Heavy Metal Resistant Bacteria Research Articles

Isolation and Identification of Rhizospheric and Endophytic Bacteria from Cucumber Plants Irrigated with Wastewater: Exploring Their Roles in Plant Growth Promotion and Disease Suppression

Wastewater contains various emerging contaminants, including heavy metals, residues of pesticides, and pharmaceuticals. Therefore, irrigation with wastewater can enhance heavy metal contamination in soil and adversely affect plant growth. To mitigate this problem, plant growth-promoting bacteria (PGPR) can improve plant growth under heavy metal stress. This study aimed to isolate and characterize rhizospheric and endophytic bacteria from the rhizosphere soil and roots of a cucumber plant irrigated with municipal wastewater. A total of 121 morphologically distinct bacterial isolates from the rhizosphere and 90 bacterial isolates from the endophytic region were isolated and tested for heavy metal resistance and in vitro plant growth-promoting characteristics, including indole-3-acetic acid (IAA) production, phosphate solubilization, Hydrogen Cyanide (HCN) production, and siderophore production. Most of the bacteria analyzed from the rhizospheric and endophytic regions showed various plant growth-promoting characteristics and were tolerant to different heavy metals at various concentrations. Bacterial strains R1 (Proteus sp.) and E2 (Bacillus sp.) were antagonistic to Fusarium oxysporum f. sp. Lycopersici. Wastewater irrigation increases heavy metal-resistant bacteria in cucumber plants, which can alleviate heavy metal stress. Additionally, Proteus sp. and Bacillus sp. isolates are potential candidates for removing heavy metal-contaminated soil and could be potential biofertilizer candidates for selected plants and biocontrol agents.

Study of Multiple Metal Resistant Citrobacter sp. Isolated From Industrial Effluent

The pollution of the environment with toxic heavy metals is spreading throughout the world along with industrial progress. Microbe related technologies may provide an alternative or addition to conventional method of metal removal or metal recovery. The present study deals with isolation, identification and characterization of heavy metal resistant bacteria from industrial effluent. a total58 isolates were screened for heavy metal resistant from industrial effluent. The GOZPRN isolate show multiple metal resistant and antibiotic resistances. On the basis of morphological, biochemical, partial 16S rRNA gene sequencing revealed that this isolates belongs to Citrobacter sp.. The isolate showed optimum growth at 30°C and pH 7.0. This isolate was found to be resistant to nickel (Ni), lead (Pb), zinc (Zn), Chromium (Cr). The minimal tolerance concentration (MTC) of this isolate against Cr, Ni, Pb, and Zn was 2.8 mM, 80 mM, 800 mM, and 500 mM respectively. It also exhibited resistance against tetracycline. This Citrobacter Sp. has potential to be useful for the bioremediation of heavy metals.

Isolation of Multidrug-Resistant Bacteria from Raw Hides, Salted Hides, and Tannery Wastewater and Their Heavy Metal (Cr) Tolerance

Numerous leather products are created from cattle hides and skins. However, the processing of these products can release toxic heavy metals, including chromium into the environment, leading to health hazards and environmental pollution. This study aims to isolate and identify multidrug-resistant bacteria from rawhide, salted hides, and tanneries in different areas of the Savar region in Dhaka City, Bangladesh. The secondary objective is to determine the heavy metal tolerance and Minimum Inhibitory Concentration (MIC) of Cr against all isolated bacteria. The study found 206 bacterial isolates from three areas: Polashbari Kathaltola, Polashbari Bazar, and Savar Hemaythpur. Rawhide yielded 100 (48.54%) bacterial isolates, salted hide yielded 80(38.83%) isolates, and tannery wastewater yielded only 26 (12.62%) isolates. Further, Bacillus spp. (60) was the most common isolated bacteria. The other identified bacteria were Pseudomonas spp. (46), Staphylococcus spp. (40), Proteus spp. (40), and Escherichia coli (20). The isolated strains showed multidrug resistance, with Staphylococcus spp. Being highly resistant to Erythromycin (100%), followed by Trimethoprim (95%) and Tetracycline (88%). Pseudomonas spp. Were highly resistant to Azithromycin (100%) and Gentamycin (100%). The MIC and the MIC breakpoint determined the screening and evaluation of Cr tolerance against bacteria, and among the isolated bacterial isolates, Bacillus spp. showed a MIC breakpoint of 600 ppm (11.52mM) for Cr tolerance. The isolated heavy metal-resistant bacteria are useful in the bioremediation process and can aid in recovering and removing heavy metals from environmental effluents, thus preventing adverse effects on humans and animals. The government and leather companies should take legal responsibility for proper leather processing to ensure a preventative approach for safe public health. Otherwise, carcinogenic heavy metals can cause cancer in humans.

