Silica fertilization and nano-MnO2 amendment on bacterial community composition in high arsenic paddy soils

Nano zero-valent iron and melatonin synergistically alters uptake and translocation of Cd and As in soil-rice system and mechanism in soil chemistry and microbiology

Nanoscale zero-valent iron (Fe) is a promising nanomaterial for remediating heavy metal-contaminated soils. Melatonin (MT) is essential to alleviate environmental stress in plants. However, the conjunction effects of Fe and MT (FeMT) on rice Cd, As accumulation and the mechanism of soil chemical and microbial factors interaction are unclear. Here, a pot experiment was conducted to evaluated the effects of the FeMT for rice Cd, As accumulation and underlying mechanisms. The findings showed that FeMT significantly reduced grains Cd by 92%-87% and As by over 90%, whereas improving grains Fe by over 213%. Soil available-Cd and iron plaques-Cd (extracted by dithionite-citrate-bicarbonate solution, DCB-Cd) significantly regulated roots Cd, thus affected Cd transport to grains. Soil pH significantly affected soil As and DCB-As, which further influenced roots As uptake and the transport to shoots and grains. The interactions between the soil bacterial community and soil Fe, available Fe, and DCB-Fe together affected root Fe absorption and transportation in rice. FeMT significantly influenced rhizosphere soil bacterial α- and β-diversity. Firmicutes as the dominant phylum exhibited a significant positive response to FeMT measure, and acted a key role in reducing soil Cd and As availability mainly by improving iron-manganese plaques. The increase of soil pH caused by FeMT was beneficial only for Actinobacteriota growth, which reduced Cd, As availability probably through complexation and adsorption. FeMT also showed greater potential in reducing human health and ecological risks by rice consumption and straw returning. These results showed the important role of both soil chemical and microbial factors in FeMT-mediated rice Cd, As reduction efficiency. This study opens a novel strategy for safe rice production and improvement of rice iron nutrition level in heavy-metals polluted soil, but also provides new insights into the intricate regulatory relationships among soil biochemistry, toxic elements, microorganism, and plants.

Long-term performance and biofilms of the novel nano manganese dioxide coupling carbon source pre-loaded biological activated carbon filters for drinking water

In order to accelerate the start-up of biological activated carbon (BAC) filters and enhance ammonium (NH4+-N) removal performance, three substrates (sucrose and/or nano manganese dioxide (nMnO2)) pre-loaded BAC filters were set up to investigate the pollutants removals and microbiological characteristics for a long-term operation of 197 days. The average NH4+-N removal performance treated by the sucrose coupled with nMnO2 loaded BAC filter was the highest (71.18 %), which was 3.83 times of that by the control filter (18.58 %). 29 % of NH4+-N treated by the sucrose coupled with nMnO2 loaded BAC removed through the traditional nitrification and denitrification, or simultaneous nitrification and denitrification (SND) pathways according to the calculation of the alkalinity consumption (6.12 mmol/L). There was no leakage of carbon source and Mn, and no accumulation of nitrite from the substrates loaded BAC. The dominant bacteria in the sucrose coupled with nMnO2 loaded BAC were Dechloromona (accounting for 8.02% of the total bacterial) and Acidaminobacter (accounting for 15.16% of total bacterial) on the Day 180, which had the capacity of nitrification or denitrification. NH4+-N and micropollutants removals treated by the combined process of peracetic acid (PAA) pre-oxidation and substrates loaded BAC were significant due to the generation of assimilable organic carbon (AOC) (5.98 ± 1.93 μg-C/mL) by PAA (100 μM)/Fe2+ pre-oxidation and the higher biomass ((4.57 ± 3.07) × 107 cells/g DW BAC) in the sucrose coupled with nMnO2 loaded BAC filter. Therefore, nMnO2 coupling carbon source pre-loading strategy could not only enhance initial colonization, but also promote pollutants removals for long-term operation.

The application of mixed stabilizing materials promotes the feasibility of the intercropping system of Gynostemma pentaphyllum/Helianthus annuus L. on arsenic contaminated soil

Intercropping technology and stabilizing materials are common remediation techniques for soils contaminated with heavy metals. This study investigated the feasibility of the Gynostemma pentaphyllum (G. pentaphyllum)/Helianthus annuus L. (H. annuus) intercropping system on arsenic (As) contaminated farmland through field and pot experiments and the regulation of plant As absorption by the application of mixed stabilizing materials in this intercropping system. Field experiments demonstrated that intercropping with H. annuus increased the As concentration in G. pentaphyllum leaves to 1.79 mg kg-1 but still met the requirements of the national food standard of China (2 mg kg-1) (GB2762-2017). Meanwhile, G. pentaphyllum yield in the intercropping system decreased by 15.09%, but the difference was insignificant (P > 0.05). Additionally, the As bioconcentration (BCA) per H. annuus plant in the intercropping system was significantly higher than that in the monoculture system, increasing by 76.37% (P < 0.05). The pot experiment demonstrated that when granite powder, iron sulfate mineral, and "Weidikang" soil conditioner were applied to the soil collectively, G. pentaphyllum leaf As concentration in the intercropping system could be significantly reduced by 42.17%. Rhizosphere pH is the most crucial factor affecting As absorption by G. pentaphyllum in intercropping systems. When these three stabilizing materials were applied simultaneously, the As bioaccumulation (BCA) per H. annuus plant was significantly higher than that of normal intercropping treatment, which increased by 71.12% (P < 0.05), indicating that the application of these stabilizing materials significantly improved the As removal efficiency of the intercropping system. Dissolved organic carbon (DOC) concentration in the rhizosphere soil is the most pivotal factor affecting As absorption by H. annuus. In summary, the G. pentaphyllum-H. annuus intercropping model is worthy of being promoted in moderately As polluted farmland. The application of granite powder, iron sulfate mineral, and "Weidikang" soil conditioner collectively to the soil can effectively enhance the potential of this intercropping model to achieve "production while repairing" in the As polluted farmland.

