PrsQ2, a small periplasmic protein involved in increased uranium resistance in the bacterium Cupriavidus metallidurans.

Uranium contamination is a widespread problem caused by natural and anthropogenic activities. Although microorganisms thrive in uranium-contaminated environments, little is known about the actual molecular mechanisms mediating uranium resistance. Here, we investigated the resistance mechanisms driving the adaptation of Cupriavidus metallidurans NA4 to toxic uranium concentrations. We selected a spontaneous mutant able to grow in the presence of 1 mM uranyl nitrate compared to 250 µM for the parental strain. The increased uranium resistance was acquired via the formation of periplasmic uranium-phosphate precipitates facilitated by the increased expression of a genus-specific small periplasmic protein, PrsQ2, regulated as non-cognate target of the CzcS2-CzcR2 two-component system. This study shows that bacteria can adapt to toxic uranium concentrations and explicates the complete genetic circuit behind the adaptation.

Bioremediation of copper in sediments from a constructed wetland ex situ with the novel bacterium Cupriavidus basilensis SRS.

The H-02 constructed wetland was designed to remove metals (primarily copper and zinc) to treat building process water and storm water runoff from multiple sources associated with the Tritium Facility at the DOE-Savannah River Site, Aiken, SC. The concentration of Cu and Zn in the sediments has increased over the lifetime of the wetland and is a concern. A bioremediation option was investigated at the laboratory scale utilizing a newly isolated bacterium of the copper metabolizing genus Cupriavidus isolated from Tim's Branch Creek, a second-order stream that eventually serves as a tributary to the Savannah River, contaminated with uranium and other metals including copper, nickel, and mercury. Cupriavidus basilensis SRS is a rod-shaped, gram-negative bacterium which has been shown to have predatory tendencies. The isolate displayed resistance to the antibiotics ofloxacin, tetracycline, ciprofloxacin, select fungi, as well as Cu2+ and Zn2+. Subsequent ribosomal sequencing demonstrated a 100% confidence for placement in the genus Cupriavidus and a 99.014% match to the C. basilensis type strain. When H-02 wetland samples were inoculated with Cupriavidus basilensis SRS samples showed significant (p < 0.05) decrease in Cu2+ concentrations and variability in Zn2+ concentrations. Over the 72-h incubation there were no significant changes in the inoculate densities (106-108 cells/ML) indicating Cupriavidus basilensis SRS resiliency in this environment. This research expands our understanding of the Cupriavidus genus and demonstrates the potential for Cupriavidus basilensis SRS to bioremediate sites impacted with heavy metals, most notably copper.

Quantitative proteomic analysis reveals the metabolic characteristics and adaptive mechanism of Cupriavidus oxalaticus T2 in the process of simultaneous nitrogen and phenol removal.

Phenol and ammonia in wastewater pose a serious threat to ecosystems and human health. However, the currently limited studies on single bacterium simultaneously removing phenol and nitrogen pollution have not fully elucidated the relevant metabolic mechanisms. The differences in proteomic profile after supplementing with phenol and ammonia for 6 and 24 h, respectively, were evaluated to explore the metabolic characteristics and adaptive mechanism of Cupriavidus oxalaticus T2 during the simultaneous removal process of phenol and nitrogen. Results revealed that a new potential phenol para-degradation pathway appeared in T2. Phenol induced changes in nitrogen metabolism, resulting in increased denitrification and decreased synthesis of glutamate from ammonia at 6 h. In addition, phenol exposure enhanced the expression of cytochrome oxidases with high oxygen affinity and increased ATP synthesis. The increase in chemotaxis and flagellar assembly was conducive to the uptake and utilization of phenol. The synthesis of lipoic acid and biotin was also promoted to resist phenol toxicity. Moreover, phenol triggered cellular stress response, thereby leading to the upregulation of anti-stress proteins, such as universal stress protein, iron­sulfur cluster protein, and chaperones. This study contributes to revealing the metabolic characteristics and adaptive mechanism of T2 during simultaneous nitrogen and phenol removal. SIGNIFICANCE: Phenol and ammonia often co-exist in wastewater, causing serious environmental problems. The information on the metabolic mechanism of simultaneously removing these two pollutants by bacteria is insufficient at present. Moreover, phenol is toxic to microbial and causes cells damage. Therefore, exploring the response mechanism of bacteria to phenol stress is conducive to understand their tolerance mechanism to aromatic compounds. In this study, the metabolic characteristics and adaptive mechanism of C. oxalaticus T2 during the simultaneous removal of phenol and nitrogen process were evaluated by comparing the proteome profiles at different stages. The results revealed the degradation pathways of phenol and nitrogen by strain T2. A variety of phenol response mechanisms were determined, including enhanced energy production, improved cell motility, increased the synthesis of lipoic acid and biotin, and combined action of multiple anti-stress proteins. This study is potentially useful to future phenol and nitrogen co-pollution bioremediation strategies and provides insight into the phenolic compound resistance mechanism in bacteria.

