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The contamination of soil with the heavy metal cadmium (Cd) is increasingly prominent and severely threatens food security in China. Owing to its low cost, suitable efficacy, and ability to address the shortcomings of plant remediation by enhancing the ability of plants to take up Cd, plant–microbe combination remediation technology has become a research hotspot in heavy metal pollution remediation. A pot experiment was performed to examine the effects of inoculation with the plant-growth-promoting bacterium Brevibacillus sp. SR-9 on the biomass, Cd accumulation, and soil nutrients of hybrid Pennisetum. The purpose of this study was to determine how Brevibacillus sp. SR-9 alleviates stress caused by heavy metal contamination. High-throughput sequencing and metabolomics were used to determine the effects of inoculation on the soil bacterial community composition and microbial metabolic functions associated with hybrid Pennisetum. The results suggest that mutation of Brevibacillus sp. SR-9 effectively alleviates Cd pollution stress, leading to increased biomass and accumulation of Cd in hybrid Pennisetum. The aboveground biomass and the root weight increased by 12.08% and 27.03%, respectively. Additionally, the accumulation of Cd in the aboveground sections and roots increased by 21.16% and 15.50%, respectively. Measurements of the physicochemical properties of the soil revealed that the strain Brevibacillus sp. SR-9 slightly increased the levels of available phosphorus, total nitrogen, total phosphorus, and available potassium. High-throughput DNA sequencing revealed that Brevibacillus sp. SR-9 implantation modified the composition of the soil bacterial community by increasing the average number of Actinobacteria and Bacillus. The total nitrogen content of the soil was positively correlated with the Actinobacteria abundance, total phosphorus level, and available phosphorus level. Metabolomic analysis revealed that inoculation affected the abundance of soil metabolites, and 59 differentially abundant metabolites were identified (p < 0.05). Among these, 14 metabolites presented increased abundance, whereas 45 metabolites presented decreased abundance. Fourteen metabolic pathways were enriched in these metabolites: the folate resistance pathway, the ABC transporter pathway, D-glutamine and D-glutamic acid metabolism, purine metabolism, and pyrimidine metabolism. The abundance of the metabolites was positively correlated with the levels of available phosphorus, total potassium, total phosphorus, and total nitrogen. According to correlation analyses, the development of hybrid Pennisetum and the accumulation of Cd are strongly associated with differentially abundant metabolites, which also impact the abundance of certain bacterial populations. This work revealed that by altering the makeup of microbial communities and their metabolic processes, bacteria that promote plant development can mitigate the stress caused by Cd. These findings reveal the microbiological mechanisms through which these bacteria increase the ability of hybrid Pennisetum to take up the Cd present in contaminated soils. [ABSTRACT FROM AUTHOR]

Miscanthus is a promising candidate species of second-generation energy crops. To our knowledge, the composition and function of Miscanthus rhizosphere bacterial communities has not yet been reported. In this study, rhizosphere soil samples were collected from Miscanthus (Xiangzamang No. 1) which was grown in Nanyang City for five years and bareground (as the control) to analyze the bacterial community structure and diversity using 16S rRNA gene sequencing on the Illumina MiSeq platform. PICRUSt was used to determine the metabolic and functional abilities of soil bacterial communities. Phylogenetic analysis based on 16S rRNA gene sequences showed that sol bacteria could be divided into 23 phyla and 231 genera, with high richness of the community composition. The dominant phyla were Proteobacteria, Acidobacteria, Actinobacteria, Chloroflexi, Bacteroidetes and Gemmatimonadetes. The bacterial community diversity in the rhizosphere samples of Xiangzamang No. 1 was lower than that in unplanted samples. Rhizosphere bacterial communities were affected by Miscanthus crops. Based on the PICRUSt analysis of bacterial community functions, our results revealed a wide genetic diversity of organisms involved in various essential processes, such as amino acid transport and metabolism, cell wall/membrane/envelope biogenesis, signal transduction mechanisms. Based on the 16S rRNA gene copy number of the detected phylotypes, 22 bacterial metabolic function in the rhizosphere samples of Miscanthus was higher than that in bareground. Results from N- and P-cycling gene analysis showed that Miscanthus planting altered the N- and P-cycling metabolic capacities of soil bacteria. [ABSTRACT FROM AUTHOR]