Omics technology draws a comprehensive heavy metal resistance strategy in bacteria.

The rapid industrial revolution significantly increased heavy metal pollution, becoming a major global environmental concern. This pollution is considered as one of the most harmful and toxic threats to all environmental components (air, soil, water, animals, and plants until reaching to human). Therefore, scientists try to find a promising and eco-friendly technique to solve this problem i.e., bacterial bioremediation. Various heavy metal resistance mechanisms were reported. Omics technologies can significantly improve our understanding of heavy metal resistant bacteria and their communities. They are a potent tool for investigating the adaptation processes of microbes in severe conditions. These omics methods provide unique benefits for investigating metabolic alterations, microbial diversity, and mechanisms of resistance of individual strains or communities to harsh conditions. Starting with genome sequencing which provides us with complete and comprehensive insight into the resistance mechanism of heavy metal resistant bacteria. Moreover, genome sequencing facilitates the opportunities to identify specific metal resistance genes, operons, and regulatory elements in the genomes of individual bacteria, understand the genetic mechanisms and variations responsible for heavy metal resistance within and between bacterial species in addition to the transcriptome, proteome that obtain the real expressed genes. Moreover, at the community level, metagenome, meta transcriptome and meta proteome participate in understanding the microbial interactive network potentially novel metabolic pathways, enzymes and gene species can all be found using these methods. This review presents the state of the art and anticipated developments in the use of omics technologies in the investigation of microbes used for heavy metal bioremediation.

First report on in-depth genome and comparative genome analysis of a metal-resistant bacterium Acinetobacter pittii S-30, isolated from environmental sample.

A newly isolated bacterium Acinetobacter pittii S-30 was recovered from waste-contaminated soil in Ranchi, India. The isolated bacterium belongs to the ESKAPE organisms which represent the major nosocomial pathogens that exhibit high antibiotic resistance. Furthermore, average nucleotide identity (ANI) analysis also showed its closest match (>95%) to other A. pittii genomes. The isolate showed metal-resistant behavior and was able to survive up to 5 mM of ZnSO4. Whole genome sequencing and annotations revealed the occurrence of various genes involved in stress protection, motility, and metabolism of aromatic compounds. Moreover, genome annotation identified the gene clusters involved in secondary metabolite production (biosynthetic gene clusters) such as arylpolyene, acinetobactin like NRP-metallophore, betalactone, and hserlactone-NRPS cluster. The metabolic potential of A. pittii S-30 based on cluster of orthologous, and Kyoto Encyclopedia of Genes and Genomes indicated a high number of genes related to stress protection, metal resistance, and multiple drug-efflux systems etc., which is relatively rare in A. pittii strains. Additionally, the presence of various carbohydrate-active enzymes such as glycoside hydrolases (GHs), glycosyltransferases (GTs), and other genes associated with lignocellulose breakdown suggests that strain S-30 has strong biomass degradation potential. Furthermore, an analysis of genetic diversity and recombination in A. pittii strains was performed to understand the population expansion hypothesis of A. pittii strains. To our knowledge, this is the first report demonstrating the detailed genomic characterization of a heavy metal-resistant bacterium belonging to A. pittii. Therefore, the A. pittii S-30 could be a good candidate for the promotion of plant growth and other biotechnological applications.