Cupriavidus metallidurans NA4 actively forms polyhydroxybutyrate-associated uranium-phosphate precipitates.

Cupriavidus metallidurans is a model bacterium to study molecular metal resistance mechanisms and its use for the bioremediation of several metals has been shown. However, its mechanisms for radionuclide resistance are unexplored. We investigated the interaction with uranium and associated cellular response to uranium for Cupriavidus metallidurans NA4. Strain NA4 actively captured 98 ± 1% of the uranium in its biomass after growing 24 h in the presence of 100 µM uranyl nitrate. TEM HAADF-EDX microscopy confirmed intracellular uranium-phosphate precipitates that were mainly associated with polyhydroxybutyrate. Furthermore, whole transcriptome sequencing indicated a complex transcriptional response with upregulation of genes encoding general stress-related proteins and several genes involved in metal resistance. More in particular, gene clusters known to be involved in copper and silver resistance were differentially expressed. This study provides further insights into bacterial interactions with and their response to uranium. Our results could be promising for uranium bioremediation purposes with the multi-metal resistant bacterium C. metallidurans NA4.

Stability and Microbial Toxicity of Silver Nanoparticles under Denitrifying Conditions.

While the antibacterial effect of silver nanoparticles (AgNPs) on environmentally beneficial microbes has drawn considerable attention, the stability and microbial toxicity of AgNPs in a system where nitrate reduction is the dominant terminal electron-accepting process remain understudied. Here, we explore the impact of citrate-coated AgNPs (cit-AgNPs) on the growth and metabolism of two metal-sensitive and one nonsensitive bacterial strains under denitrifying conditions. Dose-response analysis revealed that in contrast to the bacteriostatic effect exhibited at 1 ppm, 5 ppm cit-AgNPs were bactericidal to the metal-sensitive strains. It was observed that the growth of the cells initiated Ag(I) formation, and the supplement of chloride (2.7 mM) to the cultures substantially mitigated the bactericidal capacity of cit-AgNPs, indicating that AgNP dissolution to ionic Ag(I) played a key role in AgNP toxicity. Abiotic experiments confirmed that nitrite, not nitrate, had the capacity to oxidize cit-AgNPs. Transcriptomic analysis revealed that (i) the gene encoding for membrane stress was upregulated proportionally to cit-AgNP concentrations; (ii) cit-AgNPs and Ag(I) at higher levels upregulated genes involved in oxidative stress and iron-sulfur clusters, whereas expressions of the genes responsible for electron transport, ATP synthesis, and denitrification were substantially repressed; (iii) the addition of chloride significantly altered the level of transcriptional profiles of all of the genes. These results not only provide evidence of abiotic AgNP oxidation by metabolic intermediate nitrogen species but also suggest that AgNPs and Ag(I) may induce differential toxicity modes to prokaryotes. Our findings reinforce the importance of evaluating the potential ecological toxicity and risks associated with the transformation of nanomaterials.

Biodegradation of binary mixtures of octane with benzene, toluene, ethylbenzene or xylene (BTEX): insights on the potential of Burkholderia, Pseudomonas and Cupriavidus isolates.