The coexistence of microplastics and heavy metals in soil can lead to more intricate environmental effects. While plant growth-promoting bacteria have been widely recognized for enhancing the remediation of heavy metal-contaminated soils, little research has been conducted to investigate whether they can alleviate the stress of microplastic-heavy metal composite contamination on plants. We investigated the effects of isolated and screened plant growth-promoting bacteria on the growth and cadmium （Cd） accumulation of Hybrid pennisetum under the composite pollution of Cd and polypropylene （PP） with different particle sizes （6.5 and 830 μm） in pot experiments and analyzed their effects on the composition of rhizosphere bacterial communities using high-throughput sequencing. Seven strains of bacteria were isolated and screened from soil contaminated with heavy metal-microplastic composites, identified as Enterobacter and Bacillus spp. All exhibited plant growth-promoting characteristics, including IAA production, siderophores, phosphorus solubilization, and potassium solubilization. Inoculation of plant growth-promoting bacteria increased the length and dry weight of H. pennisetum , effectively alleviating the stress caused by PP+Cd compound pollution. Plant growth-promoting bacteria increased soil available potassium and available phosphorus content, mitigating the decrease in soil mineral nutrients caused by PP+Cd composite pollution. PP+Cd compound pollution and plant growth-promoting bacterial inoculation affected the composition of the rhizosphere bacterial community of H. pennisetum , influencing dominant populations such as Proteobacteria, Firmicutes, and Actinobacteria. This study observed that the isolated and screened plant growth-promoting bacteria can effectively alleviate the plastic-heavy metal complex pollution caused by H. pennisetum. This provides a theoretical basis and data support for the remediation of microplastic heavy metal complex-contaminated soil biological pollution.

Danjiangkou Reservoir is a critical water source for the South-to-North Water Diversion Project, which harbors a diverse bacterioplankton community with varying depths, and the understanding of its nitrogen and phosphorus cycle and associated driving factors remains limited. In this study, we selected five ecological sites within Danjiangkou Reservoir and conducted metagenomics analysis to investigate the vertical distribution of bacterioplankton communities in the surface, middle, and bottom layers. Furthermore, we analyzed and predicted the function of nitrogen and phosphorus cycles, along with their driving factors. Our findings revealed the dominance of Proteobacteria, Actinobacteria, and Planctomycetes in the Danjiangkou Reservoir. Significant differences were observed in the structure of bacterioplankton communities across different depths, with temperature （ T ）, oxidation-reduction potential （ORP）, dissolved oxygen （DO）, and Chla identified as primary factors influencing the bacterioplankton composition. Analysis of nitrogen cycle functional genes identified 39 genes, including gltB , glnA , gltD , gdhA , NRT , etc., which were involved in seven main pathways, encompassing nitrogen fixation, nitrification, denitrification, and dissimilatory nitrate reduction. Phosphorus cycle function gene analysis identified 54 genes, including pstS , ppx - gppA , glpQ , ppk1 , etc., primarily participating in six main pathways, including organic P mineralization, inorganic P solubilization, and regulatory. Cluster analysis indicated that different depths were significant factors influencing the composition and abundance of nitrogen and phosphorus cycle functional genes. The composition and abundance of nitrogen and phosphorus cycle functional genes in the surface and bottom layers differed and were generally higher than those in the middle layer. Deinococcus , Hydrogenophaga , Limnohabitans , Clavibacter , and others were identified as key species involved in the nitrogen and phosphorus cycle. Additionally, we found significant correlations between nitrogen and phosphorus cycle functional genes and environmental factors such as DO, pH, T , total dissolved solids （TDS）, electrical conductivity （EC）, and Chla. Furthermore, the content of these environmental factors exhibited depth-related changes in the Danjiangkou Reservoir, resulting in a distinct vertical distribution pattern of bacterioplankton nitrogen and phosphorus cycle functional genes. Overall, this study sheds light on the composition, function, and influencing factors of bacterioplankton communities across different layers of Danjiangkou Reservoir, offering valuable insights for the ecological function and diversity protection of bacterioplankton in this crucial reservoir ecosystem.

