Heavy Metal Resistant Bacteria Research Articles

Lantana camara—an Ecological Bioindicator Plant for Decontamination of Pb-Impaired Soil Under Organic Waste-Supplemented Scenarios

Heavy metal extraction and processing from ores releases elements into the environment. Soil, being an “unfortunate” sink, has its bionomics impaired and affected by metal pollution. Metals sneak into the food chain and pose risk to humans and other edaphic-dependent organisms. For decontamination, the use of an ecosystem-friendly approach involving plants is known as phytoremediation. In this study, different lead (Pb) concentrations (80, 40, 20, and 10 mg kg−1) were used to contaminate a well-characterized soil, (un)supplemented with organic waste empty fruit bunch (EFB) or spent mushroom compost (SMC), with non-edible plant—Lantana camara. Lead removal by L. camara ranged from 45.51% to 88.03% for supplemented soil, and from 23.7% to 57.8% for unsupplemented soil (P < 0.05). The EFB-supplemented and L. camara-remediated soil showed the highest counts of heavy metal-resistant bacteria (HMRB) (79.67 × 106–56.0 × 106 colony forming units (CFU) g−1 soil), followed by SMC-supplemented and L. camara-remediated soil (63.33 × 106–39.0 × 106 CFU g−1 soil). Aerial metal uptake ranged from 32.08 ± 0.8 to 5.03 ± 0.08 mg kg−1 dry weight, and the bioaccumulation factor ranged from 0.401 to 0.643 (P < 0.05). Half-lives (t1/2) of Pb were 7.24–2.26 d in supplemented soil, 18.39–11.83 d in unsupplemented soil, and 123.75–38.72 d in the soil without plants and organic waste. Freundlich isotherms showed that the intensity of metal absorption (n) ranged from 2.44 to 2.51 for supplemented soil, with regression coefficients of determination (R2) between 0.901 2 and 0.984 0. The computed free-energy change (ΔG) for Pb absorption ranged from −5.01 to 0.49 kJ mol−1 K−1 for EFB-supplemented soil and −3.93 to 0.49 kJ mol−1 K−1 for SMC-supplemented soil.

Isolation and characterization of a biosurfactant-producing heavy metal resistant Rahnella sp. RM isolated from chromium-contaminated soil

Objective of the study was to isolate heavy metal resistant bacteria from chromium-contaminated subsurface soil and investigate biosurfactant production and heavy metal bioremediation. Based on 16S rRNA gene sequence and phylogenetic analysis, the isolate was identified as Rahnella sp. RM. The biosurfactant production by heavy metal resistant Rahnella sp. RM was optimized using Box- Behnken design (BBD). The maximum emulsification activity was obtained 66% at 6% soybean meal in pH 7.0 and 33.5°C. The biosurfactant was characterized using Field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FT-IR) and matrix assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF). The highest metal removal rates using the biosurfactant were found 74.3, 72.5, and 70.1%, respectively, at the 100 mg/L amended flasks at 48 h. This study indicated the biosurfactant from heavy metal resistant Rahnella sp. RM could be used as a potential tool to remediate the metals in contaminated environments.

Characterization of Nickel Tolerant Bacteria Isolated from Heavy Metal Polluted Glass Industry for its Potential Role in Bioremediation

ABSTRACTHeavy metal contamination of the environment is a serious concern because of their deleterious effects on biological systems. To the best of our knowledge, this is the first investigation on isolation of heavy metal resistant bacteria from contaminated sites of glass industrial area.The study focused on isolation and characterization of Ni2+ resistant bacteria from these sites and analysis of their Ni2+ accumulation potential. Out of 38 different bacterial isolates 3 bacteria were able to tolerate up to 24 mM Ni2+ concentration. These bacterial strains were identified as E. coli (AS17b), Escherichia coli (AS21) and Microbacterium sp. (AS33) by 16S rRNA (16S ribosomal RNA) sequencing and their basic local alignment search tool search analysis. Growing cell of E. coli and Microbacterium sp. revealed accumulation of 0.12, 0.08 and 0.06 µg, of Ni2+/mg dry weight of cells, respectively, by 72 hr. Similarly resting cell of these strains showed accumulation of 0.27, 0.11 and 0.08 µg of Ni2+/mg dry weight of cells by 150 min, respectively. These results reveal that strain E. coli (AS21) shows maximum accumulation efficiency for Ni2+ among different isolates studied under shaking as well as starving conditions. Hence, E. coli (AS21) could serve as an efficient and promising bacterium for bioremediation of nickel-contaminated sites.