The contamination of the environment by crude oil and its by-products, mainly composed of aliphatic and aromatic hydrocarbons, is a widespread problem. Biodegradation by bacteria is one of the processes responsible for the removal of these pollutants. This study was conducted to determine the abilities of Burkholderia sp. B5, Cupriavidus sp. B1, Pseudomonas sp. T1, and another Cupriavidus sp. X5 to degrade binary mixtures of octane (representing aliphatic hydrocarbons) with benzene, toluene, ethylbenzene, or xylene (BTEX as aromatic hydrocarbons) at a final concentration of 100 ppm under aerobic conditions. These strains were isolated from an enriched bacterial consortium (Yabase or Y consortium) that prefer to degrade aromatic hydrocarbon over aliphatic hydrocarbons. We found that B5 degraded all BTEX compounds more rapidly than octane. In contrast, B1, T1 and X5 utilized more of octane over BTX compounds. B5 also preferred to use benzene over octane with varying concentrations of up to 200 mg/l. B5 possesses alkane hydroxylase (alkB) and catechol 2,3-dioxygenase (C23D) genes, which are responsible for the degradation of alkanes and aromatic hydrocarbons, respectively. This study strongly supports our notion that Burkholderia played a key role in the preferential degradation of aromatic hydrocarbons over aliphatic hydrocarbons in the previously characterized Y consortium. The preferential degradation of more toxic aromatic hydrocarbons over aliphatics is crucial in risk-based bioremediation.

Zinc- and cadmium-tolerant endophytic bacteria from Murdannia spectabilis (Kurz) Faden. studied for plant growth-promoting properties, in vitro inoculation, and antagonism.

This research aims to isolate and identify Zn- and Cd-tolerant endophytic bacteria from Murdannia spectabilis, identify their properties with and without Zn and Cd stress, and to investigate the effect of bacterial inoculation in an in vitro system. Twenty-four isolates could survive on trypticase soya agar (TSA) supplemented with Zn (250-500 mg L-1) and/or Cd (20-50 mg L-1) that belonged to the genera Bacillus, Pantoea, Microbacterium, Curtobacterium, Chryseobacterium, Cupriavidus, Siphonobacter, and Pseudomonas. Each strain had different indole-3-acetic acid (IAA), 1-aminocyclopropane-1-carboxylate (ACC) deaminase and siderophore production, nitrogen fixation, phosphate solubilization, and lignocellulosic enzyme characteristics. Cupriavidus plantarum MDR5 and Chryseobacterium sp. MDR7 were selected for inoculation into plantlets that were already occupied by Curtobacterium sp. TMIL due to them have a high tolerance for Zn and Cd while showing no pathogenicity. As determined via an in vitro system, Cupriavidus plantarum MDR5 remained in the plants to a greater extent than Chryseobacterium sp. MDR7, while Curtobacterium sp. TMIL was the dominant species. The Zn plus Cd treatment supported the persistence of Cupriavidus plantarum MDR5. Dual and mixed cultivation showed no antagonistic effects between the endophytes. Although the plant growth and Zn/Cd accumulation were not significantly affected by the Zn-/Cd-tolerant endophytes, the inoculation did not weaken the plants. Therefore, Cupriavidus plantarum MDR5 could be applied in a bioaugmentation process.

[Characteristics of selenium nanoparticles synthesized by cell-free supernatant Cupriavidus sp. SHE].

In recent years, selenium nanoparticles (SeNPs) have been widely used in many fields such as nanotechnology, biomedicine and environmental remediation due to their good electrical conductivity, photothermal properties and anticancer properties. In this study, the cell-free supernatant, whole cell and the cell-free extracts of the strain Cupriavidus sp. SHE were used to synthesize SeNPs, and several methods were applied to analyze the crystal structure and surface functional groups of the nanoparticles. Finally, Pseudomonas sp. PI1 (G⁺) and Escherichia coli BL21 (G⁻) were selected to investigate the antibacterial properties of SeNPs. Cell-free supernatant, whole cell and cell-free extracts of the strain could synthesize SeNPs. As for the cell-free supernatant, selenite concentration of 5 mmol/L and pH=7 were favorable for the synthesis of SeNPs. TEM images show that the average size of nanospheres synthesized by the supernatant was 196 nm. XRD analysis indicates the hexagonal crystals structure of SeNPs. FTIR and SDS-PAGE confirmed the proteins bound to the surfaces of SeNPs. SeNPs synthesized by cell-free supernatant showed no antimicrobial activities against Pseudomonas sp. PI1 and Escherichia coli BL21 (DE3). These results suggest that proteins played an important role in biotransformation of SeNPs in an eco-friendly process, and SeNPs synthesized in this study were non-toxic and biologically compatible, which might be applied in other fields in the future.

