Qichun Zhang

Efficient removal of crystal violet using Fe3O4-coated biochar: the role of the Fe3O4 nanoparticles and modeling study their adsorption behavior

Biochar shows great promise for use in adsorbing pollutants. However, a process for enhancing its adsorption capacity and re-collection efficiency is yet to be further developed. Hence, in this study, we developed a type of biochar coated with magnetic Fe3O4 nanoparticles (i.e., magnetic biochar (MBC)) and assessed its use for crystal violet (CV) adsorption as well as its recycling potential. The coating of Fe3O4 nanoparticles, which was not only on the surface, but also in the interior of biochar, performed two functions. Firstly, it produced a saturation magnetization of 61.48 emu/g, which enabled the biochar being efficiently re-collected using a magnet. Secondly, it significantly enhanced the adsorption capacity of the biochar (from 80.36 to 99.19 mg/g). The adsorption capacity of the MBC was determined to be the largest by so far (349.40 mg/g) for an initial CV concentration of 400 mg/L, pH of 6.0, and temperature of 40 °C, and the adsorption capacity of re-collected MBC was 73.31 mg/g. The adsorption of CV by the MBC was found to be a spontaneous and endothermic physical process in which the intraparticle diffusion was the limiting step. These findings inspire us to use other similar materials to tackle the menace of pollutions.

Revealing the characteristics of a novel bioflocculant and its flocculation performance in Microcystis aeruginosa removal

In the present work, a novel bioflocculant, EPS-1, was prepared and used to flocculate the kaolin suspension and Microcystis aeruginosa. We focused on the characteristics and flocculation performance of EPS-1, especially with regard to its protein components. An important attribute of EPS-1 was its protein content, with 18 protein types identified that occupied a total content of 31.70% in the EPS-1. Moreover, the flocculating activity of these protein components was estimated to be no less than 33.93%. Additionally, polysaccharides that occupied 57.12% of the total EPS-1 content consisted of four monosaccharides: maltose, D-xylose, mannose, and D-fructose. In addition, carbonyl, amino, and hydroxyl groups were identified as the main functional groups. Three main elements, namely C1s, N1s, and O1s, were present in EPS-1 with relative atomic percentages of 62.63%, 24.91%, and 10.5%, respectively. Zeta potential analysis indicated that charge neutralization contributed to kaolin flocculation, but was not involved in M. aeruginosa flocculation. The flocculation conditions of EPS-1 were optimized, and the maximum flocculating efficiencies were 93.34% within 2 min for kaolin suspension and 87.98% within 10 min for M. aeruginosa. These results suggest that EPS-1 could be an alternative to chemical flocculants for treating wastewaters and cyanobacterium-polluted freshwater.

Enhancement of algicidal properties of immobilized Bacillus methylotrophicus ZJU by coating with magnetic Fe3O4 nanoparticles and wheat bran

Algicidal bacteria offer a promising option for killing cyanobacteria. In this study, a newly isolated strain of Bacillus methylotrophicus, ZJU, was used to control Microcystis aeruginosa. Analyses of relative reactive oxygen level, malondialdehyde content, superoxide dismutase activity, and fluorescence staining indicated that oxidative damage caused by the algicidal supernatant of strain ZJU mainly affected the cell membrane and consequently the membrane permeability and membrane potential of M. aeruginosa cells. Furthermore, an embedded immobilization technique was employed to improve the practical application of strain ZJU as an algicidal agent. On this basis, we proposed a novel concept of enhancing the algicidal properties of immobilized ZJU by adding Fe3O4 nanoparticles and wheat bran in the process of immobilization. Our studies showed that Fe3O4 nanoparticles conferred the immobilized bacteria with a magnetization of 30.87 emu/g, and this magnetization enabled efficient re-collection of the immobilized bacteria by magnetic means. Moreover, wheat bran endowed the immobilized bacteria with 10.34% higher algicidal activity than immobilized bacteria without wheat bran. The results indicate a novel concept of enhancing the algicidal property of bacteria against M. aeruginosa by adding Fe3O4 nanoparticles and wheat bran.

