• Cyanobacterial blooms contribute to the diversity of antibiotic-resistance genes in aquatic ecosystems.

      Zhang, Qi; Zhang, Zhenyan; Lu, Tao; Peijnenburg, W J G M; Gillings, Michael; Yang, Xiaoru; Chen, Jianmeng; Penuelas, Josep; Zhu, Yong-Guan; Zhou, Ning-Yi; et al. (2020-12-04)
    • Evaluation of the taxonomic and functional variation of freshwater plankton communities induced by trace amounts of the antibiotic ciprofloxacin.

      Lu, Tao; Zhu, Youchao; Ke, Mingjing; Peijnenburg, W J G M; Zhang, Meng; Wang, Tingzhang; Chen, Jun; Qian, Haifeng (2019-02-27)
      Ciprofloxacin (CIP), one of the most frequently detected antibiotics in water systems, has become an aquatic contaminant because of improper disposal and excretion by humans and animals. It is still unknown how trace amounts of CIP affect the aquatic microbial community diversity and function. We therefore investigated the effects of CIP on the structure and function of freshwater microbial communities via 16S/18S rRNA gene sequencing and metatranscriptomic analyses. CIP treatment (7 μg/L) did not significantly alter the physical and chemical condition of the water body as well as the composition of the main species in the community, but slightly increased the relative abundance of cyanobacteria and decreased the relative abundance of eukaryotes. Metatranscriptomic results showed that bacteria enhanced their phosphorus transport and photosynthesis after CIP exposure. The replication, transcription, translation and cell proliferation were all suppressed in eukaryotes, while the bacteria were not affected in any of these aspects. This interesting phenomenon was the exact opposite to both the antibacterial property of CIP and its safety for eukaryotes. We hypothesize that reciprocal and antagonistic interactions in the microcosm both contribute to this result: cyanobacteria may enhance their tolerance to CIP through benefiting from cross-feeding and some secreted substances that withstand bacterial CIP stress would also affect eukaryotic growth. The present study thus indicates that a detailed assessment of the aquatic ecotoxicity of CIP is essential, as the effects of CIP are much more complicated in microbial communities than in monocultures. CIP will continue to be an environmental contaminant due to its wide usage and production and more attention should be given to the negative effects of antibiotics as well as other bioactive pollutants on aquatic environments.
    • Impact of copper nanoparticles and ionic copper exposure on wheat (Triticum aestivum L.) root morphology and antioxidant response.

      Zhang, Zhenyan; Ke, Mingjing; Qu, Qian; Peijnenburg, W J G M; Lu, Tao; Zhang, Qi; Ye, Yizhi; Xu, Pengfei; Du, Benben; Sun, Liwei; et al. (2018-04-28)
      Copper nanoparticles (nCu) are widely used in industry and in daily life, due to their unique physical, chemical, and biological properties. Few studies have focused on nCu phytotoxicity, especially with regard to toxicity mechanisms in crop plants. The present study examined the effect of 15.6 μM nCu exposure on the root morphology, physiology, and gene transcription levels of wheat (Triticum aestivum L.), a major crop cultivated worldwide. The results obtained were compared with the effects of exposing wheat to an equivalent molar concentration of ionic Cu (Cu2+ released from CuSO4) and to control plants. The relative growth rate of roots decreased to approximately 60% and the formation of lateral roots was stimulated under nCu exposure, possibly due to the enhancement of nitrogen uptake and accumulation of auxin in lateral roots. The expression of four of the genes involved in the positive regulation of cell proliferation and negative regulation of programmed cell death decreased to 50% in the Cu2+ treatment compared to that of the control, while only one gene was down-regulated to about half of the control in nCu treatment. This explained the decreased root cell proliferation and higher extent of induced cell death in Cu2+- than in nCu-exposed plants. The increased methane dicarboxylic aldehyde accumulation (2.17-fold increase compared with the control) and decreased antioxidant enzyme activities (more than 50% decrease compared with the control) observed in the Cu2+ treatment in relation to the nCu treatment indicated higher oxidative stress in Cu2+- than in nCu-exposed plants. Antioxidant (e.g., proline) synthesis was pronouncedly induced by nCu to scavenge excess reactive oxygen species, alleviating phytotoxicity to wheat exposed to this form of Cu. Overall, oxidative stress and root growth inhibition were the main causes of nCu toxicity.
    • Insights into the transcriptional responses of a microbial community to silver nanoparticles in a freshwater microcosm.

      Lu, Tao; Qu, Qian; Lavoie, Michel; Pan, Xiangjie; Peijnenburg, W J G M; Zhou, Zhigao; Pan, Xiangliang; Cai, Zhiqiang; Qian, Haifeng (2020-03-01)
      Silver nanoparticles (AgNPs) are widely used because of their excellent antibacterial properties. They are, however, easily discharged into the water environment, causing potential adverse environmental effects. Meta-transcriptomic analyses are helpful to study the transcriptional response of prokaryotic and eukaryotic aquatic microorganisms to AgNPs. In the present study, microcosms were used to investigate the toxicity of AgNPs to a natural aquatic microbial community. It was found that a 7-day exposure to 10 μg L-1 silver nanoparticles (AgNPs) dramatically affected the structure of the microbial community. Aquatic micro eukaryota (including eukaryotic algae, fungi, and zooplankton) and bacteria (i.e., heterotrophic bacteria and cyanobacteria) responded differently to the AgNPs stress. Meta-transcriptomic analyses demonstrated that eukaryota could use multiple cellular strategies to cope with AgNPs stress, such as enhancing nitrogen and sulfur metabolism, over-expressing genes related to translation, amino acids biosynthesis, and promoting bacterial-eukaryotic algae interactions. By contrast, bacteria were negatively affected by AgNPs with less signs of detoxification than in case of eukaryota; various pathways related to energy metabolism, DNA replication and genetic repair were seriously inhibited by AgNPs. As a result, eukaryotic algae (mainly Chlorophyta) dominated over cyanobacteria in the AgNPs treated microcosms over the 7-d exposure. The present study helps to understand the effects of AgNPs on aquatic microorganisms and provides insights into the contrasting AgNPs toxicity in eukaryota and bacteria.
    • The interactive effects of diclofop-methyl and silver nanoparticles on Arabidopsis thaliana: Growth, photosynthesis and antioxidant system.

