Mercury-resistant Bacteria Research Articles

Mercury absorption using rice husk charcoal inoculated with five resistant bacteria

Abstract The use of biosorption for the rehabilitation of polluted water and soils has recently gained popularity. Biosorption is a low-risk method that immobilizes harmful compounds by employing organic waste. Mercury contamination in Indonesia requires an immediate remedy that is both inexpensive and applicable in rural regions where pollution sources are concentrated. The current study aims to investigate the usage of various organic materials, namely rice husk charcoal, compost, coco dust, and zeolite, as biosorption agents for mercury remediation through collaboration with mercury-resistant bacteria. Five previously examined bacteria strains were shown to be viable only in compost and rice husk charcoal after 30 days of observation. Further research on rice husk charcoal has shown that it might reduce mercury contamination in liquid medium with and without the inclusion of microorganisms. At 24 hours, the partnership of rice husk charcoal and mercury-resistant bacteria was shown to be more successful in absorbing the mercury by up to 66 percent. In contrast, biochar alone can only absorb mercury by up to 31 percent. This suggests that the activity of the bacteria can boost biochar’s capability to immobilize the mercury compound. Thus, the utilization of rice husk biochar amended with mercury-resistant bacteria is valuable and should be further studied as a possible mercury bioremediation agent.

Isolation and characterization mercury-resistant bacteria from gold mining in Lebong, Bengkulu

Lebong a regency in Bengkulu Province, possesses prominent potential in gold mining. This mining activity is conducted through amalgamation techniques, resulting in the deposition of mining residue containing mercury, subsequently leading to environmental pollution. Recognizing the hazards associated with such pollution, it becomes imperative to mitigate the presence of mercury through effective remediation strategies. Bioremediation, utilizing Mercury Resistant Bacteria (MRB), widely known as a viable method for mitigating mercury contamination. This study aims to isolate and characterize MRB to facilitate their potential application in addressing heavy metal pollution. This study involved the isolation and characterization of MRB through morphological observations, Gram staining, and biochemical tests (glucose, sucrose, fructose, citrate utilization, starch hydrolysis, urease activity, and catalase production). A total of 43 bacterial isolates were obtained from water, sediment, and soil samples collected from surrounding gold mining waste disposal. Among these isolates, bacteria resistant to mercury were selected on NA supplemented with various concentrations of mercury. Five potential candidates of MRB were identified, with the highest mercury concentration tested being 1000 ppm. Based on identification using Bergey’s Manual of Determinative Bacteriology, it was determined that four out of the five isolates belonged was Pseudomonas, while another belonged to Staphylococcus.

Mercury remediation potential of mercury-resistant strain Rheinheimera metallidurans sp. nov. isolated from a municipal waste dumping site

A novel mercury-resistant bacterium, designated strain DCL_24T, was isolated from the legacy waste at the Daddu Majra dumping site in Chandigarh, India. It showed resistance up to 300 µM of inorganic mercury (mercuric chloride). The isolate was found to be a Gram-negative, facultative anaerobic, motile, and rod-shaped bacterium that can grow at 4 – 30 °C (optimum 25 °C), pH 6.0 – 12.0 (optimum 7.0), and 0 – 4.0 % (w/v) NaCl (optimum 0.5 – 2.0 %). The 16 S rRNA gene-based phylogenetic analysis showed that DCL_ 24 T shared a 97.53 % similarity with itsºlosest type strain Rheinheimera muenzenbergensis E-49T. Insilico DNA-DNA hybridization and average nucleotide identity values were found to be 18.60 % and 73.77 %, respectively, between the genomes of DCL_24T and R. muenzenbergensis E-49T. The strain DCL_24T has 44.33 DNA G+C content (mol %). Based on the phenotypic, chemotaxonomic, and genotypic data, the strain DCL_24T represents a novel species within the genus Rheinheimera, for which the name Rheinheimera metallidurans sp. nov is proposed. The type strain is DCL_24T (MTCC13203T = NBRC115780T = JCM 35551 T). The isolate was found to volatilize and remove mercury efficiently, as demonstrated by X-ray film and dithizone-based colorimetric methods. Around 92 % of mercury removal was observed within 48 h. The mercury-resistant determinant mer operon consisting of merA, encoding the mercuric reductase enzyme, and transport and regulatory genes (merT, merP, merD, and merR) were found in the isolate. Relative expression analysis of merA at increasing concentrations of HgCl2 was confirmed by quantitative real-time PCR. These data indicate the merA-mediated reduction of toxic Hg2+ into a non-toxic volatile Hg0. The phytotoxicity assay performed using Arabidopsis thaliana seeds further demonstrated the mercury toxicity reduction potential of DCL_24T. The study shows that this novel isolate, DCL_24T, is an interesting candidate for mercury bioremediation. However, further studies are required to assess the bioremediation efficacy of the strain under the harsh environmental conditions prevailing in polluted sites.