Simultaneous removal of nitrate, phosphorous and cadmium using a novel multifunctional biomaterial immobilized aerobic strain Proteobacteria Cupriavidus H29.

A novel biomaterial FeCl3/CaCl2/KH2PO4 modified municipal sludge biochar (FCPC) was synthesized. And the impacts of critical factors such as HRT, temperature and C/N ratio on simultaneous denitrification, dephosphorization and Cd(II) removal were investigated. Results show that the highest nitrate removal efficiency reached 92.22% (8.49 mg·L-1·h-1) in test group A and approximately 100% (9.19 mg·L-1·h-1) in test group B. Very low phosphate concentrations (approximately 2.50 mg/L) were detected in the effluent. The average removal efficiency of Cd(II) reached 86.40% (4.42 mg·L-1·h-1) in experimental group A and 90.15% (4.61 mg·L-1·h-1) in experimental group B. Gas emissions and biological precipitation in the bioreactors were monitored, further to confirming contaminant removal mechanisms. Additionally, Cupriavidus H29 was found to contribute dominantly to the FCPC bioreactor activity.

Characteristics of selenium nanoparticles synthesized by cell-free supernatant Cupriavidus sp. SHE / 生物工程学报

In recent years, selenium nanoparticles (SeNPs) have been widely used in many fields such as nanotechnology, biomedicine and environmental remediation due to their good electrical conductivity, photothermal properties and anticancer properties. In this study, the cell-free supernatant, whole cell and the cell-free extracts of the strain Cupriavidus sp. SHE were used to synthesize SeNPs, and several methods were applied to analyze the crystal structure and surface functional groups of the nanoparticles. Finally, Pseudomonas sp. PI1 (G⁺) and Escherichia coli BL21 (G⁻) were selected to investigate the antibacterial properties of SeNPs. Cell-free supernatant, whole cell and cell-free extracts of the strain could synthesize SeNPs. As for the cell-free supernatant, selenite concentration of 5 mmol/L and pH=7 were favorable for the synthesis of SeNPs. TEM images show that the average size of nanospheres synthesized by the supernatant was 196 nm. XRD analysis indicates the hexagonal crystals structure of SeNPs. FTIR and SDS-PAGE confirmed the proteins bound to the surfaces of SeNPs. SeNPs synthesized by cell-free supernatant showed no antimicrobial activities against Pseudomonas sp. PI1 and Escherichia coli BL21 (DE3). These results suggest that proteins played an important role in biotransformation of SeNPs in an eco-friendly process, and SeNPs synthesized in this study were non-toxic and biologically compatible, which might be applied in other fields in the future.

Production and characterization of extracellular polymeric substances (EPS) generated by a carbofuran degrading strain Cupriavidus sp. ISTL7.

The present study demonstrates EPS production by Cupriavidus sp. ISTL7 along with its capability to remediate a toxic carbamate pesticide, carbofuran. The strain ISTL7 efficiently degraded approximately 98% of carbofuran (400 ppm) within 96 h. GC-MS analysis showed catabolic metabolites of degradation which included carbofuran-7-phenol, methylamine, 2-hydroxy-3-(3-methylpropan-2-ol)benzene-N-methyl-carbamate etc. EPS production from the mineral medium supplemented with carbofuran was observed to be 3.112 ±â€¯0.3682 g L-1. FTIR confirmed its carbohydrate composition and the monomeric sugars: glucose, xylose, sorbitol and fructose were identified by GC-MS analysis. The toxic potential of degradation experiment and the produced EPS was evaluated on HepG2 (mammalian liver cell line). The cytotoxicity of carbofuran was reduced upon bacterial degradation and the formed EPS was found to be non-toxic as inferred from percentage cell viability. The present research can possibly influence the development strategies of biological remediation.