Saline-alkali stress reduces soil bacterial community diversity and soil enzyme activities

Saline-alkalisation of the soil environment and microorganism is a global challenge. However, relevant studies on the effects of saline-alkali stress on soil bacterial communities are limited. In this study, we investigated the effects of saline-alkali stress on the carbon source metabolic utilisation of the microbial community, bacterial diversity, and composition in soil using Biolog Ecoplate and 16S rRNA gene amplicon sequencing. Biolog Ecoplate results showed that saline-alkali stress decreased the metabolic activity and functional diversity, and changed the utilisation characteristics of carbon sources in soil microorganisms. Particularly, high level of saline-alkali stress significantly decreased the utilisation of carbohydrates and amino acids carbon sources. The results of 16S rRNA gene amplicon sequencing showed that high level of saline-alkali stress significantly reduced the diversity of soil bacterial communities. In addition, high level of saline-alkali stress significantly decreased the relative abundances of some key bacterial taxa, such as Gemmatimonas, Sphingomonas, and Bradyrhizobium. Furthermore, as saline-alkali content increased, the soil catalase, protease, urease, and sucrase activities also significantly decreased. Collectively, these results provide new insight for studies on the changes in the soil bacterial community and soil enzyme activity under saline-alkali stress.

Chloride application weakens cadmium immobilization by lime in paddy rice soil

Contamination of agricultural products by cadmium (Cd) is a global health problem, causing chronic abnormalities. The consumption of rice, the most-consumed foods, is an important exposure route of Cd to human body. Chloride (Cl^-) is reported to increase Cd uptake by rice; however, the effect on Cd uptake and accumulation by rice in the presence of lime is not clear. Therefore, a pot culture experiment was performed to explore the influence of Cl^- on the absorption and accumulation of Cd in rice plants under lime remediation and its possible mechanisms. The results showed that Cl^- promoted Cd accumulation in rice grains, mainly because of increased Cd bioavailability in the soil and by impeding the formation of iron plaques on rice roots, which reduced chelating and precipitation of Cd. Moreover, increased overexpression of the main transporters of Cd in rice roots, including OsNramp5, OsNramp1, OsIRTs and OsHMA2, favored the upward translocation of Cd from the root to shoot and increased the transfer factors (TFs) from soil to root, root-stem, leaf to grain, and soil to grain. Therefore, the application of Cl-rich materials to Cd-contaminated rice fields should be avoided during liming of the soil for Cd immobilization.

Phytoremediation potential evaluation of three rhubarb species and comparative analysis of their rhizosphere characteristics in a Cd- and Pb-contaminated soil

Screening or breeding exceptional plant species for heavy metal phytoremediation is as important as adopting feasible measures to enhance phytoremediation efficiency, which are largely based on clarifying the mechanisms of heavy metal tolerance and accumulation by plants. In this study, cadmium (Cd) and lead (Pb) tolerance and accumulation characteristics of Rheum officinale, R. palmatum, and R. tanguticum were analysed to assess their phytoremediation potential. The seed germination test indicated that these three rhubarb species could tolerate 10 mg L^-1 Cd and 100 mg L^-1 Pb. However, when sown in Cd- and Pb-contaminated soil, all three rhubarb species exhibited a relatively high Cd accumulation capacity but a considerably low Pb accumulation capacity according to the bioconcentration factors of Cd (0.42-0.47 in shoots and 0.11-0.15 in roots) and Pb (0.004-0.008 in shoots and 0.007-0.013 in roots). The high Cd translocation factors (3.04-4.24) indicated that these three rhubarb species were suitable for Cd phytoextraction. The changes in rhizospheric physicochemical indices were generally similar among the three rhubarb plants in comparison with those of the unplanted soil. However, differential indicator rhizobacteria were identified for the three rhubarb plants, which may be primarily attributed to their different root system characteristics. These enriched rhizobacteria included many plant growth-promoting bacteria, and several of them were also involved in regulating heavy metal uptake by plants, indicating that three rhubarb species likely recruit differentially beneficial rhizobacteria to maintain plant growth and vitality and to regulate heavy metal uptake in the Cd- and Pb-polluted soil. This study identifies new candidate plant resources for the phytoremediation of Cd-polluted soils and provides novel insights into understanding the interactions among heavy metals, rhizobacteria, and plants.