Mercury-resistant biofilm-forming bacteria and local plants in phytoremediation of small-scale gold mine tailings in Lombok Island, Indonesia

Small-scale gold mining is one of the sectors that contribute to the world's largest mercury contamination through the tailings it produces. Many efforts have been made to reduce mercury concentrations from tailings, one of which is by utilizing a combination of plants and bacteria. This study aims to analyze the combination of mercury-resistant biofilm-forming bacteria and local plants in the phytoremediation of small-scale gold mine tailings. This study used ten plant species divided into three groups and three biofilm-forming mercury-resistant bacteria (<em>Bacillus toyonensis</em>, <em>Burkholderia cepacia</em>, and <em>Microbacterium chocolatum</em>). Parameters observed included plant biomass, total chlorophyll, plant mercury content and media. The results showed that adding bacteria to each plant in the treatment had a different effect. Some plants with the addition of biofilm-forming bacteria had a higher wet weight than others. However, the addition of bacteria was not effective in increasing plant dry weight. The combination of biofilm-forming bacteria in the first and second plant groups reduced tailings mercury concentrations better than without the addition of bacteria. The combination of plants and bacteria in the third group gave higher media and plant mercury concentrations. This study shows that the addition of biofilm-forming bacteria can lead to increased remediation by plants. The second plant group treatment with a combination of <em>P. indica, P. conjugatum</em>, and <em>S. sesban</em> plants was the most effective in reducing tailings mercury content.

Quantification of heavy metals and mercury-resistant bacteria in artisanal and small-scale gold mining sites, Maniema region, Democratic Republic of the Congo

Quantification of heavy metals and mercury-resistant bacteria in artisanal and small-scale gold mining sites, Maniema region, Democratic Republic of the Congo

Bacterial Metal-Scavengers Newly Isolated from Indonesian Gold Mine-Impacted Area: Bacillus altitudinis MIM12 as Novel Tools for Bio-Transformation of Mercury.

Selikat river, located in the north part of Bengkulu Province, Indonesia, has critical environmental and ecological issues of contamination by mercury due to artisanal small-scale gold mining (ASGM) activities. The present study focused on the identification and bioremediation efficiency of the mercury-resistant bacteria (MRB) isolated from ASGM-impacted areas in Lebong Tambang village, Bengkulu Province, and analyzed their merA gene function in transforming Hg2+ to Hg0. Thirty-four MRB isolates were isolated, and four out of the 34 isolates exhibited not only the highest degree of resistance to Hg (up to 200ppm) but also to cadmium (Cd), chromium (Cr), copper (Cu), and lead (Pb). Further analysis shows that all four selected isolates harbor a merA operon-encoded mercuric ion (Hg2+) reductase enzyme, with the Hg bioremediation efficiency varying from 71.60 to 91.30%. Additionally, the bioremediation efficiency for Cd, Cr, Cu, and Pb ranged from 54.36 to 98.37%. Among the 34, two isolates identified as Bacillus altitudinis possess effective and superior multi-metal degrading capacity up to 91.30% for Hg, 98.07% for Cu, and 54.36% for Cr. A pilot-scale study exhibited significant in situ bioremediation of Hg from gold mine tailings of 82.10 and 95.16% at 4- and 8-day intervals, respectively. Interestingly, translated nucleotide blast against bacteria and Bacilli merA sequence databases suggested that B. altitudinis harbor merA gene is the first case among Bacilli with the possibility exhibits a novel mechanism of bioremediation, considering our new finding. This study is the first to report the structural and functional Hg-resistant bacterial diversity of unexplored ASGM-impacted areas, emphasizing their biotechnological potential as novel tools for the biological transformation and adsorption of mercury and other toxic metals.

