Metal-resistant Bacteria Research Articles

Heavy Metal Resistant Bacteria from Soil as Potential Bioremediation Targets: Isolation, Screening andamp; Biochemical Identification

This study investigates the role of bacterial species capable of mitigating metal-induced toxicity by bioaccumulation and biotransformation. Study focuses on five metals including Pb+2, Ni+2, Cd+2, Cr+2, and Cu+2 in a range of 50-300and#181;g/ml of concentration initially in qualitative (metal-specific) and subsequently quantitative (dose-specific) approach, but results turned out to be much in favor of a quantitative impact of the study. Thirty 30 bacterial strains from soil were isolated and biochemically identified that showed promising metal-resisting behavior. Identification of bacterial strain was based upon biochemical (phenotypic) method. The isolate number 1, 12, 29 and 30 showed high degree of resistance against all metals of concentration up to 300and#181;g/ml suggesting the potential possibility of these species of bacteria to provide some beneficial tools for bio-mining, and bioremediation as well as removing of metal contaminations from heavy metal contaminated sites.

An insight into the mechanism of ‘symbiotic-bioremoval’ of heavy metal ions from synthetic and industrial samples using bacterial consortium

Abstract Almost all the compartments of the environment have been severely polluted by heavy metals anthropologically, rendering its intrinsic values. In this approach, the present work has been aimed at developing a consortium of heavy metal resistant bacteria isolated from various wastewater sites. The designed bioaugmentation was aimed to specifically remove lead (Pb 2 + ) and nickel (Ni 2 + ) metal ions from the aqueous solutions. From the total 17 different industrial collection sites, 2 strains viz. Bacillus cereus and Bacillus pumilus have shown remarkable removal of Pb 2 + (95.93%) and Ni 2 + (95.54%) ions from the wastewater samples. The influential parameters like pH, incubation time, inoculum size, and initial metal concentration have been monitored for better insight into the interactional mechanism. The mechanism of heavy metals removal involves uptake of metal ions (Pb 2 + and Ni 2 + ) by means of complex formation, crystallization, and surface adsorption; invigorated with intracellular uptake and stabilization. The obtained results witness the hauling potential of the B. cereus and B. pumilus against the removal of bioavailable fractions of heavy metals thus projects of their practice on a commercial level.

Can biochar regulate the fate of heavy metals (Cu and Zn) resistant bacteria community during the poultry manure composting?

In this study, the influence of coconut shell biochar addition (CSB) on heavy metals (Cu and Zn) resistance bacterial fate and there correlation with physicochemical parameters were evaluated during poultry manure composting. High-throughput sequencing was carried out on five treatments, namely T1−T5, where T2 to T5 were supplemented with 2.5%, 5%, 7.5% and 10% CSB, while T1 was used as control for the comparison. The results of HMRB indicated that the relative abundance of major potential bacterial host altered were Firmicutes (52.88–14.32%), Actinobacteria (35.20–4.99%), Bacteroidetes (0.05–15.07%) and Proteobacteria (0.01–20.28%) with elevated biochar concentration (0%−10%). Beta and alpha diversity as well as network analysis illustrated composting micro-environmental ecology with exogenous additive biochar to remarkably affect the dominant resistant bacterial community distribution by adjusting the interacting between driving environmental parameters with potential host bacterial in composting. Ultimately, the amendment of 7.5% CSB into poultry manure composting was able to significantly reduce the HMRB abundance, improve the composting efficiency and end product quality.

Cobalt Resistance via Detoxification and Mineralization in the Iron-Reducing Bacterium Geobacter sulfurreducens.

Bacteria in the genus Geobacter thrive in iron- and manganese-rich environments where the divalent cobalt cation (CoII) accumulates to potentially toxic concentrations. Consistent with selective pressure from environmental exposure, the model laboratory representative Geobacter sulfurreducens grew with CoCl2 concentrations (1 mM) typically used to enrich for metal-resistant bacteria from contaminated sites. We reconstructed from genomic data canonical pathways for CoII import and assimilation into cofactors (cobamides) that support the growth of numerous syntrophic partners. We also identified several metal efflux pumps, including one that was specifically upregulated by CoII. Cells acclimated to metal stress by downregulating non-essential proteins with metals and thiol groups that CoII preferentially targets. They also activated sensory and regulatory proteins involved in detoxification as well as pathways for protein and DNA repair. In addition, G. sulfurreducens upregulated respiratory chains that could have contributed to the reductive mineralization of the metal on the cell surface. Transcriptomic evidence also revealed pathways for cell envelope modification that increased metal resistance and promoted cell-cell aggregation and biofilm formation in stationary phase. These complex adaptive responses confer on Geobacter a competitive advantage for growth in metal-rich environments that are essential to the sustainability of cobamide-dependent microbiomes and the sequestration of the metal in hitherto unknown biomineralization reactions.

