Novel players in organogenesis and flavonoid biosynthesis in cucumber glandular trichomes.

Glandular trichomes (GTs) are outgrowths of plant epidermal cells that secrete and store specialized secondary metabolites that protect plants against biotic and abiotic stresses and have economic importance for human use. While extensive work has been done to understand the molecular mechanisms of trichome organogenesis in Arabidopsis (Arabidopsis thaliana), which forms unicellular, nonglandular trichomes (NGTs), little is known about the mechanisms of GT development or regulation of secondary metabolites in plants with multicellular GTs. Here, we identified and functionally characterized genes associated with GT organogenesis and secondary metabolism in GTs of cucumber (Cucumis sativus). We developed a method for effective separation and isolation of cucumber GTs and NGTs. Transcriptomic and metabolomic analyses showed that flavonoid accumulation in cucumber GTs is positively associated with increased expression of related biosynthesis genes. We identified 67 GT development-related genes, the functions of 7 of which were validated by virus-induced gene silencing. We further validated the role of cucumber ECERIFERUM1 (CsCER1) in GT organogenesis by overexpression and RNA interference transgenic approaches. We further show that the transcription factor TINY BRANCHED HAIR (CsTBH) serves as a central regulator of flavonoid biosynthesis in cucumber GTs. Work from this study provides insight into the development of secondary metabolite biosynthesis in multicellular GTs.

Knockdown of miR-361-5p promotes the induced activation of SHF-stem cells through FOXM1 mediated Wnt/ß-catenin pathway in cashmere goats.

The inducing activation event of secondary hair follicle (SHF)-stem cells is considered a key biological process in the SHF regeneration, and the morphogenesis of cashmere fiber in cashmere goats. The miR-361-5p was essentially implicated in the induced activation of SHF-stem cells of cashmere goats, but its functional mechanisms are unclear. Here, we confirmed miR-361-5p was significantly downregulated in anagen SHF bugle of cashmere goats compared with that at telogen, and miR-361-5p expression was significantly lower in SHF-stem cells after activation than its counterpart before activation. Further, we found that miR-361-5p could negatively regulate the induced activation event of SHF-stem cells in cashmere goats. Mechanistically, through dual-luciferase reporter assays, miR-361-5p specifically bound with FOXM1 mRNA in SHF-stem cells of cashmere goats and negatively regulated the expression of FOXM1 gene. Also, through overexpression/knockdown analysis of FOXM1 gene, our results indicated that FOXM1 upregulated the expression of Wnt/ß-catenin pathway related genes in SHF-stem cells. Moreover, based on TOP/FOP-flash Wnt report assays, the knockdown of miR-361-5p promotes the Wnt/ß-catenin pathway activation through upregulating the FOXM1 expression in SHF-stem cells. Finally, we demonstrated that miR-361-5p negatively regulated the induced activation of SHF-stem cells through FOXM1 mediated Wnt/ß-catenin pathway in cashmere goats.

Zinc Finger-Homeodomain Transcriptional Factors (ZHDs) in Cucumber (Cucumis sativus L.): Identification, Evolution, Expression Profiles, and Function under Abiotic Stresses.

Cucumber (Cucumis sativus L.) is a globally prevalent and extensively cultivated vegetable whose yield is significantly influenced by various abiotic stresses, including drought, heat, and salinity. Transcription factors, such as zinc finger-homeodomain proteins (ZHDs), a plant-specific subgroup of Homeobox, play a crucial regulatory role in stress resistance. In this study, we identified 13 CsZHDs distributed across all six cucumber chromosomes except chromosome 7. Phylogenetic analysis classified these genes into five clades (ZHDI-IV and MIF) with different gene structures but similar conserved motifs. Collinearity analysis revealed that members of clades ZHD III, IV, and MIF experienced amplification through segmental duplication events. Additionally, a closer evolutionary relationship was observed between the ZHDs in Cucumis sativus (C. sativus) and Arabidopsis thaliana (A. thaliana) compared to Oryza sativa (O. sativa). Quantitative real-time PCR (qRT-PCR) analysis demonstrated the general expression of CsZHD genes across all tissues, with notable expression in leaf and flower buds. Moreover, most of the CsZHDs, particularly CsZHD9-11, exhibited varying responses to drought, heat, and salt stresses. Virus-induced gene silencing (VIGS) experiments highlighted the potential functions of CsZHD9 and CsZHD10, suggesting their positive regulation of stomatal movement and responsiveness to drought stress. In summary, these findings provide a valuable resource for future analysis of potential mechanisms underlying CsZHD genes in response to stresses.