Evaluating the Metal Tolerance Capacity of Microbial Communities Isolated from Alberta Oil Sands Process Water.

Anthropogenic activities have resulted in the intensified use of water resources. For example, open pit bitumen extraction by Canada's oil sands operations uses an estimated volume of three barrels of water for every barrel of oil produced. The waste tailings-oil sands process water (OSPW)-are stored in holding ponds, and present an environmental concern as they are comprised of residual hydrocarbons and metals. Following the hypothesis that endogenous OSPW microbial communities have an enhanced tolerance to heavy metals, we tested the capacity of planktonic and biofilm populations from OSPW to withstand metal ion challenges, using Cupriavidus metallidurans, a known metal-resistant organism, for comparison. The toxicity of the metals toward biofilm and planktonic bacterial populations was determined by measuring the minimum biofilm inhibitory concentrations (MBICs) and planktonic minimum inhibitory concentrations (MICs) using the MBEC ™ assay. We observed that the OSPW community and C. metallidurans had similar tolerances to 22 different metals. While thiophillic elements (Te, Ag, Cd, Ni) were found to be most toxic, the OSPW consortia demonstrated higher tolerance to metals reported in tailings ponds (Al, Fe, Mo, Pb). Metal toxicity correlated with a number of physicochemical characteristics of the metals. Parameters reflecting metal-ligand affinities showed fewer and weaker correlations for the community compared to C. metallidurans, suggesting that the OSPW consortia may have developed tolerance mechanisms toward metals present in their environment.

Rock geochemistry induces stress and starvation responses in the bacterial proteome.

Interactions between microorganisms and rocks play an important role in Earth system processes. However, little is known about the molecular capabilities microorganisms require to live in rocky environments. Using a quantitative label-free proteomics approach, we show that a model bacterium (Cupriavidus metallidurans CH34) can use volcanic rock to satisfy some elemental requirements, resulting in increased rates of cell division in both magnesium- and iron-limited media. However, the rocks also introduced multiple new stresses via chemical changes associated with pH, elemental leaching and surface adsorption of nutrients that were reflected in the proteome. For example, the loss of bioavailable phosphorus was observed and resulted in the upregulation of diverse phosphate limitation proteins, which facilitate increase phosphate uptake and scavenging within the cell. Our results revealed that despite the provision of essential elements, rock chemistry drives complex metabolic reorganization within rock-dwelling organisms, requiring tight regulation of cellular processes at the protein level. This study advances our ability to identify key microbial responses that enable life to persist in rock environments.

Aerobic biotransformation of 3-methylindole to ring cleavage products by Cupriavidus sp. strain KK10.

3-Methylindole, also referred to as skatole, is a pollutant of environmental concern due to its persistence, mobility and potential health impacts. Petroleum refining, intensive livestock production and application of biosolids to agricultural lands result in releases of 3-methylindole to the environment. Even so, little is known about the aerobic biodegradation of 3-methylindole and comprehensive biotransformation pathways have not been established. Using glycerol as feedstock, the soil bacterium Cupriavidus sp. strain KK10 biodegraded 100 mg/L of 3-methylindole in 24 h. Cometabolic 3-methylindole biodegradation was confirmed by the identification of biotransformation products through liquid chromatography electrospray ionization tandem mass spectrometry analyses. In all, 14 3-methylindole biotransformation products were identified which revealed that biotransformation occurred through different pathways that included carbocyclic aromatic ring-fission of 3-methylindole to single-ring pyrrole carboxylic acids. This work provides first comprehensive evidence for the aerobic biotransformation mechanisms of 3-methylindole by a soil bacterium and expands our understanding of the biodegradative capabilities of members of the genus Cupriavidus towards heteroaromatic pollutants.