Assessment and bioremediation of mercury pollutants by highly mercury-resistant bacteria immobilized in biochar from small-scale artisanal gold mining areas

Small-scale gold mining activities in Indonesia still use amalgamation techniques, which have the potential to cause mercury (Hg) pollution and affect the quality and number of microorganisms. Mercury-resistant bacteria can survive and adapt to mercury-exposed environments and can be developed as bioremediation agents. The bioremediation activity of these bacteria can be increased through immobilization using biochar. The results of observations of physicochemical qualities in three samples in the mining area, showed significant differences. The TOC in the rhizosphere soil sample of <em>Calliandra calothyrsus</em> L. showed the significantly highest value at 14.5%, and the pH of the three samples indicated acidity and exhibited no difference (p<0.05). The highest concentration measured in the tailing sample was 9.9 ng/g (p<0.05). The number of heterotrophic bacteria in the rhizosphere soil was the highest at 7.2 × 10<sup>8</sup> CFU/g. On the other hand, the number of mercury-resistant bacteria in the tailing sample showed the highest value of 6.3 × 10<sup>3</sup> CFU/g. In the selection based on the toxicity profile of 30 mercury-resistant bacteria obtained, the highest results were observed in the LMP1B5 bacterial isolate from the river sediment, with 50% effective concentration (EC50) and minimum inhibitory concentration (MIC) values of 225 and 250 mg/L, respectively. Polyphasic identification based on phenotypic and genotypic characteristics using the 16S rRNA gene showed that the bacterial isolate was identified as <em>Escherichia fergusonii</em>. The growth and mercury removal activity of <em>E. fergusonii</em> LMP1B5 increased by 21% and 52%, respectively, after the immobilization with biochar. Thus, immobilized <em>E</em>.<em> fergusonii</em> LMP1B5 was effective in removing mercury pollutants.

Unraveling the potential of bacteria isolated from the equatorial region of Indian Ocean in mercury detoxification

The marine environment is most vital and flexible with continual variations in salinity, temperature, and pressure. As a result, bacteria living in such an environment maintain the adaption mechanisms that are inherent in unstable environmental conditions. The harboring of metal-resistant genes in marine bacteria contributes to their effectiveness in metal remediation relative to their terrestrial counterparts. A total of four mercury-resistant bacteria (MRB) i.e. NIOT-EQR_J7 (Alcanivorax xenomutans); NIOT-EQR_J248 and NIOT-EQR_J251 (Halomonas sp.); and NIOT-EQR_J258 (Marinobacter hydrocarbonoclasticus) were isolated from the equatorial region of the Indian Ocean (ERIO) and identified by analyzing the 16S rDNA sequence. The MRBs can reduce up to 70% of Hg(II). The mercuric reductase (merA) gene was amplified and the mercury (Hg) volatilization was confirmed by the X-ray film method. The outcomes obtained from ICP-MS validated that the Halomonas sp. NIOT-EQR_J251 was more proficient in removing the Hg from culture media than other isolates. Fourier transform infrared (FT-IR) spectroscopy results revealed alteration in several functional groups attributing to the Hg tolerance and reduction. The Gas Chromatography-Mass Spectrometry (GC-MS) analysis confirmed that strain Halomonas sp. (NIOT-EQR_J248 and NIOT-EQR_J251) released Isooctyl thioglycolate (IOTG) compound under mercury stress. The molecular docking results suggested that IOTG can efficiently bind with the glutathione S-transferase (GST) enzyme. A pathway has been hypothesized based on the GC-MS metabolic profile and molecular docking results, suggesting that the compound IOTG may mediate mercuric reduction via merA-GST related detoxification pathway.