Cable bacteria at oxygen-releasing roots of aquatic plants: a widespread and diverse plant-microbe association

Cable bacteria are sulfide-oxidising, filamentous bacteria that reduce toxic sulfide levels, suppress methane emissions and drive nutrient and carbon cycling in sediments. Recently, cable bacteria have been found associated with roots of aquatic plants and rice (Oryza sativa). However, the extent to which cable bacteria are associated with aquatic plants in nature remains unexplored. Using newly generated and public 16S rRNA gene sequence datasets combined with fluorescence in situ hybridisation, we investigated the distribution of cable bacteria around the roots of aquatic plants, encompassing seagrass (including seagrass seedlings), rice, freshwater and saltmarsh plants. Diverse cable bacteria were found associated with roots of 16 out of 28 plant species and at 36 out of 55 investigated sites, across four continents. Plant-associated cable bacteria were confirmed across a variety of ecosystems, including marine coastal environments, estuaries, freshwater streams, isolated pristine lakes and intensive agricultural systems. This pattern indicates that this plant-microbe relationship is globally widespread and neither obligate nor species specific. The occurrence of cable bacteria in plant rhizospheres may be of general importance to vegetation vitality, primary productivity, coastal restoration practices and greenhouse gas balance of rice fields and wetlands.

Effects of silicon on heavy metal uptake at the soil-plant interphase: A review

Silicon (Si) is the second richest element in the soil and surface of earth crust with a variety of positive roles in soils and plants. Different soil factors influence the Si bioavailability in soil-plant system. The Si involves in the mitigation of various biotic (insect pests and pathogenic diseases) and abiotic stresses (salt, drought, heat, and heavy metals etc.) in plants by improving plant tolerance mechanism at various levels. However, Si-mediated restrictions in heavy metals uptake and translocation from soil to plants and within plants require deep understandings. Recently, Si-based improvements in plant defense system, cell damage repair, cell homeostasis, and regulation of metabolism under heavy metal stress are getting more attention. However, limited knowledge is available on the molecular mechanisms by which Si can reduce the toxicity of heavy metals, their uptake and transfer from soil to plant roots. Thus, this review is focused the following facets in greater detail to provide better understandings about the role of Si at molecular level; (i) how Si improves tolerance in plants to variable environmental conditions, (ii) how biological factors affect Si pools in the soil (iii) how soil properties impact the release and capability of Si to decrease the bioavailability of heavy metals in soil and their accumulation in plant roots; (iv) how Si influences the plant root system with respect to heavy metals uptake or sequestration, root Fe/Mn plaque, root cell wall and compartment; (v) how Si makes complexes with heavy metals and restricts their translocation/transfer in root cell and influences the plant hormonal regulation; (vi) the competition of uptake between Si and heavy metals such as arsenic, aluminum, and cadmium due to similar membrane transporters, and (vii) how Si-mediated regulation of gene expression involves in the uptake, transportation and accumulation of heavy metals by plants and their possible detoxification mechanisms. Furthermore, future research work with respect to mitigation of heavy metal toxicity in plants is also discussed.

Inhibition effects of long-term calcium-magnesia phosphate fertilizer application on Cd uptake in rice: Regulation of the iron-nitrogen coupling cycle driven by the soil microbial community

Cadmium (Cd) pollution in paddy soil seriously endangers food safety production. To investigate the effects and microbiological mechanisms of calcium-magnesium-phosphate (CMP) fertilizer application on Cd reduction in rice, field experiments were conducted in Cd-contaminated paddy soil. Compared with conventional compound fertilizer, CMP fertilizer treatments inhibited Cd uptake through plant roots, significantly decreasing Cd content in rice grains from 0.340 to 0.062 mg/kg. Soil pH and total Ca, Mg and P contents increased after CMP fertilizer application, resulting in a further decrease in soil available Cd content from 0.246 to 0.181 mg/kg. Specific extraction analysis recorded a decrease in both available Fe content and the ratio of nitrate to ammonium nitrogen, indicating that the soil Fe-N cycle was affected by the addition of CMP fertilizer. This finding was also recorded using soil bacterial community sequencing, with CMP fertilizer promoting the progress of nitrate-dependent Fe-oxidation driven by Thiobacillus (1.60-2.83%) and subsequent dissimilatory nitrate reduction to ammonium (DNRA) driven by Ignavibacteriae (1.01-1.92%); Fe-reduction driven by Anaeromyxobacter (3.09-2.23%) was also inhibited. Our results indicate that CMP fertilizer application regulates the Fe-N coupling cycle driven by the soil microbial community to benefit remediation of Cd contaminated paddy soil.

A powerful arsenite-oxidizing biofilm bioreactor derived from a single chemoautotrophic bacterial strain: Bioreactor construction, long-term operations and kinetic analysis

Microbial oxidation of As(III) by biofilm bioreactors followed by adsorption is a promising and environment friendly approach to remediate As(III) contaminated groundwater; however, poor activity, stability and expandability of the bioreactors hampered their industrious applications. To resolve this issue, we constructed a new biofilm bioreactor using a powerful chemoautotrophic As(III)-oxidizing bacterium Rhizobium sp. A219. This strain has strong ability to form biofilms and possesses very high As(III)-oxidizing activities in both planktonic and biofilm forms. Perlites were used as the biofilm carriers. Long-term operations suggest that the bioreactor has very high efficiency, stability and scalability under different geochemical conditions, and it is cheap and easy to construct and operate. During the operations, it is only required to supply air, nothing else. All the common contaminants in groundwater slightly affected the bioreactor As(III)-oxidizing activity. The common contaminants in groundwater can be largely removed through assimilation by the bacterial cells as nutrition. The bioreactor completely oxidize 1.0, 5.0, 10.0, 20.0 and 30.0 mg/L As(III) in 12, 18, 20, 25 and 30 min, respectively. Approximately 18, 18, 12, 12 and 21 min were needed to oxidize 1.1 mg/L As(III) at 20, 25, 30, 35 and 40 °C, respectively. The bioreactor works well under the pH values of 5-8, and the most optimal was 7.0. The data suggest that this bioreactor possesses the highest efficiency and stability, and thus has the great potential for industrial applications among all the described As(III)-oxidizing bioreactors derived from a single bacterium.