Cadmium and lead tolerant bacteria isolated from industrial waste water

An in vitro study was conducted to isolate, identify and characterize heavy metal resistant bacteria from industrial waste water and to determine their tolerance capacity to cadmium and lead. Different morphological, physiological and biochemical tests were carried out to identify the bacterial isolates in the waste water. A total of eight bacterial isolates viz., Staphyllococcus intermedius, Pseudomonas aeruginosa, Bacillus cereus, Bacillus subtilis, Escherichia coli, Acinetobacter baumanii, Pseudomonas flavescens and Acinetobacter lwofii were identified from metal polluted tannery and steel industrial areas. Bacterial response to cadmium tolerance was determined by treating them with CdCl2 solution at a rate of 1, 2, 2.5 and 5 μg/ml. In case of lead tolerant bacteria, PbCl2 solution was applied at a rate of 0.05, 0.125, 0.2 and 0.5 μg/ml. Pseudomonas aeruginosa isolated from waste water of steel industries and Bacillus cereus from tannery area was found to be the most tolerant species to the different doses of cadmium and lead. The study indicated that Pseudomonas aeruginosa and Bacillus cereus could be good candidates for the treatment and elimination of heavy metals from industrial waste water. The present study may be helpful to the bioremediation of heavy metals in the contaminated environment.&#x0D; Dhaka Univ. J. Biol. Sci. 26(1): 29-38, 2017 (January)

Assessment of heavy metal concentrations and associated resistant bacterial communities in bulk and rhizosphere soil of Avicennia marina of Pichavaram mangrove, India

Heavy metals are known to pose a potential threat to terrestrial and aquatic flora and fauna. Due to increasing human influence, heavy metal concentrations are rising in many mangrove ecosystems. Therefore, an assessment of heavy metal (Cd, Cr, Cu, Ni, Pb, Fe, Mn, and Zn) concentrations was conducted within the bulk soil and rhizosphere soil of Avicennia marina at the Pichavaram Mangrove Forest in India. The rhizosphere soil showed higher concentrations of metals than the bulk soil. Compared to the bulk soil, the metals Cd, Fe, Mn, and Zn were 6.0–16.7% higher, whereas Cr, Cu, Ni, and Pb were 1.7–2.8% higher concentration. Among the three selected sampling sites (dense mangrove forest, estuarine region, and sea region), the sea region had the highest concentration of all heavy metals except Zn. The trend of the mean metal concentration was Fe > Mn > Cr > Ni > Cu > Pb > Zn > Cd. Heavy metals concentrations elevated by the 2004 tsunami were persistent even after 4 years, due to sedimentary soil processes, the rhizosphere effect of mangroves, and anthropogenic deposition. Analysis of the heavy metal-resistant bacteria showed highest bacterial count for Cr-resistant bacteria and rhizosphere soil. The maximum level of heavy metal-resistant bacteria was observed at the site with the highest heavy metal contamination. The heavy metal-resistant bacteria can be used as indicator of heavy metal pollution and furthermore in bioremediation.

The occurrence of heavy metals and metal-resistant bacteria in water and bottom sediments of the Straszyn reservoir (Poland)

The aim of this study is to investigate the distribution of selected heavy metals and metal–resistant bacteria in water and bottom sediments of the surface drinking water reservoir for Gdansk. The following sequence of metals in regard to metal concentration in sediments can be written down: Zn > Pb > Cu > Cd. The evaluation of metals accumulation was performed using the Muller index, to indicate the bottom sediment's contamination and geochemical classification of sediment quality according to Polish standards. The Muller geochemical index was changing in a wide range: < 1–4.1. Although the maximum value of Muller's geochemical index determined for copper indicates that the sediment is ‘strongly contaminated’, in general the analysed bottom sediments were classified as the I and II category according to Polish geochemical standards. From the microbiological side a significant part of heterotrophic bacteria isolated from the bottom sediment and surface water (raw and treated water) showed a resistance to 0.2 mM and 2 mM concentrations of zinc, copper and lead. The highest percentages of metal–resistant bacteria were recorded in the sediments of the reservoir (60%–88%). The share of metal–resistant strains in the raw water was significantly lower (34%–61%). The results indicate also that water treatment processes may contribute to the selection of resistant strains.

