Metal-tolerant Bacteria Research Articles

Antagonic and plant growth-promoting effects of bacteria isolated from mine tailings at El Fraile, Mexico

Mine tailings contain high concentrations of heavy metals such as As, Pb, Cu, Mn, and Fe, which are detrimental to the health of humans and the environment. In tailings at the El Fraile mine in Guerrero, Mexico, some plant species are apparently tolerant of heavy metals and can be found growing in the tailings. These plants could be associating with heavy metal-tolerant bacteria that promote plant growth and improve biomass production, and these bacteria could be a useful alternative for bacteria-assisted phytoremediation. The objective of this study was to isolate bacteria detected in the mine tailings at El Fraile-Taxco, focusing on those in the soil from the rhizosphere, the inner tissue of the root, leachate, and water, which have the potential to promote plant growth. The ability of the isolated bacteria to promote plant growth was evaluated in vitro. Of the 151 morphotypes isolated, 51% fix nitrogen, 12% dissolve phosphates, and 12%, 39.7%, and 48.3% produce indole acetic acid, gibberellins, and siderophores, respectively. In addition, 66.7% were observed to produce lytic enzymes, such as proteases, celluloses, lipases, esterases, and amylases, which exhibited activity against Fusarium, Aspergillus, and Colletotrichum. The use of 16S rRNA analysis led to the identification of the bacterial genera Chryseobacterium, Bacillus, Pseudomonas, Mycobacterium, Staphylococcus, Curtobacterium, Enterobacter, Agrobacterium, Ochrobactrum, Serratia, Stenotrophomonas, and Acinetobacter. The bacteria isolated from the rhizosphere exhibited the greatest ability to fix nitrogen and produced indole acetic acid, gibberellins, siderophore, and lytic enzymes. In addition, the isolates collected from the soil samples demonstrated ability to solubilize phosphate.

Inoculation of Cd-contaminated paddy soil with biochar-supported microbial cell composite: A novel approach to reducing cadmium accumulation in rice grains

Bioremediation of heavy metal-contaminated soil using metal-resistant microbes is a promising remediation technology. However, as exogenous bacteria sometimes struggle to survive and grow when introduced to new soils, it is important to develop appropriate carriers for microbial populations. In this study, we report a novel approach to remediating Cd-contaminated rice paddy soil using biochar-supported microbial cell composites (BMCs) produced from agricultural waste (cornstalks). Pot experiments showed that amendment with BMC was more efficient at reducing root and grain Cd content than pure bacteria, while improving soil Cd fractionation toward more stabilized and less labile forms. Bacteria in the BMC medium grew more readily with more abundant metabolites than those raised in free cells, probably because biochar provides shelter via porous structures (as confirmed by scanning electron microscopy) as well as additional nutrients. Overall, the improved long-term production of microbial biomass caused by BMC inoculation results in a higher remediation efficiency. Our results demonstrate the feasibility of using biochar as an appropriate carrier for metal-tolerant bacteria to remediate Cd-contaminated paddy fields.

Assessment of microbial diversity and enumeration of metal tolerant autochthonous bacteria from tailings of magnesite and bauxite mines

The magnesite and bauxite mines are a major source for some minerals and metals. The tailings of these magnesite and bauxite mines contains massive amount of Mn. (3221.2 ± 6.51 & 7102.8.4 ± 10.24), Cd (40.95 ± 2.12 & 892.86 ± 8.48), Zn (951.08 ± 4.31 &724.12 ± 3.18), and Pb (425.8 ± 5.21 & 812.13 ± 9.19 mg Kg−1) with alkaline and acid pH respectively. In the microbial diversity analysis, the results 8 (Thiobacillus thiooxidans, Leptospirillum ferrooxidans, Acetobacter methanolicus, T. intermedius, Bacillus cereus, Sulfobacillus acidophilus, Methylobacterium sp, and Thiobacillus ferooxidans) and 12 (Serratia marcescens, Metalogenium symbioticum 1, Metallogenium symbioticum 2, Bacillus alcalophilus, Aminobacter sp, Naumaniella neustonica, Staphylococcus aureus 1, Methylbacillus sp, Pandoraea sputorum, Acenetobacter sp, S. aureus 2, Pseudomonas aeruginosa) bacteria species were isolated from bauxite and magnesite mine tailings. The fungus such as Rhizopus arrhizus, Mucor sp, Aspergillus niger and Penicillium sp were obtained in both acid and alkaline environment. Among this microbial diversity, P. sputorum and B. cereus (identified through 16S rDNA sequencing) were shown better resistance to these four metals for up to 250 mg L−1. The bacterial diversity indexes, concludes that there was least diverse among the three sites. The evenness/equitability index also conform lower level of variation among these sites.