With the vigorous development of agriculture in China， plastic mulch film and pesticides are widely used in agricultural production. However， the accumulation of microplastics （formed by the degradation of plastic mulch film） and pesticides in soil has also caused many environmental problems. At present， the environmental biological effects of microplastics or pesticides have been reported， but there are few studies on the combined effects on crop growth and the rhizosphere soil bacterial community. Therefore， in this study， the high density polyethylene microplastics （HDPE， 500 mesh） were designed to be co-treated with sulfonylurea herbicide chlorimuron-ethyl to study their effects on soybean growth. In addition， the effects of the combined stress of HDPE and chlorimuron-ethyl on soybean rhizosphere soil bacterial community diversity， structure composition， microbial community network， and soil function were investigated using high-throughput sequencing technology， interaction network， and PICRUSt2 function analysis to clarify the combined toxicity of HDPE and chlorimuron-ethyl to soybean. The results showed that the half-life of chlorimuron-ethyl in soil was prolonged by the 1% HDPE treatment （from 11.5 d to 14.3 d）， and the combined stress of HDPE and chlorimuron-ethyl had more obvious inhibition effects on soybean growth than that of the single pollutant or control. The HiSeq 2 500 sequencing showed that the rhizosphere bacterial community of soybean was composed of 20 phyla and 312 genera under combined stress， the number of phyla and genera was significantly less than that of the control and single pollutant treatment， and the relative abundances of bacteria with potential biological control and plant growth-promoting characteristics （such as Nocardioides and Sphingomonas ） were reduced. Alpha diversity analysis showed that the combined stress significantly reduced the richness and diversity of the soybean rhizosphere bacterial community， and Beta diversity analysis showed that the combined stress significantly changed the structure of the bacterial community. The dominant flora of the rhizosphere bacterial community were regulated， and the abundances of secondary functional layers such as amino acid metabolism， energy metabolism， and lipid metabolism were reduced under combined stress by the analysis of LEfSe and PICRUSt2. It was inferred from the network analysis that the combined stress of HDPE and chlorimuron-ethyl reduced the total number of connections and network density of soil bacteria， simplified the network structure， and changed the important flora species to maintain the stability of the network. The results above indicated that the combined stress of HDPE and chlorimuron-ethyl significantly affected the growth of soybean and changed the rhizosphere bacterial community structure， soil function， and network structure. Compared with that of the single pollutant treatment， the potential risk of combined stress was greater. The results of this study can provide guidance for evaluating the ecological risks of polyethylene microplastics and chlorimuron-ethyl and for the remediation of contaminated soil.

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.

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.

