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Members of the high-affinity potassium transporter (HKT) protein family regulate the uptake and homeostasis of sodium and potassium ions, but little research describes their roles in response to abiotic stresses in rapeseed (Brassica napus L.). In this study, we identified and characterized a total of 36 HKT genes from the species comprising the triangle of U model (U-triangle species): B. rapa, B. nigra, B. oleracea, B. juncea, B. napus, and B. carinata. We analyzed the phylogenetic relationships, gene structures, motif compositions, and chromosomal distributions of the HKT family members of rapeseed. Based on their phylogenetic relationships and assemblage of functional domains, we classified the HKT members into four subgroups, HKT1;1 to HKT1;4. Analysis of the nonsynonymous substitutions (Ka), synonymous substitutions (Ks), and the Ka/Ks ratios of HKT gene pairs suggested that these genes have experienced strong purifying selective pressure after duplication, with their evolutionary relationships supporting the U-triangle theory. Furthermore, the expression profiles of BnaHKT genes varies among potassium, phytohormone and heavy-metal treatment. Their repression provides resistance to heavy-metal stress, possibly by limiting uptake. Our results systematically reveal the characteristics of HKT family proteins and their encoding genes in six Brassica species and lay a foundation for further exploration of the role of HKT family genes in heavy-metal tolerance. [ABSTRACT FROM AUTHOR]

Noccaea caerulescens (J. Presl & C. Presl) F. K. Mey. is a heavy metal hyperaccumulator exhibiting extreme tolerance to various environmental stresses. To date, the functional role of Ca2+-binding protein in this plant is largely unknown. To investigate the function of calmodulins (CaMs) in N. caerulescens , CaM2 , a Ca2+ sensor encoding gene, was identified and functionally characterised. Protein structure analysis showed that NcCaM2 contains four classic exchange factor (EF)-hand motifs with high sequence similarity to the CaM proteins from model plant Arabidopsis thaliana L. Tissue specific expression analysis showed that NcCaM2 is constitutively expressed in stems, leaves, and roots. Expression level of NcCaM2 was significantly upregulated under various environmental stimulus, indicating a potential involvement of NcCaM2 in the tolerance to abiotic stresses. The heterologous expression of NcCaM2 in a yeast mutant strain increased the heavy metal tolerance in yeast cells. Furthermore, the constitutive expression of NcCaM2 enhanced the heavy metal tolerance capability of transgenic tobacco (Nicotiana tabacum L.) plants. Our data suggested an important role of NcCaM2 in the responses to environmental stresses and provided a potential target gene to enhance of the ability to hyperaccumulate metals. Noccaea caerulescens (J. Presl & C. Presl) F. K. Mey. is a heavy metal hyperaccumulator exhibiting extreme tolerance to various heavy metal stresses. A Ca2+-binding protein in N. caerulescens has been cloned and functional identified. Our data provides a clue to reveal the adaptation strategy of plants to metalliferous soils. [ABSTRACT FROM AUTHOR]

The Wonderfonteinspruit, South Africa, is highly impacted by a century of gold mining activities. The aim of this study was to investigate the physico-chemical properties of the Wonderfonteinspruit and the receiving Mooi River system, the levels of antimicrobial (metals and antibiotics) resistance characteristics and heterotrophic bacteria levels in these water systems. Various physico-chemical parameters were determined. R2A agar and R2A agar supplemented with antimicrobials were used to enumerate heterotrophic bacteria. Morphologically distinct antimicrobial-resistant isolates were purified and screened for antibiotic susceptibility by a disc diffusion method. Selected isolates were identified, and minimum inhibitory concentration ranges determined. Among the antimicrobial resistant isolates, 87% were resistant to at least one antibiotic. Of these, almost 50% were resistant to more than 3 antibiotic classes. A large proportion was resistant to all 7 antibiotics tested. Phyla detected were Proteobacteria, Firmicutes and Bacteriodetes. High MIC levels for metals and antibiotics were detected among all the genera. Results demonstrate potential impacts of physico-chemical properties on levels of antimicrobial-resistant bacteria. Metal-resistant bacteria were also resistant to multiple antibiotics, suggesting that metal pollution from mining may be responsible for co-selection and maintenance of antibiotic-resistant bacteria in this aquatic system. [ABSTRACT FROM AUTHOR]