Root colonization by heavy metal resistant Enterobacter and its influence on metal induced oxidative stress on Cajanus cajan.

Heavy metal resistant bacterium Enterobacter sp. C1D was evaluated for cadmium (Cd) mediated exopolysaccharide production, biofilm formation and legume root colonization ability under Cd stress to alleviate metal induced stress. The plant was sensitive to Cd (IC50 3-4μg mL-1 ), whereas the bacterium showed high Cd tolerance (MIC99 120 μg mL-1 ). Confocal laser scanning microscopy of the Cajanus cajan roots showed heavy loads of green fluorescence protein labelled Enterobacter sp. C1D on the surface of plant root, specifically at the point of root hair/lateral root formation along with cortex, even under metal stress. The root colonizing ability of Enterobacter sp. C1D was not affected by the presence of Rhizobium and the bacteria could be observed after 30 days of incubation in soil. Various plant growth parameters, antioxidant metabolites and oxidative stress indicator were significantly influenced by bacterial treatment, which, overall, reduced the adverse effect of Cd. Heavy metal tolerant bacteria may be a good choice for the development of biofertilizers and may work well with the native soil microbes such as Rhizobium under the metal polluted soil. © 2019 Society of Chemical Industry.

Effect of basic oxygen furnace slag on succession of the bacterial community and immobilization of various metal ions in acidic contaminated mine soil

As an immobilizing agent for metal ions, basic oxygen furnace slag may affect bacterial community succession, thus further promote metal ion immobilization in acidic contaminated soil. In this work, pot experiments were conducted to study the effects of adding 10 g/kg (S10) and 15 g/kg (S15) slag on soil properties, plant growth, bacterial community succession and various metal ion immobilization in acidic mine soils contaminated by Pb, Zn, Cu, Cr and Cd. The results showed that after 93 days of potting, the soil pH, electrical conductivity, total nitrogen and organic carbon content increased significantly (P < 0.05), and the dry weight of Poa pratensis L. increased significantly (P < 0.05) in S10 and S15 compared with in original soil group. With slag addition and plant growth, the diversity and richness indices of bacterial communities greatly improved, and at the genus level, the abundance of metal-tolerant bacteria and bacteria beneficial to plant growth increased, while the abundance of acidophiles decreased. After adding slag to the soil, the various metals were immobilized because slag could not only immobilize metal ions through ion exchange and coprecipitation, but also benefit plant growth and bacterial community succession which further promote the immobilization of metal ions.

Copper oxide nanoparticles as an effective anti-biofilm agent against a copper tolerant marine bacterium, Staphylococcus lentus

Biofilm formation on antifouling coatings is a serious concern in seawater cooling systems and the maritime industry. A prolific biofilm forming strain (Staphylococcus lentus), possessing high tolerance (>1,000 µg ml−1) to dissolved copper ions (Cu++) was isolated from titanium coupons exposed in the coastal waters of Kalpakkam, east coast of India. S. lentus formed increased biofilm (p < 0.05) at 100 µg ml−1 of Cu++ ions, when compared with the untreated control. To combat biofilm formation of this strain, the efficacy of copper oxide nanoparticles synthesized from copper nitrate by varying the concentrations of hexamine and cetyl trimethyl ammonium bromide (CTAB), was investigated. Complete (100%) inhibition of biofilm formation was observed with plain CuO NP (0.5 M hexamine, uncapped) at 1,000 µg ml−1. Capping with CTAB, influenced the morphology and the purity of the synthesized CuO NPs but did not alter their surface charge. Capping reduced metal ion release from CuO NPs and their antibacterial and anti-biofilm property against S. lentus. Overall, uncapped CuO NPs were effective in controlling biofilm formation of S. lentus. Concurrent release of copper ions and contact mediated physical damage by CuO NPs offer a promising approach to tackle metal tolerant biofilm bacteria.