Illumina Sequencing of 18S/16S rRNA Reveals Microbial Community Composition, Diversity, and Potential Pathogens in 17 Turfgrass Seeds

The increasing need for turfgrass seeds is coupled with the high risk of dangerous microbial pathogens being transmitted through the domestic and international trade of seeds. Concerns continue to be raised about seed safety and quality. Here, we show that next-generation sequencing (NGS) of DNA represents an effective and reliable tactic to monitor the microbial communities within turfgrass seeds. A comparison of DNA sequence data with reference databases revealed the presence of 26 different fungal orders. Among them, serious plant disease pathogens such as Bipolaris sorokiniana, Boeremia exigua, Claviceps purpurea, and Rhizoctonia zeae were detected. Seedborne bacteria, including Erwinia persicina and Acidovorax avenae, were identified from different bacterial orders. Our study indicated that the traditional culturing method and the NGS approach for pathogen identification complement each other. The reliability of culturing and NGS methods was further validated by PCR with specific primers. The combination of these different techniques ensures maximum sensitivity and specificity for turfgrass seed pathogen testing assay.

Ameliorative effects of silicon fertilizer on soil bacterial community and pakchoi (Brassica chinensis L.) grown on soil contaminated with multiple heavy metals

Contamination of soil with heavy metals seriously harms the growth of crops. Silicon fertilizer is known to promote growth of crops and alleviate heavy metals stresses in vegetables. However, little is known about the effects of silicon fertilizer on pakchoi vegetable growth and soil microbial community in soil contaminated with multiple heavy metals. In order to elucidate this question, current study was designed to analyze the impact of different silicon fertilizer doses on the growth of pakchoi, heavy metals accumulation in pakchoi, and diversity and composition of bacterial community in heavy metals contaminated soil. Results of the study showed that, silicon fertilizer application significantly improved the yield of pakchoi and reduced the content of heavy metals in pakchoi. Moreover, the silicon fertilizer led to the heterogeneity of bacterial community structure in soil. Linear discriminant analysis (LDA) effect size (LEfSe) test showed the change of soil bacterial community structures under the higher silicon fertilizer doses (0.8-3.2%). Similarly, soil bacteria associated with heavy metal resistance and carbon/nitrogen metabolism showed a more active response to medium fertilizer dose (0.8% w/w). In addition, Mantel test and Redundancy analysis (RDA) showed that both the soil bacterial community structures and pakchoi growth were significantly correlated with soil EC, available K and pH. Study suggested that the application of silicon fertilizer provided richer bacteria associated with heavy metal resistance and plant growth, and more favorable soil physicochemical environment for the growth of pakchoi under multiple heavy metal contamination, and the impact was dependent on fertilizing dose.

Sediment Bacterial Community Structure Under the Influence of Different Domestic Sewage Types

Sediment bacterial communities are critical to the biogeochemical cycle in river ecosystems, but our understanding of the relationship between sediment bacterial communities and their specific input streams in rivers remains insufficient. In this study, we analyzed the sediment bacterial community structure in a local river receiving discharge of urban domestic sewage by applying Illumina MiSeq high-throughput sequencing. The results showed that the bacterial communities of sediments samples of different pollution types had similar dominant phyla, mainly Proteobacteria, Actinobacteria, Chloroflexi and Firmicutes, but their relative abundances were different. Moreover, there were great differences at the genus level. For example, the genus Bacillus showed statistically significant differences in the hotel site. The clustering of bacterial communities at various sites and the dominant families (i.e., Nocardioidaceae, and Sphingomonadaceae) observed in the residential quarter differed from other sites. This result suggested that environmentally induced species sorting greatly influenced the sediment bacterial community composition. The bacterial cooccurrence patterns showed that the river bacteria had a nonrandom modular structure. Microbial taxonomy from the same module had strong ecological links (such as the nitrogenium cycle and degradation of organic pollutants). Additionally, PICRUSt metabolic inference analysis showed the most important function of river bacterial communities under the influence of different types of domestic sewage was metabolism (e.g., genes related to xenobiotic degradation predominated in residential quarter samples). In general, our results emphasize that the adaptive changes and interactions in the bacterial community structure of river sediment represent responses to different exogenous pollution sources.

Impact of long-term industrial contamination on the bacterial communities in urban river sediments

BACKGROUND

The contamination of the aquatic environment of urban rivers with industrial wastewater has affected the abiotic conditions and biological activities of the trophic levels of the ecosystem, particularly sediments. However, most current research about microorganism in urban aquatic environments has focused on indicator bacteria related to feces and organic pollution. Meanwhile, they ignored the interactions among microorganisms. To deeply understand the impact of industrial contamination on microbial community, we study the bacterial community structure and diversity in river sediments under the influence of different types of industrial pollution by Illumina MiSeq high-throughput sequencing technology and conduct a more detailed analysis of microbial community structure through co-occurrence networks.