Transcriptomic and functional analysis provides molecular insights into multicellular trichome development.

Trichomes, the hair-like structures located on aerial parts of most vascular plants, are associated with a wide array of biological processes and affect the economic value of certain species. The processes involved in unicellular trichome formation have been well-studied in Arabidopsis (Arabidopsis thaliana). However, our understanding of the morphological changes and the underlying molecular processes involved in multicellular trichome development is limited. Here, we studied the dynamic developmental processes involved in glandular and nonglandular multicellular trichome formation in cucumber (Cucumis sativus L.) and divided these processes into five sequential stages. To gain insights into the underlying mechanisms of multicellular trichome formation, we performed a time-course transcriptome analysis using RNA-sequencing analysis. A total of 711 multicellular trichome-related genes were screened and a model for multicellular trichome formation was developed. The transcriptome and co-expression datasets were validated by reverse transcription-quantitative PCR and in situ hybridization. In addition, virus-induced gene silencing analysis revealed that CsHOMEOBOX3 (CsHOX3) and CsbHLH1 are involved in nonglandular trichome elongation and glandular trichome formation, respectively, which corresponds with the transcriptome data. This study presents a transcriptome atlas that provides insights into the molecular processes involved in multicellular trichome formation in cucumber and can be an important resource for future functional studies.

CsCER6 and CsCER7 Influence Fruit Glossiness by Regulating Fruit Cuticular Wax Accumulation in Cucumber.

Fruit glossiness is an important external fruit quality trait that greatly affects the marketability of fresh cucumber (Cucumis sativus) fruits. A few reports have suggested that the extent of cuticular wax loading influences the glossiness of the fruit surface. In the present study, we tested the wax contents of two inbred cucumber lines, comparing a line with waxy fruit (3401) and a line with glossy fruit (3413). Wax content analysis and dewaxing analysis demonstrate that fruit cuticular wax loads negatively correlate with fruit glossiness in cucumber. Identifying genes that were differentially expressed in fruit pericarps between 3401 and 3413 and genes induced by abscisic acid suggested that the wax biosynthesis gene CsCER6 (Cucumis sativus ECERIFERUM 6) and the regulatory gene CsCER7 may affect wax accumulation on cucumber fruit. Expression analysis via RT-qPCR, GUS-staining, and in situ hybridization revealed that CsCER6 and CsCER7 are abundantly expressed in the epidermis cells in cucumber fruits. Furthermore, the overexpression and RNAi lines of CsCER6 and CsCER7 showed dramatic effects on fruit cuticular wax contents, fruit glossiness, and cuticle permeability. Our results suggest that CsCER6 and CsCER7 positively regulate fruit cuticular wax accumulation and negatively influence fruit glossiness.

Advance Research on the Pre-Harvest Sprouting Trait in Vegetable Crop Seeds.

Pre-harvest sprouting (PHS), the germination of seeds on the plant prior to harvest, poses significant challenges to agriculture. It not only reduces seed and grain yield, but also impairs the commodity quality of the fruit, ultimately affecting the success of the subsequent crop cycle. A deeper understanding of PHS is essential for guiding future breeding strategies, mitigating its impact on seed production rates and the commercial quality of fruits. PHS is a complex phenomenon influenced by genetic, physiological, and environmental factors. Many of these factors exert their influence on PHS through the intricate regulation of plant hormones responsible for seed germination. While numerous genes related to PHS have been identified in food crops, the study of PHS in vegetable crops is still in its early stages. This review delves into the regulatory elements, functional genes, and recent research developments related to PHS in vegetable crops. Meanwhile, this paper presents a novel understanding of PHS, aiming to serve as a reference for the study of this trait in vegetable crops.

Identification and Functional Characterization of CsMYCs in Cucumber Glandular Trichome Development.

