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Geomicrobiology of mine tailing from Asia’s largest open-cast Cu mine at Malanjkhand was established, emphasizing the roles of microorganisms in acidification process using 16S rRNA gene amplicon a...

Anaerobic enrichment of As5+ reducing bacteria in the presence and/or absence of organic carbon (OC) and As5+ from As contaminated soil of Brahmaputra river basin (BRB) (Jorhat, Assam) was performe...

Molecular and eco-physiological characterization of arsenic (As)-transforming and hydrocarbon-utilizing Achromobacter type strain KAs 3–5T has been investigated in order to gain an insight into As-...

Metal resistance and uranium (U) sequestration abilities of bacteria residing in subsurface U ore was investigated using 122 pure culture strains isolated through enrichment. The cumulative frequencies of isolates resistant to each metal tested were as follows: As(V), 74%; Zn, 58%; Ni, 53%; Cd, 47%; Cr(VI), 41%; Co, 40%; Cu, 20%; and Hg, 4%. 16S rRNA gene analysis revealed that isolated bacteria belonged to 14 genera with abundance of Arthrobacter, Microbacterium, Acinetobacter and Stenotrophomonas. Cobalt did not interfere with the growth of most of the bacterial isolates belonging to different groups while U allowed growth of four different genera of which Stenotrophomonas and Microbacterium showed high U tolerance. Interestingly, tolerance to Ni, Zn, Cu, and Hg was observed only in Microbacterium, Arthrobacter, Paenibacillus¸ and Acinetobacter, respectively. However, Microbacterium was found to be dominant when isolated from other five different metal enrichments including U. Uranium removal study showed that 84% of the test bacteria could remove more than 50mgUg(-1) dry weight from 80 or 160mgL(-1) U within 48h. In general, Microbacterium, Arthrobacter and Acinetobacter could remove a higher amount of U. High resolution transmission electron microscopy (HRTEM) study of U exposed cells revealed that accumulated U sequestered mostly around the cell periphery. The study highlights that indigenous U ore deposit bacteria have the potential to interact with U, and thus could be applied for bioremediation of U contaminated sites or wastes.

A uranium (U)-resistant and -accumulating Pseudomonas aeruginosa strain was characterized to assess the response of toxic metals toward its growth and expression of metal resistance determinants. The bacterium showed MIC (minimum inhibitory concentration) values of 6, 3, and 2 mM for Zn, Cu, and Cd, respectively; with resistance phenotype conferred by periplasmic Cu sequestering copA and RND type heavy metal efflux czcA genes. Real-time PCR-based expression analysis revealed significant upregulation of both these genes upon exposure to low concentrations of metals for short duration, whereas the global stress response gene sodA encoding superoxide dismutase enzyme was upregulated only at higher metal concentrations or longer exposure time. It could also be inferred that copA and czcA are involved in providing resistance only at low metal concentrations, whereas involvement of "global stress response" phenomenon (expression of sodA) at higher metal concentration or increased exposure was evident. This study provides significant understanding of the adaptive response of bacteria surviving in metal and radionuclide contaminated environments along with the development of real-time PCR-based quantification method of using metal resistance genes as biomarker for monitoring relevant bacteria in such habitats.

Uranium and other metallic wastes released due to geochemical and several anthropogenic activities cause enormous damage to the environment. The fate and mobility of uranium (U) in the environment is affected by diverse microorganisms which interact through different mechanisms. Uranium at contaminated sites exists predominantly in two most common and stable valence states forms—the most oxidized valence state U(VI) exists as the highly soluble and toxic uranyl species (UO2 2+) while the reduced insoluble and less mobile, U(IV) is stable in the form of the mineral uraninite (UO2) under anoxic conditions. Reduced U(IV) species is less toxic and poorly soluble but it is liable to reoxidation and subsequent remobilization to soluble and more toxic U(VI) under oxic conditions. Fundamental understanding of nonreductive bacterial interaction mechanisms affecting the mobility and solubility of U(VI) in the environment is useful for developing suitable remediation and long-term management plan for U-contaminated sites. The present study gives an overview of various nonreductive bacterial interaction processes which affects the mobility and solubility of U(VI) in oxygenic environments.

