Bioreduction of Cr(VI) by alkaliphilic Bacillus subtilis and interaction of the membrane groups

AbstractDetoxification of Cr(VI) under alkaline pH requires attention due to the alkaline nature of many effluents. An alkaliphilic gram-positive Bacillus subtilis isolated from tannery effluent contaminated soil was found to grow and reduce Cr(VI) up to 100% at an alkaline pH9. Decrease in pH to acidic range with growth of the bacterium signified the role played by metabolites (organic acids) in chromium resistance and reduction mechanism. The XPS and FT-IR spectra confirmed the reduction of Cr(VI) by bacteria into +3 oxidation state. Chromate reductase assay indicated that the reduction was mediated by constitutive membrane bound enzymes. The kinetics of Cr(VI) reduction activity derived using the monod equation proved (Ks=0.00032) high affinity of the organism to the metal. This study thus helped to localize the reduction activity at subcellular level in a chromium resistant alkaliphilic Bacillus sp

Bound Pairs: Direct Evidence for Long-range Attraction between Like-Charged Colloids

We report observations of stable bound pairs in very dilute deionized aqueous suspensions of highly charged polystyrene colloidal particles, with monovalent counterions, using a confocal laser scanning microscope. Through an analysis of several thousands of time series of confocal images recorded deep inside the bulk suspension, we find that the measured pair-potential, U(r) has a long-range attractive component with well depths larger than the thermal energy. These observations provide a direct and unequivocal evidence for the existence of long-range attraction in U(r) of like-charged colloidal particles.Comment: 8 pages, 4 figures, submitted to Phys. Rev. Let

Structure and Dynamics in Polyacrylami de Hydrogels With and Without Probe Particles : A Light Scattering Study

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Dynamics of Deinococcus radiodurans under Controlled Growth Conditions

Deinococcus radiodurans is a potent radiation resistant bacterium with immense potential in nuclear waste treatment. In this investigation, the translational and rotational dynamics of dilute suspensions of D. radiodurans cultured under controlled growth conditions was studied by the polarized and depolarized dynamic light-scattering (DLS) techniques. Additionally, confocal laser scanning microscopy was used for characterizing the cultured samples and also for identification of D. radiodurans dimer, tetramer, and multimer morphologies. The data obtained showed translational diffusion coefficients (D(T)) of 1.2 × 10(−9), 1.97 × 10(−9), and 2.12 × 10(−9) cm(2) /s, corresponding to an average size of 3.61, 2.22, and 2.06 μm, respectively, for live multimer, tetramer, and dimer forms of D. radiodurans. Depolarized DLS experiments showed very slow rotational diffusion coefficients (D(R)) of 0.182/s for dimer and 0.098/s for tetramer morphologies. No measurable rotational diffusion was observed for multimer form. Polarized DLS measurements on live D. radiodurans confirmed that the bacterium is nonmotile in nature. The dynamics of the dead dimer and tetramer D. radiodurans were also studied using polarized and depolarized DLS experiments and compared with the dynamics of live species. The dead cells were slightly smaller in size when compared to the live cells. However, no additional information could be obtained for dead cells from the polarized and depolarized dynamic light-scattering studies