Plastic mulch, especially polyethylene mulch, is widely used in agricultural production in China, but the microplastics formed by its degradation gradually have accumulated in soil, causing a series of environmental problems. At present, there have been many reports on the environmental biological effects of microplastics in farmland soil, but studies on the effects of microplastics on crop growth, disease occurrence, and rhizosphere soil bacterial communities are still lacking. In the previous study, it was found that 1% high-density polyethylene (HDPE, 500 mesh) could increase the incidence rate of cotton Fusarium wilt (33.3%) and inhibit growth, but this phenomenon was not found after soil sterilization. It was speculated that HDPE could affect the growth and occurrence of Fusarium wilt by regulating the soil microbial community. Therefore, high-throughput sequencing technology, combined with network and FAPROTAX function analysis, were used to investigate the effects of HDPE on the bacterial community structure, interaction network, and soil function in cotton rhizosphere in order to analyze the mechanism of HDPE. NovaSeq sequencing showed that the bacterial community of HDPE-treated cotton rhizosphere soil was composed of 54 phyla and 472 genera; the number of phyla and genera was higher than that in untreated soil. The α and β diversity and ANOSIM/Adonis analyses showed that HDPE significantly reduced the richness of the bacterial community and changed the composition of the community structure. Based on a T -test species difference analysis, HDPE significantly reduced the relative abundance of bacteria with biological control, pollutant degradation, and antifungal drug synthesis (such as Kribbella , Massiliam , Hailiangium , and Ramlibacter ).The change in the bacterial community will lead to the change in soil bacterial function. Further analysis of FAPROTAX function revealed that HDPE weakened some biochemical functions of bacteria in the cotton rhizosphere soil, such as aerobic chemoheterotrophy, fermentation, and nitrate reduction. The correlation network at the genus level showed that HDPE treatment weakened the interaction between rhizosphere bacteria, reduced the number of positive correlation connections, increased the number of negative correlation connections, simplified network structure, and changed the key flora. The above results showed that HDPE could reduce the cotton growth and the occurrence of Fusarium wilt by changing the bacterial community, interaction, and functional metabolism in rhizosphere soil, which can provide guidance for evaluating the ecological risk of polyethylene microplastics and the remediation of contaminated soil.

Heavy metal contamination affects microbial composition and diversity. The interaction between heavy metal contamination and soil microorganisms has been a hot topic in ecological research. Battery manufacturing has been going on for over six decades in Xinxiang City, resulting in severe soil heavy metal contamination due to battery wastewater runoff. Few studies have investigated the effect of heavy metal contamination due to long-term battery wastewater runoff on microbial diversity and metabolomics in Xinxiang City. In this study, we collected samples from three heavy metal contaminated sites in Xinxiang City and found that Cd and Pb exceeded the recommended thresholds by 34-66 fold and 1.5-2.32 fold, respectively. High-throughput sequencing showed that Bacillus, Arthrobacter, Sphingomonas , and Streptomyces were the dominant bacteria genera, while Olpidium, Plectosphaerella , and Gibellulopsis were the dominant fungi genera, indicating that heavy metal contaminated soil in Xinxiang City was rich in heavy metal tolerant bacteria and fungi due to the long-term heavy metal stress. Correlation analysis showed that total Cu, DTPA extract Cu, and water soluble Pb were significant factors in bacterial diversity, while total Cd, total Ni, total Pb, total Zn, DTPA extract Cu, and water soluble Pb were significant factors in fungal diversity. To better understand the effect of heavy metal contamination on the metabolism of soil microorganisms, we conducted non-targeted metabolomic profiling, which showed significant differences in metabolites across the samples. Pathway enrichment analysis showed that these differential metabolites were involved in pathways such as metabolism, environmental information processing, and genetic Information Processing, which may play a role in heavy metal stress mitigation and environmental adaptation.

Some functional microorganisms in the soil immobilize heavy metals by adsorption and precipitation, prevent the absorption of heavy metals by crops, and play an important role in the passivation and remediation of medium and mild heavy metal-contaminated soil. A pot experiment was conducted to study the effects of the exogenous polyamine-producing bacterium Bacillus sp. N3 on Cd uptake and the bacterial community composition and function in the rhizosphere soil. The results showed that strain N3 significantly reduced the contents of Cd (64.7%) in wheat grain and DTPA-Cd (50.1%) in rhizosphere soil and increased the pH (from 6.84 to 6.97) and polyamine content. High-throughput sequencing results showed that inoculation of strain N3 reduced the diversity of the bacterial community; however, it increased the relative abundances of β -Proteobacteria, Bacteroidetes, and Firmicutes in wheat rhizosphere soil. Meanwhile, strain N3 also increased the relative abundances of heavy metal-immobilizing bacteria and plant growth-promoting bacteria ( Bacillus, Arthrobacter, Brevundimonas, Ensifer, Pedobacter, Rhizobium, Pseudomonas, Enterobacter , and Serratia ) in wheat rhizosphere soil. The PICRUSt function prediction showed that strain N3 increased the copy number of genes involved in antioxidant capacity, hormone synthesis, and sulfur metabolism in wheat rhizosphere soil. These results indicated that the polyamine-producing bacteria N3 reduced the DTPA-Cd content by increasing the pH; the polyamine contents; the abundances of bacteria with heavy metal-immobilizing or plant growth-promoting traits; and the metabolic pathway involved in antioxidant capacity, hormone synthesis, and sulfur metabolism in wheat rhizosphere soil, thus inhibiting the absorption of Cd by wheat. The results provide theoretical basis and technical support for restoring farmland with excessive heavy metals and ensuring the safe production of wheat.

