Pinaki Sar

Metal adsorption and desorption by lyophilized Pseudomonas aeruginosa

Biosorption of nickel (Ni2+) and copper (Cu2+) by lyophilized Pseudomonas aeruginosa cells was investigated based on Freundlich isotherm. Bacterial biomass showed significant sorption of both Ni (265 mg g−1) or Cu (137.6 mg g−1), and was also superior over the cation exchanger, IRA 400 (98 mg Ni g−1 or 26.6 mg Cu g−1). Metal binding by the test organism was a fast saturating, pH-dependent process. The optimum pH for Cu adsorption was 7.0 and for Ni 8.0. X-ray diffraction studies revealed that both cations were deposited on the cell predominantly as phosphide crystals. The participation of carboxyl, carbonyl, and phosphoryl groups along with H-bonding in metal sorption was evident in IR spectra. Biomass pretreatment by agents like NaOH, NH4OH or toluene enhanced the metal loading capacity, whereas, oven heating (80°C), autoclaving (120°C, 15 lb (in.2)−1), acid, detergent and acetone treatments were inhibitory. In bimetallic combination, Na, K or Ca increased sorption of Ni as well as Cu in contrast to Cd or Pb. Mineral acids (HCl, H2SO4 and HNO3) and NTA could recover more than 75% (on average) Ni or Cu adsorbed on the biomass. Calcium carbonate (10 mM) was efficient in Ni desorption (71%) compared to Cu (57%). Noticeably sodium carbonate remained specific for Cu remobilization (88%) than Ni (21%). The data are in favour of deployment of the test biomass as an efficient metal removal/recovery system.

Uranium and thorium sequestration by a Pseudomonas sp.: Mechanism and chemical characterization

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.

Extracellular polysaccharides of a copper-sensitive and a copper-resistant Pseudomonas aeruginosa strain: synthesis, chemical nature and copper binding

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.

Uranium biomineralization by a metal resistant Pseudomonas aeruginosa strain isolated from contaminated mine waste.

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.

Characterization of a metal resistant Pseudomonas sp. isolated from uranium mine for its potential in heavy metal (Ni2+, Co2+, Cu2+, and Cd2+) sequestration.

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 Ni(2+) followed by 845 nmol Co(2+), 828 nmol Cu(2+) and 700 nmol Cd(2+)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 Cu(2+)>Ni(2+)>Co(2+)>Cd(2+). 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.

Intracellular nickel accumulation by Pseudomonas aeruginosa and its chemical nature

Aims: To investigate intracellular localization of nickel and its chemical nature in Pseudomonas aeruginosa.

Copper uptake and its compartmentalization in Pseudomonas aeruginosa strains: Chemical nature of cellular metal

Copper-sensitive (Cus) and copper-resistant (Cur) strains of Pseudomonas aeruginosa were characterized in terms of Cu2+ sensitivity, uptake and its compartmentalization in the possible cell sectors. Minimum inhibitory concentrations (MICs) of Cu2+ for the Cur strain (3.2 mM and 0.12 mM in enriched- and in minimal-medium, respectively) were almost 5-fold higher over that of its sensitive counterpart. While Cus strain accumulated Cu2+ to a maximum of 1.8 μ mol mg−1 protein, Cur strain increased it to 2.37 μmol mg−1 protein. Both the strains also demonstrated energy- and pH-dependent Cu2+ uptake through the broad-substrate range divalent cation (Zn2+, Mg2+, Co2+) uptake system as well as through the system specific for Cu2+. Cell-fractionation study revealed that in Cur strain, periplasm and membrane are the main Cu2+ binding sites, whereas, in case of Cus strain, it is the cytoplasm. The overall observations indicate that the Cur strain restricted Cu2+ sequestration exterior to the cytoplasm as the possible strategy for Cu-resistance. The chemical nature of Cu2+ deposition in the respective strains was also ascertained by X-ray powder diffraction analysis.

Culture-dependent and -independent molecular analysis of the bacterial community within uranium ore

The bacterial community structure within a uranium ore was investigated using culture‐dependent and ‐independent clone library analysis and denaturing gradient gel electrophoresis of 16S rRNA genes. The major aerobic heterotrophic bacteria were isolated and identified, and their resistance to uranium and other heavy metals was characterized. Together with near neutral pH, moderate organic carbon content, elevated U and other heavy metals (V, Ni, Mn, Cu, etc.), the ore showed high microbial counts and phylotype richness. The bacterial community mainly consisted of uncultured Proteobacteria, with the predominance of γ ‐ over β ‐ and α ‐subdivisions, along with Actinobacteria and Firmicutes. A phylogenetic study revealed that nearly one‐third of the community was affiliated to as yet uncultured and unidentified bacteria having a closer relationship to Pseudomonas. Lineages of Burkholderiaceae and Moraxellaceae were relatively more abundant in the total community, while genera affiliated to Xanthomonadaceae and Microbacteriaceae and Exiguobacterium were detected in the culturable fraction. More than 50% of the bacterial isolates affiliated to Stenotrophomonas, Microbacterium, Acinetobacter, Pseudomonas and Enterobacter showed resistance to uranium and other heavy metals. The study showed for the first time that uranium ore harbors major bacterial groups related to organisms having a wide range of environmentally significant functional attributes, and the most abundant members are possibly new groups/taxa. These findings provide new insights into U‐ore geomicrobiology that could be useful in biohydrometallurgy and bioremediation applications. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Uranium Sorption by Pseudomonas Biomass Immobilized in Radiation Polymerized Polyacrylamide Bio-Beads

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.

Diversity, metabolic properties and arsenic mobilization potential of indigenous bacteria in arsenic contaminated groundwater of West Bengal, India.

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.