Effects of combined microplastic and cadmium pollution on sorghum growth, Cd accumulation, and rhizosphere microbial functions.

The interaction between microplastics (MPs) and cadmium (Cd) poses a threat to agricultural soil environments, and their effects on plant growth and rhizosphere microbial community functions are not yet clear. In this study, energy sorghum was used as a test plant to investigate the effects of two types of MPs, polystyrene (PS) and polyethylene (PE), at different particle sizes (13 µm, 550 µm) and concentrations (0.1%, 1% w/w), and Cd, as well as their interactions, on the growth of sorghum in a soil-cultivation pot experiment. The results showed that the combined effects of MP and Cd pollution on the dry weight and Cd accumulation rate in sorghum varied depending on the type, concentration, and particle size of the MPs, with an overall trend of increasing stress from combined pollution with increasing Cd content and accumulation. High-throughput sequencing analysis revealed that combined MP and Cd pollution increased bacterial diversity, and the most significant increase was observed in the abundance-based coverage estimator (ACE), Shannon, and Sobs indices in the 13 µm 1% PS+Cd treatment group. Metagenomic analysis based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) metabolic pathways revealed that 19 groups of metabolic pathways, including microbial metabolism and methane metabolism, differed significantly under combined MP and Cd pollution. Hierarchical clustering results indicated that Cd treatment and combined MP and Cd treatment affected the abundances of sorghum rhizosphere soil nitrogen (N) and phosphorus (P) cycling genes and that the type of MP present was an important factor affecting N and P cycling genes. The results of this study provide a basis for exploring the toxic effects of combined MP and Cd pollution and for conducting soil environmental risk assessments.

[Transcriptome Analysis of Plant Growth-promoting Bacteria Alleviating Microplastic and Heavy Metal Combined Pollution Stress in Sorghum].

Microplastics can become potential transport carriers of other environmental pollutants (such as heavy metals), so the combined pollution of microplastics and heavy metals has attracted increasing attention from researchers. To explore the mechanism of plant growth-promoting bacteria VY-1 alleviating the combined pollution stress of heavy metals and microplastics in sorghum, the effects of inoculation on biomass and accumulation of heavy metals in sorghum were analyzed using a hydroponics experiment, and the effects of inoculation on gene expression in sorghum were analyzed via transcriptomics. The results showed that the combined pollution of polyethylene (PE) and cadmium (Cd) decreased the dry weight of above-ground and underground parts by 17.04% and 10.36%, respectively, compared with that under the single Cd pollution, which showed that the combined toxicity effect of the combined pollution on plant growth was enhanced. The inoculation of plant growth-promoting bacteria VY-1 could alleviate the toxicity of Cd-PE combined pollution and increase the length of aboveground and underground parts by 33.83% and 73.21% and the dry weight by 56.64% and 33.44%, respectively. Transcriptome sequencing showed that 904 genes were up-regulated after inoculation with VY-1. Inoculation with growth-promoting bacteria VY-1 could up-regulate the expression of several genes in the auxin, abscisic acid, flavonoid synthesis, and lignin biosynthesis pathways, which promoted the response ability of sorghum under Cd-PE combined pollution stress and improved its resistance. The above results indicated that plant growth-promoting bacteria could alleviate the stress of heavy metal and microplastic combined pollution by regulating plant gene expression, which provided a reference for plant-microbial joint remediation of heavy metal and microplastic combined pollution.

[Effects of Combined Pollution of Microplastics and Cadmium on Microbial Community Structure and Function of Pennisetum hydridum Rhizosphere Soil].

The combined pollution of microplastics and heavy metals can potentially interact. This may have an important impact on the growth and development of plants and the rhizosphere microbial community and function. In this study, the effects of heavy metal cadmium combined with different types of microplastics(PE and PS), different particle sizes(13 µm and 550 µm), and different concentrations(0.1% and 1%) on Pennisetum hydridum growth were studied under pot conditions. The results showed that the effects of the combined pollution of MPs and Cd on plant dry weight and Cd accumulation varied with different types, concentrations, and particle sizes of MPs, and the combined pollution stress increased, whereas the Cd content and Cd accumulation decreased. Metagenomic analysis showed that the combined contamination of MPs and Cd could change the composition of the bacterial community and reduce bacterial diversity, among which the ACE index and Chao1 index in the 550 µm 0.1% PE+Cd treatment group were the most significant. Metagenomic analysis of microbial species function showed that the main functional groups were metabolism, amino acid transport and metabolism, energy generation and conversion, and signal transduction mechanisms. Compared with that under single Cd pollution, the addition of MPs could change the gene abundance of functional groups such as metabolism, amino acid transport and metabolism, and energy generation and conversion, and the effects of different MPs types, concentrations, and particle sizes varied. In this study, metagenomics and amplification sequencing were used to analyze the effects of the combined pollution of MPs and Cd on the bacterial community and function in P. hydridum in order to provide basic data and scientific basis for the ecotoxicological effects of the combined heavy metal pollution of MPs and its biological remediation.

