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Despite the vital role of microorganisms for ecosystem functioning and human welfare, our understanding of their global diversity and biogeographical patterns lags significantly behind that of plants and animals. We conducted a meta-analysis including ~600 soil samples from all continents to evaluate the biogeographical patterns and drivers of bacterial diversity in terrestrial ecosystems at the global scale. Similar to what has been found with plants and animals, the diversity of soil bacteria in the Southern Hemisphere decreased from the equator to Antarctica. However, soil bacteria showed similar levels of diversity across the Northern Hemisphere. The composition of bacterial communities followed dissimilar patterns between hemispheres, as the Southern and Northern Hemispheres were dominated by Actinobacteria and Acidobacteria, respectively. However, Proteobacteria was co-dominant in both hemispheres. Moreover, we found a decrease in soil bacterial diversity with altitude. Climatic features (e.g., high diurnal temperature range and low temperature) were correlated with the lower diversity found at high elevations, but geographical gradients in soil total carbon and species turnover were important drivers of the observed latitudinal patterns. We thus found both parallels and differences in the biogeographical patterns of aboveground vs. soil bacterial diversity. Our findings support previous studies that highlighted soil pH, spatial influence, and organic matter as important drivers of bacterial diversity and composition. Furthermore, our results provide a novel integrative view of how climate and soil factors influence soil bacterial diversity at the global scale, which is critical to improve ecosystem and earth system simulation models and for formulating sustainable ecosystem management and conservation policies. [ABSTRACT FROM AUTHOR]

Microorganisms play a key role in degradation of polycyclic aromatic hydrocarbons (PAHs) in environments. Dissolved organic matter (DOM) can enhance microbial degradation of PAHs in soils. However, it is not clear how will the soil microbial community respond to addition of DOM during bioremediation of PAH-contaminated soils. In this study, DOMs derived from various agricultural wastes were applied to remediate the aging PAH-contaminated soils in a 90-day microcosm experiment. Results showed that the addition of DOMs offered a more efficient and persistent elimination of soil PAHs compared to the control which had no DOM addition. PAH removal effects were different among treatments with various DOMs; the addition of DOMs with high proportion of hydrophobic fraction could remove PAHs more efficiently from the soil. Low-molecular-weight (LMW) PAHs were more easily eliminated than that with high-molecular-weight (HMW). Addition of DOMs significantly increased abundance of 16S ribosomal RNA (rRNA), pdo1, nah, and C12O genes and obviously changed community compositions of nah and C12O genes in different ways in the PAH-contaminated soil. Phylogenetic analyses of clone libraries exhibited that all of nah sequences and most of C12O sequences were affiliated into Gammaproteobacteria and Betaproteobacteria. These results suggested that external stimuli produced by DOMs could enhance the microbial degradation of PAHs in soils through not only solubilizing PAHs but also altering abundance and composition of indigenous microbial degraders. Our results reinforce the understanding of role of DOMs in mediating degradation of PAHs by microorganims in soils. [ABSTRACT FROM AUTHOR]

Nickel pollution imposes deleterious effects on soil ecosystem. The responses of soil microorganisms to long-term nickel pollution under field conditions remain largely unknown. Here, we used high-throughput sequencing to elucidate the impacts of long-term nickel pollution on soil bacterial communities in two contrasting agricultural soils. Our results found that the soil microbial biomass carbon consistently decreased along the nickel gradients in both soils. Nickel pollution selectively favored or impeded the prevalence of several dominant bacterial guilds, in particular, Actinobacteria showed tolerance, while Acidobacteria and Planctomycetes displayed sensitivity. Despite the apparent shifts in the bacterial community composition, no clear tendency in the bacterial diversity and abundance was identified along the nickel gradients in either soil. Collectively, we provide evidence that long-term nickel pollution shifted the soil bacterial communities, resulting in the decrease of microbial biomass although the bacterial diversity was not significantly changed. [ABSTRACT FROM AUTHOR]

Metal aging in soils has been considered an important factor influencing its availability and toxicity to organisms. In this study, we report the influence of 5 years field aging on the nickel (Ni) toxicity to collembolan Folsomia candida based on two different types of soil from Dezhou (DZ) and Qiyang (QY) counties in China. Acute and chronic toxicity of Ni to F. candida was assessed in both freshly spiked and field aging contaminated soils. We found that 5 years field aging increased the EC and 2d-LC values of Ni to F. candida in the DZ soil, while little influence on the Ni toxicity was observed in the QY soil. There was no adverse effect of the long-term field aging on the Ni toxicity to the survival of F. candida in the two tested soils. In addition, field aging of the two soils impacted differently the water-soluble Ni concentrations, which were significantly correlated to the juvenile production of F. candida based on a logistic model. Our study highlights different effects of long-term field aging on the Ni toxicity to F. candida between divergent types of soil, and this should be taken into account in future toxicity testing and risk assessment practices. [ABSTRACT FROM AUTHOR]

