gorges Dam of the Yangtze River, China.

Construction of a dam in a large river alters its hydrodynamic condition and geochemical gradient, but the effect of such anthropogenic activity on microbial ecology remains poorly understood. To assess this effect, we investigated the relative importance of advective flow versus environmental condition in shaping ammonia oxidizing bacteria (AOB) and archaea (AOA) community from 110 km upstream to the Three Gorges Dam (TGD) of the Yangtze River, China. Water physicochemical conditions, including turbidity, conductivity, redox state and nutrient level, were fairly constant from 110 to 45 km upstream of the TGD, but significantly oscillated near the dam. AOB and AOA in the Yangtze River were dominated by Nitrosospira- and Nitrosopumilus-affiliated clusters, respectively, and these compositions were invariant throughout the sampled 110 km flow path, suggesting that AOB and AOA communities in the river were largely transported from upstream by advection with minor local and transient inputs from surrounding soils and tributaries. However, the abundance of AOB and AOA was influenced by local geochemical conditions, possibly via the growth/decay mechanisms. The source of AOB in the Yangtze River appeared to be derived from soil near the headwater, but its abundance was enhanced during downstream transport, likely due to survival and growth.

Actinobacterial Diversity in the Sediments of Five Cold Springs on the Qinghai-Tibet Plateau.

The actinobacterial diversity was investigated in the sediments of five cold springs in Wuli region on the Qinghai-Tibet Plateau using 16S rRNA gene phylogenetic analysis. The actinobacterial communities of the studied cold springs were diverse and the obtained actinobacterial operational taxonomic units were classified into 12 actinobacterial orders (e.g., Acidimicrobiales, Corynebacteriales, Gaiellales, Geodermatophilales, Jiangellales, Kineosporiales, Micromonosporales, Micrococcales, Nakamurellales, Propionibacteriales, Pseudonocardiales, Streptomycetales) and unclassified Actinobacteria. The actinobacterial composition varied among the investigated cold springs and were significantly correlated (r = 0.748, P = 0.021) to environmental variables. The actinobacterial communities in the cold springs were more diverse than other cold habitats on the Tibetan Plateau, and their compositions showed unique geographical distribution characteristics. Statistical analyses showed that biogeographical isolation and unique environmental conditions might be major factors influencing actinobacterial distribution among the investigated cold springs.

Greater temporal changes of sediment microbial community than its waterborne counterpart in Tengchong hot springs, Yunnan Province, China.

Temporal variation in geochemistry can cause changes in microbial community structure and diversity. Here we studied temporal changes of microbial communities in Tengchong hot springs of Yunnan Province, China in response to geochemical variations by using microbial and geochemical data collected in January, June and August of 2011. Greater temporal variations were observed in individual taxa than at the whole community structure level. Water and sediment communities exhibited different temporal variation patterns. Water communities were largely stable across three sampling times and dominated by similar microbial lineages: Hydrogenobaculum in moderate-temperature acidic springs, Sulfolobus in high-temperature acidic springs, and Hydrogenobacter in high-temperature circumneutral to alkaline springs. Sediment communities were more diverse and responsive to changing physicochemical conditions. Most of the sediment communities in January and June were similar to those in waters. However, the August sediment community was more diverse and contained more anaerobic heterotrophs than the January and June: Desulfurella and Acidicaldus in moderate-temperature acidic springs, Ignisphaera and Desulfurococcus in high-temperature acidic springs, the candidate division OP1 and Fervidobacterium in alkaline springs, and Thermus and GAL35 in neutral springs. Temporal variations in physicochemical parameters including temperature, pH, and dissolved organic carbon may have triggered the observed microbial community shifts.

Genomovar assignment of Pseudomonas stutzeri populations inhabiting produced oil reservoirs.