Biofilm formation by mercury resistant bacteria from polluted soil small-scale gold mining waste

Abstract. Nurfitriani S, Arisoesilaningsih E, Nuraini Y, Handayanto E. 2021. Biofilm formation by mercury resistant bacteria from polluted soil small-scale gold mining waste. Biodiversitas 23: 992-999. Small-scale gold mining has a major impact on living things and the environment due to mercury contamination. Bacteria are known to have a defense mechanism in mercury-contaminated soil. The biofilm produced by bacteria helps them survive and protect them from environmental stresses. This study aimed to find mercury-resistant bacteria capable of forming biofilms from mercury-contaminated soil in small-scale gold mining. Samples for bacterial isolation were mercury-contaminated soil from three gold processing sites in Lombok, Indonesia. The obtained mercury-resistant bacteria were tested to form biofilms on the media according to the test dose. The bacterial biofilms formed were observed, and each biofilm's adsorption capacity was measured. The three bacteria with highest adsorption values were identified molecularly using 16S rDNA. The results showed that most mercury-resistant bacteria were able to form biofilms at a dose of 25 ppm. However, only four bacteria were able to produce biofilms at a dose of 50 ppm. Biofilms of three bacteria had the highest adsorption values, ranging between 2.78-3.5. The three bacteria were identified as Bacillus toyonensis (JGT-F1), Burkholderia cepacia (PJT-K), and Microbacterium chocolatum (PJT-D). This study indicates that biofilm-producing bacteria are one of the remediation agents and can be used in mercury bioremediation.

Indigenous mercury-resistant bacteria isolated from contaminated soils around artisanal gold processing centers in Sukabumi, Indonesia

In Indonesia, the largest mercury pollution comes from artisanal and small-scale gold mining (ASGM), which may cause the distribution of mercury to agricultural land and can be absorbed by food crops. Sukabumi Regency in West Java, well-known as one hotspot of illegal artisanal gold mining and national rice producer, is potentially threatened by mercury pollution. Efforts to remediate mercury contaminated agricultural land can be done by using mercury-reducing bacteria. This research aims to select the most potential indigenous bacteria for mercury remediation. Soil and sludge samples were collected from 2 districts in Sukabumi, where gold processing using mercury is common. Bacteria were selectively isolated from cultured colonies grown in Luria Bertani broth supplemented with HgCl2 30 mg/L. We obtained 27 isolates that belong to 16 species, as identified by API® 20 E and 20 NE (BioMérieux, USA). The growth of each isolate was assessed by measuring the optical density of inoculated LB broth contained HgCl2 30 mg/L for 5 consecutive days. All isolates showed normal growth. The log phase reached its maximum value on the second or third day after inoculation and lag phase afterward. Twelve identified isolates were chosen for evaluation of their resistance to mercury by growing them in Mueller-Hinton agar supplemented with HgCl2 (30 mg/L, 50 mg/L, 100 mg/L, 150 mg/L, and 200 mg/L). Seven isolates were able to grow in media with HgCl2, but only Mer07 survived on HgCl2 150 mg/L.

Deep-sea mercury resistant bacteria from the Central Indian Ocean: A potential candidate for mercury bioremediation

Deep-sea bacteria when grown in normal environmental conditions get morphologically and genetically adapted to resist the provided culture conditions for their survival, making them a possible aspirant in mercury bioremediation. In this study, seawater samples were collected from different depths of the Central Indian Ocean and seven mercury resistant bacteria (resistant to 100 mg L-1 concentration of inorganic Hg as HgCl2) were isolated. Based on 16S rRNA gene sequencing, the identified isolates belong to the genera Pseudomonas, Bacillus and Pseudoalteromonas. The presence of the merA gene in the isolates contributes to the effective volatilization of mercury. The Inductively Coupled Plasma Mass-Spectroscopy analysis revealed that the isolates can reduce up to >80% of inorganic mercury. Moreover, Fourier Transform Infrared spectrum analysis indicates that functional groups play a key role in the mechanism of adaptation towards Hg2+ reduction. Thus, the deep-sea bacteria expressed significant tolerance and reduction potential towards ionic mercury.