RESULTS

The overall community composition and abundance of individual bacterial groups differed between samples. In addition, redundancy analysis indicated that the structure of the bacterial community in river sediments was influenced by a variety of environmental factors. TN, TP, TOC and metals (Cu, Zn and Cd) were the most important driving factors that determined the bacterial community in urban river sediments (P < 0.01). According to PICRUSt analysis, the bacterial communities in different locations had similar overall functional profiles. It is worth noting that the 15 functional genes related to xenobiotics biodegradation and metabolism were the most abundant in the same location. The non-random assembly patterns of bacterial composition in different types of industrially polluted sediments were determined by a co-occurrence network. Environmental conditions resulting from different industrial pollutants may play an important role in determining their co-occurrence patterns of these bacterial taxa. Among them, the bacterial taxa involved in carbon and nitrogen cycles in module I were relatively abundant, and the bacterial taxa in module II were involved in the repair of metal pollution.

CONCLUSIONS

Our data indicate that long-term potential interactions between different types of industrial pollution and taxa collectively affect the structure of the bacterial community in urban river sediments.

Effective stabilization of arsenic in contaminated soils with biogenic manganese oxide (BMO) materials

The role of biogenic manganese oxide (BMO) materials on the stabilization of arsenic (As) in contaminated soil was investigated. Experimental results indicated that the addition of BMO was proved to be highly effective to stabilize As in soils. Bioavailable As content was decreased from 4.56 mg kg^-1 in the control samples to 1.72-1.86 mg kg^-1 in BMO-treated soils. X-ray absorption near edge structure (XANES) results confirmed that BMO was mainly responsible for oxidizing As(III) to As(V). Sequential extraction results indicated that the transformation of As fractions was from non-specifically adsorbed fraction to poorly-crystalline hydrous oxides fraction and residual fraction, which can decrease the risk of As in contaminated soils. Moreover, BMO had a higher efficiency in stabilizing As than two types of abiotic Mn oxides. High throughput sequencing analysis indicated that the bacterial community and diversity were significantly changed after BMO treatment. The abundance of Proteobacteria phylum, including Massilia, Phenylobacterium and Sphingomonas genera significantly increased with the increasing amount of BMO. These findings suggested that BMO can be considered as a low cost, high effectiveness and environmental friendliness material for the remediation of As contaminated soils.

The responses of cadmium phytotoxicity in rice and the microbial community in contaminated paddy soils for the application of different long-term N fertilizers

An eight-year field trial was conducted to investigate the effects of four different N fertilization treatments of urea (CO(NH₂)₂, the control), ammonium sulfate ((NH₄)₂SO₄), ammonium chloride (NH₄Cl), and ammonium hydrogen phosphate [(NH₄)₂HPO₄]) on cadmium (Cd) phytotoxicity in rice and soil microbial communities in a Cd-contaminated paddy of southern China. The results demonstrate that the different N treatments exerted different effects: the application of (NH₄)₂HPO₄ and (NH₄)₂SO₄ significantly increased rice grain yield and decreased soil-extractable Cd content when compared with those of the control, while NH₄Cl had a converse effect. Expression of genes related to Cd uptake (IRT and NRAPM genes) and transport (HMA genes) by roots may be responsible for Cd phytotoxicity in rice grown in the different N fertilization treatments. Our results further demonstrate that N fertilization had stronger effects on soil bacterial communities than fungal communities. The bacterial and fungal keystone species were identified by phylogenetic molecular ecological network (pMEN) analysis and mainly fell into the categories of Gammaproteobacteria, Acidobacteria and Actinobacteria for the bacterial species and Ascomycota for the fungal species; all of these keystone species were highly enriched in the (NH₄)₂HPO₄ treatment. Soil pH and soil available-Cd content emerged as the major determinants of microbial network connectors. These results could provide effective fertilizing strategies for alleviating Cd phytotoxicity in rice and enhance the understanding of its underlying microbial mechanisms.

Phytoremediation of cadmium-contaminated soil by Sorghum bicolor and the variation of microbial community

In this paper, the growth of S. bicolor in Cd-polluted sandy clay loam soil in north China, Cd accumulation in plant and the corresponding soil microbial community were characterized when the plant matured (140 d of growth). Cadmium promoted the growth of mature S. bicolor with higher height and heavier dry mass, especially at the spiked level of 1 mg kg^-1 soil (P < 0.05). The higher microbial diversity was found under Cd stress at the spiked level of 15 mg kg^-1, which basically corresponded with its influence on the plant growth. High-throughput sequencing data demonstrated that the predominant bacterial phyla include Proteobacteria (35.99% for Cd-polluted soil and 35.22% for the control soil), Chloroflexi (21.33% and 20.58%), Actinobacteria (12.00% and 12.89%), Acidobacteria (7.47% and 11.14%), Bacteroidetes (7.37% and 6.96%), Gemmatimonadetes (5.60% and 6.65%), Firmicutes (2.82% and 1.86%), Planctomycetes (2.47% and 0.95%), Saccharibacteria (1.26% and 1.11%). The predominant fungal phyla was Ascomycota, with the relative abundance of 89.96% for the control soil and 86.2% for the Cd-polluted soil. S. bicolor could grow well in sandy clay loam soil in northern China at low Cd lvel, but it could not accumulate cadmium at higher cadmium level. S. bicolor could be used for phytoextraction of cadmium from the lightly Cd-polluted soil.