Wheat-associated Pseudomonas taiwanensis WRS8 reduces cadmium uptake by increasing root surface cadmium adsorption and decreasing cadmium uptake and transport related gene expression in wheat.

Metal-resistant bacteria can reduce Cd accumulation in plants, but mechanisms underlying this effect are poorly understood. In this study, a highly effective Cd-resistant WRS8 strain was obtained from the rhizoshere soil of Triticum aestivum L. Yangmai-13 and identified as Pseudomonas taiwanensis based on 16S rRNA gene sequence analysis. Strain WRS8 was investigated for its effects on Cd availability and wheat tissue Cd contents and the related mechanisms using a hydroponic culture experiment. In strain WRS8-inoculated solution, the Cd concentration reduced and the pH and cell-adsorbed Cd increased with time. Strain WRS8 increased the wheat root and above-ground tissue dry weights by 11-36% compared to the controls. In strain WRS8-inoculated wheat plants, the Cd contents of the roots and above-ground tissues decreased by 78-85% and 88-94% and the Cd bioconcentration and translocation factors decreased by 78-85% and 46-58% at days 3 and 10, respectively, compared with the controls. The root surface-adsorbed Cd contents increased by 99-121% in the WRS8 strain-inoculated wheat plants at days 3 and 10 compared to the controls. Furthermore, strain WRS8 colonized the wheat root surfaces and interiors and reduced the expression levels of the LCT1 and HMA2 genes involved in Cd accumulation and transport in wheat roots by 46% and 30%, respectively, compared to the controls. In the Cd-contaminated soils, strain WRS8 significantly reduced the available Cd content by 20-24% and increased the pH compared to the controls. These findings showed the important role of strain WRS8 in reducing solution and soil Cd availability and suggested that strain WRS8 reduced the wheat tissue Cd accumulation by increasing root surface Cd adsorption and decreasing wheat root Cd uptake and transport-related gene expression and may provide a new and effective wheat rhizobacteria-enhanced approach for reducing wheat Cd uptake in Cd-polluted environments.

Microbacterium sp. MRS-1, a potential bacterium for cobalt reduction and synthesis of less/non-toxic cobalt oxide nanoparticles (Co3O4)

BackgroundDetoxification of heavy metal pollutants in wastewater has become a serious problem to surrounding environment. This research was conducted to utilize a potential heavy metal-resistant bacterium for the remediation of cobalt metal and simultaneous synthesis of cobalt oxide nanoparticles in the form of powder for various industrial applications. Metal oxide nanoparticles have great applications in electrochemical devices such as supercapacitors, biosensors, and batteries.MethodA heavy metal-resistant bacterium Microbacterium sp. MRS-1 isolated from electroplating industrial effluent reduced cobalt ions from an initial concentration of 200 mg/L to 26 mg/L were analyzed by atomic absorption spectroscopy. Instrumental analysis of bacterially synthesized Co3O4 has been characterized. Cytotoxicity of synthesized nanoparticles was assessed by MTT assay.ResultsMicrobacterium sp. MRS-1 isolated from electroplating industrial effluent was found to be suitable for cobalt oxide nanoparticles as it showed tolerance towards high concentration of metal. The nutrient broth containing metal solution and Microbacterium sp. MRS-1 showed color change from light pink to dark pink indicated the formation of extracellular nanoparticles. It also converted soluble cobalt salts into less soluble cobalt oxide nanoparticles outside the cell which allows easy recovery of nanoparticles without the destruction of cells and simultaneous detoxification of toxic metal ions. Electron microscopic imaging verified that nanoparticles were predominantly surrounding the bacterial cells and SEM imaging revealed that the produced particles were in the range of 10–100 nm in size. XRD spectrum exhibited 2θ values were corresponding to cubic face-centered cobalt oxide (Co3O4) nanoparticles.ConclusionThe present study investigated new prospective for eco-friendly detoxification of toxic heavy metal Co from metal-polluted sites and the production of cobalt oxide nanoparticles in powder form for clinical and other industrial applications.