Effects of organic amendment on soil aggregation and microbial community composition during drying-rewetting alternation

The alternation of drying and rewetting events could dramatically affect the biological and structural properties of soil and consequently influence nutrient transformation. To examine whether organic amendments could improve the resistance and resilience of microbial function (extracellular enzyme activities), community composition (phospholipid fatty acids), and soil structure to drying-rewetting alternation, cropland soils with or without wheat-straw amendment were allowed to desiccate in a microcosm for two months, followed by moist incubation for five weeks, and continuously moist treatments were maintained at 50% water holding capacity during the entire period, as a control treatment. Straw amendment increased microbial biomass, extracellular enzyme activities, the relative abundance of fungal groups, dissolved organic carbon, and proportion of large macroaggregates (>2000μm), but decreased mineral nitrogen and available phosphorus. The drying-rewetting treatment increased microbial biomass carbon and β-glucosidase activities by 10% and 13% in straw-amended soils, respectively, but not in unamended soils, and decreased the urease and alkaline phosphomonoesterase activities by >15% in unamended soils, but not in amended soils. The contents of fungi, actinomycetes, Pseudomonas spp., and Bacillus spp. decreased with drying, and more so with the subsequent rewetting, but recovered by the end of the experiment. The drying-rewetting treatment caused a decrease in the nitrate content in both soils (>10%) and an increase in the macroaggregates of straw-amended soils (~8%). These results indicated that improved soil aggregation, as a result of straw amendment, protected microbial communities from drought stress and that nutrient acquisition promoted the post-rewetting colonization of heterotrophic communities characterized by hydrolase production, which consequently facilitated aggregate re-formation. Thus, straw amendment positively contributed to aggregate turnover and to both microbial and enzymatic responses to drying-rewetting events, which suggests that straw amendment is favorable to maintain soil function under conditions of increasing rainfall variability.

Management practices have a major impact on nitrifier and denitrifier communities in a semiarid grassland ecosystem

PurposeNitrification and denitrification, two of the key nitrogen (N) transformation processes in the soil, are carried out by a diverse range of microorganisms and catalyzed by a series of enzymes. Different management practices, such as continuous grazing, mowing, and periodic fencing off from grazing, dramatically influenced grassland ecosystems. This study aimed to examine the effects of management practices on the abundance and community structure of nitrifier and denitrifier communities in grassland ecosystems.Materials and methodsSoil samples were collected from a semiarid grassland ecosystem in Xilingol region, Inner Mongolia, where long-term management practices including free-grazing, different periods of enclosure from grazing, and different frequencies of mowing were conducted. Real-time quantitative polymerase chain reaction (Q-PCR), denaturing gradient gel electrophoresis (DGGE), sequencing, and phylogenetic analysis were applied to estimate the abundance and composition of amoA, nirS, nirK, and nosZ genes.Results and discussionThe ammonia-oxidizing archaea (AOA) amoA copies were in the range 5.99 × 108 to 8.60 × 108, while those of ammonia-oxidizing bacteria (AOB) varied from 3.02 × 107 to 4.61 × 107. The abundance of AOA was substantially higher in the light grazing treatment (LG) than in the mowing treatments. The quantity and intensity of DGGE bands of AOA varied with pasture management. In stark contrast, AOB population abundance and community structure remained largely unchanged in all the soils irrespective of the management practices. All these results suggested that ammonia oxidizers were dominated by AOA. The higher gene abundance and greater intensity of DGGE bands of nirS and nosZ under the enclosure treatments would suggest greater stimulated denitrification. The ratio of nosZ/(nirS + nirK) was higher in mowing treatments than in the free-grazing and enclosure treatments, possibly leading to more complete denitrification. Correlation analysis indicated that soil moisture and inorganic nitrogen content were the two main soil environmental variables that influence the community structure of nitrifiers and denitrifiers.ConclusionsIn this semiarid neutral to alkaline grassland ecosystem under low temperature conditions, AOA mainly affiliated with Nitrososphaera dominated nitrification. These results clearly demonstrate that grassland management practices can have a major impact on nitrifier and denitrifier communities in this semiarid grassland ecosystem, under low temperature conditions.