Evaluation of Heavy Metals Resistant Micrococcus sp. Isolated from Rivers in Basra, Iraq

The present study aims to isolation, identification and characterization of heavy metal resistant bacteria from six rivers in Basra Southern Iraq. Two species of Micrococcus (M. halobius and M. kristinae) were isolated on the basis of morphological and biochemical profiles and selected based on high levels of heavy metals (cadmium, lead, copper and nickel) resistance. The concentrations of dissolved heavy metals (Cd, Pb, Cu and Ni) in rivers were determined. The maximum tolerance concentration (MTC) of isolates against Pb, Cu, Cd and Ni was determined in solid media after 72 h incubation. All isolates were resistant to Pb (2200-2600) μg mL-1, Cu (400) μg mL-1, Cd (300-400) μg mL-1 and Ni (200-300) μg ml-1. Living biomass of M. halobius and M. kristinae were used for the removal of heavy metal ions at different concentrations (25, 50 and 100) μg mL-1 from aqueous metal solutions. The best concentration of removal was 25 μg mL-1 after 72 h incubation at 120 rpm. Percent removal efficiency of M. kristinae was 47.22, 26.26 for Cu and Pb respectively, and for M. halobius was 31.52, 27.87 for Cd and Ni respectively.

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Cd immobilization and reduced tissue Cd accumulation of rice (Oryza sativa wuyun-23) in the presence of heavy metal-resistant bacteria

Two metal-resistant Bacillus megaterium H3 and Neorhizobium huautlense T1-17 were investigated for their immobilization of Cd in solution and tissue Cd accumulation of rice (Oryza sativa wuyun-23) in the Cd-contaminated soil. Strains H3 and T1-17 decreased 79–96% of water-soluble Cd in solution and increased grain biomass in the high Cd-contaminated soil. Inoculation with H3 and T1-17 significantly decreased the root (ranging from 25% to 58%), above-ground tissue (ranging from 13% to 34%), and polished rice (ranging from 45% to 72%) Cd contents as well as Cd bioconcentration factor of the rice compared to the controls. Furthermore, H3 and T1-17 significantly reduced the exchangeable Cd content of the rhizosphere soils compared with the controls. Notably, strain T1-17 had significantly higher ability to reduce Cd bioconcentration factor and polished rice Cd uptake than strain H3. The results demonstrated that H3 and T1-17 decreased the tissue (especially polished rice) Cd uptake by decreasing Cd availability in soil and Cd bioconcentration factor and the effect on the reduced polished rice Cd uptake was dependent on the strains. The results may provide an effective synergistic bioremediation of Cd-contaminated soils in the bacteria and rice plants and bacterial-assisted safe production of rice in Cd-contaminated soils.

Diversity and Distribution of Heavy Metal-Resistant Bacteria in Polluted Sediments of the Araça Bay, São Sebastião (SP), and the Relationship Between Heavy Metals and Organic Matter Concentrations.

Heavy metals influence the population size, diversity, and metabolic activity of bacteria. In turn, bacteria can develop heavy metal resistance mechanisms, and this can be used in bioremediation of contaminated areas. The purpose of the present study was to understand how heavy metals concentration influence on diversity and distribution of heavy metal-resistant bacteria in Araça Bay, São Sebastião, on the São Paulo coast of Brazil. The hypothesis is that activities that contribute for heavy metal disposal and the increase of metals concentrations in environment can influence in density, diversity, and distribution of heavy metal-resistant bacteria. Only 12% of the isolated bacteria were sensitive to all of the metals tested. We observed that the highest percentage of resistant strains were in areas closest to the São Sebastião channel, where port activity occurs and have bigger heavy metals concentrations. Bacterial isolated were most resistant to Cr, followed by Zn, Cd, and Cu. Few strains resisted to Cd levels greater than 200mgL(-1). In respect to Cr, 36% of the strains were able to grow in the presence of as much as 3200mgL(-1). Few strains were able to grow at concentrations of Zn and Cu as high as 1600mgL(-1), and none grew at the highest concentration of 3200mgL(-1). Bacillus sp. was most frequently isolated and may be the dominant genus in heavy metal-polluted areas. Staphylococcus sp., Planococcus maritimus, and Vibrio aginolyticus were also isolated, suggesting their potential in bioremediation of contaminated sites.