Detection of Coliform Bacteria in Raw Milk Samples Collected from Industrial Cities of Pakistan

Antibiotics and heavy metals-resistant bacteria in livestock environments can result in economic losses and raise public health and environmental problems. There is a crisis in the world's access to and pipeline for antibiotics. Objective: To screen raw milk samples collected from three different industrial cities Gujranwala, Lahore, and Sheikhupura, situated in the province of Punjab, Pakistan. Methods: In this regard, a total of 26 samples were having 84 coliform strains. Separated coliform colonies were processed for Gram's staining, catalase, indole production, and Simmon's citrate and motility tests. Results: Metal resistance of bacterial strains was also checked and 39.5% and 45.23% of bacteria were found to be resistant to ZnCl2 1% and 0.5%. 69.045% and 77.38% bacteria were found to be resistant to CuSo4 salt solution1% and 0.5%. 17.85% and 27% bacteria were found to be resistant to Na2CrO4 salt solution1% and 0.5% respectively. 80% of bacteria were found to be resistant to Cefuroxime, 26.19% to Cephradine, 84.52% to Aztroeonam 41.67% to Erythromycin, 91.667% to Trimethoprim 89.28% to Lincomycins. Conclusions: The raw milk samples were not only contaminated with coliforms but the bacteria were also resistant to heavy metals and certain antibiotics which might be considered indicative of industrial and anthropogenic pollution. Cephradine, 84.52% to Aztroeonam 41.67% to Erythromycin, 91.667% to Trimethoprim 89.28% to Lincomycins. Conclusions: The raw milk samples were not only contaminated with coliforms but the bacteria were also resistant to heavy metals and certain antibiotics which might be considered indicative of industrial and anthropogenic pollution.

Inoculation of heavy metal resistant bacteria alleviated heavy metal-induced oxidative stress biomarkers in spinach (Spinacia oleracea L.)

Most vegetable crops are severely affected by the uptake of heavy metals from the soil. Heavy metals in vegetable bodies generate reactive oxygen species (ROS) that unbalance the antioxidant defense system. This study was initiated to determine the physiological and biochemical characteristics of spinach plants grown on soil contaminated with heavy metals and responding to Bacillus cereus and Bacillus aerius were isolated from soil contaminated with heavy metals. Heavy metal contamination led to a significant reduction in seed germination, seedling biomass, protein, and total nitrogen content of spinach plants grown in contaminated soils compared to control soils. In contrast, a significant increase in the content of metallothioneins and antioxidant enzymes was observed. Plants inoculated with B. cereus and B. aerius significantly reduced the oxidative stress induced by heavy metals by improving seed germination (%), seedling growth, nitrogen, and protein content. The content of metallothioneins and the activities of antioxidant enzymes were reduced in spinach plants grown from seeds inoculated with bacterial strains. In addition, plants inoculated with, B. cereus and B. aerius showed greater stomata opening than plants grown on soil contaminated with heavy metals, whose stomata were almost closed. These results suggested that both bacterial strains enhanced plant growth by reducing oxidative stress caused by metals.

Screening and Identification of Chromium Resistant Bacteria from Poultry Excreta

The occurrence of heavy metal-resistant bacteria in the environment acts as an indicator of heavy metal pollution. The impact of heavy metal contamination in co-selection and proliferation of antimicrobial[1]resistant bacteria is well-documented in existing literature. The present study aims to determine the occurrence of chromium-resistant bacteria (CRB) in poultry feces and to characterize their antimicrobial resistance and biofilm formation ability. 28 CRBs were isolated by inoculating samples on chromium-amended media. 6 of 28 isolates were resistant to a maximum of 1000 ppm chromium. Isolated CRBs also showed varying degrees of resistance to other heavy metals, including Cd, Ni, and Hg. Biofilm formation was observed in 67.8% isolates, of which 60.7% and 7.1% were weak and moderate biofilm former, respectively. All the isolates exhibited sensitivity to Gentamicin, Chloramphenicol, Imipenem, and Amikacin. Only one isolate was multi-drug resistant. In addition, all the isolates possessed chromate reductase gene that confirmed their chromium-reducing activity. Two isolates were identified as Bacillus altituidinis and Brevibcillus parabrevis on the basis of 16s rRNA analysis. Further estimation of chromium-reduction capacity and whole genome analysis will reveal their bioremediation potential.
 Bangladesh J Microbiol, Volume 40, Number 1, June 2023, pp 1-6