Growth of soil bacteria, on penicillin and neomycin, not previously exposed to these antibiotics

There is growing evidence that bacteria, in the natural environment (e.g. the soil), can exhibit naturally occurring resistance/degradation against synthetic antibiotics. Our aim was to assess whether soils, not previously exposed to synthetic antibiotics, contained bacterial strains that were not only antibiotic resistant, but could actually utilize the antibiotics for energy and nutrients. We isolated 19 bacteria from four diverse soils that had the capability of growing on penicillin and neomycin as sole carbon sources up to concentrations of 1000 mg L(-1). The 19 bacterial isolates represent a diverse set of species in the phyla Proteobacteria (84%) and Bacteroidetes (16%). Nine antibiotic resistant genes were detected in the four soils but some of these genes (i.e. tetM, ermB, and sulI) were not detected in the soil isolates indicating the presence of unculturable antibiotic resistant bacteria. Most isolates that could subsist on penicillin or neomycin as sole carbon sources were also resistant to the presence of these two antibiotics and six other antibiotics at concentrations of either 20 or 1000 mg L(-1). The potentially large and diverse pool of antibiotic resistant and degradation genes implies ecological and health impacts yet to be explored and fully understood.

Wheat Bran Enhances the Cytotoxicity of Immobilized Alcaligenes aquatilis F8 against Microcystis aeruginosa.

Algicidal bacteria offer a promising option for killing cyanobacteria. Therefore, a new Alcaligenes aquatilis strain F8 was isolated to control Microcystis aeruginosa in this study. The algicidal activity of strain F8 was dependent on the cell density of M. aeruginosa, and the maximal algicidal rate of the free bacterium reached 88.45% within 72 h. With a view to its application to the control of M. aeruginosa in the natural environment, strain F8 was immobilized in sodium alginate beads, but immobilization of the strain decreased its algicidal rate compared to that of the free bacterium. However, addition of wheat bran to the sodium alginate matrix used to immobilize strain F8 not only eliminated the adverse effects of immobilization on the bacteria but also resulted in an 8.83% higher algicidal rate of the immobilized than free bacteria. Exclusion and recovery methods were used to identify key ingredients of wheat bran and gain insight into the mechanism underlying the observed enhancement of algicidal activity. This analysis indicated that certain factors in wheat bran, including vitamins B1, B2, B9, and E were responsible for promoting bacterial growth and thereby improving the algicidal rate of immobilized strain F8. Our findings indicate that wheat bran is able to improve the algicidal efficiency of A. aquatilis strain F8 for killing M. aeruginosa and is a good source of not only carbon and nitrogen but also vitamins for bacteria.

Effects of various fertilization regimes on abundance and activity of anaerobic ammonium oxidation bacteria in rice-wheat cropping systems in China