Overproduction and Purification of Organomercuric Lyase (MerB) from Mercury-resistant Bacteria Pseudomonas aeruginosa Isolate 4B2

Mercury is a very toxic element even though there is very little concentration in the body. Although all chemical forms of mercury are toxic, public health attention is focused on organic mercury which is the most toxic form of mercury. Organic mercury can, however, be detoxified by organomercuric lyase (MerB) protein derived from mercury resistant bacteria. This study aims to overproduce of MerB protein by transforming merB gene into E. coli BL-21(DE3). Nucleotide sequence of merB gene of mercury resistant bacteria Pseudomonas aeruginosa isolates 4B2, optimized by using gene program designers (www.dna20/com) then commercially synthesized and cloned in pET16b expression plasmid vector. Plasmid pET16b_merB (syntetic gene) was transformed into E. coli BL21(DE3) to produce MerB protein recombinant, induced with isopropyl-β-D-thiogalactopyranoside (IPTG) and purified by imidazol. Overproduction and purification of MerB protein was successfully performed in E. coli BL21 mediated by plasmid pET16b, resulting MerB protein with a molecular weight of 25.6 kDa, with the optimum at 37°C incubation temperature, incubation time of 3 hours and 0.1 mM IPTG induction. MerB protein obtained can be used in further research on the enzymatic detoxification of organic mercury.

Potential bacteria capable of remediating mercury contaminated soils

Mercury content in ex-artisanal and small-scale gold mining areas in Cianjur District, Province of West Java, Indonesia was 7 to 36 mg L−1. It has exceeded the threshold value for industrial land. Bioremediation of mercury using mercury-resistant bacteria is attractive to remove mercury from the environment because it is more effective and less expensive. The objective of this study was to obtain potential bacteria capable of accumulating mercury to be used to remediate mercury contaminated soils in ex-gold mining areas. Potential bacteria isolates were characterized for their phenotypic and biochemical properties using the Biolog system. Thirty-two mercury-resistant bacteria were successfully isolated from the rhizosphere of Pityrogramma tartarea growing predominantly around tailings of ex-artisanal gold mining. After screening the presence of mercury, the three best isolates showing high resistances are Pseudomonas putida R2.13 and P. maculicola R4.27 that are capable to tolerate 180 mg L−1 mercury, and Enterobacter aerogenes R3.24 that is capable to survive at 170 mg L−1. Furthermore, the three bacteria also can fix atmospheric nitrogen and solubilize phosphate, but they cannot solubilize potassium. These indicate that P. maculicola R4.27, P. putida R2.13, and E. aerogenes R3.24 are potential as bioaccumulation agents on mercury-contaminated soils.

Fabrication of an artificial ionic gate inspired by mercury-resistant bacteria for simple and sensitive detection of mercury ion

Bioremediation of mercury pollution by mercury-resistant bacteria requires the key steps of mercury ions (Hg2+) capture and transportation. Inspired by the functions of mercury transporters in mercury-resistant bacteria, we have fabricated an artificial ionic gate, which may further behave as an Hg2+ biosensor. The gate is constructed by using the asymmetrically modified porous anodic alumina (PAA) film capable of forming Hg2+-activated complexes to control ionic current, while the gate works due to the changes between graphene oxide (GO) and different DNA structures. Specifically, single strand poly(T)n DNA on PAA film may transform into duplex structure through T-Hg2+-T coordination chemistry when Hg2+ exists. Compared with the ring by ring delivery via S-Hg intermediates in bacteria, this artificial gate may show better flexibility for Hg2+ transport, because the poly(T)n-Hg2+ complex can be wrapped in a chain structure with controllable DNA length. Furthermore, with the advantages of simple structure, convenient operation and good practicality, the constructed artificial Hg2+-activated ionic gate has been developed as a biosensor for sensitive detection of Hg2+, with the limit of detection (LOD) down to 0.07 fM. The fabricated ionic gate may be used for building an instrument that can absorb and detect Hg2+ from wastewater in the future.