Mine tailings represent a great environmental concern due to their high contents of heavy metals. Cultivation analysis of microbiota of Tarnowskie Góry (Poland) mine tailing showed the occurrence of bacteria with colony-forming units as low as 5.7 × 104 per one gram of dried substrate. Among 110 bacterial isolates identified by a combination of MALDI-TOF mass spectrometry and 16S rRNA gene sequencing, phylum Actinobacteria was dominant, followed by Firmicutes and Proteobacteria. Extremely high levels of heavy-metal resistance were observed in Arthrobacter spp., particularly for zinc (500 mg/L), lead (1500 mg/L), and cadmium (1000 mg/L). On the other hand, Staphylococcus spp. showed high tolerance to several antibiotics tested, especially ampicillin, partly due to blaZ gene presence. Due to the occurrence of antibiotic-resistant bacteria, mine tailings are not the cause of heavy-metal contamination only, but also a source of antibiotic-resistant bacteria and thus may represent a serious risk for public health. [ABSTRACT FROM AUTHOR]

A field survey of herbaceous plants growing on the Huice lead (Pb)–zinc (Zn) mining area in Yunnan, China was conducted to identify species accumulating concentrations of cadmium (Cd), Pb, and Zn. In total, 200 plant samples of 112 species from 34 families were collected. At the same time, 200 soil samples were collected. Based on Cd, Pb, and Zn tolerance and growth, wildOxyria sinensisHemsl. was chosen as a primary pioneer plant. Then, to confirm ifOxyria sinensisHemsl. may be used as a pioneer plant, the tolerance to Cd, Pb, and Zn and growth of two ecotypes (mining-area ecotype and non-mining-area ecotype)Oxyria sinensisHemsl. were studied further with pot experiments. In 10 samples of wildOxyria sinensisHemsl. in the Huice lead–zinc mine, concentrations of Cd, Pb, and Zn in the soil did not correlate with those in the root (P> 0.05) and shoot (P> 0.05), respectively. Correlations between Cd concentrations in root and shoot were not observed (P> 0.05), whereas those of Pb and Zn were observed (P< 0.05). Both the enrichment coefficient and translocation factor were <1 for Cd, Pb, and Zn for the wildOxyria sinensisHemsl. In the two ecotypes ofOxyria sinensisHemsl., in pot experiments, the treatment concentrations of Cd, Pb, and Zn did not correlate (P> 0.05) with concentrations of Cd, Pb, and Zn in root and shoot. Significant correlations between the concentrations of Cd, Pb, and Zn in root (P< 0.01) and shoot (P< 0.05) were observed in the two ecotypes. Both enrichment coefficient and translocation factors were <1 for Cd, Pb, and Zn in the two ecotypes, respectively. Treatment concentrations of Cd, Pb, and Zn did not significantly correlate (P> 0.05) with plant height and crowns of the two ecotypes. Treatment concentrations of Pb and Zn did not correlate (P> 0.05) with the biomass of the two ecotypes, whereas that of Cd related significantly to biomass in the two ecotypes.Oxyria sinensisHemsl. was suggested to utilize a tolerant strategy to heavy metals (i.e., exclusion). It was a pioneer plant and will be used in restoration of a vegetation cover in a Pb–Zn mine after further research in tolerant mechanisms and restoration ability are conducted. [ABSTRACT FROM AUTHOR]

Microorganisms have adapted intricate signal transduction mechanisms to coordinate tolerance to toxic levels of metals, including two-component regulatory systems (TCRS). In particular, both cop and czc operons are regulated by TCRS; the cop operon plays a key role in bacterial tolerance to copper, whereas the czc operon is involved in the efflux of cadmium, zinc, and cobalt from the cell. Although the molecular physiology of heavy metal tolerance genes has been extensively studied, their evolutionary relationships are not well-understood. Phylogenetic relationships among heavy-metal efflux proteins and their corresponding two-component regulatory proteins revealed orthologous and paralogous relationships from species divergences and ancient gene duplications. The presence of heavy metal tolerance genes on bacterial plasmids suggests these genes may be prone to spread through horizontal gene transfer. Phylogenetic inferences revealed nine potential examples of lateral gene transfer associated with metal efflux proteins and two examples for regulatory proteins. Notably, four of the examples suggest lateral transfer across major evolutionary domains. In most cases, differences in GC content in metal tolerance genes and their corresponding host genomes confirmed lateral gene transfer events. Three-dimensional protein structures predicted for the response regulators encoded by cop and czc operons showed a high degree of structural similarity with other known proteins involved in TCRS signal transduction, which suggests common evolutionary origins of functional phenotypes and similar mechanisms of action for these response regulators. [ABSTRACT FROM AUTHOR]