Anaerobic ammonium oxidation (anammox) is an important process in many marine and paddy ecosystems. However, few studies have reported on the contribution to the nitrogen cycle of anammox and its dynamics in rice-wheat cropping systems with different fertilization regimes. Here, isotope tracing and molecular techniques were used to determine the potential rates of anammox and their association with bacterial abundance, diversity, and activity. Rice-wheat cropping systems at two sites in Jiangsu Province, China were selected and the treatments at each site were: 1) no fertilization (CK), 2) 100% chemical fertilization (CF), 3) pig manure compost plus 50% chemical fertilization (PMCF), and 4) straw plus 100% chemical fertilization (SRCF). The results revealed that anammox bacteria with high abundance were detected in both the wheat and rice seasons. The abundance of anammox in PMCF treatment was higher than that in SRCF treatment in both Changshu and Jintan. Moreover, the abundance of anammox bacteria in CF treatment was significantly higher than that in CK in Changshu. Analysis of anammox hydrazine synthase β subunit (hzs-β) gene sequences showed that in the rice season, the anammox bacteria Ca. Brocadia, Ca. Scalindua, and Ca. Jettenia were present. In contrast, all of the anammox hydrazine oxidase (hzo) genes were affiliated with Ca. Brocadia, suggesting that hzs genes are more representative of anammox biological diversity compared to hzo. Sequences from the PMCF treatment where affiliated with both Ca. Jettenia and Ca. Brocadia, and showed the highest diversity. Anammox activity was detected in both the wheat and rice seasons, but there were significant differences between seasons. The anammox rates were in the range 0.34 to 1.04nmol dinitrogen gas∙g-1 dry soil∙h-1, and 3.15 to 9.62% of dinitrogen gas emissions were attributed to anammox. However, no significant difference among the fertilizer treatments for anammox activity was found in the study.

Effect of Soil Drying Intensity on Nutrient Transformation and Microbial Community Composition

Abstract Soil drying-rewetting (DRW) events affect nutrient transformation and microbial community composition; however, little is known about the influence of drying intensity during the DRW events. Therefore, we analyzed soil nutrient composition and microbial communities with exposure to various drying intensities during an experimental drying-rewetting event, using a silt loam from a grassland of northern China, where the semi-arid climate exposes soils to a wide range of moisture conditions, and grasslands account for over 40% of the nations land area. We also conducted a sterilization experiment to examine the contribution of soil microbes to nutrient pulses. Soil drying-rewetting decreased carbon (C) mineralization by 9%–27%. Both monosaccharide and mineral nitrogen (N) contents increased with higher drying intensities (drying to ≤ 10% gravimetric water content), with the increases being 204% and 110% with the highest drying intensity (drying to 2% gravimetric water content), respectively, whereas labile phosphorus (P) only increased (by 105%) with the highest drying intensity. Moreover, levels of microbial biomass C and N and dissolved organic N decreased with increasing drying intensity and were correlated with increases in dissolved organic C and mineral N, respectively, whereas the increases in labile P were not consistent with reductions in microbial biomass P. The sterilization experiment results indicated that microbes were primarily responsible for the C and N pulses, whereas non-microbial factors were the main contributors to the labile P pulses. Phospholipid fatty acid analysis indicated that soil microbes were highly resistant to drying-rewetting events and that drought-resistant groups were probably responsible for nutrient transformation. Therefore, the present study demonstrated that moderate soil drying during drying-rewetting events could improve the mineralization of N, but not P, and that different mechanisms were responsible for the C, N, and P pulses observed during drying-rewetting events.

Alterations in soil microbial communities caused by treatments with penicillin or neomycin

Antibiotic residues in soils can lead to serious health risk and ecological hazards. In this study, the effects of penicillin and neomycin, two antibiotics widely used in animal production, were investigated on soil bacterial communities. Changes in the community structure were monitored using three 16S ribosomal DNA (rDNA) polymerase chain reaction-based approaches, including denaturing gradient gel electrophoresis (DGGE), amplified rDNA restriction analysis (ARDRA), and terminal-restriction fragment length polymorphism (T-RFLP) analysis. The prominent DGGE bands were excised from gels and sequenced, and the data indicated the prevalence of Gammaproteobacteria in the soils. The total soil bacterial community, including uncultured bacteria, exhibited a higher diversity than that of cultured bacteria. Some microbial strains were capable of surviving and even subsisting on penicillin or neomycin. We also observed toxic effects of the antibiotics on the indigenous soil bacterial communities since some genotypes disappeared after the treatments (e.g., Pseudomonas sp., Stenotrophomonas sp., Salinimonas, and uncultured Acinetobacter sp.). The implications of these findings are that the functions of soil bacterial communities may be negatively affected if key microbial community members are lost.