Co-occurrence of Heavy Metal and Antibiotics Resistance Traits in Bacteria Isolated from Poultry Droppings and Soil in Badagry, Lagos

Background: Heavy metal and antibiotic resistance are two pressing global concerns affecting the agri-cultural and food sectors. Moreover, heavy metals tend to select antibiotic resistance in the absence of antibiotics. This study aimed to isolate, screen and identify heavy metal-resistant bacteria that can resist multiple antibiotics in agricultural settings. Methods: Using standard cultural techniques, twenty-six heavy metal tolerant bacteria were isolated from poultry droppings and soil samples collected from Lagos State Food Processing Centre located at Badagry, Lagos. The isolates were presumptively identified by their morphological characteristics and subjected to antibiotics sensitivity test using the disc diffusion method. The identities of isolates exhib-iting multi-drug resistance (MDR) among the metal tolerance isolates were authenticated using 16S rRNA gene sequence analysis. Results: All isolates recovered from the soil sample tolerated 3 mM of lead and nickel, while isolates from poultry droppings recorded the least tolerable concentrations of 1 mM and 2 mM of cadmium and lead, respectively. Each isolate exhibited resistance to at least a group of antibiotics phenotypically. Resistance to colistin (42.31%) was the highest among the isolates, closely followed by chlorampheni-col (23.08%), while gentamicin (3.85%) was the lowest among the isolates. However, six isolates were shown to be MDR strain, and they were identified as Bacillus pumilus, Bacillus cereus, Brevundimonas naejangsanensis, Pseudochrobactrum asaccharolyticum, Pseudochrobactrum saccharolyticum and Lysinibacillus xylanilyticus. Conclusion: This study further draws attention to the increasing dual resistance of bacteria to heavy metals and antibiotics, which may hinder the fight against antimicrobial resistance in agricultural set-tings

Heavy Metal Resistant Bacteria in Rhizospheric Soil: A Review

Concern over heavy metal contamination is a common issue related to soil health. Soil is an excellent habitat for various microbes. Microbial activities in soil are negatively impacted by high concentrations of heavy metals. The physico-chemical changes of soil microorganisms are recognized as a sensitive indicator to assess soil quality. Some plants can absorb metals, and eventually, through food chains, humans and other animals are exposed to them. As a result of ongoing exposure to heavy metals, the rhizospheric bacteria of metal accumulator plants develop intrinsic or extrinsic resistance mechanisms. Through their critical contribution to metal detoxification, these resistance mechanisms either directly or indirectly support plant growth and development. Therefore, it is crucial to look into the correct mechanisms of plantrhizospheric microbe interaction in metal-contaminated soils. The current review sought to highlight the metal-resistant bacterial communities in rhizospheric soils and their part in plant health management.

Molecular characterization and human health risk assessment of multi-drug and heavy metals tolerant bacteria from urban river water

The present study characterized the multi-drug and heavy metal-resistant bacteria and their human health risks in the six major urban rivers. The bacterial strains were identified by molecular techniques based on 16 s rDNA gene sequence analysis, where most of the isolates belong to Bacillus spp. and Staphylococcus spp. The minimum inhibitory concentration (MIC) of the bacterial strains to different heavy metals like chromium, lead, cadmium, cobalt, mercury, and nickel ranged up to 3000 mg/L. The antibiotic susceptibility tests revealed that 69.23% of the strains resistant to ceftriaxone, while 61.54% were resilient to cefotaxime, 53.85% to ampicillin, 46.15% to amoxicillin, 30.77% to streptomycin, 15.38% to azithromycin, 15.38% to chloramphenicol, 7.69% to tetracycline, 7.69% to gentamycin, 7.69% to vancomycin. Interestingly, ciprofloxacin was found highly sensitive to all the bacterial strains in the present study. The multiple heavy metals resistance (MHMR) index of all the bacterial strains in the present study was very high compared to the standard value of 0.50. The multiple antibiotics resistance (MAR) index was highest for Bacillus cereus MKSMPbT1 (0.45), while it was lowest in B. xiamenesis MKSMCrB1 and B. pumilus MKSMNiT1 (0.09). The results of the hemolytic assay revealed that almost all the bacterial strains identified in the present study are highly pathogenic in nature. In essence, the bacterial strains identified in the present study could pose significant environmental and public health concerns that draw strict government attention.