Antibiotic and Heavy Metal Resistant Bacteria Isolated from Aegean Sea Water and Sediment in Güllük Bay, Turkey

Heavy metal and antibiotic-resistant bacteria have potential for environmental bioremediation applications. Resistant bacteria were investigated in sediment and seawater samples taken from the Aegean Sea, Turkey, between 2011 and 2013. Bioindicator bacteria in seawater samples were tested using the membrane filtration technique. The spread plate technique and VITEK® 2 Compact 30 micro identification system were used for heterotrophic aerobic bacteria in the samples. The minimum inhibition concentration method was used for heavy metal-resistant bacteria. Antibiotic-resistant bacteria were tested using the disk diffusion method. All bacteria isolated from sediment samples showed 100% resistance to rifampicin, sulfonamide, tetracycline and ampicillin. 98% of isolates were resistant against nitrofurantoin and oxytetracycline. Higher antibiotic and heavy metal resistance was recorded in bacteria isolated from sediment than seawater samples. The highest levels of bacterial metal resistance were recorded against copper (58.3%), zinc (33.8%), lead (32.1%), chromium (31%) and iron (25.2%). The results show that antibiotic and heavy metal resistance in bacteria from sediment and seawater can be observed as responses to environmental influences including pollution in marine areas.

Impact of Plant Growth Promoting Bacteria on Salicornia ramosissima Ecophysiology and Heavy Metal Phytoremediation Capacity in Estuarine Soils.

Salicornia ramosissima is a C3 halophyte that grows naturally in South Western Spain salt marshes, under soil salinity and heavy metal pollution (mostly Cu, Zn, As, and Pb) caused by both natural and anthropogenic pressure. However, very few works have reported the phytoremediation potential of S. ramosissima. In this work, we studied a microbe-assisted phytoremediation strategy under greenhouse conditions. We inoculated plant growth promoting (PGP) and heavy metal resistant bacteria in pots with S. ramosissima and natural non-polluted and polluted sediments collected from Spanish estuaries. Then, we analyzed plant ecophysiological and metal phytoaccumulation response. Our data suggested that inoculation in polluted sediments improved S. ramosissima plant growth in terms of relative growth rate (RGR) (32%) and number of new branches (61%). S. ramosissima photosynthetic fitness was affected by heavy metal presence in soil, but bacteria inoculation improved the photochemical apparatus integrity and functionality, as reflected by increments in net photosynthetic rate (21%), functionality of PSII (Fm and Fv/Fm) and electron transport rate, according to OJIP derived parameters. Beneficial effect of bacteria in polluted sediments was also observed by augmentation of intrinsic water use efficiency (28%) and slightly water content (2%) in inoculated S. ramosissima. Finally, our results demonstrated that S. ramosissima was able to accumulate great concentrations of heavy metals, mostly at root level, up to 200 mg Kg–1 arsenic, 0.50 mg Kg–1 cadmium, 400 mg Kg–1 copper, 25 mg Kg–1 nickel, 300 mg Kg–1 lead, and 300 mg Kg–1 zinc. Bioaugmentation incremented S. ramosissima heavy metal phytoremediation potential due to plant biomass increment, which enabled a greater accumulation capacity. Thus, our results suggest the potential use of heavy metal resistant PGPB to ameliorate the capacity of S. ramosissima as candidate for phytoremediation of salty polluted ecosystems.

Sustainable conversion of palm juice wastewater into extracellular polysaccharides for absorption of heavy metals from Saudi Arabian wastewater

The main aim of the study was to use palm juice wastewater as an alternative feedstock for the production of extracellular polysaccharide and to remove heavy metals from the wastewater. Heavy metal resistant bacteria were screened from soil sediment samples, and metal resistant properties were analysed. A total of five bacterial strains were selected for the analysis of maximum tolerance limit against five toxic heavy metals (Cu2+, Cd2+, Pb2+, Co2+ and Zn2+). Among the five bacterial strains, Pseudomonas aeruginosa Al-Dhabi144 showed resistance against Cu2+, Cd2+, Pb2+, Cu2+ and Zn2+ and maximum tolerance limit was 400, 350, 2000, 100 and 350 mg/L, respectively. Wastewater was used as the feedstock for the production of extracellular polysaccharide in submerged fermentation. Extracellular polysaccharide production was enhanced after 72 h incubation (4.8 ± 0.37 g/L), 1.5% inoculums (4.96 ± 0.15 g/L), 10% date syrup wastewater (8.3 ± 0.041 g/L), pH 7.5 (7.9 ± 0.059 g/L), 0.5% yeast extract (8.1 ± 0.074 g/L) and 0.5% starch (9.74 ± 0.036 g/L). The metal-absorption properties of extracellular polysaccharides revealed that P. aeruginosa Al-Dhabi144 extracellular polysaccharides had the ability to remove Cu2+ (300 ± 5.3 mg/g), Cd2+ (250 ± 10.4 mg/g), Pb2+ (380 ± 5.1 mg/g), Co2+ (225 ± 5.6 mg/g) and Zn2+ (250 ± 10.7 mg/g) from the wastewater.