Bioremediation of Cadmium Contaminated Effluent by Sporosarcina luteola: A Bacterium Isolated from Soil near Wazirpur Industrial Area, New Delhi, India

Heavy metals pollution is emerging as a threat to ecological systems causing various problems to mankind, plants and animals. Aim of the present study was to isolate and identify cadmium tolerant bacteria from the soil of Wazirpur industrial area of New Delhi (India). The study involved physico-chemical characterization of the polluted soil which was found to contain high concentration of iron, manganese and cadmium at 352, 15.3 g/kg soil and 3.16 ppm, respectively. One bacterial strain was identified as Sporosarcina luteola on the basis of morphological, biochemical and phylogeny analysis. Strain Sporosarcina luteola was highly resistant to Cd up to 5mM (mM= millimolar) when cultured in solidified nutrient agar plates and 7.2 mM in nutrient broth. Sporosarcina luteola has also showed substantial growth in presence of Co, Pb, Fe and Mn upto 2.0, 2.0, 3.5 and 4.0 mM, respectively in liquid medium. Optimum growth of identified bacteria was shown at 37 ºC, 7.0 pH and it tolerated up to 3 % sodium chloride (w/v). This is reported for the first time that Sporosarcina luteola (metal-tolerant bacteria) has potential of removal of cadmium from industrially contaminated soil.

Kinetics of hydrocarbon degradation by a newly isolated heavy metal tolerant bacterium Novosphingobium panipatense P5:ABC

This study report kinetics of PAHs and crude oil degradation by a newly isolated multiple heavy metal tolerant Novosphingobium panipatense P5:ABC. The isolate showed hydrocarbon degrading enzyme activities namely alkane hydroxylase, catechol 1,2-dioxygenase and catechol 2,3-dioxygenase. The level of C23O activity was 9.63 times higher than C12O thus suggesting active involvement of meta-cleavage pathway. The data of biodegradation of hydrocarbons fitted well to the first order kinetic model. The degradation rate was highest for phenanthrene followed by crude oil, and fluoranthene. We have further reported the estimate of fundamental kinetic parameters, half-saturation constant (Ks) and maximum degradation rates (Vmax) for biodegradation of phenanthrene and fluoranthene. Overall characterization underscores the potential of Novosphingobium in bioremediation of crude oil polluted sites.

Isolasi dan identifikasi bakteri toleran logam berat dari sedimen mangrove di Pengudang dan Tanjung Uban, Pulau Bintan, Indonesia

&lt;strong&gt;Isolation and Identification of Heavy Metals Tolerant Bacteria from Mangrove Sediment in Pengudang and Tanjung Uban, Bintan Island, Indonesia&lt;/strong&gt;. Bacterial searches for remediation of heavy metal pollutants continue to be carried out due to the increasing pollution in the ecosystem as a result of industrialization. This research aims to identification bacteria strains that are tolerant of heavy metals from mangrove sediments in the Pengudang and Tanjung Uban, Bintan Island in 2018. Bacterial isolation was carried out by pour plate method and purified using marine agar (MA) medium. Screening of bacterial isolates was carried out by growing isolates on MA medium with the addition of 100 ppm Pb. In addition, the determination of minimum inhibitory concentration (MIC) was performed on the isolates were tolerant to Pb, Cu, and Cd by addition of heavy metals in 50-1000 ppm concentrations. Identification of heavy metal tolerant isolates was carried out by sequencing the 16S rRNA gene. The results of bacterial isolation from mangrove sediments obtained 48 isolates used for testing the ability of heavy metals tolerant. Screening tests showed that PGD1A, PGD5A, PGD22A, PGD1B, PGD9B, PGD5C, PGD6C, TJU1, TJU5, and TJU7 isolates were heavy metal resistant. The results showed that bacterial isolated from mangrove sediments had MIC values of 800-900 ppm for Pb, 100-800 ppm for Cu and 100-200 ppm for Cd. There are 3 isolates that have high resistance to three kinds of heavy metals such as Bacillus oceanisediminis PGD1A, Vibrio alginolyticus PGD5A, and Halobacillus kuroshimensis PGD9B. This indicates that the isolate can be used efficiently for removal of heavy metals from the ecosystem.