Physiochemical analyses and molecular characterization of heavy metal-resistant bacteria from Ilesha gold mining sites in Nigeria

BackgroundThe contribution of the processes involved and waste generated during gold mining to the increment of heavy metals concentration in the environment has been well established. While certain heavy metals are required for the normal functioning of an organism, certain heavy metals have been identified for their deleterious effects on the ecosystem and non-physiological roles in organisms. Hence, efforts aimed at reducing their concentration level are crucial. To this end, soil and water samples were collected from Ilesha gold mining, Osun State, Nigeria, and they were subjected to various analyses aimed at evaluating their various physicochemical parameters, heavy metal concentration, heavy metal-resistant bacteria isolation, and other analyses which culminated in the molecular characterization of heavy metal-resistant bacteria. ResultsNotably, the results obtained from this study revealed that the concentration of heavy metal in the water samples around the mining site was in the order Co > Zn > Cd > Pb > Hg while that of the soil samples was in the order Co > Cd > Pb > Hg > Zn. A minimum inhibitory concentration test performed on the bacteria isolates from the samples revealed some of the isolates could resist as high as 800 ppm of Co, Cd, and Zn, 400 ppm, and 100 ppm of Pb and Hg respectively. Molecular characterization of the isolates revealed them as Priestia aryabhattai and Enterobacter cloacae. ConclusionFurther analysis revealed the presence of heavy metal-resistant genes (HMRGs) including merA, cnrA, and pocC in the isolated Enterobacter cloacae. Ultimately, the bacteria identified in this study are good candidates for bioremediation and merit further investigation in efforts to bioremediate heavy metals in gold mining sites.

Extracellular proteins enhance Cupriavidus pauculus nickel tolerance and cell aggregate formation

Heavy metal-resistant bacteria secrete extracellular proteins (e-PNs). However, the role of e-PNs in heavy metal resistance remains elusive. Here Fourier Transform Infrared Spectroscopy implied that N-H, C = O and NH2-R played a crucial role in the adsorption and resistance of Ni2+ in the model organism Cuprividus pauculus 1490 (C. pauculus). Proteinase K treatment reduced Ni2+ resistance of C. pauculus underlining the essential role of e-PNs. Further three-dimension excitation-emission matrix fluorescence spectroscopy analysis demonstrated that tryptophan proteins as part of the e-PNs increased significantly with Ni2+ treatment. Proteomic and quantitative real-time polymerase chain reaction data indicated that major changes were induced in the metabolism of C. pauculus in response to Ni2+. Among those lipopolysaccharide biosynthesis, general secretion pathways, Ni2+-affiliated transporters and multidrug efflux play an essential role in Ni2+ resistance. Altogether the results provide a conceptual model for comprehending how e-PNs contribute to bacterial resistance and adsorption of Ni2+.

Bacterial heavy metal resistance related to environmental conditions

Contaminated water bodies such as rivers provide reservoirs for bacterial resistance. This field study tested the water quality and the bacterial resistance to heavy metals of Qishan River water pollution. Wastewater discharged to environmental surface waters is a major pathway of heavy metals and heavy metal-resistant bacteria. Contaminated water bodies such as rivers provide reservoirs for bacterial resistance. This field study tested the water quality and bacterial resistance to heavy metals of Qishan River water pollution. Guided by our research hypothesis that an overall increase in downstream heavy metal resistance levels was following an increase in human settlements were eight sites sampled along the Qishan River. These were situated upstream and downstream to the confluence of the Qishan River with the Kaoping River. In the laboratory bacterial heavy metal resistance was bio-assayed by disk diffusion and micro-dilution with six widely used heavy metals. The comparison of bacterial resistance was among Qishan River upstream sites (sites 1–6) and downstream sites (sites 7–9). Multi-drug-resistant bacteria and co-resistance against heavy metals and antibacterials appeared at site 8. This research discusses the correlation between environmental factors, and antibacterial and heavy metal resistance. The results provide stakeholders and authorities responsible for environmental pollution with a reference for risk assessment and management of bacterial resistance.