Production of methylmercury by sulphate-reducing bacteria in sediments from the orbetello lagoon in presence of high macroalgal loads

Methylmercury is a potent neurotoxin affecting shallow-water ecosystems. Mercury polluted sediment samples were collected at six different sites in the Orbetello Lagoon (central Italy) characterized by high levels of silt, iron, manganese hydroxides, and organic matter originated the latter originated from the decomposition of macroalgae. Porous water pointed out the presence of sulphates, methylmercury, and sulphides. Slurries arranged in anaerobic conditions from sediment aliquots from the six sites, with the addition of ionic mercury, highlighted the production of methylmercury. Sulphate reducing bacteria (SRB) were quantified in lagoon sediments; furthermore, sediments cultured under anaerobic conditions showed SRBs active in mercury methylation. Anaerobic cultures of SRB, amended with ionic mercury, produced methylmercury during the growth of bacterial cells. The percentage of aerobic mercury resistant bacteria was pointed out at each sampling site, evidencing the presence of bioavailable mercury. Several aerobic mercury resistant bacteria were isolated and their level of resistance to inorganic and organic forms of mercury was evaluated. These isolates may be potentially used for eventual bioremediation processes. Mercury methylation by SRB in the Orbetello Lagoon sediments was described for the first time, focusing the attention on the need for possible bioremediation processes by using autochthonous mercury resistant bacteria. Moreover, the influence of algal biomass on mercury methylation was highlighted for the first time in this lagoon ecosystem. The importance of removing algal biomass, as it represents a source of organic matter favouring the process of mercury methylation, was strongly pointed out in this study.

Effects of Mercury II on Cupriavidus metallidurans Strain MSR33 during Mercury Bioremediation under Aerobic and Anaerobic Conditions

Mercury is a toxic element that harms organisms and disturbs biogeochemical cycles. Mercury bioremediation is based on the reduction of Hg (II) to Hg (0) by mercury-resistant bacteria. Cupriavidus metallidurans MSR33 possesses a broad-spectrum mercury resistance. This study aims to establish the effects of mercury on growth, oxygen uptake, and mercury removal parameters by C. metallidurans MSR33 in aqueous solution during aerobic and anaerobic mercury bioremediation. A new culture medium (GBC) was designed. The effects of mercury (II) (20 ppm) on growth parameters, oxygen uptake, and mercury removal were evaluated in GBC medium in a bioreactor (3 L) under aerobiosis. The anaerobic kinetics of mercury removal was evaluated by nitrogen replacement during mercury bioremediation in a bioreactor. Strain MSR33 reached a growth rate of µ = 0.43 h−1 in the bioreactor. Mercury inhibited oxygen uptake and bacterial growth; however, this inhibition was reversed after 5 h. Strain MSR33 was able to reduce Hg (II) under aerobic and anaerobic conditions, reaching, at 24 h, a metal removal of 97% and 71%, respectively. Therefore, oxygen was crucial for efficient mercury removal by this bacterium. Strain MSR33 was capable of tolerating the toxic effects of mercury (II) during aerobic bioremediation and recovered its metabolic activity.

Molecular Characterization of Mercury Resistant Bacteria Isolated from Tannery Wastewater

Molecular Characterization of Mercury Resistant Bacteria Isolated from Tannery Wastewater

Identification of A Novel Arsenic Resistance Transposon Nested in A Mercury Resistance Transposon of Bacillus sp. MB24.