Multiple metal tolerance of Paenibacillus dentritiformis isolated from metal contaminated soils west Godavari district (Andhra Pradesh)

Sugar industrial effluents possess high amounts of toxic pollutants and contaminate the receiving sites. Treatment of contaminated sites by using microorganisms provides an alternate to conventional methods hence demands in the identification of metal tolerant microorganisms has been increasing day by day. Therefore in this study soil samples collected from Tanuku sugar factory residual effluent point (bank of Gosthani river), west Godavari district A.P were analyzed for the bacterial tolerance to Copper (Cu), Zinc (Zn) and Lead (Pb) in their chloride forms. Additionally, the study was carried out to identify the metal tolerant bacteria by morphological, biochemical and 16S rRNA gene sequencing studies. Four potential bacterial isolates were selected to analyze metal tolerance against CuCl2, ZnCl2, and PbCl2. The sequences were compared with those in NCBI and submitted in gene bank with accession numbers MK100333 (Paenibacillus cookie), MK100334 (Bacillus cereus), MK100335 (Aneurini bacillus sp) and MK100387 (Paenibacillus sp.). A Phylogenetic tree was constructed to Paenibacillus sp. the highly efficient bacterial strain among the four isolates using MEGA 7 soft ware. The results of this study showed that P. dentritiformis had multiple metal tolerances (Cu, Zn and Pb) up to 500mg/L after 72 hrs. The identified bacterial strain proved to be the strong heavy metal tolerant bacterial strain. Hence, its usage will be helpful in the treatment of heavy metals specifically Cu, Zn and Pb contaminated soils and further optimization of these cultures is required to improve its metal resistant capacity.

Microsegmented flow-assisted miniaturized culturing for isolation and characterization of heavy metal-tolerant bacteria

Soils are complex ecosystem, and their function in the environment is mainly determined by the microbial communities. Metal-tolerant micro-organisms have an important function in the formation of soil and the development of microbial communities in all areas where heavy metals are released by natural erosion processes or by human activities. The investigation of dose-dependent growth and behaviour is an essential part of the search for heavy metal-tolerant microorganism communities and their characterization. In this study, next-generation sequencing was used for the analysis of soil sample and reduced communities and droplet-based microfluidics was used to assess the growth behaviour of unknown bacterial communities and single strains in response to different heavy metal ions. Highly resolved dose–response functions of the bacterial communities reflect the specific character in their concentration-dependent response to different culture media and heavy metals of copper, nickel and cobalt. Besides the characterization of community responses, they allowed to characterize newly isolated strains. Concentration-dependent growth patterns of the micro-organisms in the droplets could be observed. The investigation demonstrates the potential of droplet-based microfluidics for miniaturized eco-toxicological studies and their suitability for the discovery of novel strains with special tolerance features.

Molecular insight into the expression of metal transporter genes in Chryseobacterium sp. PMSZPI isolated from uranium deposit.