Plasmid Profiling and Effect of Different Physiological Parameters on the Chromium Reduction Potential of Microbes

Chromium is toxic for both human and aquatic life. It is recommended to eradicate from wastewaters or to alter its oxidation state to less toxic level The purpose of current research was to isolate heavy metal (Cr) resistant bacteria from different industrial effluents (soil and waste water), to determine their potential for chromium reduction (CRP) at different parameters (time period, pH, temperature and concentrations of chromium) and to determine the plasmid profiles of Cr (VI) resistant bacterial isolates. The growth of chromium resistant bacteria was determined by checking the influence of pH, concentration of chromium, time period and temperature on isolates using UV spectrophotometer, while chromium reduction potential was also investigated using Deleo and Ehrlich method. Plasmid profiling was performed and analyzed using agarose gel electrophoresis (0.8%) to determine the number, size and relationship of plasmid with heavy metal resistance. Results showed that the identified bacterial isolates (S. aureus and S. epidermidis) were resistant to heavy metal (Cr) confirmed by resistance profiling. The maximum growth of bacterial isolate was recorded after 24-hour incubation period (1.154), at pH 8 (1.512), temperature 37ºC (1.615) and 500 µg/mL chromium concentration (1.978), while suitable conditions observed for chromium reduction potential was 24-hour incubation period (57%), pH 7 (62.6%), temperature 30ºC (60%), and 500 µg/mL concentration of chromium (60%). The plasmid profiles revealed that plasmid were randomly distributed among the bacterial isolates with average plasmid number (2.9) ranging from 0-5 and molecular size (100-12000bps). Overall, no defined relationship was observed among resistance pattern and plasmid mediated profiles.

Role of Heavy Metal Resistant Bacteria for Bioremediation of Polluted Environment

Bioremediation refers to the use of microorganisms to reduce or eliminate contaminants from water and soil. In the current research, different bacterial strains were screened for their chromate and arsenate reduction potential. For the removal of arsenic, eight arsenic resistant bacterial strains AsK03, AsK04, AsK06, AsK07, AsK08, AsK09, AsK15 and AsK18 and for chromium removal, eight chromium resistant bacterial strains CrK02, CrK08, CrK12, CrK14, CrK16, CrK19, CrK20 and CrK21 were isolated and selected, respectively, from several contaminated soil and water samples taken from tanneries located in Kasur. Resistance to chromium and arsenic was shown by all the strains on nutrient agar at preliminary concentration of 500 µg ml-1 . The maximum tolerable concentration (MTC) of these isolates was also studied. It was found that for arsenic resistance, two strains AsK04 and AsK09 had highest MTC of 100 mg ml-1 , AsK18 had 75 mg ml-1 , AsK03, AsK06 and AsK15 had 50 mg ml-1 and AsK07 and AsK08 had 45 mg ml-1 of Na2HAsO4 concentration. Similarly, chromium resistant strains were also checked for their MTC against K2CrO4. Here MTC of CrK16 and CrK19 were highest (75 mg ml-1 ), CrK08 and CrK12 were 50 mg ml-1 , CrK02 and CrK20 were 25 mg ml-1 , CrK14 and CrK21 had least MTC of 7.5 mg ml-1 . Fifteen of the bacterial strains were genetically identified by sequencing of 16S rRNA gene. BLAST analysis revealed that the seven strains are homologous to genus Bacillus.