Glandular trichomes (GTs), specialized structures formed by the differentiation of plant epidermal cells, are known to play important roles in the resistance of plants to external biotic and abiotic stresses. These structures are capable of storing and secreting secondary metabolites, which often have important agricultural and medicinal values. In order to better understand the molecular developmental mechanisms of GTs, studies have been conducted in a variety of crops, including tomato (Solanum lycopersicum), sweetworm (Artemisia annua), and cotton (Gossypium hirsutum). The MYC transcription factor of the basic helix-loop-helix (bHLH) transcription factor family has been found to play an important role in GT development. In this study, a total of 13 cucumber MYC transcription factors were identified in the cucumber (Cucumis sativus L.) genome. After performing phylogenetic analyses and conserved motifs on the 13 CsMYCs in comparison to previously reported MYC transcription factors that regulate trichome development, seven candidate MYC transcription factors were selected. Through virus-induced gene silencing (VIGS), CsMYC2 is found to negatively regulate GT formation while CsMYC4, CsMYC5, CsMYC6, CsMYC7, and CsMYC8 are found to positively regulate GT formation. Furthermore, the two master effector genes, CsMYC2 and CsMYC7, are observed to have similar expression patterns indicating that they co-regulate the balance of GT development in an antagonistic way.

Design strategies and mechanisms of g-C3N4-based photoanodes for photoelectrocatalytic degradation of organic pollutants in water.

Emerging photoelectrocatalytic (PEC) systems integrate the advantages of photocatalysis and electrocatalysis and are considered as a promising technology for solving the global organic pollution problem in water environments. Among the photoelectrocatalytic materials applied for organic pollutant degradation, graphitic carbon nitride (CN) has the combined advantages of environmental compatibility, stability, low cost, and visible light response. However, pristine CN has disadvantages such as low specific surface area, low electrical conductivity, and high charge complexation rate, and how to improve the degradation efficiency of PEC reaction and the mineralization rate of organic matter is the main problem faced in this field. Therefore, this paper reviews the progress of various functionalized CN used for PEC reaction in recent years, and the degradation efficiency of these CN-based materials is critically evaluated. First, the basic principles of PEC degradation of organic pollutants are outlined. Then, engineering strategies to enhance the PEC activity of CN (including morphology control, elemental doping, and heterojunction construction) are focused on, and the structure-activity relationships between these engineering strategies and PEC activity are discussed. In addition, the important role of influencing factors on the PEC system is summarized in terms of mechanism, to provide guidance for the subsequent research. Finally, suggestions and perspectives are provided for the preparation of efficient and stable CN-based photoelectrocatalysts for practical wastewater treatment applications.

TINY BRANCHED HAIR functions in multicellular trichome development through an ethylene pathway in Cucumis sativus L.

The fruit trichomes of Cucurbitaceae are widely desired in many Asian countries and have been a key determinant of cucumber (Cucumis sativus L.) cultivar selection for commercial production and breeding. However, our understanding of the initiation and development of cucumber trichomes is still limited. Here, we found that the cucumber TINY BRANCHED HAIR (TBH) gene is preferentially expressed in multicellular trichomes. Overexpression of CsTBH in tbh mutants restored the trichome phenotype and increased the percentage of female flowers, whereas silencing of CsTBH in wild-type plants resulted in stunted trichomes with a lower rate of female flowers. Furthermore, we provide evidence that CsTBH can directly bind to the promoters of cucumber 1-Aminocyclopropane-1-Carboxylate Synthase (CsACS) genes and regulate their expression, which affects multicellular trichome development, ethylene accumulation, and sex expression. Two cucumber acs mutants with different trichome morphology and sex morphs compared with their near-isogenic line further support our findings. Collectively, our study provides new information on the molecular mechanism of CsTBH in regulating multicellular trichome development and sex expression through an ethylene pathway.

CsTFL1 inhibits determinate growth and terminal flower formation through interaction with CsNOT2a in cucumber.

Cucumber (Cucumis sativus L.) is an important vegetable crop that carries on vegetative growth and reproductive growth simultaneously. Indeterminate growth is favourable for fresh market under protected environments, whereas determinate growth is preferred for pickling cucumber in the once-over mechanical harvest system. The genetic basis of determinacy is largely unknown in cucumber. In this study, map-based cloning of the de locus showed that the determinate growth habit is caused by a non-synonymous SNP in CsTFL1CsTFL1 is expressed in the subapical regions of the shoot apical meristem, lateral meristem and young stems. Ectopic expression of CsTFL1 rescued the terminal flower phenotype in the Arabidopsis tfl1-11 mutant and delayed flowering in wild-type Arabidopsis Knockdown of CsTFL1 resulted in determinate growth and formation of terminal flowers in cucumber. Biochemical analyses indicated that CsTFL1 interacts with a homolog of the miRNA biogenesis gene CsNOT2a; CsNOT2a interacts with FDP. Cucumber CsFT directly interacts with CsNOT2a and CsFD, and CsFD interacts with two 14-3-3 proteins. These data suggest that CsTFL1 competes with CsFT for interaction with CsNOT2a-CsFDP to inhibit determinate growth and terminal flower formation in cucumber.