Nine arsenic (As)-resistant bacterial strains isolated from As-rich groundwater samples of West Bengal were characterized to elucidate their potential in geomicrobial transformation and bioremediation aspects. The 16S rRNA gene-based phylogenetic analysis revealed that the strains were affiliated with genera Actinobacteria, Microbacterium, Pseudomonas and Rhizobium. The strains exhibited high resistance to As [Minimum inhibitory concentration (MIC) ≥ 10 mM As(3+) and MIC ≥ 450 mM As(5+)] and other heavy metals, e.g., Cu(2+), Cr(2+), Ni(2+), etc. (MIC ≥ 2 mM) as well as As transformation (As(3+) oxidation and As(5+) reduction) capabilities. Their ability to utilize diverse carbon source(s) including hydrocarbons and different alternative electron acceptor(s) (As(5+), SO4(2-), S2O3(2-), etc.) during anaerobic growth was noted. Growth at wide range of pH, temperature and salinity, production of siderophore and biofilm were observed. Together with these, growth pattern and transformation kinetics indicated a high As(3+) oxidation activity of the isolates Rhizobium sp. CAS934i, Microbacterium sp. CAS905i and Pseudomonas sp. CAS912i. A positive relation between high As(3+) resistance and As(3+) oxidation and the supportive role of As(3+) in bacterial growth was noted. The results highlighted As(3+) oxidation process and metabolic repertory of strains indigenous to contaminated groundwater and indicates their potential in As(3+) detoxification. Thus, such metabolically well equipped bacterial strains with highest As(3+) oxidation activities may be used for bioremediation of As contaminated water and effluents in the near future.

Ten different Gram-negative arsenic (As)-resistant and As-transforming bacteria isolated from As-rich groundwater of West Bengal were characterized to assess their role in As mobilization. 16S rRNA gene analysis confirmed the affiliation of these bacteria to genera Achromobacter, Brevundimonas, Rhizobium, Ochrobactrum, and Pseudoxanthomonas. Along with superior As-resistance and As-transformation abilities, the isolates showed broad metabolic capacity in terms of utilizing a variety of electron donors and acceptors (including As) under aerobic and anaerobic conditions, respectively. Arsenic transformation studies performed under various conditions indicated highly efficient As(3+) oxidation or As(5+) reduction kinetics. Genes encoding As(3+) oxidase (aioA), cytosolic As(5+) reductase (arsC), and As(3+) efflux pump (arsB and acr3) were detected within the test isolates. Sequence analyses suggested that As homeostasis genes (particularly arsC, arsB, and acr3) were acquired by most of the bacteria through horizontal gene transfer. A strong correlation between As resistance phenotype and the presence of As(3+) transporter genes was observed. Microcosm study showed that bacterial strain having cytosolic As(5+) reductase property could play important role in mobilizing As (as As(3+)) from subsurface sediment.

Microbial diversity within uranium mine tailings and mine water sediment from the Jaduguda uranium mine, India was characterized by metagenome-derived 16S rRNA gene clone libraries. Samples from fresh tailings (JFT244), abandoned (vegetated) tailings (JOT245) and mine water sediment (J1-5) having wide ranges of pH (5.7 to 10.4), nitrogen, phosphorus and organic carbon [150-5700 ppm, 800-9100 ppm and 0.18-6.5% (w/w)] and elevated metals (Ni, Cu, Zn and U) were used to explore the inhabitant bacterial and archaeal community structures. Consistent to the sample's physicochemical properties, up to four orders of magnitude variation in bacterial CFU counts was observed. The data showed that with increasing metal and decreasing nutrient (organic C, N, P, etc.) contents, microbial diversity indices decrease within the samples. Culture-independent analyses revealed predominance of phyla Proteobacteria and/or Acidobacteria within the samples along with members of Actinobacteria, Cyanobacteria, Chloroflexi, Genera incertae sedis OP10, Firmicutes and Planctomycete as relatively minor groups. Abundance of Crenarchaeota in tailings samples and Euryachaeota in mine water sediment was noted. Diversity of dissimilatory sulfate reductase gene (dsr) was studied. Putative metabolic properties as derived from taxonomy and phylogenetic lineages indicated presence of chemolithotrophic and heteotrophic aerobic and anaerobic organisms capable of nitrogen fixation, nitrate reduction and biogeochemical cycling of metals, sulfur and methane. The data indicated that indigenous microbial populations are capable of maintaining self-sustenance in these highly hazardous environments and possess catalytic potential for their use in in situ bioremediation.