Purpose: Although coastal marine sediments harbor diverse bacteria with important ecological and environmental functions, a comprehensive view of their community characteristics is still lacking in typical environments along the China coast. We studied the diversity and composition of bacterial community in the sediment of Jiaozhou Bay and characterized their spatiotemporal patterns, aiming to analyze the effects of geographic heterogeneity, seasonal difference, anthropogenic activity, and eutrophication gradient on the bacterial ecology. Materials and methods: Sixteen full-length bacterial 16S rRNA gene clone libraries were constructed from the sediment bacteria at four stations (A5, B2, D1, and D7) of Jiaozhou Bay over four seasons (February, May, August, and November). The bacterial diversity and community structure variation were analyzed. Results and discussion: A total of 1088 16S rRNA gene sequences and 746 distinct operational taxonomic units (OTUs) (at 97 % sequence similarity level) were retrieved from the 16 clone libraries. Libraries of each sample revealed a high diversity, and a total of 17 bacterial phyla were identified. Bacteria lineages Proteobacteria (mostly γ- Proteobacteria and δ- Proteobacteria), Actinobacteria, Bacteroidetes, and Planctomycetes, which are commonly found in marine sediments, were the dominant divisions in our samples. Meanwhile, some uncommon phyla, such as Deinococcus- Thermus and Lentisphaerae, were also detected. Distinct spatial patterns and noticeable seasonal variations of bacteria community were observed, indicating that environmental heterogeneity in spatial variation other than in temporal variation may be more important in determining the bacterial communities. Most of the abundant OTUs were related to sequences retrieved from the heavy-metal-polluted environments, indicating that the Jiaozhou Bay might be influenced by pollution. Conclusions: The bacterial communities in Jiaozhou Bay sediments are highly diverse. The four typical stations that we chose might experience different anthropogenic effects and eutrophication gradients, which shaped their bacterial community composition. The environment of Jiaozhou Bay may be under pressure exerted by multi-dimension anthropogenic activities. This study provided a novel insight into the bacterial community variations in Jiaozhou Bay, enriching knowledge about ecological bioindicators and mechanisms that maintain bacterial diversity and shape bacterial community composition. [ABSTRACT FROM AUTHOR]

Natural sepiolite was used as an adsorbent for the investigation of the adsorption kinetics, isotherms, thermodynamic parameters of an acid blue 25 (AB25), methylene blue (MB) from aqueous solution at various pHs, temperatures, the kinetics, and thermodynamics for the removal of the two dyes onto natural sepiolite have also been investigated. The adsorbed amounts of AB25 increased with decreasing pH and the optimum pH value for the AB25 and MB were found to be 3.0 and 9.0. respectively. The adsorption capacity of AB25 onto natural sepiolite increased with the increasing temperature, indicating that AB25 and MB dye adsorption on the natural sepiolite was an endothermic process, the second-order model is found to be more suitable to describe the adsorption kinetic data than the first-order model for natural sepiolite on the AB25 and MB and the adsorption process of AB25 and MB are showing pseudo–second-order kinetic behavior, respectively. The adsorption of AB25 and MB on natural sepiolite may be followed by an intraparticle diffusion up to 60 and 90 min, respectively, and the Langmuir equation represents the adsorption process better. The fit of the data for AB25 and MB adsorption onto natural sepiolite suggests that the D-R model gave slightly closer fittings than those of Langmuir and Freundlich models. The adsorption of AB25 on natural sepiolite has a low potential barrier, which is also indicates a physical adsorption. The negative values of ΔG0and positive ΔH0which has been obtained indicates that the MB adsorption process is a spontaneous and endothermic. [ABSTRACT FROM AUTHOR]

