Xincheng Zhang

COLONIZATION AND MODULATION OF HOST GROWTH AND METAL UPTAKE BY ENDOPHYTIC BACTERIA OF SEDUM ALFREDII

Sedum alfredii Hance is a Zn and Cd co-hyperaccumulating plant species found in an old mining area in China. Four bacterial strains, Burkholderia sp. SaZR4, Burkholderia sp. SaMR10, Sphingomonas sp. SaMR12 and Variovorax sp. SaNR1, isolated from surface-sterilized S. alfredii plants were used to investigate their endophytic nature and root colonization patterns and effects on phytoextraction of Zn and Cd. Laser scanning confocal microscopy revealed that gfp-tagged SaZR4, SaMR12, and SaNR1 cells formed biofilms on roots and that SaZR4 and SaMR12 cells could invade root tissues. SaMR10 showed the lowest total population associated with S. alfredii and little effect on plant growth and phytoextraction. SaZR4 significantly promoted Zn-extraction but not Cd-extraction. SaMR12 and SaNR1 significantly promoted plant growth in substrates supplemented with Zn or Cd and phytoextraction of Zn and Cd. Together, this study have shown that the four native endophytic bacteria differently colonize the host plants and modulate metal uptake and growth of host plant, and that SaMR12 and SaNR1 strains are promising assistants of S. alfredii plants for phytoremediation of Zn/Cd-contaminated soil.

Bioremediation of Cd-DDT co-contaminated soil using the Cd-hyperaccumulator Sedum alfredii and DDT-degrading microbes

The development of an integrated strategy for the remediation of soil co-contaminated by heavy metals and persistent organic pollutants is a major research priority for the decontamination of soil slated for use in agricultural production. The objective of this study was to develop a bioremediation strategy for fields co-contaminated with cadmium (Cd), dichlorodiphenyltrichloroethane (DDT), and its metabolites 1, 1-dichloro-2, 2-bis (4-chlorophenyl) ethylene (DDE) and 1, 1-dichloro-2, 2-bis (4-chlorophenyl) ethane (DDD) (DDT, DDE, and DDD are collectively called DDs) using an identified Cd-hyperaccumulator plant Sedum alfredii (SA) and DDT-degrading microbes (DDT-1). Initially, inoculation with DDT-1 was shown to increase SA root biomass in a pot experiment. When SA was applied together with DDT-1, the levels of Cd and DDs in the co-contaminated soil decreased by 32.1-40.3% and 33.9-37.6%, respectively, in a pot experiment over 18 months compared to 3.25% and 3.76% decreases in soil Cd and DDs, respectively, in unplanted, untreated controls. A subsequent field study (18-month duration) in which the levels of Cd and DDs decreased by 31.1% and 53.6%, respectively, confirmed the beneficial results of this approach. This study demonstrates that the integrated bioremediation strategy is effective for the remediation of Cd-DDs co-contaminated soils.

Improved Plant Growth and Zn Accumulation in Grains of Rice (Oryza sativa L.) by Inoculation of Endophytic Microbes Isolated from a Zn Hyperaccumulator, Sedum alfredii H.

This study is to investigate the possibility of zinc (Zn) biofortification in the grains of rice (Oryza sativa L.) by inoculation of endophytic strains isolated from a Zn hyperaccumulator, Sedum alfredii Hance. Five endophytic strains, Burkholderia sp. SaZR4, Burkholderia sp. SaMR10, Sphingomonas sp. SaMR12, Variovorax sp. SaNR1, and Enterobacter sp. SaCS20, isolated from S. alfredii, were inoculated in the roots of Japonica rice Nipponbare under hydroponic condition. Fluorescence images showed that endophytic strains successfully colonized rice roots after 72 h. Improved root morphology and plant growth of rice was observed after inoculation with endophytic strains especially SaMR12 and SaCS20. Under hydroponic conditions, endophytic inoculation with SaMR12 and SaCS20 increased Zn concentration by 44.4% and 51.1% in shoots, and by 73.6% and 83.4% in roots, respectively. Under soil conditions, endophytic inoculation with SaMR12 and SaCS20 resulted in an increase of grain yields and elevated Zn concentrations by 20.3% and 21.9% in brown rice and by 13.7% and 11.2% in polished rice, respectively. After inoculation of SaMR12 and SaCS20, rhizosphere soils of rice plants contained higher concentration of DTPA-Zn by 10.4% and 20.6%, respectively. In situ micro-X-ray fluorescence mapping of Zn confirmed the elevated Zn content in the rhizosphere zone of rice treated with SaMR12 as compared with the control. The above results suggested that endophytic microbes isolated from S. alfredii could successfully colonize rice roots, resulting in improved root morphology and plant growth, increased Zn bioavailability in rhizosphere soils, and elevated grain yields and Zn densities in grains.