Metal tolerant bacterium Chryseobacterium sp. PMSZPI previously isolated and characterized from uranium ore deposit was studied for elucidating the role of metal transporter genes belonging to the Cation Diffusion Facilitator (CDF), Root-Nodulation-Division (RND) and PIB-type ATPase family in cadmium and uranium tolerance. The bacterium showed tolerance towards cadmium (MIC~6mM) and uranium (MIC~2mM) and was found to harbor metal transporter genes belonging to CDF, RND and PIB-type ATPase family of proteins. Expression studies by real-time PCR showed an upregulation of czcA(RND), czcD(CDF) and cadA(PIB-type ATPase) genes in presence of cadmium or uranium. Higher expression of czcA and czcD was found when the bacterium was treated with cadmium and uranium respectively. This study provides significant insight into the molecular mechanism that plays a role in cadmium and uranium tolerance in bacteria.

Copper tolerance and antibiotic resistance in soil bacteria from olive tree agricultural fields routinely treated with copper compounds.

Heavy metal pollution may act as persistent selective pressure that favors the spread of antimicrobial resistance in natural environments. The aim of this study was to isolate and identify metal-tolerant bacteria from soils in olive tree fields routinely treated with copper-derived compounds and to evaluate the tolerance of bacterial strains to other metals and their resistance to clinically relevant antibiotics. Five hundred and ninety-five bacterial isolates from 45 olive tree agricultural fields were studied. Minimum inhibitory concentrations (MICs) ≥ 16 mmol L-1 were detected for copper (57% of isolates), zinc (37%) and lead (62%), while only 3% had MICs ≥ 12 mmol L-1 for nickel. Ninety-six metal-tolerant strains were selected for identification and antibiotic resistance determination. Most isolates belonged to the genera Pseudomonas (37%), Bacillus (23%) and Chryseobacterium (20%), while 6% were identified as Variovorax, 4% as Stenotrophomonas and 2% as Serratia or Burkholderia. Highest copper tolerance was detected among Pseudomonas. Over 75% of the strains with high copper tolerance were also resistant to vancomycin, 50% to ampicillin and 40% to erythromycin or trimethoprim/sulfamethoxazole. Bacteria from olive soils are tolerant to metals, mainly copper, but also zinc and lead, as well as resistant to clinically important antibiotics, which could be a troublesome issue in clinical settings. © 2019 Society of Chemical Industry.

Metal tolerant bacteria enhanced phytoextraction of lead by two accumulator ornamental species

Microbially enhanced availability and phytoextraction is a promising technique for phytoremediation of lead (Pb). In this study, Pb resistant strains were isolated and investigated for potential effects on plant growth and Pb phytoextraction. Incubation experiments were carried for inoculated and un–inoculated soil containing different levels of Pb. Results revealed that 20% of the isolated bacteria could tolerate Pb up to 800 mg L−1. Five Pb resistant strains with plant growth promoting (PGP) abilities were evaluated for possible influence on water soluble Pb through soil incubation experiments and significant increase i.e. 1.85– and 1.49–folds in water soluble Pb was observed for NCCP–1848 and NCCP–1862 strains, respectively. Pot experiments indicated significantly higher uptake by Pelargonium hortorum than that by Mesembryanthemum criniflorrum at all levels of soil Pb concentrations with the highest increase (1.9–folds) in plants inoculated with NCCP–1848 followed by NCCP–1862 (1.8–folds increase) compared to the control (Pb and without bacterial strain). The strains NCCP–1848 and NCCP–1862 were identified by 16S rRNA gene sequencing as Microbacterium sp. and Klebsiella sp. The results of present study suggest that Pb resistant plant growth promoting bacteria can serve as an effective bio–inoculant through wide action spectrum for maximizing efficiency of phytoremediation system.