Cupriavidus yeoncheonense sp. nov., isolated from soil of ginseng.

A novel bacterial strain, DCY86(T) (=KCTC 42053(T) = JCM 19890(T)) was isolated from soil of a ginseng field in Yeoncheon province (38°04'00″N 126°57'00″E), Republic of Korea using a serial dilution method. Strain DCY86(T) was observed to be Gram-stain negative, strictly aerobic, to grow optimally at 25-30 °C, at pH 7-7.5 and on tryptic soya agar medium. The cells were found to be sensitive to ceftazidine and tetracycline. Based on 16S rRNA gene sequence comparisons, strain DCY86(T) was found to be most closely related to Cupriavidus basilensis LMG 18990(T) (98.48 %), Cupriavidus numazensis LMG 26411(T) (98.34 %), Cupriavidus pinatabonesis KCTC 22125(T) (98.34 %) and Cupriavidus laharis KCTC 22126(T) (98.00 %). The G+C content was determined to be 64.23 mol %. The only isoprenoid quinone detected in strain DCY86(T) was ubiquinone Q-8. The major polar lipids were identified as diphosphatidylglycerol, phosphtidylethanolamine, phosphatidylglycerol, unidentified aminophosphoglycolipids and unidentified phospholipids. The major fatty acids were identified as C16:0 summed feature 3 (C16:1 ω7c/ω6c and/or iso-C15 : 0 2-OH) and summed feature 8 (C18:1 ω7c and/or C18:1 ω6c). These data support the affiliation of strain DCY86(T) to the genus Cupriavidus. Strain DCY86(T) was also found to be able to solubilize phosphate and produce siderophores. The results of physiological and biochemical tests enabled strain DCY86(T) to be differentiated genotypically and phenotypically from the recognized species of the genus Cupriaividus. Therefore, the novel isolate can be considered to represent a novel species, for which the name Cupriavidus yeoncheonense sp. nov. is proposed here. The type strain is DCY86(T) (=KCTC 42053(T) = JCM 19890(T)).

Poly-ß-hydroxyalkanoates production from cassava starch hydrolysate by Cupriavidus sp. KKU38.

A bacterium capable of accumulating polyhydroxyalkanoates (PHAs), Cupriavidus sp. KKU38 (GenBank Accession no. AM260479), was isolated from cassava starch wastewater of cassava starch manufacturing process. KKU38 can utilize glucose, fructose, maltose and xylose for PHA production. Glucose was the most suitable sugar for PHA production giving the highest PHA content and yield of 73.88% and 0.16 g/g-total sugar consumed, respectively. Lactose and sucrose were not suitable carbon sources for both biomass and PHA productions. PHA production from cassava starch hydrolysate (CSH) by the strain KKU38 was maximized under N-limited conditions (COD:N:P of 100:1:2.43). The moderately high biomass concentrations of 5.97 g/L with PHA content and yield of 61.60% and 0.20 g/g-total sugar consumed, respectively, were obtained under the optimum conditions. The analysis of PHA produced under the optimum conditions by (1)H NMR, (13)C NMR and FT-IR indicated that the produced polymer is homopolymer polyhydroxybutyrate (PHB).

Uranium interaction with two multi-resistant environmental bacteria: Cupriavidus metallidurans CH34 and Rhodopseudomonas palustris.

Depending on speciation, U environmental contamination may be spread through the environment or inversely restrained to a limited area. Induction of U precipitation via biogenic or non-biogenic processes would reduce the dissemination of U contamination. To this aim U oxidation/reduction processes triggered by bacteria are presently intensively studied. Using X-ray absorption analysis, we describe in the present article the ability of Cupriavidus metallidurans CH34 and Rhodopseudomonas palustris, highly resistant to a variety of metals and metalloids or to organic pollutants, to withstand high concentrations of U and to immobilize it either through biosorption or through reduction to non-uraninite U(IV)-phosphate or U(IV)-carboxylate compounds. These bacterial strains are thus good candidates for U bioremediation strategies, particularly in the context of multi-pollutant or mixed-waste contaminations.