Composition of bacterial communities in municipal wastewater treatment plant

Efforts to understand the environmental and biological factors that influence the dynamics of microbial communities have received substantial attention in microbial ecology. In this study, Illumina MiSeq high-throughput sequencing technology was used to examine the microbial community structure of activated sludge in municipal wastewater treatment systems (Chuzhou city, China). Overall, Proteobacteria, Chloroflexi, Actinobacteria, Acidobacteria, Actinobacteria, Bacteroidetes, and Firmicutes were the most dominant phyla in the five activated sludge samples. However, the community structure of nitrifying bacteria was relatively simple, and diversity was low; only AOB (Nitrosomonas) and NOB (Nitrospira) were detected. The dominant bacteria in the anaerobic sludge, anoxic sludge and oxic sludge were the same, and each bacterial species was relatively uniform, with differences only in proportions. Redundancy analysis indicated that pH, TP and COD were strong environmental factors influencing the bacterial community distribution. PICRUSt was used to describe the metabolic and functional abilities of the activated sludge bacterial communities. The results emphasized the vast genetic diversity of these organisms, which are involved in various essential processes such as amino acid transport and metabolism, energy production and conversion, cell wall/membrane/envelope/biogenesis, signal transduction mechanisms, and carbohydrate transport and metabolism. Activated sludge of municipal wastewater treatment systems can be ranked in the following order based on the 16S rRNA gene copy numbers of the detected phylotypes: S1 > S2 > S4 > S5 > S3. This study provides basic data and a theoretical analysis of the optimal design and operation in wastewater treatment plants.

Bacterial community shift in response to a deep municipal tail wastewater treatment system

In previous studies, ozone oyster shell fixed-bed bioreactor and membrane bioreactor (OFBR-MBR) were developed for municipal tail wastewater treatment, and qualified good effects. This study mainly discussed the bacterial community shift in response to the treatment process of OFBR-MBR. Proteobacteria, Chloroflexi, Planctomycetes, Actinobacteria and Firmicutes were dominant bacteria after ozone treatment in phylum level in OFBR-MBR; Aciditerrimonas, Blastopirellula, Pasteuria, Planctomyces, Paracoccus, Caldilinea and Defluviicoccus were adapted and enriched after ozone treatment in genus level in OFBR-MBR. Ozone played key role in the species selection of bacteria in OFBR-MBR. The chemical oxygen demand (COD), ammonium and total phosphorus (TP) removal efficiency possessed by OFBR-MBR were 79.05%, 98.74% and 38.10%, which due to the function of ozone and these enriched bacteria. OFBR-MBR has exhibited huge potential for municipal tail wastewater, and it would also provide an alternative and promising technology for other kinds of tail wastewater recycling in future.

Immobilization of cadmium and improvement of bacterial community in contaminated soil following a continuous amendment with lime mixed with fertilizers: A four-season field experiment

The effects of the continuous amendments with lime (L), lime mixed with organic manure (LO), or phosphate fertilizer (LP) on the soil bacterial community, soil available cadmium (Cd) content, and Cd accumulation in rice planted in a Cd contaminated paddy soil were determined through a four-season field experiment. The results showed that with continuous application of amendments during the four seasons, the soil pH increased significantly compared with the control, while the soil available Cd content significantly decreased by 12.9-18.2%, 13.1-17.3% and 0.09-23.2% under the L, LO, or LP treatments, and the Cd content of rice was significantly reduced by 28.5-56.2%, 37.6-53.4%, and 31.2-44.6%, respectively. The rice Cd content in each season at amendment treatments was lower than the National Food Safety Standard of China (maximum level of Cd in grains is 0.2 mg/kg). The diversity and richness of soil bacteria significantly increased after the continuous amendments in soil for four-season cropping. Soil pH and available Cd content were important factors for soil bacterial community. Lime mixed with phosphate fertilizer or organic manure had been characterized by a significant increase of Proteobacteria, Nitrospirae, and Chloroflexi and a decrease of Acidobacteria based on an Illumina Miseq sequencing analysis. The results indicate that the continuous application of lime mixed with organic manure or phosphate fertilizer is a very important measure to ensure the quality safety of rice and improve soil quality in a Cd-contaminated paddy.

Biodegradation of oxytetracycline and electricity generation in microbial fuel cell with in situ dual graphene modified bioelectrode

A three-step method to prepare dual graphene modified bioelectrode (D-GM-BE) in microbial fuel cell (MFC) in previous studies. This study explored the biodegradation of oxytetracycline (OTC) and electricity generation in O-D-GM-BE MFC. The OTC removal efficiency of graphene modified biocathode and bioanode (O-GM-BC, O-GM-BA) was 95.0% and 91.8% in eight days. The maximum power density generated by O-D-GM-BE MFC was 86.6 ± 5.1 mW m^-2, which was 2.1 times of that in OTC control bioelectrode (O-C-BE) MFC. The Rct of O-GM-BA and O-GM-BC were decreased significantly by 78.3% and 76.3%. OTC was biodegraded to monocyclic benzene compounds by bacteria. O-GM-BA was affected strongly by OTC, and Salmonella and Trabulsiella were accounted for 83.0%, while typical exoelectrogens (Geobacter) were still enriched after the maturity of biofilm. In O-GM-BC, bacteria related with OTC biodegradation (Comamonas, Ensifer, Sphingopyxis, Pseudomonas, Dechloromonas, etc.) were enriched, which contributed to the high removal efficiency of OTC.