A novel TnMERI1-like transposon designated as TnMARS1 was identified from mercury resistant Bacilli isolated from Minamata Bay sediment. Two adjacent ars operon-like gene clusters, ars1 and ars2, flanked by a pair of 78-bp inverted repeat sequences, which resulted in a 13.8-kbp transposon-like fragment, were found to be sandwiched between two transposable genes of the TnMERI1-like transposon of a mercury resistant bacterium, Bacillus sp. MB24. The presence of a single transcription start site in each cluster determined by 5′-RACE suggested that both are operons. Quantitative real time RT-PCR showed that the transcription of the arsR genes contained in each operon was induced by arsenite, while arsR2 responded to arsenite more sensitively and strikingly than arsR1 did. Further, arsenic resistance complementary experiments showed that the ars2 operon conferred arsenate and arsenite resistance to an arsB-knocked out Bacillus host, while the ars1 operon only raised arsenite resistance slightly. This transposon nested in TnMARS1 was designated as TnARS1. Multi-gene cluster blast against bacteria and Bacilli whole genome sequence databases suggested that TnMARS1 is the first case of a TnMERI1-like transposon combined with an arsenic resistance transposon. The findings of this study suggested that TnMERI1-like transposons could recruit other mobile elements into its genetic structure, and subsequently cause horizontal dissemination of both mercury and arsenic resistances among Bacilli in Minamata Bay.

Quantification and characterization of mercury resistant bacteria in sediments contaminated by artisanal small-scale gold mining activities, Kedougou region, Senegal

This study describes Hg-resistant bacterial present in the aquatic sediments artisanal small-scale gold mining ASGM activities along Gambia River Kedougou, Senegal. Mercury (Hg) is used for gold amalgamation in artisanal small-scale gold mining (ASGM) activities. The level of total Hg in sediment samples was determined by automatic mercury analyser. Bacterial (colony-forming units) susceptibility to Hg was evaluated by minimal inhibitory concentrations. The phylogenetic diversity analysis of the Hg-resistant bacteria was performed by PCR amplification of 16S rDNA on isolated bacterial strains, followed by restriction fragment length polymorphism, cloning and sequencing. The results documented high concentrations of Hg in ASGM activity areas ranging from 2.4 to 6.2 mg kg-1. Population densities of heterotrophic bacteria in wet sediment ranging from 3.7 × 106 to 4.6 × 108 CFU g−1. The isolated bacterial strains from highly Hg-contaminated sites can grow to medium containing up to 17 mg L−1 of Hg2+. In this study, bacterial strains resistant to Hg are Stenotrophomonas maltophilia, Dyella ginsengisoli, Arthrobacter defluvi, Arthrobacter pascens, Bacillus firmus and Pseudomonas moraviensis. Our results demonstrate the occurrence the presence of diverse groups of bacterial strains resistant to metal (Hg) under tropical conditions. The isolated strains are particularly interesting for further studies to evaluate their role in bioremediation of Hg in contaminated aquatic ecosystems.

Bioremediation treatment process through mercury-resistant bacteria isolated from Mithi river

Unorganized development all over the world has resulted in the deterioration of the environment. The Mithi river located in Mumbai area is also one of the victims of this unorganized development. It has become a dumping site for industrial effluents, which contains various toxic materials including heavy metals such as mercury, chromium, arsenic. Physicochemical analysis of the Mithi river water samples has confirmed the deterioration of river water. Various parameters of Mithi river water such as electrical conductivity (EC), total dissolved salts (TDS), salinity, chemical oxygen demand (COD) and biological oxygen demand (BOD) were found to be higher than the normal values prescribed for the river water. In the present study, mercury-resistant bacteria were isolated from Mithi river and identified by biochemical and molecular analysis. The molecular identification of the mercury-resistant bacteria was done by 16S rDNA identification, which were identified as Bacillus sp. strain CSB_B078, Klebsiella pneumoniae strain FY2, Klebsiella pneumoniae isolate 23, Enterobacter sp. strain Amic_7, Enterobacter sp. strain 08, Acinetobacter seohaensis strain S34, Acinetobacter sp. 815B5_12ER2A. Mercury-resistant bacteria were isolated from both low- and high-salinity sites of Mithi river. The minimum inhibitory concentration of bacterial isolates against mercury was determined. Bacterial isolates could tolerate and grow in the presence of 700 ppm mercury and could also tolerate a high salinity of 35 ppt of NaCl. Resistance of bacterial isolates to high concentration of mercury and high-salinity stress suggests that the bacterial isolates could be an efficient candidate for bioremediation of mercury.