Sixty-four arsenic (As) resistant bacteria isolated from an arsenic rich groundwater sample of West Bengal were characterized to investigate their potential role in subsurface arsenic mobilization. Among the isolated strains predominance of genera Agrobacterium/Rhizobium, Ochrobactrum and Achromobacter which could grow chemolitrophically and utilize arsenic as electron donor were detected. Higher tolerance to As(3+) [maximum tolerable concentration (MTC): ≥10 mM], As(5+) (MTC: ≥100 mM) and other heavy metals like Cu(2+), Cr(2+), Ni(2+) etc. (MTC: ≥10 mM), presence of arsenate reductase and siderophore was frequently observed among the isolates. Ability to produce arsenite oxidase and phosphatase enzyme was detected in 50 and 34 % of the isolates, respectively. Although no direct correlation among taxonomic identity of bacterial strains and their metabolic abilities as mentioned above was apparent, several isolates affiliated to genera Ochrobactrum, Achromobacter and unclassified Rhizobiaceae members were found to be highly resistant to As(3+) and As(5+) and positive for all the test properties. Arsenate reductase activity was found to be conferred by arsC gene, which in many strains was coupled with arsenite efflux gene arsB as well. Phylogenetic incongruence between the 16S rRNA and ars genes lineages indicated possible incidence of horizontal gene transfer for ars genes. Based on the results we propose that under the prevailing low nutrient condition inhabitant bacteria capable of using inorganic electron donors play a synergistic role wherein siderophores and phosphatase activities facilitate the release of sediment bound As(5+), which is subsequently reduced by arsenate reductase resulting into the mobilization of As(3+) in groundwater.

Background Hexavalent chromium (Cr(6+)) contamination is one of the mejor problems of environmental protection for its carcinogenic effect on human health. Remediation of Cr(6+) contaminated environment thus becomes highest priority. Methods A Gram positive tiny rod shaped chromate (Cr(6+)) reducing bacterium strain A1 was isolated from uranium ore collected from Jaduguda, East Singhbhum, Jharkhand. The strain was identified and characterized in terms of its potential to reduce more toxic Cr(6+) to its less toxic form for its application in bioremediation of Cr(6+) contaminated environments. Results 16S rRNA gene based phylogentic analysis identified the strain as Microbacterium oleivorans. Along with Cr(6+), the strain showed resistance to other heavy metals including Ag, Cu, Co, Hg, Ni and Zn also. Complete reduction of Cr(6+) (750 µM) was achieved within 84 h with optimum reduction at pH 9 and 30°C. Effect of different parameters including cell mass concentration, pH, induction with Cr(6+), SO4 = ion, heavy metals, etc. on Cr(6+) reduction were studied thoroughly at resting cell condition to study its potential towards Cr(6+) bioremediation. Chromate reductase gene (chrA) was detected within this strain. Conclusion Along with presence of appropriate genetic determinant, efficient Cr(6+) reduction ability of the strain indicated its potential for developing redox based Cr(6+) remediation system for varied concentrations of Cr6+ under a wide range of environmental conditions. Patent data have suggested the efficient application of Cr(6+) reducing bacteria in cleaning up of Cr(6+) contaminated environments.