Poly-γ-glutamic acid enhanced the drought resistance of maize by improving photosynthesis and affecting the rhizosphere microbial community.

BACKGROUND: Compared with other abiotic stresses, drought stress causes serious crop yield reductions. Poly-γ-glutamic acid (γ-PGA), as an environmentally friendly biomacromolecule, plays an important role in plant growth and regulation. RESULTS: In this project, the effect of exogenous application of γ-PGA on drought tolerance of maize (Zea mays. L) and its mechanism were studied. Drought dramatically inhibited the growth and development of maize, but the exogenous application of γ-PGA significantly increased the dry weight of maize, the contents of ABA, soluble sugar, proline, and chlorophyll, and the photosynthetic rate under severe drought stress. RNA-seq data showed that γ-PGA may enhance drought resistance in maize by affecting the expression of ABA biosynthesis, signal transduction, and photosynthesis-related genes and other stress-responsive genes, which was also confirmed by RT-PCR and promoter motif analysis. In addition, diversity and structure analysis of the rhizosphere soil bacterial community demonstrated that γ-PGA enriched plant growth promoting bacteria such as Actinobacteria, Chloroflexi, Firmicutes, Alphaproteobacteria and Deltaproteobacteria. Moreover, γ-PGA significantly improved root development, urease activity and the ABA contents of maize rhizospheric soil under drought stress. This study emphasized the possibility of using γ-PGA to improve crop drought resistance and the soil environment under drought conditions and revealed its preliminary mechanism. CONCLUSIONS: Exogenous application of poly-γ-glutamic acid could significantly enhance the drought resistance of maize by improving photosynthesis, and root development and affecting the rhizosphere microbial community.

A chitinase CsChi23 promoter polymorphism underlies cucumber resistance against Fusarium oxysporum f. sp. cucumerinum.

Fusarium wilt disease, caused by Fusarium oxysporum f. sp. cucumerinum (Foc), leads to widespread yield loss and quality decline in cucumber. However, the molecular mechanisms underlying Foc resistance remain poorly understood. We report the mapping and functional characterisation of CsChi23, encoding a cucumber class I chitinase with antifungal properties. We assessed sequence variations at CsChi23 and the associated defence response against Foc. We functionally characterised CsChi23 using transgenic assay and expression analysis. The mechanism regulating CsChi23 expression was assessed by genetic and molecular approaches. CsChi23 was induced by Foc infection, which led to rapid upregulation in resistant cucumber lines. Overexpressing CsChi23 enhanced fusarium wilt resistance and reduced fungal biomass accumulation, whereas silencing CsChi23 causes loss of resistance. CsHB15, a homeodomain leucine zipper (HD-Zip) III transcription factor, was found to bind to the CsChi23 promoter region and activate its expression. Furthermore, silencing of CsHB15 reduces CsChi23 expression. A single-nucleotide polymorphism variation -400 bp upstream of CsChi23 abolished the HD-Zip III binding site in a susceptible cucumber line. Collectively, our study indicates that CsChi23 is sufficient to enhance fusarium wilt resistance and reveals a novel function of an HD-Zip III transcription factor in regulating chitinase expression in cucumber defence against fusarium wilt.

Combined effects of Penicillium oxalicum and tricalcium phosphate on lead immobilization: Performance, mechanisms and stabilities.

Phosphorus (P) containing minerals are identified as effective Pb stabilizers in soil, while their low solubility limit the Pb immobilization efficiency. In this work, the combination of phosphate solubilizing fungi (PSF) Penicillium oxalicum and tricalcium phosphate (TCP) was constructed and applied to improve Pb immobilization stabilities in medium and soils. P. oxalicum+ TCP could significantly improve Pb2+ removal to above 99% under different TCP/Pb2+ and pH values. TCP and P. oxalicum could remarkably immobilize Pb by ion exchange, and PbC2O4 precipitation or surface adsorption, respectively. While the enhanced Pb immobilization in P. oxalicum+ TCP was explained by stronger Pb2+ interaction with tryptophan protein-like substances in extracellular polymeric substance, and the formation of the most stable Pb-phosphate compound hydroxypyromorphite (Pb5(PO4)3OH). Toxicity characteristic leaching procedure test showed that only 0.91% of Pb2+ was leachable in P. oxalicum+ TCP treatment, significantly lower than that in P. oxalicum (2.90%) and TCP (7.52%) treatments. In addition, the lowest soil exchangeable Pb fraction (37.1%) and the highest available soil P (88.0 mg/kg) were both found in P. oxalicum+ TCP treatment. By synergistically forming stable Pb-containing products, thus the combination of PSF and P minerals could significantly improve Pb2+ immobilization and stability in soils.