Plant growth-promoting bacteria modulate gene expression and induce antioxidant tolerance to alleviate synergistic toxicity from combined microplastic and Cd pollution in sorghum.

Microplastics (MPs) can act as carriers for environmental pollutants; therefore, MPs combined with heavy metal pollution are attracting increasing attention from researchers. In this study, the potential of the plant growth-promoting bacterium Bacillus sp. SL-413 to mitigate the stress caused by exposure to both MPs and cadmium (Cd) in sorghum plants was investigated. The effects of inoculation on sorghum biomass were investigated using hydroponic experiments, and evaluation of Cd accumulation and enzyme activity changes and transcriptomics approaches were used to analyze its effect on sorghum gene expression. The results showed that combined polyethylene (PE) and Cd pollution reduced the length and the fresh and dry weights of sorghum plants and thus exerted a synergistic toxic effect. However, inoculation with the strains alleviated the stress caused by the combined pollution and significantly increased the biomass. Inoculation increased the dry weights of the aboveground and belowground parts by 11.5-44.6% and 14.9-38.4%, respectively. Plant physiological measurements indicated that inoculation reduced the reactive oxygen species (ROS) content of sorghum by 10.5-27.2% and thereby alleviated oxidative stress. Transcriptome sequencing showed that exposure to combined Cd+MP contamination induced downregulation of gene expression, particularly that of genes related to amino sugar and nucleotide sugar metabolism, starch and sucrose metabolism, and plant hormone signal transduction, in sorghum. However, inoculation with Bacillus sp. SL-413 resulted in an increase in the proportion of upregulated genes involved in signal transduction, antioxidant defense, cell wall biology, and other metabolic pathways, which included the phenylpropanoid biosynthesis, photosynthesis, flavonoid biosynthesis, and MAPK signaling pathways. The upregulation of these genes promoted the tolerance of sorghum under combined Cd+MP pollution stress and alleviated the stress induced by these conditions. This study provides the first demonstration that plant growth-promoting bacteria can alleviate the stress caused by combined pollution with MPs and Cd by regulating plant gene expression. These findings provide a reference for the combined plant-microbial remediation of MPs and Cd.

[Shifts in Rhizosphere Bacterial Community Structure, Co-occurrence Network, and Function of Miscanthus Following Cadmium Exposure].

As a representative of second-generation bioenergy plants, Miscanthus has received increasing attention in the studies of heavy metal (HM)-contaminated soil remediation. Currently, few studies have examined the effects of using Miscanthus to remediate HM-contaminated soils on the composition and function of microbial communities. In this study, the Miscanthus cultivar M. saccariflorus was examined for its tolerance and enrichment abilities when grown in soils containing 100 mg ·kg-1 of cadmium (Cd). The structure, function, and co-occurrence network of their rhizosphere bacterial communities were analyzed during the remediation process. MiSeq sequencing showed that the Miscanthus rhizosphere bacterial community comprised 32 phyla and 425 genera, including plant growth-promoting rhizobacteria (PGPR), such as Sphingomonas, Bacillus, Gemmatimonas, and Streptomyces. The addition of Cd affected the Miscanthus rhizosphere bacterial community and reduced community diversity. Phylogenetic molecular ecological networks indicated that Cd addition reduced the interactions between Miscanthus rhizosphere bacteria to generate a simpler network structure, increased the number of negative-correlation links, enhanced the competition between rhizosphere bacterial species, and changed the composition of key bacteria. PICRUSt functional predictive analysis indicated that Cd stress reduced soil bacterial functions in the Miscanthus rhizosphere. The results of this study provide a reference for the subsequent regulation of efficient Miscanthus remediation by PGPRs or key bacteria.

Effects of Plant Growth-Promoting Bacteria (PGPB) Inoculation on the Growth, Antioxidant Activity, Cu Uptake, and Bacterial Community Structure of Rape (Brassica napus L.) Grown in Cu-Contaminated Agricultural Soil.