Impact of uranium (U) ore and soluble uranium (at pH 4.0) contamination on agricultural soil bacterial diversity was assessed by using laboratory microcosms for one year. Diversity and abundance of metabolically active bacterial populations in periodically collected microcosm’s samples were analyzed by extracting total RNA and preparation of cDNA followed by analysis of 16S rRNA gene by DGGE and real time PCR. DGGE analysis revealed prominent shift of soil bacterial population due to uranium ore contamination within 12 months while uranium ore along with soluble U completely destroyed the soil bacterial diversity within first six months. Real time PCR based analysis indicated 100–200 folds increase in 16S rRNA gene copies of total as well as individual bacterial taxa in both U ore amended and unamended soils in first six months while increase in incubation period upto 12 months showed reduction of the same only in U ore amended soil. Antagonistic effect of U ore contamination on soil bacterial diversity indicated the severe impact of U mining likely to have on nearby ecosystems. Role of U at acidic pH in destroying the diversity completely is noteworthy as it corroborated the disastrous consequence of acid mine drainage generated from U mine sites.

Uranium accumulation by a Pseudomonas strain was characterized in terms of kinetics, effect on cell viability and role of various regulatory factors (viz. pH, Co ions and metabolism). This strain was identified as Pseudomonas aeruginosa based on 16S rRNA gene and Fatty Acid Methyl Ester (FAME) analyses. The bacterium exhibited rapid, concentration and pH dependent, uranium accumulation with maximum loading of 275 mg uranium g−1 dry wt. at pH 4.0. Survival studies during the period of uranium exposure indicated a viable but non growing state of the cells. Uranium accumulation remains largely insensitive to metabolic activity and presence of other co-ions except Fe3+. Transmission electron microscopy (TEM) confirmed the deposition of bioaccumulated uranium by live cells within the cell envelope region. Our findings suggest that the P. aeruginosa J007 has intrinsic uranium-removal and -resistance properties. Accumulated uranium is deposited within the cell envelope region providing a possible survival strategy to the bacterium. Our study contributed significantly to gain insight into bacterial interaction with uranium and will be useful in understanding the role of native microorganisms inhabiting in uranium contaminated sites in biogeochemical cycling of uranium and in bioremediation applications.

Prevalence of toxic arsenic (As) oxyanion species in oligotrophic groundwater of south-east Asiatic regions (India and Bangladesh) has threatened the health of millions of people. As-transforming bacteria alter the mobility, speciation and bioavailability of As in the aquifer ecosystem, hence play important roles in the biogeochemical cycling of As. Till date, only 19 cultivable As-transforming bacterial strains have been reported but with no description on their detail genomic and physiological perspective of As homeostasis. In this study, the draft genome (5.7 Mbp) of an As-transforming, aromatic hydrocarbon utilizing and iron disproportioning indigenous groundwater bacterium KAs 3-5 has been obtained by Ion-Torrent sequencing revealed 65% genomic GC content, 5100 protein coding genes, and taxonomic affiliation to the members of genus Achromobacter, with >85% of genomic completeness. Phylogenomic signatures like MLST of 10 house-keeping genes, cut-off of

Heavy metal sequestration by a multimetal resistant Pseudomonas strain isolated from a uranium mine was characterized for its potential application in metal bioremediation. 16S rRNA gene analysis revealed phylogenetic relatedness of this isolate to Pseudomonas fluorescens. Metal uptake by this bacterium was monophasic, fast saturating, concentration and pH dependent with maximum loading of 1048 nmol Ni2+ followed by 845 nmol Co2+, 828 nmol Cu2+ and 700 nmol Cd2+ mg−1 dry wt. Preferential metal deposition in cell envelope was confirmed by TEM and cell fractionation. FTIR spectroscopy and EDX analysis revealed a major role of carboxyl and phosphoryl groups along with a possible ion exchange mechanism in cation binding. Binary system demonstrated selective metal binding affinity in the order of Cu2+ > Ni2+ > Co2+ > Cd2+. A comparison with similar metal uptake reports considering live bacteria strongly indicated the superiority of this strain in metal sequestration, which could be useful for developing efficient metal removal system.

Extracellular polysaccharide (EPS) produced by a Pseudomonas aeruginosa strain BU2 was characterized for its ability to remove uranium from aqueous solution. The EPS was acidic in nature and found as a potent biosorbent for uranium (U), showing pH dependence and fast saturating metal sorption, being maximum (985 mg U g− 1 EPS) at pH 5.0. The polymer showed enhanced uranium sorption capacity and affinity with increasing solution pH, suggesting a preferential sorption of monovalent uranyl hydroxide ions over the nonhydroxylated divalent species. Pseudo-first-order and pseudo-second-order kinetic models were applied to the experimental data, assuming that the external mass transfer limitations in the system can be neglected and biosorption is sorption controlled. Equilibrium metal binding showing conformity to the Freundlich model suggested a multilayer sorption involving specific binding sites with affinity distribution. The presence of two types of metal binding sites corresponding to strong and w...