Polyaromatic hydrocarbon (PAH) degradation potential of a new acid tolerant, diazotrophic P-solubilizing and heavy metal resistant bacterium Cupriavidus sp. MTS-7 isolated from long-term mixed contaminated soil

An isolate of Cupriavidus (strain MTS-7) was identified from a long-term PAHs and heavy metals mixed contaminated soil with the potential to biodegrade both LMW and HMW PAHs with added unique traits of acid and alkali tolerance, heavy metal tolerance, self-nutrient assimilation by N fixation and P solubilization. This strain completely degraded the model 3 (150 mg L−1 Phe), 4 (150 mg L−1 Pyr) and 5 (50 mg L−1 BaP) ring PAHs in 4, 20 and 30 days, respectively. It could mineralize 90–100% of PAHs (200 mg L−1 of Phe and Pyr) within 15 days across pH ranging from 5 to 8 and even in the presence of toxic metal contaminations. During biodegradation, the minimum inhibitory concentrations were 5 (Cu2+) and 3 (Cd2+, Pb2+, Zn2+) mg L−1 of the potentially bioavailable metal ions and over 17 mg L−1 metal levels was lethal for the microbe. Further, it could fix 217–274 μg mL−1 of N and solubilize 79–135 μg mL−1 of P while PAHs degradation. MTS-7 as a superior candidate could be thus used in the enhanced bioaugmentation and/or phytoremediation of long-term mixed contaminated sites.

Metal resistant and phosphate solubilizing bacterium improves maize (Zea mays) growth and mitigates metal accumulation in plant

Abstract The current study focuses on plant promoting and metal detoxifying properties of a heavy metal resistant bacterium with phosphate (P) solubilizing and Indole-3-acetic acid (IAA) producing capabilities. The bacterium was a strain of Pseudomonas putida Ws3 selected from an agricultural land irrigated with sewage water. It could solubilize P up to 300 mg/l and produce IAA up to 200 µg/l in seven days at optimal culture condition, i.e. NaCl (0.5%), KCl (0.01–0.04%), Mg/Cl2 (0.3%) and NH4Cl (0.5%) and 30 °C. Regarding soluble P and IAA concentrations in Pikovskaya (PVK) liquid media, the activity of the bacterium declined in media containing CuCl2 (500 mg/l), PbCl2 (300 mg/l) or CdCl2 (300 mg/l). The metals at elevated levels limited the bacterial population growth in a soil-like substrate supporting roots of a model plant (maize or Zea mays). Weekly bacterial inoculation to the substrate for 40 days alleviated the condition for plant growth, led to increased plant dry weight and decreased the metals accumulated in plant with large effect sizes in the shoot (g=1.49) and root (g=1.36).

Mycorrhiza and heavy metal resistant bacteria enhance growth, nutrient uptake and alter metabolic profile of sorghum grown in marginal soil

The main challenge for plants growing in nutrient poor, contaminated soil is biomass reduction, nutrient deficiency and presence of heavy metals. Our aim is to overcome these challenges using different microbial combinations in mining-impacted soil and focus on their physiological and biochemical impacts on a model plant system, which has multiple applications. In the current study, sorghum BTx623 seedlings grown in mining-impacted soil in greenhouse were subjected to plant growth promoting bacteria (PGPB or B) alone, PGPB with arbuscular mycorrhizal fungi (My), My alone and control group with no treatment. Root biomass and uptake of most of the elements showed significant increase in all treatment groups in comparison with control. Mycorrhiza group showed the best effect followed by My + B and B groups for uptake of majority of the elements by roots. On the contrary, biomass of both shoot and root was more influenced by B treatment than My + B and My treatments. Metabolomics identified compounds whose levels changed in roots of treatment groups significantly in comparison to control. Upregulation of stearic acid, sorbitol, sebacic acid and ferulic acid correlated positively with biomass and uptake of almost all elements. Two biochemical pathways, fatty acid biosynthesis and galactose metabolism, were regulated in all treatment groups. Three common pathways were upregulated only in My and My + B groups. Our results suggest that PGPB enhanced metabolic activities which resulted in increase in element uptake and sorghum root biomass whether accompanied with mycorrhiza or used solely.

Biological synthesis of fluorescent nanoparticles by cadmium and tellurite resistant Antarctic bacteria: exploring novel natural nanofactories.