The role of biochar-microbe interaction in alleviating heavy metal toxicity in Hordeum vulgare L. grown in highly polluted soils

The influence of heavy metal-tolerant bacteria, biochar, and their joint application on Hordeum vulgare L., grown in highly polluted soils was analysed for the first time. The high concentrations of heavy metals (HMs) (Zn, Mn, Cr, Cu, Pb, Ni, Cd) were determined in the polluted soil (Spolic Technosol) obtained from the Lake Atamanskoe. The effects of these HMs led to marked differences in H. vulgare L. growth. HMs toxicity slows down the development of the plant by changing morphometric parameters. Application of biochar and microbes reduced the HMs accumulation and enhanced H. vulgare L. growth compared with plants grown in polluted soil without amendments. However, all treatments showed high accumulation of HMs in above- and underground tissues as compared with plants grown in unpolluted soil. The application of biochar and HM-tolerant bacteria decreased the HM content 1.78–9.23 fold and 1.79–5.30 fold, respectively, while the addition of both bacteria and biochar has led to a 3.11–17 fold decrease in HMs content and was the most effective to decrease the translocation of all the studied metals. The metal-tolerant bacteria influenced the plant growth to a large extent. The most prominent impact of biochar + bacteria application was observed for leaves length and dry weight of plants: the parameters were significantly higher and reached those of unpolluted control. However, all of the tested amendments improved the growth performance of plants in polluted soil. The alleviation of metal toxicity by the addition of biochar may be beneficial for the introduced bacteria and increase their activity.

Effects of modified carbon black nanoparticles on plant-microbe remediation of petroleum and heavy metal co-contaminated soils

Little is known about the effect of modified carbon black nanoparticles (MNCB) on the availability of heavy metals and petroleum degradation in petroleum and heavy metals co-contaminated soils. The overall objective of this study was to investigate the simultaneous effect of MNCB on heavy metal immobilization and petroleum biodegradation in co-contaminated soil in plant and plant-microbe combined remediation. The results showed that the petroleum degradation increased by 50% in petroleum-Cd co-contaminated soil and 65% in petroleum-Ni co-contaminated soil in plant-microbe combined remediation, comparing with the plant remediation and the application of MNCB did not show significant improvement on petroleum degradation in both plant and plant-microbe combined remediation. MNCB could significantly reduce the availability of heavy metals in soil and the uptakes of Cd and Ni by Suaeda salsa by roughly 18 and 10% and improve the growth of plant by alleviating the growth inhibition caused by heavy metals. The application of Bacillus subtilis and Sphingobacterium multivorum (heavy metal tolerant bacteria) inhibited the biomass of Suaeda salsa by enhancing the petroleum degradation. It could be concluded that MNCB played a major role in immobilizing the heavy metals and bacteria dominated the petroleum degradation in petroleum-metal co-contaminated soil.

Heavy metal mediated phytotoxic impact on winter wheat: oxidative stress and microbial management of toxicity by Bacillus subtilis BM2.

Heavy metals are toxic environmental contaminants, which severely affect microbial composition and functions and, concurrently, crop production. Due to these issues, the present study focussed on the selection of metal tolerant microbes endowed with metal detoxification abilities and their role in the management and remediation of metal contaminated soils. The metal tolerant bacterium BM2, identified as Bacillus subtilis by 16SrRNA gene sequencing, survived well under metal pressure and tolerated 1600 and 2000 μg mL−1 of Ni and Pb, respectively. The inhibitory impact of metals on wheat increased consistently with a progressive increase in metal concentration. Deposition of Ni and Pb within root and leaf and oxidative stress were validated by SEM, EDX and CLSM. The overall growth parameters of wheat grown under metal stress were improved following B. subtilis BM2 colonization. As an example, B. subtilis with 195 mg Pb kg−1 enhanced the length and dry biomass of shoots by 14% and 23%, respectively, over the control. Also, strain BM2 improved the grain yield significantly by 49% at 870 mg Ni kg−1 and by 50% at 585 mg Pb kg−1 compared to uninoculated plants. Moreover, B. subtilis BM2 relieved the metal stress on wheat and caused a significant drop in proline and malondialdehyde content and the activities of antioxidant enzymes, like catalase (CAT), superoxide dismutase (SOD) and glutathione reductase (GR). This study, therefore, provided solutions to the metal toxicity problems faced by winter wheat and clearly suggests that the metal detoxification potential of B. subtilis BM2 could be greatly useful in the management of metal polluted soils.