Oil reservoirs are specific habitats for the survival and growth of microorganisms in general. Pseudomonas stutzeri which is believed to be an exogenous organism inoculated into oil reservoirs during the process of oil production was detected frequently in samples from oil reservoirs. Very little is known, however, about the distribution and genetic structure of P. stutzeri in the special environment of oil reservoirs. In this study, we collected 59 P. stutzeri 16S rRNA gene sequences that were identified in 42 samples from 25 different oil reservoirs and we isolated 11 cultured strains from two representative oil reservoirs aiming to analyze the diversity and genomovar assignment of the species in oil reservoirs. High diversity of P. stutzeri was observed, which was exemplified in the detection of sequences assigned to four known genomovars 1, 2, 3, 20 and eight unknown genomic groups of P. stutzeri. The frequent detection and predominance of strains belonging to genomovar 1 in most of the oil reservoirs under study indicated an association of genomovars of P. stutzeri with the oil field environments.

Cultivation and characterization of thermophilic Nitrospira species from geothermal springs in the US Great Basin, China, and Armenia.

Despite its importance in the nitrogen cycle, little is known about nitrite oxidation at high temperatures. To bridge this gap, enrichment cultures were inoculated with sediment slurries from a variety of geothermal springs. While nitrite-oxidizing bacteria (NOB) were successfully enriched from seven hot springs located in US Great Basin, south-western China, and Armenia at ≤ 57.9 °C, all attempts to enrich NOB from > 10 hot springs at ≥ 61 °C failed. The stoichiometric conversion of nitrite to nitrate, chlorate sensitivity, and sensitivity to autoclaving all confirmed biological nitrite oxidation. Regardless of origin, all successful enrichments contained organisms with high 16S rRNA gene sequence identity (≥ 97%) with Nitrospira calida. In addition, Armenian enrichments also contained close relatives of Nitrospira moscoviensis. Physiological properties of all enrichments were similar, with a temperature optimum of 45-50 °C, yielding nitrite oxidation rates of 7.53 ± 1.20 to 23.0 ± 2.73 fmoles cell(-1) h(-1), and an upper temperature limit between 60 and 65 °C. The highest rates of NOB activity occurred with initial NO2 - concentrations of 0.5-0.75 mM; however, lower initial nitrite concentrations resulted in shorter lag times. The results presented here suggest a possible upper temperature limit of 60-65 °C for Nitrospira and demonstrate the wide geographic range of Nitrospira species in geothermal environments.

Control of temperature on microbial community structure in hot springs of the Tibetan Plateau.

The Tibetan Plateau in Northwest China hosts a number of hot springs that represent a biodiversity hotspot for thermophiles, yet their diversity and relationship to environmental conditions are poorly explored in these habitats. In this study we investigated microbial diversity and community composition in 13 Tibetan hot springs with a wide range of temperatures (22.1-75°C) and other geochemical conditions by using the 16S rRNA gene pyrosequencing approach. Bacteria (10(8)-10(11) copy/g; 42 bacterial phyla) in Tibetan hot springs were more abundant and far more diverse than Archaea (10(7)-10(10) copy/g; 5 archaeal phyla). The dominant bacterial phyla systematically varied with temperature. Moderate temperatures (75-66°C) favored Aquificae, GAL35, and novel Bacteria, whereas low temperatures (60-22.1°C) selected for Deinococcus-Thermus, Cyanobacteria, and Chloroflexi. The relative abundance of Aquificae was correlated positively with temperature, but the abundances of Deinococcus-Thermus, Cyanobacteria, and Chloroflexi were negatively correlated with temperature. Cyanobacteria and Chloroflexi were abundant in Tibetan hot springs and their abundances were positively correlated at low temperatures (55-43°C) but negatively correlated at moderate temperatures (75-55°C). These correlation patterns suggest a complex physiological relationship between these two phyla. Most archaeal sequences were related to Crenarchaeota with only a few related to Euryarchaeota and Thaumarchaeota. Despite the fact that microbial composition in Tibetan hot springs was strongly shaped by temperature, microbial diversity (richness, evenness and Shannon diversity) was not significantly correlated with temperature change. The results of this study expand our current understanding of microbial ecology in Tibetan hot springs and provide a basis for a global comparison.