Dehydrin gene transcript could be induced by heavy metals, and some dehydrins possess the ability to bind metals. However, the correlation between dehydrins and heavy-metal stress is unknown. In order to elucidate the contribution of dehydrins to heavy-metal stress tolerance in plants, we cloned two SK2-type dehydrin genes from heavy-metal hyperaccumulator Brassica juncea, and investigated their Cd/Zn tolerance in transgenic plants. Semi-quantitative RT-PCR analysis revealed that BjDHN2/ BjDHN3 expressed in the leaves, stems and roots at a low level and were up-regulated by heavy metals. Antisense BjDHN3 Brassica juncea plants showed more electrolyte leakage and higher malondialdehyde production than the control plants when exposed to heavy metals, and the total amount of metals accumulated in the whole plant was reduced. Transgenic tobacco plants overexpressing BjDHN2/ BjDHN3 showed lower electrolyte leakage and malondialdehyde production than the control plants when exposed to Cd/Zn. These results indicated that BjDHN2/ BjDHN3 enhanced the tolerance for heavy metals by reducing lipid peroxidation and maintaining membrane stability in the plants. [ABSTRACT FROM AUTHOR]

summary: This paper is the first to report cadmium tolerance in a dicotyledonous species, Silene vulgaris (Moench.) Garcke. The response to cadmium of five populations originating from one uncontaminated and various heavy‐metal contaminated sites was examined under standardized conditions for three weeks. The tolerance index (TI), based on the mean relative growth rate (R), was determined. Populations originating from cadmium‐contaminated sites showed a distinct tolerance to cadmium. A population from a site enriched only with copper also exhibited a marked co‐tolerance to cadmium. A clear difference in biomass production between the sensitive and tolerant populations was attained at 1 μM cadmium. An optimum biomass production in tolerant populations at a metal concentration higher than in the control, as demonstrated for zinc and copper, could not be established for cadmium. The pattern of cadmium uptake and translocation differed between tolerant and sensitive populations. All tolerant populations accumulated cadmium in the roots and showed some degree of restricted transport to the shoots. The effect of cadmium on the elemental distribution in roots and shoots was population‐independent for some elements (copper, zinc, potassium) and population‐specific for others (phosphorus, magnesium and sodium). The phenomenon of co‐tolerance to cadmium is discussed in relation to possible tolerance mechanisms, especially with regard to metal‐binding compounds (metallothioneins, phytochelatins). [ABSTRACT FROM AUTHOR]

Ten individuals from each of four populations of the moss, Funaria hygrometrica Hedw., were grown on tow copper and two zinc treatments and a control in order to assess tolerance to these metals. Tolerances of two life-history stages (protonemal growth and stem production) showed significant variation among populations, and among individuals within all population that originated on a copper mine. Phenotypic correlations among growth responses to the five experimental treatments were similar in the four populations, but this reflected a greater similarly among the environmental correlations than among the genotypic correlations. There was evidence of positive genetic correlations between growth of control medium and growth on media enriched with copper or zinc. This is contrast to data from flowering plants and fungi, and raises the question of why tolerant individuals are restricted to contaminated sites in nature. [ABSTRACT FROM AUTHOR]

We investigated a microbe-based approach to be used for the biorecovery of valuable metals from e-waste. E-waste is a heterogeneous matrix at the microbial scale. Therefore, this study aims at taking advantage of bacterial-fungal (BF) interactions in order to mobilize and immobilize a selected metal present in e-waste. We used cadmium (Cd) and a selection of Cd-tolerant microorganisms from our culture collection or isolated from a naturally cadmium-contaminated soil. Several experiments were designed in order to use the synergistic bioremediation capabilities of BF couples to mobilize and immobilize Cd from a culture medium. Initial results showed that the selected synergistic BF couples are more tolerant to Cd concentrations than the organisms alone. However, setting the conditions leading to effective immobilization of this toxic metal still need further work. Using microbial consortia rather than single species represents an innovative alternative to traditional bioremediation approaches for the development of new biotechnological approaches in urban mining. [ABSTRACT FROM AUTHOR]