Arsenic (As) mobilization in alluvial aquifers is caused by a complex interplay of hydro-geo-microbiological activities. Nevertheless, diversity and biogeochemical significance of indigenous bacteria in Bengal Delta Plain are not well documented. We have deciphered bacterial community compositions and metabolic properties in As contaminated groundwater of West Bengal to define their role in As mobilization. Groundwater samples showed characteristic high As, low organic carbon and reducing property. Culture-independent and -dependent analyses revealed presence of diverse, yet near consistent community composition mostly represented by genera Pseudomonas, Flavobacterium, Brevundimonas, Polaromonas, Rhodococcus, Methyloversatilis and Methylotenera. Along with As-resistance and -reductase activities, abilities to metabolize a wide range carbon substrates including long chain and polyaromatic hydrocarbons and HCO3, As3+ as electron donor and As5+/Fe3+ as terminal electron acceptor during anaerobic growth were frequently observed within the cultivable bacteria. Genes encoding cytosolic As5+ reductase (arsC) and As3+ efflux/transporter [arsB and acr3(2)] were found to be more abundant than the dissimilatory As5+ reductase gene arrA. The observed metabolic characteristics showed a good agreement with the same derived from phylogenetic lineages of constituent populations. Selected bacterial strains incubated anaerobically over 300 days using natural orange sand of Pleistocene aquifer showed release of soluble As mostly as As3+ along with several other elements (Al, Fe, Mn, K, etc.). Together with the production of oxalic acid within the biotic microcosms, change in sediment composition and mineralogy indicated dissolution of orange sand coupled with As/Fe reduction. Presence of arsC gene, As5+ reductase activity and oxalic acid production by the bacteria were found to be closely related to their ability to mobilize sediment bound As. Overall observations suggest that indigenous bacteria in oligotrophic groundwater possess adequate catabolic ability to mobilize As by a cascade of reactions, mostly linked to bacterial necessity for essential nutrients and detoxification.

Lanthanum biosorption by a Pseudomonas sp. was characterized in terms of equilibrium metal loading, model fitting, kinetics, effect of solution pH, lanthanum-bacteria interaction mechanism and recovery of sorbed metal. Lanthanum sorption by the bacterium was rapid and optimum at pH 5.0 with equilibrium metal loading as high as 950 mg g(-1) biomass dry wt. Scatchard model and potentiometric titration suggested the presence of at least two types of metal-binding sites, corresponding to a strong and a weak binding affinity. The chemical nature of metal-microbe interaction has been elucidated employing FTIR spectroscopy, energy dispersive X-ray analysis (EDX) and X-ray diffraction analysis (XRD). FTIR spectroscopy and XRD analysis revealed strong involvement of cellular carboxyl and phosphate groups in lanthanum binding by the bacterial biomass. EDX and the elemental analysis of the sorption solution ascertained the binding of lanthanum with the bacterial biomass via displacement of cellular potassium and calcium. Transmission electron microscopy exhibited La accumulation throughout the bacterial cell with some granular deposits in cell periphery and in cytoplasm. XRD confirmed the presence of LaPO4 crystals onto the bacterial biomass after La accumulation for a long period. A combined ion-exchange-complexation-microprecipitation mechanism could be involved in lanthanum accumulation by the biomass. Almost 98% of biomass-bound La could be recovered using CaCO3 as the desorbing agent.