BackgroundFluorescent nanoparticles or quantum dots (QDs) have been intensely studied for basic and applied research due to their unique size-dependent properties. There is an increasing interest in developing ecofriendly methods to synthesize these nanoparticles since they improve biocompatibility and avoid the generation of toxic byproducts. The use of biological systems, particularly prokaryotes, has emerged as a promising alternative. Recent studies indicate that QDs biosynthesis is related to factors such as cellular redox status and antioxidant defenses. Based on this, the mixture of extreme conditions of Antarctica would allow the development of natural QDs producing bacteria.ResultsIn this study we isolated and characterized cadmium and tellurite resistant Antarctic bacteria capable of synthesizing CdS and CdTe QDs when exposed to these oxidizing heavy metals. A time dependent change in fluorescence emission color, moving from green to red, was determined on bacterial cells exposed to metals. Biosynthesis was observed in cells grown at different temperatures and high metal concentrations. Electron microscopy analysis of treated cells revealed nanometric electron-dense elements and structures resembling membrane vesicles mostly associated to periplasmic space. Purified biosynthesized QDs displayed broad absorption and emission spectra characteristic of biogenic Cd nanoparticles.ConclusionsOur work presents a novel and simple biological approach to produce QDs at room temperature by using heavy metal resistant Antarctic bacteria, highlighting the unique properties of these microorganisms as potent natural producers of nano-scale materials and promising candidates for bioremediation purposes.

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In the present study heavy metals resistant bacteria were isolated from soil collected from Al-Zubair district in Basra governorate south of Iraq. On the basis of morphological, biochemical, 16S rRNA gene sequencing and phylogeny analysis, the isolates were authentically identified as Shewanella oneidensis in addition to Bacillus thuringiensis and Deinococcus radiodurans. The minimal inhibitory concentration (MIC) of isolates against cadmium (Cd) and lead (Pb) was determined on solid medium. S. oneidensis showed significant resistance to high concentrations of Cd (1000 mgl-1) and Pb (700 mgl-1). The bioaccumilation capabilities of S. oneidensis for Cd and Pb were monitored at different ion concentrations and contact times. The transmission electron microscope (TEM) study confirmed the accumulation of Cd and Pb by S. oneindensis causing morphological changes. Key words: Shewanella oneidensis, bioaccumulation, minimal inhibitory concentration, heavy metals, transmission electron microscope.

Complete genome sequence of the heavy metal resistant bacterium Altererythrobacter atlanticus 26DY36T, isolated from deep-sea sediment of the North Atlantic Mid-ocean ridge

Altererythrobacter atlanticus 26DY36T (CGMCC 1.12411T=JCM 18865T) was isolated from the North Atlantic Mid-Ocean Ridge. The strain is resistant to heavy metals, such as Mn2+ (200mM), Co2+ (2.0mM), Cu2+ (1mM), Zn2+ (1mM), Hg2+ (0.1mM) and Cd2+ (0.5mM). Here we describe the genome sequence and annotation, as well as the features of the organism. A. atlanticus 26DY36T harbors a chromosome (3,386,291bp) and a circular plasmid (88,815bp). The genome contains 3322 protein-coding genes (2483 with predicted functions), 47 tRNA genes and 6 rRNA genes. A. atlanticus 26DY36T encodes dozens of genes related to heavy metal resistance and has potential applications in the bioremediation of heavy metal-contaminated environments.

Assessment of phytoremediation potentials of Lantana camara in Pb impacted soil with organic waste additives

Abstract Anthropogenic metal activities have led to soil contamination, posing a severe risk to each trophic level. Therefore, ecosustainable remediation techniques and/or strategy which is the focus of this study must be continuously explored, since metal processing and accidental leakages and depositions into the environment are both inevitable in the global drive for industrialization. Different concentrations at 80–10 mg/kg of Lead (Pb), were used to contaminate a characterized (Mollisol) soil with empty fruit bunch (EFB) and spent mushroom compost (SMC) as amendments with Lantana camara alongside controls. Metal reductions ranged 52.46 to 88.03% and 45.10 to 82.73% were recorded under EFB and SMC, respectively. Heavy metal resistant bacteria (HMRB) counts of 79.67 × 10 6 to 56.1 × 10 6 CFU/g soil and 63.33 × 10 6 to 39.0 × 10 6 CFU/g soil were recorded under EFB and SMC conditions, respectively, at “Freundlich model” absorption intensity ( n ) of 2.51 ( R 2 = 0.9840) and 2.44 ( R 2 = 0.9012) in same order as above. Results validation with free energy change, kinetics and diffusion studies revealed that L. camara is a potential indicator plant for phytoremediation.