Biosynthesis of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and characterisation of its blend with oil palm empty fruit bunch fibers.

Poly(3-hydroxybutyrate-co-38 mol%-3-hydroxyvalerate) [P(3HB-co-38mol%-3HV)] was produced by Cupriavidus sp. USMAA2-4 in the presence of oleic acid and 1-pentanol. Due to enormous production of empty fruit bunch (EFB) in the oil palm plantation and high production cost of P(3HB-co-3HV), oil palm EFB fibers were used for biocomposites preparation. In this study, maleic anhydride (MA) and benzoyl peroxide (DBPO) were used to improve the miscibility between P(3HB-co-3HV) and EFB fibers. Introduction of MA into P(3HB-co-3HV) backbone reduced the molecular weight and improved the thermal stability of P(3HB-co-3HV). Thermal stability of P(3HB-co-3HV)/EFB composites was shown to be comparable to that of commercial packaging product. Composites with 35% EFB fibers content have the highest tensile strength compared to 30% and 40%. P(3HB-co-3HV)/EFB blends showed less chemicals leached compared to commercial packaging.

Characterization of phosphate solubilizing bacteria in sediments from a shallow eutrophic lake and a wetland: isolation, molecular identification and phosphorus release ability determination.

The transformation of phosphorus (P) is a major factor of lake eutrophication, and phosphate releasing bacteria play an important role in the release process. Experiments were conducted to investigate P content and characterize phosphate solubilizing bacterial composition at the molecular level in a shallow eutrophic lake and a wetland. Results showed that P concentrations were relatively high and derived from agricultural runoff and domestic or industrial pollution. Enumeration and molecular identification of these strains indicated that these bacterial groups were abundant in the ecosystem and various kinds of bacteria participated in the phosphorus release process. Twelve phosphate solubilizing bacteria, including eight organic P-solubilizing bacteria (OPBs) and four inorganic P-solubilizing bacteria (IPBs), which belonged to three different families, were isolated and identified. Cupriavidus basilensis was found for the first time to have the ability to mineralize organic P (OP). Laboratory tests on P release ability revealed that IPBs were more effective at releasing P than OPBs. The most efficient IPB strain could accumulate over 170 mg·L-1 orthophosphate, while the equivalent OPB strain only liberated less than 4 mg·L-1 orthophosphate in liquid culture. The results obtained from this investigation should help clarify the roles of microorganisms in aquatic systems and the mechanisms of eutrophication.

Amine- and carboxyl- quantum dots affect membrane integrity of bacterium Cupriavidus metallidurans CH34.

The present study examines the interaction of amine- and carboxyl- PEG core/shell quantum dots (QDs) with metal resistant bacterium Cupriavidus metallidurans CH34. The evolution of the number of QDs, their hydrodynamic radius, diffusion coefficients, and single particle fluorescence were characterized before and during the contact with bacterium by fluorescence correlation spectroscopy (FCS). The obtained results showed that at nanomolar concentrations the amine- and carboxyl-PEG-QDs with average hydrodynamic radiuses of 16.4 and 13.5 nm, form stable dispersions in the absence and presence of 15 mgC L(-1) HA. The decrease of the number of fluorescent particles in the bacterial medium, determined by FCS, together with the increase of the fluorescence of bacterial cells over the background, found by flow cytometry (FCM), demonstrated the association of QDs to C. metallidurans. Furthermore, QDs enhanced the level of the reactive oxygen species in the bacterial cells and augmented the percentage of the cells with damaged and leaky membranes as probed by FCM in combination with 5-(and-6)-carboxy-27'-dichlorodihydrofluorescein diacetate and propidium iodide stains. No difference in the behavior of amine- and carboxyl-PEG-QDs was found, suggesting that different functional groups in the surface coating have no effect on bacterium-QD interactions under the studied conditions. The presence of HA does not affect the hydrodynamic characteristics of the functionalized QDs, but prevented the damage to the bacterial membrane. The slight decrease in the bacterial growth found after exposure of C. metallidurans to these QDs was attributed to the nanoparticles themselves rather the cadmium, zinc, or selenium ions released from the QDs.