A Pseudomonas strain identified as a potent biosorbent of uranium (U) and thorium was immobilized in radiation-induced polyacrylamide matrix for its application in radionuclide containing wastewater treatment. The immobilized biomass exhibited a high U sorption of 202 mg g(-1) dry wt. with its optimum at pH 5.0. A good fit of experimental data to the Freundlich model suggested multilayered uranium binding with an affinity distribution among biomass metal binding sites. Scanning electron microscopy revealed a highly porous nature of the radiation-polymerized beads with bacterial cells mostly entrapped on pore walls. Energy dispersive X-ray analysis (EDXA) coupled with SEM ascertained the accumulation of uranium by the immobilized biomass without any physical damage to the cells. A significant (90%) part of biosorbed uranium was recovered using sodium bicarbonate with the immobilized biomass maintaining their U resorption capacity for multiple sorption-desorption cycles. Uranium loading and elution behavior of immobilized biomass evaluated within a continuous up-flow packed bed columnar reactor showed its effectiveness in removing uranium from low concentration (50 mg U L(-1)) followed by its recovery resulting in a 4-5-fold waste volume reduction. The data suggested the suitability of radiation polymerization in obtaining bacterial beads for metal removal and also the potential of Pseudomonas biomass in treatment of radionuclide containing waste streams.

A Pseudomonas strain, characterized as part of a project to develop a biosorbent for removal of toxic radionuclides from nuclear waste streams, was a potent accumulator of uranium (VI) and thorium (IV), with the metal sequestration process being unaffected by culture age, presence of carbon/energy source and metabolic inhibitor but sensitive to the composition of the growth medium. Further characterization of radionuclide biosorption using lyophilized biomass revealed rapid cation binding of >90% within 1– 10 min of contact and complete removal of U and Th was observed at initial concentrations up to 100 mg l −1 . Initial solution pH strongly affected radionuclide biosorption with an optimum at pH 4.0–5.0. High affinity, efficient and high capacity uranium and thorium binding was indicated, with maximum loading of 541 mg U g −1 dry mass or 430 mg Th g −1 dry mass. Good conformity of sorption data with the Langmuir model suggests monolayered U and Th binding. Sorption in presence of several interfering cations and anions indicates a specific U and Th binding by the biomass with significant antagonism offered only by iron (III). Transmission electron microscopy and energy dispersive X-ray fluorescence analysis of metal loaded biomass revealed intracellular U and Th sequestration. More than 90% of biomass-bound radionuclide was recovered using sodium or calcium carbonate. For continuous process application an immobilized biomass system was developed and tested with multiple cycles of sorption–desorption. Overall, the biosorbent appeared suitable for realistic bioremediation.

Lyophilized biomass of a Pseudomonas soilisolate adsorbed thorium (IV) (430 mg g−1 dry wt) optimally at pH 4, with 91% of equilibrium loading being reached in 1 min. Equilibrium metal sorption showing conformity to Langmuir isotherm model suggested a monolayered thorium binding. Thorium binding remained unaffected or slightly affected (< 20% inhibition) in presence of equimolar (430 μM) concentration of several interfering ions except Fe3+ (40% inhibition). More than 90% of loaded thorium could be recovered using 1 M CaCO3, though mineral acids and Na2CO3 were also effective.

Extracellular polysaccharides (EPS) of a copper-sensitive (Cus) and a copper-resistant (Cur) Pseudomonas aeruginosa strain were investigated in terms of their production, chemical nature and response towards copper exposure. The extent of EPS synthesis by the resistant strain (4.78 mg mg−1 cell dry wt.) was considerably higher over its sensitive counterpart (2.78 mg mg−1 dry wt.). FTIR-spectroscopy and gas chromatography revealed that both the polymers were acidic in nature, containing alginate as the major component along with various neutral- and amino-sugars. Acid content in the Cur EPS (480.54 mg g−1) was greater than that in the Cus EPS (442.0 mg g−1). Presence of Cu2+ in the growth medium caused a dramatic stimulation (approximately 4-fold) in EPS synthesis by the Cur strain, while in a similar condition, the Cus failed to exhibit such response. The polymer of the resistant strain showed elevated Cu2+ binding (320 mg g−1 EPS) compared to that of the sensitive type (270 mg g−1). The overall observations show the potential of the Cur EPS for its deployment in metal bioremediation.