Dissimilatory arsenate-respiring prokaryotes catalyze the dissolution, reduction and release of arsenic from paddy soils into groundwater: implication for the effect of sulfate

The paddy soils in some areas in Jianghan Plain were severely contaminated by arsenic. However, little is known about the activity and diversity of the dissimilatory arsenate-respiring prokaryotes (DARPs) in the paddy soils, and the effects of sulfate on the microbial mobilization and release of arsenic from soils into solution. To address this issue, we collected arsenic-rich soils from the depths of 1.6 and 4.6 m in a paddy region in the Xiantao city, Hubei Province, China. Microcosm assays indicated that all of the soils have significant arsenate-respiring activities using lactate, pyruvate or acetate as the sole electron donor. Functional gene cloning and analysis suggest that there are diverse DARPs in the indigenous microbial communities of the soils. They efficiently promoted the mobilization, reduction and release of arsenic and iron from soils under anaerobic conditions. Remarkably, when sulfate was amended into the microcosms, the microorganisms-catalyzed reduction and release of arsenic and iron were significantly increased. We further found that sulfate significantly enhanced the arsenate-respiring reductase gene abundances in the soils. Taken together, a diversity of DARPs in the paddy soils significantly catalyzed the dissolution, reduction and release of arsenic and iron from insoluble phase into solution, and the presence of sulfate significantly increased the microbial reactions.

Microbially Mediated Methylation of Arsenic in the Arsenic-Rich Soils and Sediments of Jianghan Plain

Almost nothing is known about the activities and diversities of microbial communities involved in As methylation in arsenic-rich shallow and deep sediments; the correlations between As biomethylation and environmental parameters also remain to be elucidated. To address these issues, we collected 9 arsenic-rich soil/sediment samples from the depths of 1, 30, 65, 95, 114, 135, 175, 200, and 223 m in Jianghan Plain, China. We used microcosm assays to determine the As-methylating activities of the microbial communities in the samples. To exclude false negative results, we amended the microcosms with 0.2 mM As(III) and 20.0 mM lactate. The results indicated that the microbial communities in all of the samples significantly catalyzed arsenic methylation. The arsM genes were detectable from all the samples with the exception of 175 m, and 90 different arsM genes were identified. All of these genes code for new or new-type ArsM proteins, suggesting that new As-methylating microorganisms are widely distributed in the samples from shallow to deep sediments. To determine whether microbial biomethylation of As occurs in the sediments under natural geochemical conditions, we conducted microcosm assays without exogenous As and carbons. After 80.0 days of incubation, approximately 4.5–15.5 μg/L DMAs^V were detected in all of the microcosms with the exception of that from 30 m, and 2.0–9.0 μg/L MMAs^V were detected in the microcosms of 65, 114, 135, 175, 200, and 223 m; moreover, approximately 18.7–151.5 μg/L soluble As(V) were detected from the nine sediment samples. This suggests that approximately 5.3, 0, 8.1, 28.9, 18.0, 8.7, 13.8, 10.2, and 14.9% of total dissolved As were methylated by the microbial communities in the sediment samples from 1, 30, 65, 95, 114, 135, 175, 200, and 223 m, respectively. The concentrations of biogenic DMAs^V show significant positive correlations with the depths of sediments, and negative correlations with the environmental NH₄⁺ and NaCl concentrations, but show no significant correlations with other environmental parameters, such as NO₃^-, SO₄²⁺, TOC, TON, Fe, Sb, Cu, K, Ca, Mg, Mn, and Al. This work helps to better understand the biogeochemical cycles of arsenic in arsenic-rich shallow and deep sediments.

Implication of graphene oxide in Cd-contaminated soil: A case study of bacterial communities

The application of graphene oxide (GO) has attracted increasing concerns in the past decade regarding its environmental impacts, except for the impact of GO on a metal-contaminated soil system, due to its special properties. In the present work, the effects of GO on the migration and transformation of heavy metals and soil bacterial communities in Cd-contaminant soil were systematically evaluated. Soil samples were exposed to different doses of GO (0, 1, and 2 g kg^-1) over 60 days. The Community Bureau of Reference (BCR) sequential extraction procedure was used to reflect the interaction between GO and Cd. Several microbial parameters, including enzyme activities and bacterial community structure, were measured to determine the impacts of GO on polluted soil microbial communities. It was shown that Cd was immobilized by GO throughout the entire exposure period. Interestingly, the structure of the bacterial community changed. The relative abundance of the major bacterial phyla (e.g., Acidobacteria and Actinobacteria) increased, which was possibly attributed to the reduced toxicity of Cd in the presence of GO. However, GO exerted an adverse influence on the relative abundance of some phyla (e.g., WD272 and TM6). The diversity of bacterial communities was slightly restricted. The functional bacteria related to carbon and the nitrogen cycling were also affected, which, consequently, may influence the nutrient cycling in soil.