Rhizobacteria of Populus euphratica Promoting Plant Growth Against Heavy Metals

The heavy metal-resistant bacteria from rhizospheric soils of wild Populus euphratica forest growing in arid and saline area of northwestern China were investigated by cultivation-dependent methods. After screening on medium sparked with zinc, copper, nickel and lead, 146 bacteria strains with different morphology were isolated and most of them were found to be resistant to at least two kinds of heavy metals. Significant increase in fresh weight and leaf surface area of Arabidopsis thaliana seedlings under metal stress were noticed after inoculated with strains especially those having multiple-resistance to heavy metals such as Phyllobacterium sp. strain C65. Investigation on relationship between auxin production and exogenous zinc concentration revealed that Phyllobacterium sp. strain C65 produced auxin, and production decreased as the concentration of zinc in medium increased. For wheat seedlings treated with zinc of 2 mM, zinc contents in roots of inoculated plants decreased by 27% (P < 0.05) compared to the uninoculated control. Meanwhile, zinc accumulation in the above-ground tissues increased by 22% (P < 0.05). The translocation of zinc from root to above-ground tissues induced by Phyllobacterium sp. strain C65 helped host plants extract zinc from contaminated environments more efficiently thus alleviated the growth inhibition caused by heavy metals.

Isolation and molecular characterization of bacteria to heavy metals isolated from soil samples in Bokaro Coal Mines, India

In recent years, environmental pollution by coal mining is a long-established human activity affecting all levels of life with various environmental impacts by generating heavy metals. The presence of heavy metals even in trace amount is toxic and detrimental to all living organisms. The coal mine area in Bokaro is one of the “Toxic Hotspot” in India. Bacteria have evolved uptake and efflux mechanisms to adapt in heavy metals contaminated environments and thus represent a potential source for bioremediation processes. In the present study, we isolated and characterized eight heavy metal resistant bacteria (NK-1 to 8) from soil sample in Bokaro coal mines, India. Isolates were selected based on high level of heavy metal resistance and its biochemical characterization. The following bacteria were identified based on 16S rRNA gene sequencing Enterobacter ludwigii (KM029957; NK-1), Klebsiella pneumonia (KM029958; NK-2), Enterobacter ludwigii (KM029959; NK-3), Enterobacter ludwigii (KM029960; NK-4), Klebsiella oxytoca (KM029961; NK-5), Enterobacter cloacae (KM029962; NK-6), Acinetobacter gyllenbergii (KM029963; NK-7), Enterobacter cloacae (KM029964; NK-8). A high degree of metal resistance associated with multiple antibiotic resistances was also detected in the selected isolate which was confirmed by the presence of plasmid. These isolates can further be used for bioremediation of heavy metals from contaminated site.

Isolation and Molecular Characterization of Heavy Metal-Resistant Alcaligenes faecalis from Sewage Wastewater and Synthesis of Silver Nanoparticles

Environmental pollution with toxic heavy metals is increasing throughout the world alongside industrial development. Microorganisms and microbial products can be highly efficient bioaccumulators of soluble and particulate forms of metals, especially dilute external solutions. Microbe related technologies (Biotechnology) may provide an alternative or additive conventional method for metal removal or metal recovery. This study dealt with isolation, identification and characterization of heavy metal-resistant (Pb2+, Cd2+, Al3+, Cu2+, Ag2+ and Sn2+) bacteria from sewage wastewater at Taif Province, Saudi Arabia. Nine bacterial isolates were selected by using an enrichment isolation procedure based on high level of heavy metal resistance. All the isolates showed high resistance to heavy metals with Minimum Inhibitor Concentration (MIC) ranging from 800 μg/ml to 1400 μg/ml. All nine resistant isolates showed multiple tolerances to heavy metals. On the basis of morphological, biochemical and 16S rRNA characterization, the most potent isolates (Cd1-1, Ag1-1, Ag1-3 and Sn1-1) were identified as Alcaligenes faecalis. Scanning electron microscope analysis showed that the morphology of Alcaligenes faecalis Ag1-1 was unchanged after growth in medium without and with addition of Ag2+ indicative Ag2+ is not toxic to the isolate under the conditions tested. The ability of Alcaligenes faecalis Ag1-1 to synthesize sliver nanoparticles was examined. The heavy metal-resistant bacteria obtained could be useful for the bioremediation of heavy metal-contaminated environment.