The biosorptive uranium(VI) uptake capacity of live and lyophilized Pseudomonas cells was characterized in terms of equilibrium metal loading, effect of solution pH and possible interference by selected co-ions. Uranium binding by the test biomass was rapid, achieving >90% sorption efficiency within 10 min of contact and the equilibrium was attained after 1 h. pH-dependent uranium sorption was observed for both biomass types with the maximum being at pH 5.0. Metal uptake by live cells was not affected by culture age and the presence of an energy source or metabolic inhibitor. Sorption isotherm studies at a solution pH of either 3.5 or 5.0 indicated efficient and exceptionally high uranium loading by the test biomass, particularly at the higher pH level. At equilibrium, the lyophilized Pseudomonas exhibited a metal loading of 541 ± 34.21 mg g−1 compared with a lower value by the live organisms (410 ± 25.93 mg g−1). Experimental sorption data showing conformity to both Freundlich and Langmuir isotherm models indicate monolayered uranium binding by the test biomass. In bimetallic combinations a significant interference in uranium loading was offered by cations such as thorium(IV), iron(II and III), aluminium(III) and copper(II), while the anions tested, except carbonate, were ineffective. Uranium sorption studies in the presence of a range of Fe3+ and SO42− concentrations indicate a strong inhibition (80%) by the former at an equimolar ratio while more than 70% adsorption efficiency was retained even at a high sulfate level (30 000 mg dm−3). Overall data indicate the suitability of the Pseudomonas sp biomass in developing a biosorbent for uranium removal from aqueous waste streams. © 2001 Society of Chemical Industry

Diversity of culturable bacterial populations within the Arsenic (As) contaminated groundwater of North Eastern state (Assam) of India is studied. From nine As contaminated samples 89 bacterial strains are isolated. 16S rRNA gene sequence analysis reveals predominance of Brevundimonas (35%) and Acidovorax (23%) along with Acinetobacter (10%), Pseudomonas (9%) and relatively less abundant (5%) Undibacterium, Herbaspirillum, Rhodococcus, Staphylococcus, Bosea, Bacillus, Ralstonia, Caulobacter and Rhizobiales members. High As(III) resistance (MTC 10-50 mM) is observed for the isolates obtained from As(III) enrichment, particularly for 3 isolates of genus Brevundimonas (MTC 50 mM). In contrast, high resistance to As(V) (MTC as high as 550 mM) is present as a ubiquitous property, irrespective of isolates' enrichment condition. Bacterial genera affiliated to other groups showed relatively lower degree of As resistance [MTCs of 15-20 mM As(III) and 250-350 mM As(V)]. As(V) reductase activity is detected in strains with high As(V) as well as As(III) resistance. A strong correlation could be established among isolates capable of reductase activity and siderophore production as well as As(III) tolerance. A large number of isolates (nearly 50%) is capable of anaerobic respiration using alternate inorganic electron acceptors [As(V), Se(VI), Fe(III), [NO(3)(2), SO(4)(2), S(2)O(3)(2). Ability to utilize different carbon sources ranging from C2-C6 compounds along with some complex sugars is also observed. Particularly, a number of strains is found to possess ability to grow chemolithotrophically using As(III) as the electron donor. The study reports for the first time the identity and metabolic abilities of bacteria in As contaminated ground water of North East India, useful to elucidate the microbial role in influencing mobilization of As in the region.

Ten bacterial strains isolated from uranium mine wastes were characterized in terms of their uranium and other metal resistance and accumulation. 16S rRNA gene sequence analysis identified the strains as members of genera Bacillus, Serratia, and Arthrobacter. Strains were able to utilize various carbon sources, particularly aromatic hydrocarbons, grow at broad pH and temperature ranges and produce non specific acid phosphatase relevant for metal phosphate precipitation in contaminated environment. The isolates exhibited high uranium and other heavy metals (Ni, Co, Cu and Cd) resistance and accumulation capacities. Particularly, Arthrobacter sp. J001 and Bacillus sp. J003 were superior in terms of U resistance at low pH (pH 4.0) along with metals and actinides (U and Th) removal with maximum cell loading of 1088 μmol U, 1293 μmol Th, 425 μmol Cu, 305 μmol Cd, 377 μmol Zn, 250 μmol Ni g(-1) cell dry wt. Genes encoding P(1B)-type ATPases (Cu-CPx and Zn-CPx) and ABC transporters (nik) as catalytic tools for maintaining cellular metal homeostasis were detected within several Bacillus spp., with possible incidence of horizontal gene transfer for the later gene showing phylogenetic lineage to α Proteobacteria members. The study provides evidence on intrinsic abilities of indigenous bacteria from U-mine suitable for survival and cleaning up of contaminated mine sites.