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.

The use of heavy metal passivators to prevent vegetables from absorbing heavy metals is an important measure to control heavy metal-polluted vegetable fields and to ensure the safe production of vegetables. A pot experiment of planting three times in succession was conducted to study the effects of Bacillus megaterium N3 (N3), rice husk biochar (BC), sheep manure organic fertilizer (SM), strain N3 combined with biochar (BC+N3), and strain N3 combined with sheep manure (SM+N3) on Cd uptake and the functional stability of lettuce using a heavy metal passivator only at the first planting. The comprehensive applicability of the passivation materials was evaluated by the dynamic weighted comprehensive function. The results showed that when lettuce was planted for the first time, compared with the control, all the heavy metal passivators could significantly reduce (61.2%-81%) the Cd content in the edible part of the lettuce. However, in the third cultivation of lettuce, only SM+N3 could significantly reduce the Cd uptake by lettuce, which indicated that SM+N3 had the best functional stability. The dynamic weighted comprehensive function was used to evaluate the Cd content in the edible part of fresh lettuce, available Cd content in the soil, yield, and remediation cost. The results showed that the comprehensive applicability of SM+N3 was the best, followed by that of SM, BC+N3, and BC, and the comprehensive evaluation effect of strain N3 was the worst. The results of this study provide a theoretical basis and technical support for remediation of heavy metal-contaminated vegetable fields.

The Laoguan River is the tributary of Danjiangkou Reservoir located nearest to the water diversion outlet, and water quality here directly affects the safety of the diverted water. To explore the community composition and functional change of bacterioplankton in the Laoguan River before and after the flood season, four representative sites were sampled in the main stream before (May) and after (October) the 2018 and 2019 flood seasons. Water quality was assessed and high-throughput sequencing of bacterioplankton was performed. Yanghe (YH) was slightly disturbed, Xixiabei (XX) was moderately disturbed, Dangziling (DZL) was heavily disturbed, and Zhangying (ZY) was moderately disturbed. In total, 599 genera from 40 phyla were collected. The diversity of bacterioplankton before the flood season was higher than afterwards, and moderate levels of disturbance increased the Shannon-Wiener diversity index. LEfSe analysis indicated that significant differences existed in some dominant phyla; Armatimonadete in Yanghe, Epsilonbacteraeota and Firmicutes in Xixiabei, and Cyanophyta in Dangziling dominated before flood season, while significant differences only occurred in Firmicutes and Cyanophyta in Dangziling after the flood season. The PCoA of the bacterioplankton community showed that the sampling points were distinct before and after the flood season, and that differences among samples were greater before the flood season. The RDA and CCA indicated that total nitrogen and ammonia nitrogen were the main environmental factors causing declines in bacterioplankton diversity. PICRUSt showed a total of ten dominant categories of COG function genes. A total of 30 KO function genes related to nitrogen metabolism group also different between the two periods, with greater differences before flood season. The genes cynt and can in Yanghe were significant different from the other three sampling points before the flood season. Overall, nitrogen and phosphorus were the main factors regulating the bacterioplankton community structure and eutrophication in the Laoguan River. Changes in nitrogen inputs will result in changes in microbial nitrogen metabolic function in different regions of the river.