Nanocrystalline tungsten carbide encapsulated in carbon shells

Abstract Nanocrystalline tungsten carbide with an average grain size of 12 nm was synthesized using the ion arc method. The characterization was carried out by means of XRD, TEM, and TGA. The experimental results indicate that the as-synthesized powders are mainly cubic WC 1 − x . Besides, a small amount of α-W 2 C is also observed. These tungsten carbide powders are encapsulated within crystalline graphite. Owing to the ultrafine sizes of the powers, oxidation of the graphite occurs at about 350 °C. The nanocrystalline tungsten carbide transforms into WO 3 at about 670 °C.

The Endophytic Bacterium, Sphingomonas SaMR12 , Improves the Potential for Zinc Phytoremediation by Its Host, Sedum alfredii

The endophytic bacterium, Sphingomonas SaMR12, isolated from Sedum alfredii Hance, appears to increase plant biomass and zinc-extraction from contaminated soil; however, the mechanism by which this occurs is not clear. Here, the ability of SaMR12 to promote zinc extraction and its effects on root morphology and exudation were examined in hydroponics. Zinc treatment increased shoot biomass by 30 to 45%, and by a further 10 to 19% when combined with SaMR12 inoculation. Zinc treatment also increased zinc accumulation modestly and this too was enhanced with SaMR12. Both biomass and zinc levels increased in a dose-dependent manner with significant effects seen at 50 µM zinc and apparent saturation at 500 µM. Zinc and the endophyte also increased levels of auxin but not at 50 µM and zinc increased levels of superoxide and hydrogen peroxide but mainly at 500 µM. As for root morphology, SaMR12 increased root branching, the number of root tips, and surface area. Zinc and SaMR12 also increased the exudation of oxalic acid. For most assays the effects of the endophyte and zinc were additive, with the notable exception of SaMR12 strongly reducing the production of reactive oxygen species at 500 µM zinc. Taken together, these results suggest that the promotion of growth and zinc uptake by exposure to zinc and to SaMR12 are independent of reactive oxygen and do not involve increases in auxin.

Variation in copper and zinc tolerance and accumulation in 12 willow clones: implications for phytoextraction *

Willows (Salix spp.) have shown high potential for the phytoextraction of heavy metals. This study compares variations in copper (Cu) and zinc (Zn) tolerance and accumulation potential among 12 willow clones grown in a nutrient solution treated with 50 μmol/L of Cu or Zn, respectively. The results showed differences in the tolerance and accumulation of Cu and Zn with respect to different species/clones. The biomass variation among clones in response to Cu or Zn exposure ranged from the stimulation of growth to inhibition, and all of the clones tested showed higher tolerance to Cu than to Zn. The clones exhibited less variation in Cu accumulation but larger variation in Zn accumulation. Based on translocation factors, it was found that most of the Cu was retained in the roots and that Zn was more mobile than Cu for all clones. It is concluded that most willow clones are good accumulators of Zn and Cu.概要研究目的柳树(Salix spp.)已广泛用于修复重金属污染, 而且修复效率与树种及无性系有关。 目前涉及柳树研究主要为铜(Cu)和锌(Zn)的毒性效应, 而不是富集能力。 本研究以中国常见的柳树无性系评价对Cu 和Zn 耐性与富集能力。创新要点目前大多数研究仍集中Cu 和Zn 对柳树的毒性效应, 尤其是Cu, 对它们富集能力仍没有评价。 中国为柳树的主要分布区。 本文以12 种优良的常见柳树无性系, 通过温室营养液法评价对Cu 和Zn 耐性及富集潜力差异。 利用柳树无性系的耐性与富集变异, 旨在选择高耐性与高富集的无性系, 提高环境修复效率和加快修复进程。研究方法选择高生物量12 种柳树无性系, 采用温室营养液培养法添加Cu 或Zn 处理, 测定生物量参数并计算耐性指数, 估计耐性差异; 用原子吸收法测定组织中金属浓度并计算金属位移系数, 评价富集差异。重要结论无性系对Cu 和Zn 耐性显著不同, 生物量变化从无影响、 抑制到促进生长。 无性系对Cu 耐性高于对Zn 耐性, 无性系对Zn 富集变异幅度大于对Cu 富集变异幅度。 Cu 主要富集于根部, 而Zn 较易运输到地上部分。 总之测定的大部分柳树无性系为Cu 与Zn 高富集植物, 显示出较高的植物提取能力。

Variations of growth, nitrogen accumulation and nitrogen use efficiency among 18 willow clones under two nitrogen regimes

Willows (Salix spp.) have excellent capacity for acquiring nutrients, and are widely used for removing excess nutrients in wastewater purification system. In this study, 18 willow clones were evaluated in terms of growth parameters, nitrogen (N) accumulation and N use efficiency under two N regimes (low N and high N) with a sand culture system. Clonal differences were observed in biomass production, relative growth rate, N accumulation and use efficiency under two N regimes, which were contributed to the clone level. For all clones, nitrogen use efficiency was lower under high N condition than under low N condition. Nitrogen removal efficiency differed by 7-fold (low N regime) and 10-fold (high N regime) based on shoot N contents between the lowest and the highest clone. Among all the clones, J799 had the highest N content in shoots, showing largest N removal potential. These results confirmed that growth analysis and nutrient use strategy are efficient method of selecting Salix clones for improving the N removal potential.