Uranium biomineralization by a metal-resistant Pseudomonas aeruginosa strain isolated from uranium mine waste was characterized for its potential in bioremediation. Uranium resistance, its cellular localization and chemical nature of uranium-bacteria interaction were elucidated. Survival and uranium biomineralization from mine water were investigated using microcosm experiments. The selected bacterium showed U resistance and accumulation (maximum of 275 mg U g(-1)cell dry wt.) following incubation in 100 mg U L(-1), pH 4.0, for 6 h. Transmission electron microscopy and X-ray diffraction analyses revealed that bioaccumulated uranium was deposited within the cell envelope as needle shaped U-phosphate compounds that attain crystallinity only at pH 4.0. A synergistic involvement of deprotonated phosphate and carboxyl moieties in facilitating bioprecipitation of uranium was evident from FTIR analysis. Based on these findings we attribute the localized U sequestration by this bacterium as innocuous complex to its possible mechanism of uranium resistance. Microcosm data confirmed that the strain can remove soluble uranium (99%) and sequester it as U oxide and phosphate minerals while maintaining its viability. The study showed that indigenous bacteria from contaminated site that can survive uranium and other heavy metal toxicity and sequester soluble uranium as biominerals could play important role in uranium bioremediation.

The mechanism and chemical nature of uranium and thorium sequestration by a Pseudomonas strain was investigated by transmission electron microscopy, energy dispersive X-ray (EDX) analysis, FTIR spectroscopy and X-ray diffractometry. Atomic force microscopy (AFM) used in the tapping mode elucidated the morphological changes in bacterial cells following uranium and thorium binding. Transmission electron microscopy revealed intracellular sequestration of uranium and thorium throughout the cell cytoplasm with electron dense microprecipitations of accumulated metals. Energy dispersive X-ray analysis confirmed the cellular deposition of uranium and thorium. EDX and elemental analysis of sorption solution indicated the binding of uranium and thorium by the bacterial biomass via displacement of cellular potassium and calcium. The strong involvement of cellular phosphate, carboxyl and amide groups in radionuclide binding was ascertained by FTIR spectroscopy. X-ray powder diffraction (XRD) analyses confirmed cellular sequestration of crystalline uranium and thorium phosphates. Overall results indicate that a combined ion-exchange-complexation-microprecipitation mechanism could be involved in uranium and thorium sequestration by this bacterium. Atomic force microscopy and topography analysis revealed an undamaged cell surface with an increase in cell length, width and height following radionuclide accumulation. The arithmetic average roughness (R(a)) and root mean square (RMS) roughness (R(q)) values indicated an increase in surface roughness following uranium and thorium sequestration.

Aims: To investigate intracellular localization of nickel and its chemical nature in Pseudomonas aeruginosa. Methods and Results: Transmission electron micrographs of Ni-loaded bacteria exhibited a darkened electron opaque zone throughout the cell periphery. Energy dispersive X-ray analysis confirmed the deposition of metallic nickel. Cell fractionation revealed that 88% of the accumulated nickel was restricted to the periplasm and membrane. X-ray diffraction patterns ascertained the chemical nature of cellular Ni as phosphide (Ni5P4, NiP2 and Ni12P5) and carbide (Ni3C) crystals. Conclusions:Pseudomonas aeruginosa accumulated nickel as its phosphide and carbide crystal mostly in the cell envelope region, indicating the predominant role of phosphoryl and carboxyl/carbonyl groups of cell wall/membrane components in cation sequestration. Significance and Impact of the Study: The data contribute significantly to a better understanding of bacteria–metal interaction and will be useful in developing biotechnological strategies for toxic metal bioremediation.