Effective production of keratinase by gellan gum-immobilised Alcaligenes sp. AQ05-001 using heavy metal-free and polluted feather wastes as substrates.

The ability of gellan gum-immobilised cells of the heavy metal-tolerant bacterium Alcaligenes sp. AQ05-001 to utilise both heavy metal-free and heavy metal-polluted feathers (HMPFs) as substrates to produce keratinase enzyme was studied. Optimisation of the media pH, incubation temperature and immobilisation parameters (bead size, bead number, gellan gum concentration) was determined for the best possible production of keratinase using the one-factor-at-a-time technique. The results showed that the immobilised cells could tolerate a broader range of heavy metal concentrations and produced higher keratinase activity at a gellan gum concentration of 0.8% (w/v), a bead size of 3mm, bead number of 250, pH of 8 and temperature of 30°C. The entrapped bacterium was used repeatedly for ten cycles to produce keratinase using feathers polluted with 25ppm of Co, Cu and Ag as substrates without the need for desorption. However, its inability to tolerate/utilise feathers polluted with Hg, Pb, and Zn above 5ppm, and Ag and Cd above 10ppm resulted in a considerable decrease in keratinase production. Furthermore, the immobilised cells could retain approximately 95% of their keratinase production capacity when 5ppm of Co, Cu, and Ag, and 10ppm of As and Cd were used to pollute feathers. When the feathers containing a mixture of Ag, Co, and Cu at 25ppm each and Hg, Ni, Pb, and Zn at 5ppm each were used as substrates, the immobilised cells maintained their operational stability and biological activity (keratinase production) at the end of 3rd and 4th cycles, respectively. The study indicates that HMPF can be effectively utilised as a substrate by the immobilised-cell system of Alcaligenes sp. AQ05-001 for the semi-continuous production of keratinase enzyme.

Isolation, Characterization and Symbiotic Efficiency of Nitrogen-Fixing and Heavy Metal-Tolerant Bacteria from a Coalmine Wasteland

ABSTRACT: Areas affected by coal mining can be recovered by revegetation with leguminous plants associated with nitrogen-fixing bacteria. This study addressed the isolation and characterization of native nitrogen-fixing bacteria from coalmine wasteland under different vegetation restoration approaches using Macroptilium atropurpureum (DC) Urb and Vicia sativa L. as trap plants. The bacteria were characterized and identified on the basis of 16S rRNA sequences. Additionally, nitrogen-fixing strains were characterized for tolerance to high heavy metal and low pH levels, as well as [...]

Metal-immobilizing Serratia liquefaciens CL-1 and Bacillus thuringiensis X30 increase biomass and reduce heavy metal accumulation of radish under field conditions

In this study, metal-tolerant bacteria Serratia liquefaciens CL-1 and Bacillus thuringiensis X30 were compared for their Cd and Pb immobilization in solution and impacts on biomass and Cd and Pb uptake in a radish in metal-contaminated soils under field conditions. Strains CL-1 and X30 significantly reduced water-soluble Cd and Pb concentrations (45–67%) and increased the pH in solution compared to the controls. These strains significantly increased the biomass (25–99%) and decreased edible tissue Cd and Pb uptake in the radish (37–81%) and DTPA-extractable Cd and Pb contents (18–44%) of the rhizosphere soil compared to the un-inoculated controls. Strain CL-1 had higher potential to reduce edible tissue Cd and Pb uptake in the radish and DTPA-extractable Cd content than strain X30. Also, these strains significantly increased Cd translocation factor and strain CL-1 also significantly increased Pb translocation factor of the radish. Furthermore, strain CL-1 significantly increased the ratio of small soil aggregates (< 0.25 mm and 0.25–0.50 mm) of the rhizosphere soil. The results showed that these strains reduced the edible tissue Cd and Pb uptake through decreasing Cd and Pb availability in the soil and increasing Cd or Pb translocation from the roots to the leaves of the radish. The results also suggested the bacteria-related differences in reduced heavy metal uptake in the radish and the mechanisms involved under field conditions.