Bacterial community shift and incurred performance in response to in situ microbial self-assembly graphene and polarity reversion in microbial fuel cell

In this work, bacterial community shift and incurred performance of graphene modified bioelectrode (GM-BE) in microbial fuel cell (MFC) were illustrated by high throughput sequencing technology and electrochemical analysis. The results showed that Firmicutes occupied 48.75% in graphene modified bioanode (GM-BA), while Proteobacteria occupied 62.99% in graphene modified biocathode (GM-BC), both were dominant bacteria in phylum level respectively. Typical exoelectrogens, including Geobacter, Clostridium, Pseudomonas, Geothrix and Hydrogenophaga, were counted 26.66% and 17.53% in GM-BA and GM-BC. GM-BE was tended to decrease the bacterial diversity and enrich the dominant species. Because of the enrichment of exoelectrogens and excellent electrical conductivity of graphene, the maximum power density of MFC with GM-BA and GM-BC increased 33.1% and 21.6% respectively, and the transfer resistance decreased 83.8% and 73.6% compared with blank bioelectrode. This study aimed to enrich the microbial study in MFC and broaden the development and application for bioelectrode.

Bacterial community shift and improved performance induced by in situ preparing dual graphene modified bioelectrode in microbial fuel cell

Dual graphene modified bioelectrode (D-GM-BE) was prepared by in situ microbial-induced reduction of graphene oxide (GO) and polarity reversion in microbial fuel cell (MFC). Next Generation Sequencing technology was used to elucidate bacterial community shift in response to improved performance in D-GM-BE MFC. The results indicated an increase in the relative ratio of Proteobacteria, but a decrease of Firmicutes was observed in graphene modified bioanode (GM-BA); increase of Proteobacteria and Firmicutes were observed in graphene modified biocathode (GM-BC). Genus analysis demonstrated that GM-BE was beneficial to enrich electrogens. Typical exoelectrogens were accounted for 13.02% and 8.83% in GM-BA and GM-BC. Morphology showed that both GM-BA and GM-BC formed 3D-like graphene/biofilm architectures and revealed that the biofilm viability and thickness would decrease to some extent when GM-BE was formed. D-GM-BE MFC obtained the maximum power density by 124.58±6.32mWm^-2, which was 2.34 times over C-BE MFC.

Microbial communities involved in arsenic mobilization and release from the deep sediments into groundwater in Jianghan plain, Central China

It was shown that groundwater in Jianghan Plain was severely contaminated by arsenic; however, little is known about the mechanism by which the mineral arsenic was mobilized and released into groundwater from the high-arsenic sediments in this area. Here, we collected sediment samples from the depths of 5-230m in Jianghan Plain. Although all of the samples contain high contents of total arsenic, the soluble arsenic was only detectable in few of the shallow sediments, but was readily detectable in all of the deep sediments at the depths of 190-230m. Analysis of the genes of arsenate-respiring reductases indicated that they were not present in all of the shallow sediments from the depths of 5-185m, but were detectable in all of the deep sediments from the depths of 190-230m; all of the identified reductase genes are new or new-type, and they display unique diversity. Microcosm assay indicated that the microbial communities from the deep sediments were able to reduce As(V) into As(III) using lactate, formate, pyruvate or acetate as an electron donor under anaerobic condition. Arsenic release assay demonstrated that these microbial communalities efficiently catalyzed the mobilization and release of the mineral arsenic into aqueous phase. We also isolated a novel cultivable dissimilatory As(V)-respiring bacterium Aeromonas sp. JH155 from the sediments. It is able to completely reduce 2.0mM As(V) into As(III) in 72h, and efficiently promote the reduction and release of the mineral arsenic into aqueous phase. Analysis of the 16S rRNA genes indicated that the deep sediments contain diversities of microbial communities, which were shaped by the environmental factors, such as As, SO₄^2-, NO₃^-, Fe and pH value. These data suggest that the microorganisms in the deep sediments in Jianghan Plain played key roles in the mobilization and release of insoluble arsenic into the groundwater.

Silicon Supplementation Alters the Composition of Herbivore Induced Plant Volatiles and Enhances Attraction of Parasitoids to Infested Rice Plants

Silicon (Si) is important in plant defenses that operate in a direct manner against herbivores, and work in rice (Oryza sativa) has established that this is mediated by the jasmonate signaling pathway. Plant defenses also operate indirectly, by the production of herbivore induced plant volatiles (HIPVs) that attract predators and parasitoids of herbivores. These indirect defenses too are mediated by the jasmonate pathway but no earlier work has demonstrated an effect of Si on HIPVs. In this study, we tested the effect of Si supplementation versus Si deprivation to rice plants on subsequent HIPV production following feeding by the important pest, rice leaffolder (Cnaphalocrocis medinalis). Gas chromatography-mass spectrometry analyses showed lower production of α-bergamotene, β-sesquiohellandrene, hexanal 2-ethyl, and cedrol from +Si herbivore-infested plants compared with -Si infested plants. These changes in plant chemistry were ecologically significant in altering the extent to which parasitoids were attracted to infested plants. Adult females of Trathala flavo-orbitalis and Microplitis mediator both exhibited greater attraction to the HIPV blend of +Si plants infested with their respective insect hosts compared to -Si infested plants. In equivalent studies using RNAi rice plants in which jasmonate perception was silenced there was no equivalent change to the HIPV blend associated with Si treatment; indicating that the effects of Si on HIPVs are modulated by the jasmonate pathway. Further, this work demonstrates that silicon alters the HIPV blend of herbivore-infested rice plants. The significance of this finding is that there are no earlier-published studies of this phenomenon in rice or any other plant species. Si treatment to crops offers scope for enhancing induced, indirect defenses and associated biological control of pests because parasitoids are more strongly attracted by the HIPVs produced by +Si plants.