Heavy-metal tolerant bacterial strains isolated from industrial sites and scrap yards in Kashmir, India.

Heavy metal pollution has posed a severe danger to environmental stability due to its high toxicity and lack of biodegradability. The present study deals with the appraisement of tolerance shown by various bacteria in varied copper and iron concentrations. Among the 20 isolates, four isolates, GN2, SC5, SC8, and SC10, exhibiting more significant iron and copper tolerance, were selected and identified by 16 S ribosomal ribonucleic acid (rRNA) gene sequence analysis as Pantoea agglomerans strain GN2, Pantoea sp. strain SC5, Bacillus sp. strain SC8 and Priestia aryabhattaistrain SC10. The minimum inhibitory concentration of molecularly identified strains revealed that P. agglomerans strain GN2 showed tolerance to iron sulfate and copper sulfate upto 600 and 400 µg/mL, whereas Bacillus sp. SC8 (OQ202165) showed tolerance of 700 and 250 µg/mL were tolerant to iron sulfate and copper sulfate up to 700 and 150 µg/mL, respectively. Pantoea sp. strain SC5 showed significant tolerance to both heavy metals. The isolates were further studied for their ability to grow at varying temperatures and pH ranges. Most of the isolates showed optimal growth at 37°C and pH 7. However, Pantoea sp. SC5 was competent to have prominent growth at 45°C and pH 8.0. Microbial remediation, which is eco-friendly, has proven the most effective method for bioremediation of heavy metal-contaminated environments. Using heavy metal-resistant bacteria for microbial remediation of iron and copper-contaminated environments could be a viable and valuable strategy. These isolates could also be used to decontaminate heavy metal-polluted agricultural soils.

An In Silico Bioremediation Study to Identify Essential Residues of Metallothionein Enhancing the Bioaccumulation of Heavy Metals in Pseudomonas aeruginosa.

Microorganisms are ubiquitously present in the environment and exert significant influence on numerous natural phenomena. The soil and groundwater systems, precipitation, and effluent outfalls from factories, refineries, and waste treatment facilities are all sources of heavy metal contamination. For example, Madinah, Saudi Arabia, has alarmingly high levels of lead and cadmium. The non-essential minerals cadmium (Cd) and lead (Pb) have been linked to damage to vital organs. Bioremediation is an essential component in the process of cleaning up polluted soil and water where biological agents such as bacteria are used to remove the contaminants. It is demonstrated that Pseudomonas aeruginosa (P. aeruginosa) isolated from activated sludge was able to remove Cd and Pb from water. The protein sequence of metallothionein from P. aeruginosa was retrieved to explore it for physicoparameters, orthologs, domain, family, motifs, and conserved residues. The homology structure was generated, and models were validated. Docking of the best model with the heavy metals was carried out to inspect the intramolecular interactions. The target protein was found to belong to the "metallothionein_pro" family, containing six motifs, and showed a close orthologous relationship with other heavy metal-resistant bacteria. The best model was generated by Phyre2. In this study, three key residues of metallothionein were identified that participate in heavy metal (Pb and Cd) binding, viz., Ala33, Ser34, and Glu59. In addition, the study provides an essential basis to explore protein engineering for the optimum use of metallothionein protein to reduce/remove heavy metals from the environment.

Isolation and Characterization of Heavy Metals Resistant Bacteria in Water Samples from Mambilla Artisanal Mining Site, Nguroje, Taraba State

Isolation and Characterization of Heavy Metals Resistant Bacteria in Water Samples from Mambilla Artisanal Mining Site, Nguroje, Taraba State

A potential heavy metals detoxification system in composting: Biotic and abiotic synergy mediated by shell powder