Molecular characterization, antibiogram and distribution of zntA gene in zinc-resistant Escherichia coli population recovered from anthropogenically-influenced surface water sources in Nigeria

BackgroundAnthropogenic activities have been largely responsible for the elevated concentration of metals in the environment. The presence of these metals has necessitated the acquisition of resistance mechanisms by bacteria to metals and other environmental toxicants. This study aimed at investigating the occurrence and distribution of zntA gene, and antibiogram of zinc-resistant Escherichia coli (E. coli) from selected anthropogenically-influenced surface waters in Ibadan, Nigeria. MethodsWater samples were collected and analyzed for zinc concentration using atomic absorption spectrophotometer. Zinc-resistant E. coli were isolated on CHROMagar E. coli incorporated with 1 mM of zinc salt and antibiotic susceptibility testing on the isolates was carried out using the disc diffusion method. The identity of the isolates was confirmed by detecting the presence of uidA gene using specific primers, while the detection of zinc resistance gene (zntA) was done using polymerase chain reaction (PCR). ResultsThe zinc concentrations in the surface water samples were: AG (6.12 mg/L), ZAR (5.54 mg/L), UB (0.01 mg/L) and OG (6.61 mg/L). A total of fifty-four zinc-resistant E. coli were obtained. The percentage resistance to the antibiotics was: ampicillin (92.6%), imipenem (77.8%), amoxicillin-clavulanate (68.5%), sulfamethoxazole-trimethoprim (53.7%), doxycycline (68.5%), cefotaxime (27.8%), ciprofloxacin (7.41%), colistin sulphate (13%), chloramphenicol (1.9%) and gentamicin (0%). zntA gene was detected in fifteen (27.8%) of the isolates, while fifty-one (94.4%) of the isolates were multidrug resistant (MDR). ConclusionThis study has confirmed that surface waters in South-west Nigeria could be potential reservoirs of metal and antibiotic resistant bacteria and their genes.

Enterococci and Bacilli from surface water: assessment of their resistance to copper and antibiotics

Heavy metal-resistant bacteria can be efficient bioremediators of metals and might provide an alternative method for metal removal in contaminated environments. The present study aims to isolate bacteria from the aquatic environment and evaluate their potential tolerance to copper metal, aiming at bioremediation processes. Also, compare co-resistance to heavy metal and antibiotics. The morphology of isolates was observed, and sequence analysis (16S ribosomal DNA) revealed that isolated strains were closely related to species belonging to the genera Enterococcus and Bacillus. Bacterial isolates were resistant to CuSO4, with a minimum inhibitory concentration of 0.78 mg ml-1. Enterococcus lactis was resistant to a combination of copper and tetracycline. The other tested isolates were sensitive to the tested antimicrobials. The metal removal ability of these isolates was assayed using atomic absorption spectroscopy, and the strains 27, 23, and E. lactis were best at removing heavy metals, at 87.7%. Enterococcus casseliflavus EC55 was 62%, followed by Bacillus aerius (18.4%), E. casseliflavus EC70 (10%) and Bacillus licheniformis (10%). Based on our findings, Enterococcus sp and Bacillus sp. have potential applications in enhanced remediation of contaminated environments.

Bacterial diversity on an abandoned, industrial wasteland contaminated by polychlorinated biphenyls, dioxins, furans and trace metals

Most former industrial sites are contaminated by mixtures of trace elements and organic pollutants. Levels of pollutants do not provide information regarding their biological impact, bioavailability and possible interactions between substances. There is genuine interest in combining chemical analyses with biological investigations. We studied a brownfield where several industrial activities were carried out starting in the 1970s, (incineration of pyralene transformers, recovery of copper by burning cables in the open air). Four representative plots showing different levels of polychlorobiphenyls were selected. Organic and trace metal levels were measured together with soil pedological characteristics. The bacterial community structure and functional diversity were assessed by 16S metagenomics with deep sequencing and community-level physiological profiling. Additionally, a vegetation survey was performed. Polychlorobiphenyls (8 mg.kg−1 to 1500 mg.kg−1) were from 2.4 × 103-fold to 6 × 105-fold higher than the European background level of 2.5 μg.kg−1. Polychlorinated dibenzo-p-dioxins and dibenzofurans ranged from 0.5 to 8.0 μg.kg−1. The soil was also contaminated with trace metals, i.e., Cu > 187, Zn > 217 and Pb > 372 mg.kg−1. Location within the study area, trace metal content and soil humidity were stronger determinants than organic pollutants of bacterial community structures and activities. Thus, the highest biological activity and the greatest bacteriological richness were observed in the plot that was less contaminated with trace metals, despite the high level of organic pollutants in the plot. Moreover, trace element pollution was associated with a relatively low presence of Actinobacteria and Rhizobia. The plot with the highest metal contamination was rich in metal-resistant bacteria such as Sphingomonadales, Geodermatophilaceae and KD4–96 (Chloroflexi phylum). Acidobacteria and Sphingomonadales, capable of resisting trace metals and degrading persistent organic pollutants, were dominant in the plots that had accumulated metal and organic contamination, but bacterial activity was lower in these plots than in the other plots.