      Li, Xingxing; Ke, Mingjing; Zhang, Meng; Peijnenburg, W J G M; Fan, Xiaoji; Xu, Jiahui; Zhang, Zhenyan; Lu, Tao; Fu, Zhengwei; Qian, Haifeng (2018-01)
      Diclofop-methyl (DM), a common post-emergence herbicide, is frequently used in agricultural production. Silver nanoparticles (AgNPs) are one of the most widely used nanoparticles, and as such, have been detected and monitored in several environmental systems. Here we investigated the interactive effects of DM and AgNPs on the physiological morphology, photosynthesis and antioxidant system of Arabidopsis thaliana. Our results demonstrated that a 1.0 mg/L DM treatment had no significant effect on the fresh weight of plant shoots and the content of total chlorophyll and anthocyanin. However, a 0.5 mg/L AgNPs treatment was found to significantly inhibit plant growth and chlorophyll synthesis, and was found to cause more severe oxidative damage in plants compared to the effects observed in a hydroponic suspension in which DM and AgNPs were jointly present. Meanwhile, the relative transcript levels of photosynthesis related genes (psbA, rbcL, pgrl1A and pgrl1B) in the combined group were found to be slightly increased compared to transcript levels in the AgNPs group, in order to maintain ATP generation at relatively normal levels in order to repair light damage. One explanation for these observed antagonistic effects was that the existence of DM affects the stability of AgNPs and reduced Ag+ release from AgNPs in the mixed solution. Thereupon, the Ag+-content was found to decrease in shoots and roots in the combined group by 15.2% and 9.4% respectively, compared to the AgNPs group. The coexistence of herbicides and nanomaterials in aquatic environments or soil systems will continue to exist due to their wide usages. Our current study highlights that the antagonistic effects between DM and AgNPs exerted a positive impact on A. thaliana growth.
    • Investigation of Rhizospheric Microbial Communities in Wheat, Barley, and Two Rice Varieties at the Seedling Stage

      Lu, Tao; Ke, Mingjing; Peijnenburg, W. J. G. M.; Zhu, Youchao; Zhang, Meng; Sun, Liwei; Fu, Zhengwei; Qian, Haifeng (2018-02-23)
    • Multiwall carbon nanotubes modulate paraquat toxicity in Arabidopsis thaliana.

      Fan, Xiaoji; Xu, Jiahui; Lavoie, Michel; Peijnenburg, W J G M; Zhu, Youchao; Lu, Tao; Fu, Zhengwei; Zhu, Tingheng; Qian, Haifeng (2018-02)
      Carbon nanotubes can be either toxic or beneficial to plant growth and can also modulate toxicity of organic contaminants through surface sorption. The complex interacting toxic effects of carbon nanotubes and organic contaminants in plants have received little attention in the literature to date. In this study, the toxicity of multiwall carbon nanotubes (MWCNT, 50 mg/L) and paraquat (MV, 0.82 mg/L), separately or in combination, were evaluated at the physiological and the proteomic level in Arabidopsis thaliana for 7-14 days. The results revealed that the exposure to MWCNT had no inhibitory effect on the growth of shoots and leaves. Rather, MWCNT stimulated the relative electron transport rate and the effective photochemical quantum yield of PSII value as compared to the control by around 12% and lateral root production up to nearly 4-fold as compared to the control. The protective effect of MWCNT on MV toxicity on the root surface area could be quantitatively explained by the extent of MV adsorption on MWCNT and was related to stimulation of photosynthesis, antioxidant protection and number and area of lateral roots which in turn helped nutrient assimilation. The influence of MWCNT and MV on photosynthesis and oxidative stress at the physiological level was consistent with the proteomics analysis, with various over-expressed photosynthesis-related proteins (by more than 2 folds) and various under-expressed oxidative stress related proteins (by about 2-3 folds). This study brings new insights into the interactive effects of two xenobiotics (MWCNT and MV) on the physiology of a model plant.
    • Offspring toxicity of silver nanoparticles to Arabidopsis thaliana flowering and floral development.

      Ke, Mingjing; Li, Yan; Qu, Qian; Ye, Yizhi; Peijnenburg, W J G M; Zhang, Zhenyan; Xu, Nuohan; Lu, Tao; Sun, Liwei; Qian, Haifeng (2020-03-15)
    • Phytotoxic effects of silver nanoparticles and silver ions to Arabidopsis thaliana as revealed by analysis of molecular responses and of metabolic pathways

      Ke, Mingjing; Qu, Qian; Peijnenburg, W.J.G.M.; Li, Xingxing; Zhang, Meng; Zhang, Zhenyan; Lu, Tao; Pan, Xiangliang; Qian, Haifeng (2018-12)
    • Rhizosphere Microbiome Assembly and Its Impact on Plant Growth.

      Qu, Qian; Zhang, Zhenyan; Peijnenburg, W J G M; Liu, Wanyue; Lu, Tao; Hu, Baolan; Chen, Jianmeng; Chen, Jun; Lin, Zhifen; Qian, Haifeng (2020-05-06)