Regulating heavy metal resistance genes (HMRGs) was an effective method for heavy metal resistant bacteria (HMRB) to cope with heavy metal stress during dairy manure composting. This research aimed to investigate heavy metal detoxification mediated by shell powder (SP) in composting and the response of HMRB and HMRGs to changes in heavy metal bioavailability during composting. Research showed that SP additive reduced the bioavailability of Zu, Cu, and Mn by 10.64%, 13.90% and 14.14%, respectively. SP increased the composition percentage of humic acid (HA) in humus (HS) by 8%. SP enhanced the resistance of Actinobacteria to heavy metals and improved the regulation of HMRGs. Correlation analysis demonstrated that the bioavailability of heavy metals was positively correlated with most HMRGs. HA was significantly negatively correlated with the bioavailability of Zn, Cu and Mn. Therefore, SP additive could be a novel strategy for heavy metals detoxification during composting.

Whole Genome Sequence Analysis of Cupriavidus necator C39, a Multiple Heavy Metal(loid) and Antibiotic Resistant Bacterium Isolated from a Gold/Copper Mine.

Here a multiple heavy metal and antibiotic resistant bacterium Cupriavidus necator C39 (C. necator C39) was isolated from a Gold-Copper mine in Zijin, Fujian, China. C. necator C39 was able to tolerate intermediate concentrations of heavy metal(loid)s in Tris Minimal (TMM) Medium (Cu(II) 2 mM, Zn(II) 2 mM, Ni(II) 0.2 mM, Au(III) 70 μM and As(III) 2.5 mM). In addition, high resistance to multiple antibiotics was experimentally observed. Moreover, strain C39 was able to grow on TMM medium containing aromatic compounds such as benzoate, phenol, indole, p-hydroxybenzoic acid or phloroglucinol anhydrous as the sole carbon sources. The complete genome of this strain revealed 2 circular chromosomes and 1 plasmid, and showed the closest type strain is C. necator N-1T based on Genome BLAST Distance Phylogeny. The arsenic-resistance (ars) cluster GST-arsR-arsICBR-yciI and a scattered gene encoding the putative arsenite efflux pump ArsB were identified on the genome of strain C39, which thereby may provide the bacterium a robust capability for arsenic resistance. Genes encoding multidrug resistance efflux pump may confer high antibiotic resistance to strain C39. Key genes encoding functions in degradation pathways of benzene compounds, including benzoate, phenol, benzamide, catechol, 3- or 4-fluorobenzoate, 3- or 4-hydroxybenzoate and 3,4-dihydroxybenzoate, indicated its potential for degrading those benzene compounds.

Arsenic and other heavy metals resistant bacteria in rice ecosystem: Potential role in promoting plant growth and tolerance to heavy metal stress

The role of microorganisms in arsenic (As) uptake in association with terrestrial plants is identified, though their rhizosphere specific association and function in rice and barnyard grass in As contaminated soil are not elucidated. We investigated the abundance and diversity of arsenic and other heavy metal tolerant bacteria isolated from barnyard grass and rice rhizospheres, and the bulk soil from an As-contaminated paddy field. Among 83 isolated As resistant bacteria, 22 strains were screened and characterized based on their growth potential in 100 mM arsenate. One strain oxidized and reduced arsenic, whereas five isolates oxidized arsenite to arsenate and seven isolates reduced arsenate to arsenite. All the isolates were tolerant to the highest levels of Zn, Cd, Cr, Cu, Co, and Hg tested and except one, all also survived at the highest level of Pb. Molecular characterization by 16s rRNA gene analysis revealed that the selected bacteria belong to Sphingomonadaceae (13), Moraxellaceae (2), Enterobacteriaceae (2), Planococcaceae (2), Pseudomonadaceae (1), Xanthomonadaceae (1) and Cyanobacteria (1). Bacterial abundances were more in the rhizosphere than in bulk soil and diversity was more in barnyard grass rhizosphere than in rice. Among the isolates, 21 strains solubilized phosphate, produced indole acetic acid and grew in N-free medium. All the isolates that were tested, enhanced the germination and root fresh weight of rice seedlings. These isolates, based on their As and other metals resistance, As detoxification capacity, and plant growth promotion ability, especially the members of Sphingomonadaceae, could be conclusively used for plant growth promotion and microbe assisted remediation of the As and other heavy metal contaminated soil employing barnyard grass and rice.