Ekplorasi dan Karakterisasi Biokimia Bakteri Resisten Timbal (Pb) dari Sungai Tallo Makassar

Industrial progress and waste of urban domestic activities have an impact on the Pb heavy metal pollution on the environment, this will have an impact on human health. Pb metal can be overcome with biological methods by utilizing bacteria in reducing Pb metal. The study aimed to obtain the species of resistant bacterial isolates of Pb metal and determine its characteristics. Sediment and water samples were obtained from the Tallo River. Isolation and selection of Pb metal resistant bacteria were carried out on nutrient agar media is 10 ppm added of PbAgNO3, afterwards the colonies that grew and differed were characterized by morphological morphology and several biochemical tests. The characterization results obtained 8 isolates of Pb metal resistant bacteria consisted of 8 isolates from sediment samples and 3 isolates from water samples. The characteristics of each bacterial isolate on cell morphology are the same and biochemical tests show different results.

Distinction between Cr and other heavy–metal–resistant bacteria involved in C/N cycling in contaminated soils of copper producing sites

For typical copper producing provinces of Heilongjiang, Henan, Inner Mongolia, Jiangxi, Shandong, Tibet, and Yunnan in China, 90 % of sampling sites were heavily polluted with multiple heavy metals. Soil heterogeneity and mutual interference of multimetals are obstacles to explore bacterial resistance pathways in contaminated field soils. Through analyses of contamination indices and bioindicators, combined with multivariate statistical models, the antioxidant enzyme activity, urease–induced precipitation of heavy metals, excretion of extracellular polymeric substances (EPS) were attributed to different types of heavy metals. Furthermore, through redundancy analysis combined with phylogenetic analysis of metal–resistant bacteria, we identified that Verrucomicrobia, Acidobacteria, and Planctomycetes secreted EPS–polysaccharides and EPS–proteins to detoxify Cr, a metal with lower concentrations and lower ecological risk as compared to other metals. The pathway was innovatively differentiated from the multimetal resistance pathways in urease and/or catalase–producing bacteria such as Proteobacteria, Firmicutes, BRC1, Bacteroidetes, Dadabacteria, Entotheonellaeota, Nitrospirae, and Gemmatimonadetes using field studies and high–throughput sequencing. Moreover, these metal–resistant bacteria were linked to C/N cycling processes of urea hydrolysis, nitrification, denitrification, EPS production, and calcite precipitation. It will provide new insight into soil bacterial resistance to multimetals in field studies.

Deciphering the toxic effects of metals in gold mining area: Microbial community tolerance mechanism and change of antibiotic resistance genes

Mine tailing dumps represent significant threats to ecological environments due to the presence of toxic substances. The present work investigated the relationship among microbial activity, the community, antibiotic resistance genes (ARGs) and trace metals in soil surrounding gold mine tailings. Using microbial metabolic activity and high-throughput sequencing analysis, we found the trace metals Cd and Hg could be main factors influencing the microbial community. According to bacterial co-occurrence pattern analysis, the effects of total cadmium and total mercury on bacterial diversity are potentially mediated by influencing bacteria community in the keystone module II. Additionally, most of metal-resistant bacteria belong to Actinobacteria and Proteobacteria, and the metal tolerance suggested to be linked with various functions including replication, recombination and repair, as well as inorganic ion transport and metabolism based on PICRUSt2 analysis. We also found that metals generated by mining activity may trigger the co-selection of antibiotic resistance in the phyla Actinobacteria and Proteobacteria due to co-resistance or cross resistance. Additionally, PLS-PM analysis revealed that metals could indirectly affect ARGs by influencing bacterial diversity in gold mining areas.