Evaluation of potential ecological risks in potential toxic elements contaminated agricultural soils: Correlations between soil contamination and polymetallic mining activity.

Extensive mineral exploitation activities in history have aggravated potential toxic elements (PTEs) contamination in agricultural soils in China. Comprehensive ecological risk assessment is of great significance to orientate the restoration of contaminated soils, especially for those with high background values and multiple sources. The study area is located in the major rice producing area of China. Historically, there was a silver mine and a lead-zinc mine in the area, which were successively closed during the investigation. The intensive mining activities caused serious PTEs pollution in the agricultural soils around the mining area. In this study, five PTEs (As, Cd, Cr, Hg and Pb) selected to assessed the potential of geoaccumulation index in assessing agricultural soil potential risk assessment by identifying ecological risk sources. 315 of soil samples collected in 2009, 2014, 2018 were comprehensively analyzed by single pollution index evaluation (single factor index, geoaccumulation index), comprehensive evaluation (Nemerow index, potential ecological risk index) and trend analysis. Single factor index analysis showed that geoaccumulation index considered the impact of natural diagenesis of background values and human activities on the environment, ensuring high evaluation accuracy comparing to other methods used in typical complex agricultural soils. The modified potential ecological risk index revealed that the high background area did not represent high risk area, which was consistent with the implementation effect of governance measures. This study can provide important insights for policymakers and environmental engineers to quantitatively recognize the soil pollution and the effectiveness of governance based on applicable and reasonable evaluation methods.

Tissue-specific Transcriptome analysis reveals lignocellulose synthesis regulation in elephant grass (Pennisetum purpureum Schum).

BACKGROUND: The characteristics of elephant grass, especially its stem lignocellulose, are of great significance for its quality as feed or other industrial raw materials. However, the research on lignocellulose biosynthesis pathway and key genes is limited because the genome of elephant grass has not been deciphered. RESULTS: In this study, RNA sequencing (RNA-seq) combined with lignocellulose content analysis and cell wall morphology observation using elephant grass stems from different development stages as materials were applied to reveal the genes that regulate the synthesis of cellulose and lignin. A total of 3852 differentially expressed genes (DEGs) were identified in three periods of T1, T2, and T3 through RNA-seq analysis. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis of all DEGs showed that the two most abundant metabolic pathways were phenylpropane metabolism, starch and sucrose metabolism, which were closely related to cell wall development, hemicellulose, lignin and cellulose synthesis. Through weighted gene co-expression network analysis (WGCNA) of DEGs, a 'blue' module highly associated with cellulose synthesis and a 'turquoise' module highly correlated with lignin synthesis were exhibited. A total of 43 candidate genes were screened, of which 17 had function annotations in other species. Besides, by analyzing the content of lignocellulose in the stem tissues of elephant grass at different developmental stages and the expression levels of genes such as CesA, PAL, CAD, C4H, COMT, CCoAMT, F5H and CCR, it was found that the content of lignocellulose was related to the expression level of these structural genes. CONCLUSIONS: This study provides a basis for further understanding the molecular mechanisms of cellulose and lignin synthesis pathways of elephant grass, and offers a unique and extensive list of candidate genes for future specialized functional studies which may promote the development of high-quality elephant grass varieties with high cellulose and low lignin content.

The HD-ZIP IV transcription factor GL2-LIKE regulates male flowering time and fertility in cucumber.

Cucumber is dioecious by nature, having both male and female flowers, and is a model system for unisexual flower development. Knowledge related to male flowering is limited, but it is reported to be regulated by transcription factors and hormone signals. Here, we report functional characterization of the cucumber (Cucumis sativus) GL2-LIKE gene, which encodes a homeodomain leucine zipper (HD-ZIP) IV transcription factor that plays an important role in regulating male flower development. Spatial-temporal expression analyses revealed high-level expression of CsGL2-LIKE in the male flower buds and anthers. CsGL2-LIKE is closely related to AtGL2, which is known to play a key role in trichome development. However, ectopic expression of CsGL2-LIKE in Arabidopsis gl2-8 mutant was unable to rescue the gl2-8 phenotype. Interestingly, the silencing of CsGL2-LIKE delayed male flowering by inhibiting the expression of the florigen gene FT and reduced pollen vigor and seed viability. Protein-protein interaction assays showed that CsGL2-LIKE interacts with the jasmonate ZIM domain protein CsJAZ1 to form a HD-ZIP IV-CsJAZ1 complex. Collectively, our study indicates that CsGL2-LIKE regulates male flowering in cucumber, and reveals a novel function of a HD-ZIP IV transcription factor in regulating male flower development of cucumber.