Planktonic fungi are important components of aquatic ecosystems, and analyses of their community composition and function have far-reaching significance for the ecological management and maintenance of the Danjiangkou reservoir. The composition and function of the planktonic fungal community in the surface water layer of the Danjiangkou Reservoir in October 2019 was investigated using Illumina MiSeq sequencing combined with FUNGuild analyses. According to the results, the reservoir community is primarily composed of 6 phyla 213 genera, with Ascomycota and Basidiomycota being the dominant phyla. The water quality monitoring results for the Danjiangkou Reservoir met the Grade Ⅰ or Ⅱ water quality standards for the Environmental Quality Standards for Surface Water (GB 38382-2002). A redundancy analysis (RDA) of the planktonic fungal community and environmental factors showed that TN, TP, T , ORP, and TLI are important factors influencing the distribution of planktonic fungi. The Spearman correlation analysis showed that Alternaria , Cladosporium , Penicillium , Lodderomyces , and Acremonium were significantly correlated with physical and chemical water quality parameters. FUNGuild was used to predict the nutritional and functional groups of planktonic fungi, and the results showed that pathotrophs, saprotrophs, and pathotroph-saprotrophs were the major components. The pathotroph composition analysis showed that the proportions of plant pathogens and animal pathogens in the Heijizui samples were significantly higher than those observed in the other monitoring sites. The community composition, function, and influencing factors of the planktonic fungi community in the Danjiangkou Reservoir were investigated and indicated that it is potentially at ecological risk and more attention needs to be paid to planktonic fungi in the biological monitoring of water quality.

There are many types of bacteria in heavy metal-contaminated soils, including plant growth-promoting bacteria and heavy metal-immobilizing bacteria, which may potentially be used for the bioremediation of contaminated soil. In this study, the Cd-contaminated soil around a battery factory in Xinxiang City was collected and its bacterial community composition was analyzed using high-throughput sequencing (HTS) and the plate lineation separation method. The traditional culture method showed that bacteria isolated from contaminated soil belonged to four phyla (Firmicutes, Actinobacteria, Proteobacteria, and Bacteroidetes) and 30 genera including Bacillus, Arthrobacter , and Rhizobium . HTS showed that the soil contained 25 phyla including Proteobacteria, Actinobacteria, and Acidobacteria and 400 genera. The HTS analysis revealed a greater diversity of the bacterial community than the traditional culture method. Network analysis was performed using the relative abundances of bacteria based on the phylogenetic molecular ecological network (pMEN) method. Network analysis showed that the key bacteria included Arthrobacter, Marmoricola, Nocardioides, Ferruginibacter, Flavitalea, Nitrospira , and Lysobacter . The Cd fixation and adsorption abilities of the 159 cultivable strains were determined. The results showed that 30 strains from 11 genera, including Aneurinibacillus, Arthrobacter , and Bacillus , were highly efficient. Six high-efficiency strains were shown to increase the biomass of pak choi ( Brassica chinensis L.) and reduce the content of Cd in different pak choi tissues. This study provides candidate bacterial species for the remediation of heavy metal-contaminated soil in Xinxiang City and provides references for the bacterial community and its function in heavy metal-contaminated soil.

To investigate the diversity of culturable bacteria and heavy metal-immobilizing bacteria in vegetable rhizosphere soil with high concentrations of heavy metals and explore these microbial resources, two samples of Italian lettuce rhizosphere soil with high heavy metal concentration (HY) and low heavy metal concentration (DK) were collected from Xinxiang, Henan Province. The diversity of culturable bacteria and heavy metal-immobilizing bacteria in the rhizosphere soil of lettuce was compared by culturable separation technology and a solution adsorption experiment. The enhancement of Cd and Pb immobilization and lettuce growth by the strains was also investigated in a hydroponic experiment. The results showed that 400 strains belonging to 3 phyla and 14 genera were isolated from the HY sample, with β -Proteobacteria being the dominant phylum. Meanwhile, 400 strains belonging to 4 phyla and 30 genera were isolated from the DK sample, with Firmicutes being the dominant phylum. A total of 146 strains had a strong ability to immobilize heavy metal and the Cd and Pb removal rates were greater than 80% in the HY sample; Brevundimonas , Serratia , Arthrobacter , and Pseudarthrobacter were the main genera. However, 44 strains had a strong ability to immobilize heavy metal and the Cd and Pb removal rates were greater than 80% in the DK sample, with Bacillus being the main genus. Compared with the control, inoculation with Serratia liquefaciens HY-22, Bacillus thuringiensis HY-53, and Acinetobacter lwoffii HY-157 significantly increased the dry weight of roots (7.5%-77.6%) and shoots (15.4%-67.2%) of the Italian lettuce and cauliflower lettuce and reduced the contents of Cd (38.7%-66.6%) and Pb (34.7%-62.5%) in roots and shoots of Italian lettuce. In addition, the contents of Cd and Pb in the fresh shoots of Italian lettuce and cauliflower lettuce in the presence of Bacillus thuringiensis HY-53 were lower than the Cd and Pb limits set by national food safety standards. Thus, the results provided strain resources and a theoretical basis for the remediation of Cd-and Pb-contaminated farmlands for the safe production of crops.