Previous analyses of plant growth-promoting bacteria (PGPB) combined with the remediation of heavy metal pollution in soil have largely been performed under potting or greenhouse conditions, and in situ remediation experiments under field conditions have rarely been reported. In this study, the effects of the metal-resistant PGPB Microbacterium oxydans JYC17, Pseudomonas thivervalensis Y1-3-9, and Burkholderia cepacia J62 on soil Cu pollution under rape remediation were studied in the farmland surrounding the Nanjing Jiuhuashan copper mining region in China. Following inoculation treatment for 50 days, the biomasses of the rape inoculated with strains JYC17, Y1-3-9, and J62 increased, and the total amounts of Cu uptake increased by 113.38, 66.26, and 67.91%, respectively, the translocation factor (TF) of rape inoculated with J62 was 0.85, a significant increase of 70.68%, thus improving the Cu remediation efficiency of the rape. Y1-3-9 and J62 affected the bioavailability of Cu in the soil, and the water-soluble Cu contents were increased by 10.13 and 41.77%, respectively, compared with the control. The antioxidant activities in the rape leaves showed that the tested bacteria increased the contents of antioxidant non-enzymatic substances, including ascorbic acid (ASA) and glutathione (GSH), which were increased by 40.24-91.22% and 9.89-17.67%, respectively, thereby reducing the oxidative stress caused by heavy metals and the contents of thiobarbituric acid-reactive substances (TBARS) and peroxidase (POD). PCR-denaturing gradient gel electrophoresis (PCR-DGGE) was used to analyze the effects of the tested bacteria on the cultivation-dependent and cultivation-independent bacterial communities in the root endosphere and rhizosphere soil of the rape. The sequencing results of the DGGE bands indicated that the tested bacteria colonized the endosphere and rhizosphere, and they became an important component of the cultivation-dependent bacteria. The canonical correspondence analysis (CCA) of the DGGE profile and similarity cluster analysis showed that the tested bacteria affected the cultivation-dependent and cultivation-independent bacterial communities in the root endosphere and rhizosphere. In this experiment, the effects and mechanisms of the combined plant-microbe remediation under field conditions were preliminarily studied, and the results are expected to provide a theoretical basis for future combined remediation experiments.

[Composition and Predictive Functional Analysis of Rhizosphere Bacterial Communities in Riparian Buffer Strips in the Danjiangkou Reservoir, China].

Microbial communities play crucial roles in the global biogeochemical nitrogen cycle. To our knowledge, the compositions and functions of rhizosphere communities in riparian buffer strips have not been reported. In this study, rhizosphere soil samples were collected from herbs (Vetiveria zizanioides and Phragmites australis), trees (Pyrus betulifolia), and shrubs (Discocleidion rufescens) in the Danjiangkou Reservoir in June 2017. High-throughput sequencing was performed to analyze the community structure and diversity of bacteria. Phylogenetic analysis based on 16S rDNA sequences shows that the bacterial communities can be divided into 31 major phylogenetic groups. The dominant phylogenetic groups include Proteobacteria, Bacteroidetes, Actinobacteria, Gemmatimonadetes, and Acidobacteria. Phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) was used to determine the metabolic and functional abilities of the observed bacterial communities. Our results reveal a wide genetic diversity of organisms involved in various essential processes such as biosynthesis of other secondary metabolites, transcription, Glycan biosynthesis and metabolism, cell growth and death, and carbohydrate metabolism. Based on the 16S rRNA gene copy number of the detected phylotype, the bacterial rhizospheres of plants in riparian buffer strips can be ranked as follows:Discocleidion rufescens > Phragmites australis > Vetiveria zizanioides > Pyrus betulifolia. We analyzed the differences of different plants from the perspective of bacterial community composition and function and provide a foundation for vegetation construction and water environmental protection in riparian buffer strips of the Danjiangkou Reservoir.

Superoxide dismutase from venom of the ectoparasitoid Scleroderma guani inhibits melanization of hemolymph.