Classification of fruit trichomes in cucumber and effects of plant hormones on type II fruit trichome development.

MAIN CONCLUSION: Cucumber fruit trichomes could be classified into eight types; all of them are multicellular with complex and different developmental processes as compared with unicellular trichomes in other plants. The fruit trichomes or fruit spines of cucumber, Cucumis sativus L., are highly specialized structures originating from epidermal cells with diverse morphology, which grow perpendicular to the fruit surface. To understand the underlying molecular mechanisms of fruit trichome development, in this study, we conducted morphological characterization and classification of cucumber fruit trichomes and their developmental processes. We examined the fruit trichomes among 200 cucumber varieties, which could be classified into eight morphologically distinct types (I-VIII). Investigation of the organogenesis of the eight types of trichomes revealed two main developmental patterns. The development of glandular trichomes had multiple stages including initiation and expansion of the trichome precursor cell protuberating out of the epidermal surface, followed by periclinal bipartition to two cells (top and bottom) which later formed the head region and the stalk, respectively, through subsequent cell divisions. The non-glandular trichome development started with the expansion of the precursor cell perpendicularly to the epidermal plane followed by cell periclinal division to form a stalk comprising of some rectangle cells and a pointed apex cell. The base cell then started anticlinal bipartition to two cells, which then underwent many cell divisions to form a multicellular spherical structure. In addition, phytohormones as environmental cues were closely related to trichome development. We found that GA and BAP were capable of increasing trichome number per fruit with distinct effects under different concentrations.

A CsTu-TS1 regulatory module promotes fruit tubercule formation in cucumber.

The fruit epidermal features such as the size of tubercules are important fruit quality traits for cucumber production. But the mechanisms underlying tubercule formation remain elusive. Here, tubercule size locus CsTS1 was identified by map-based cloning and was found to encode an oleosin protein. Allelic variation was identified in the promoter region of CsTS1, resulting in low expression of CsTS1 in all 22 different small-warty or nonwarty cucumber lines. High CsTS1 expression levels were closely correlated with increased fruit tubercule size among 44 different cucumber lines. Transgenic complementation and RNAi-mediated gene silencing of CsTS1 in transgenic cucumber plants demonstrated that CsTS1 positively regulates the development of tubercules. CsTS1 is highly expressed in the peel at fruit tubercule forming and enlargement stage. Auxin content and expression of three auxin signalling pathway genes were altered in the 35S:CsTS1 and CsTS1-RNAi fruit tubercules, a result that was supported by comparing the cell size of the control and transgenic fruit tubercules. CsTu, a C2 H2 zinc finger domain transcription factor that regulates tubercule initiation, binds directly to the CsTS1 promoter and promotes its expression. Taken together, our results reveal a novel mechanism in which the CsTu-TS1 complex promotes fruit tubercule formation in cucumber.

Cupriavidus sp. strain Cd02-mediated pH increase favoring bioprecipitation of Cd2+ in medium and reduction of cadmium bioavailability in paddy soil.

This study investigated the effects of Cupriavidus sp. strain Cd02-mediated increase on biosorption and bioprecipitation of Cd2+ during the 144-h cultivation time as well as evaluated effectivenesses of changing soil pH and bioavailability of cadmium after bioaugmentation of strain Cd02 into Cd-contaminated paddy soil for 15 days. Results showed that strain Cd02-induced pH increase of the culture medium (from 7.40 to 8.68) facilitated biosorption of Cd2+ on Cd02 cell surface (4.82 mg/mg) and extracellular bioprecipitation in form of cadmium carbonate (3.07 mg/mg). Also, the pH values of Cd-contaminated paddy soil increased by 1.41 units after strain Cd02 was applied for 15 days, which thereby promoted the decrease of exchangeable fraction of Cd2+ by 6.5% in the tested paddy soil. Meanwhile, strain Cd02 could prosperously live in paddy soils after bioaugmentation. These results suggest that strain Cd02 may be applicable for bioremediation of the heavy metal-contaminated soils by bioaugmentation.