The effects of heavy metal contamination on farmland continues to worsen progressively with an increase in anthropogenic activities such as industrial pollution and mining. Excess Cd and Pb in agricultural soils enter the food chain and adversely affect all organisms. Therefore, it is important to find an eco-friendly way to reduce heavy metal accumulation in crops. Based on their heavy metal resistance and growth-promoting characteristics, functional bacterial strains were screened and their effects on growth and heavy metal accumulation in wheat were verified via shaking flask adsorption and sand culture tests. Eighteen functional strains were isolated from the rhizospheric soil of Salvia setaria . Among them, Bacillus megaterium N3 and Serratia liquefaciens H12 were most effective at resisting high Cd (650 mg·L -1 ) and Pb (2700 mg·L -1 ) concentrations, and at producing indole-3-acetic acid (IAA) (56.6 mg·L -1 and 69.1 mg·L -1 , respectively), siderophores, and 1-Amino-1-cyclopropanecarboxylic acid (ACC) deaminase. Static incubation experiments showed that strains N3 and H12 significantly increased the NH 4 + concentration and pH, and decreased the Cd (63.1%-73.8%) and Pb (69.1%-81.8%) concentration in solution. In sand cultures, strains N3 and H12 not only increased the dry weight of wheat roots (47.2%-97.4%) and shoots (65.3%-153%) significantly, but also significantly reduced the Cd (49.2%-68.3%) and Pb (27.4%-84.5%) content in wheat roots and shoots. Thus, the results provide strain resources and a theoretical basis for the remediation of Cd- and Pb-contaminated farmlands for the safer production of crops.

Miscanthus is a promising candidate species of second-generation energy crops. To our knowledge, the composition and function of Miscanthus rhizosphere bacterial communities has not yet been reported. In this study, rhizosphere soil samples were collected from Miscanthus (Xiangzamang No. 1) which was grown in Nanyang City for five years and bareground (as the control) to analyze the bacterial community structure and diversity using 16S rRNA gene sequencing on the Illumina MiSeq platform. PICRUSt was used to determine the metabolic and functional abilities of soil bacterial communities. Phylogenetic analysis based on 16S rRNA gene sequences showed that sol bacteria could be divided into 23 phyla and 231 genera, with high richness of the community composition. The dominant phyla were Proteobacteria, Acidobacteria, Actinobacteria, Chloroflexi, Bacteroidetes and Gemmatimonadetes. The bacterial community diversity in the rhizosphere samples of Xiangzamang No. 1 was lower than that in unplanted samples. Rhizosphere bacterial communities were affected by Miscanthus crops. Based on the PICRUSt analysis of bacterial community functions, our results revealed a wide genetic diversity of organisms involved in various essential processes,such as amino acid transport and metabolism, cell wall/membrane/envelope biogenesis, signal transduction mechanisms. Based on the 16S rRNA gene copy number of the detected phylotypes, 22 bacterial metabolic function in the rhizosphere samples of Miscanthus was higher than that in bareground. Results from N- and P-cycling gene analysis showed that Miscanthus planting altered the N- and P-cycling metabolic capacities of soil bacteria.