Superoxide dismutase (SOD) known as an important antioxidative stress protein has been recently found in venoms of several parasitoid wasps. However, its functions and characteristics as a virulent factor remain scarcely described. Here, we report the characterization of two venomous SOD genes (SguaSOD1 and SguaSOD3) from the ectoparasitoid, Scleroderma guani. The metal binding sites, cysteine amino acid positions and signature sequences of the SOD family were conserved within SguaSOD1 and SguaSOD3. Relatively high levels of their transcripts were observed in pupae followed a decrease in early adults, after which they had the highest transcriptions, indicating that their productions would be regulated in venom apparatus. Although the two genes showed lower expression in venom apparatus compared to head and thorax, the enzymatic assay revealed that SOD indeed had activity in venom. Further, we showed that recombinant SguaSOD3 suppressed melanization of host hemolymph, implying that this protein used as a virulent factor uniquely impacts the prophenoloxidase cascade.

Parasitism and venom of ectoparasitoid Scleroderma guani impairs host cellular immunity.

Venom is a prominently maternal virulent factor utilized by parasitoids to overcome hosts immune defense. With respect to roles of this toxic mixture involved in manipulating hosts immunity, great interest has been mostly restricted to Ichneumonoidea parasitoids associated with polydnavirus (PDV), of which venom is usually considered as a helper component to enhance the role of PDV, and limited Chalcidoidea species. In contrast, little information is available in other parasitoids, especially ectoparasitic species not carrying PDV. The ectoparasitoid Scleroderma guani injects venom into its host, Tenebrio molitor, implying its venom was involved in suppression of hosts immune response for successful parasitism. Thus, we investigated the effects of parasitism and venom of this parasitoid on counteracting the cellular immunity of its host by examining changes of hemocyte counts, and hemocyte spreading and encapsulation ability. Total hemocyte counts were elevated in parasitized and venom-injected pupae. The spreading behavior of both granulocytes and plasmatocytes was impaired by parasitization and venom. High concentration of venom led to more severely increased hemocyte counts and suppression of hemocyte spreading. The ability of hemocyte encapsulation was inhibited by venom in vitro. In addition to immediate effects observed, venom showed persistent interference in hosts cellular immunity. These results indicate that venom alone from S. guani plays a pivotal role in blocking hosts cellular immune response, serving as a regulator that guarantees the successful development of its progenies. The findings provide a foundation for further investigation of the underlying mechanisms in immune inhibitory action of S. guani venom.

Venomics reveals novel ion transport peptide-likes (ITPLs) from the parasitoid wasp Tetrastichus brontispae.

Despite substantial advances in uncovering constituents of parasitoid venoms due to their potential applications as insecticides and pharmaceuticals, most of these studies are primarily restricted to braconid and ichneumonid wasps. Little information is available regarding virulent factors from venom of Eulophidae. In order to provide insight into the venom components of this family and parasitoid venom evolution, a venom protein repertoire (venomics) of the endoparasitoid wasp, Tetrastichus brontispae was deciphered using a proteomic approach. A large number of diverse venom proteins/peptides were identified, including novel proteins and those proteins commonly found in the venoms of other parasitoids such as serine protease, esterase, dipeptidyl peptidase IV, acid phosphatase, major royal jelly protein, superoxide dismutase, and venom allergen 3/5. Three ion transport peptide-likes (ITPLs) were abundantly detected in T. brontispae venom. Of these, two of them are reported as a novel form for the first time, with the characteristics of lengthened amino acid sequences and additional cysteine residues. These venom ITPLs are obviously apart from other general members within the crustacean hyperglycemic hormone/ion transport peptide (CHH/ITP) family. It implies that they would evolve unique functions essential for parasitism success.

[Effects of forest gap on herbaceous plant diversity in mixed birch-fir forest of Taibai Mountain].

To better understand the effects of forest gap on the herbaceous species community in a mixed birch-fir forest of Taibai Mountain in Qinling, CCA ordination and random permutation test were employed to analyze the distribution pattern of the species composition across a gradient of gap size, and the relationships between the distribution of 55 herbaceous species with > or = 5 individuals and the habitat variables (convexity, slope, and soil total N, total P, available N, available P, pH, and organic matter). In this forest, gap area occupied 19.8% of the total land area, gap density was 20.7 per hm2, and gap size varied from 25.6 to 279.1 m2, with a mean of 93.7 m2. The species richness in herbaceous layer in gaps was significantly positively correlated with gap size, but of the 69 herbaceous species identified in the gaps, most species were found across all gap sizes, and only eight species were found in larger gaps (>120 m2). No successional change was observed in the herbaceous species distribution with gap size. The CCA ordination and random permutation test also showed that 27.3% of the 55 species with abundance > or = 5 had significant association with the eight habitat variables. It was concluded that gap size contributed to the species richness, but determined the diversity constitution in random.