The anthropogenic release of carbon dioxide into the atmosphere leads to an increase in the CO2partial pressure in the ocean, which may reach 950 μatm by the end of the 21st century. An experiment was performed to test the effects of increased sea water concentrations of CO2combined with heavy metals on mortality rates, metallothionein, immune funtion, and uptake kinetics of the bivalveMytilus edulisL. As a result, the mortality rates ofMytilus edulisL fluctuated with pH variety in all heavy metals (Cd, Pb, Cu) test seawater treatments compared to control group. It was demonstrated thatin vivoCd-, Pb-, or Cu pretreatment under acidifications can alleviate metallothionein byin vitroCd, Pb, and Cu in soft tissues and suggested that acidification can aggravate heavy metals pollution and toxicity for marine organisms. Moreover, the fraction of eosinophilic cells increased over the 21 days period for Cd exposure, then decreased with 28 and 35 days incubation, the fraction of eosinophilic cells increased similar with Cd exposure and pH 8.2. The fraction of eosinophilic cells significantly increased from 32% to 53% of the hemocyte population over the 35-day period for Pb exposure and pH8.2, the fraction of eosinophilic cells increased from 35% to 58% of the hemocyte population over the 35-day period for Pb exposure and pH 6.2. Phagocytosis levels declined with increasing exposure time for Cd alone and phagocytosis levels declined with decreasing pH (from 8.2 to 6.2) with Cd exposure on 35 days.Mytilus edulisL in Pb with reduced pH (6.2) treatments also decreased their phagocytosis levels on 35 days. Further, phagocytosis decreased bigger than that of Pb with pH 8.2. At steady state equilibrium, CF of109Cd was significantly higher at pH 6.2 and pH 7.7 than at pH 8.2, the accumulation of203Pb was significantly higher at the lowest pH 6.2 level than at the two exposure levels (pH 7.7 and pH 8.2). Similarly, the lower the seawater pH 6.2, the more63Cu was accumulated in the hemolymph ofMytilus edulisL. The results indicate that future reductions in pH caused by increased CO2concentrations in the sea may have an impact onMytilus edulisL combined with heavy metals pollution. [ABSTRACT FROM AUTHOR]

An external weak electric field is introduced into the small-world networks of Hodgkin-Huxley neurons to study the control and breakup of a spiral wave. The effect of an external electric field on the neurons in the smallworld network is described by an additive perturbation on the membrane potentials of neurons at the cellular level, in which an additive term VE is imposed on the physiological membrane potential. A statistical factor of synchronization is used to measure the collective behaviour of spiral waves by changing the electric field; it is confirmed that a smaller factor of synchronization is associated with the survival of a spiral wave. In the case of no channel noise, the spiral wave could be removed under a certain intensity of constant electric field; it keeps robustly to the weak electric field when the electric field changes periodically. In the case of weak channel noise, a breakup of the spiral wave is observed when the intensity of the electric field exceeds certain thresholds, which could be measured from the curve for synchronization factors. No drift of the spiral wave is observed under the weak electric field [ABSTRACT FROM AUTHOR]

Soil mercury (Hg) pollution has received considerable attention due to its neurotoxin effects and its potential risk to food safety. The microbial transformation of Hg plays a key role in reducing Hg toxicity by the mercuric reductase (MerA) conferred by genes arranged in the mer operon. This study investigated the effects of long-term fertilization on the diversity of bacterial mercuric reductase gene ( merA), which specify the reduction of ionic Hg2+ to the volatile elemental form Hg0, in an agricultural soil with relatively high Hg content. The soil samples were collected from different treatments, including control without fertilizer (CK), fertilizer nitrogen (N), combined fertilizers (NPK) of N, phosphorus (P) and potassium (K), and NPK plus organic manure (NPK + OM). The merA gene diversity patterns were analyzed based on the merA clone libraries and sequencing measurements. Results showed that the merA gene diversity was influenced by soil variables depending on the fertilization practices. In particular, NH4+ and NO3- contents had strong effect on the merA gene diversity pattern both in the N and NPK treatments, whereas the merA gene diversity pattern in NPK + OM treatment was distinctly influenced by the contents of organic matter, available P and K. These results suggested that long-term fertilization had significant influences on merA gene diversity, which could be helpful to understand the Hg reduction process and potentially serve microbial remediation of Hg contaminated soil. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Excessive dexamethasone (Dex) administrated into pregnant mice during critical periods of palatal development can produce a high incidence of cleft palate. Its mechanisms remain unknown. Vitamin B12 has been shown to antagonize the teratogenic effects of Dex, which, however, remains controversial. In this study, we investigated the effects of Dex and vitamin B12 on murine embryonic palatal shelf fusion using organ culture of murine embryonic shelves. The explanted palatal shelves on embryonic day 14 (E14) were cultured for 24, 48, 72 or 96 h in different concentrations of Dex and/or vitamin B12. The palatal shelves were examined histologically for the morphological alterations on the medial edge epithelium (MEE) and fusion rates among different groups. It was found that the palatal shelves were not fused at 72 h or less of culture in Dex group, while they were completely fused in the control and vitamin B12-treated groups at 72 and 96 h, respectively. The MEE still existed and proliferated. In Dex+vitamin B12 group the palatal shelves were fused at each time point in a similar rate to controls. These results may suggest that Dex causes teratogenesis of murine embryonic palatal shelves and vitamin B12 prevents the teratogenic effect of Dex on palatogenesis on murine embryos in vitro. [ABSTRACT FROM AUTHOR]