Assessment of heavy metal pollution and the effect on bacterial community in acidic and neutral soils

Abstract Mining activities have caused heavy metal pollution in Xikuangshan (XKS), China. This work aims to assess heavy metal ecological risk in XKS using a potential ecological risk (PER) index and detect the responses of the soil bacterial community under heavy metal stress at different pH levels. The PER index indicated that antimony (Sb), cadmium (Cd), and arsenic (As) posed the most serious ecological risk at the sampling sites. We compared the effects of heavy metals on the structure of the microbial community under acidic and neutral conditions. Our results suggested significant differences between microbial community responses to heavy metals in acidic and neutral soils. Zinc (Zn) and lead (Pb) were the main heavy metal factors affecting the bacterial community under acidic conditions, whereas the effect of Sb, As, and chromium (Cr) exceeded them in neutral soils. This was possibly due to the different characteristics of heavy metals and their interactions with soil properties. The main genus were positively correlated with Sb, As, Zn, Pb, and Cd in both acidic and neutral soils, which may due to increasing resistance under conditions of long-time pollution. The results of our structural equation modeling indicated that the variations in the bacterial community structure were mainly explained by heavy metals in acidic and neutral soils. The soil nutrients and pH also had significant direct influences on the bacterial community under neutral conditions, as well as indirect effects due to their impact on heavy metals in neutral and acidic soils. Several heavy metal-resistant bacteria can be used for remediation under acid and neutral conditions.

A genomic perspective of metal-resistant bacteria from gold particles: Possible survival mechanisms during gold biogeochemical cycling.

A bacterial consortium was enriched from gold particles that 'experienced' ca. 80 years of biotransformation within waste-rock piles (Australia). This bacterial consortium was exposed to 10 µM AuCl3 to obtain Au-tolerant bacteria. From these isolates, Serratia sp. and Stenotrophomonas sp. were the most Au-tolerant and reduced soluble Au as pure gold nanoparticles, indicating that passive mineralisation is a mechanism for mediating the toxic effect of soluble Au produced during particle dissolution. Genome-wide analysis demonstrated that these isolates also possessed various genes that could provide cellular defence enabling survival under heavy-metal stressed condition by mediating the toxicity of heavy metals through active efflux/reduction. Diverse metal-resistant genes or genes clusters (cop, cus, czc, zntand ars) were detected, which could confer resistance to soluble Au. Comparative genome analysis revealed that the majority of detected heavy-metal resistant genes were similar (i.e. orthologous) to those genes of Cupriavidus metallidurans CH34. The detection of heavy-metal resistance, nutrient cycling and biofilm formation genes (pgaABCD, bsmAandhmpS) may have indirect yet important roles when dealing with soluble Au during particle dissolution. In conclusion, the physiological and genomic results suggest that bacteria living on gold particles would likely use various genes to ensure survival during Au-biogeochemical cycling.

Biorremediación de metales pesados por plumas melanizadas y no melanizadas y bacterias degradantes de plumas, resistentes a metales pesados

Heavy metals are toxic and detrimental water pollutants. The continuous discharge of cadmium (Cd) and lead (Pb) containing effluents from industries within and around residential areas is worrisome since they do not only affects human beings, but also beneficial microbes, animals andvegetation due to their mobility in aqueous ecosystem, toxicity and non-biodegradability. The aim of this study is to compare the ability of black and white feathers to adsorb Cd and Pbin two aqueous media and to isolate Cd and Pb tolerant feather-degrading bacteria that will degrade the Cd and Pb polluted feather generated. Black and white chicken feathers were used as bio-adsorbent material in two Cd and Pb containing aqueous solutions (distilled water (DW)and feather meal broth(FMB)). The sorption capacity of the feathers was obtained by atomic absorption spectrometry andgravitational methods. Cd and Pb tolerant bacterium identified Bacillus sp. was isolated from the manure of local chick and used to degrade Cd and Pb polluted feathers. Result shows that black feathers possessed higher uptake capacity of Cd and Pb in FMB and DW, suggesting the high bio-absorption capacity of feathers in FMB that than in DW. A Cd and Pb resistant feather-degrading bacteria isolated from chicken manure were able to degrade about 40% Cd polluted feathers and 30% Pb polluted white feathers in 7 days. Even though the bacterium grew faster in FMB containing Cd polluted feathers, the degradation of Cd polluted white feathers was faster than black. Hydrolysates produced after complete degradation of polluted feathers contained low concentration of heavy metals. Bioremediation of heavy metals and recalcitrant chicken feather wastes can be achieved by melanised and un-melanised feathers and metal resistant feather-degrading bacteria.