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Abstract: Developing electrode-driven biocatalytic systems utilizing the P450 cytochromes for selective oxidations depends not only on achieving electron transfer (ET) but also doing so at rates that favor native-like turnover. Herein we report studies that correlate rates of heme reduction with ET pathways and resulting product distributions. We utilized single-surface cysteine mutants of the heme domain of P450 from Bacillus megaterium and modified the thiols with N-(1-pyrene)-iodoacetamide, affording proteins that could bond to basal-plane graphite. Of the proteins examined, Cys mutants at position 62, 383, and 387 were able to form electroactive monolayers with similar E1/2 values (−335 to −340mV vs AgCl/Ag). Respective ET rates (ks o) and heme-cysteine distances for 62, 383, and 387 are 50 s-1 and 16Ǻ, 0.8 s–1 and 25Ǻ, and 650 s–1 and 19Ǻ. Experiments utilizing rotated-disk electrodes were conducted to determine the products of P450-catalyzed dioxygen reduction. We found good agreement between ET rates and product distributions for the various mutants, with larger ks o values correlating with more electrons transferred per dioxygen during catalysis. [Copyright &y& Elsevier]

Abstract: Two Gram (+) bacterial strains, BSB6 and BSB12, showing resistance and potential for Se(IV) reduction among 26 moderately halotolerant isolates from the Bhitarkanika mangrove soil were characterized by biochemical and 16S rDNA sequence analyses. Both of them were strictly aerobic and able to grow in a wide range of pH (4–11), temperature (4–40°C) and salt concentration (4–12%) having an optimum growth at 37°C, pH ∼7.5 and 7% salt (NaCl). The biochemical characteristics and 16S rDNA sequence analysis of BSB6 and BSB12 showed the closest phylogenetic similarity with the species Bacillus megaterium. Both the strains effectively reduced Se(IV) and complete reduction of selenite (up to 0.25mM) was achieved within 40h. SEM with energy dispersive X-ray and TEM analyses revealed the formation of nano size spherical selenium particles in and around the bacterial cells which were also supported by the confocal micrograph study. The UV–Vis diffuse reflectance spectra and XRD of selenium precipitates revealed that the selenium particles are in the nanometric range and crystalline in nature. These bacterial strains may be exploited further for bioremediation process of Se(IV) at relatively high salt concentrations and green synthesis of selenium nanoparticles. [Copyright &y& Elsevier]

• At an optimal concentration of 25 ppm, Padina pavonica and Sargassum tenerrimuman obtained 75 and 73% inhibitory efficiency, respectively. • The Extracellular Electron Transfer (EET) of Bacillus megaterium was inhibited using the methanolic extraction of seaweeds. • The bioactive compounds of seaweeds are more potential to inhibit bacterial growth and prevent the biofilm layer. • MEPP and MEST revealed the existence of organic compounds like N, S, O blocking electron transfers reduce the corrosion rate. Biocorrosion is an aggregation of microbes on the metal surface that induces ion degradation by oxidation and reduction of chemical and electrochemical reactions. Extracellular electron transfer (EET) process was a significant phenomenon in ion deterioration. To block the EET process, the inhibitor was used to destroy or prevent extracellular electron transfer during microbial metabolism. In the present study, methanolic extraction of two different seaweeds acts as a bio-inhibitor against the corrosive biofilm forming bacteria B.megaterium SKR7 on the mild steel. The optimized concentration of biofilm inhibition efficiency of methanolic extract P.pavonica (MEPP) and S.tenerrimum (MEST) was found to be 75% and 73% at 25 ppm respectively. It was confirmed by assay of antimicrobial activity and weight loss measurement which is represented the reduction of corrosion rate S3 (A) 0.355 mm/y and S3 (B) 0.442 mm/y of both seaweed extracts than control (1.598 mm/y). This observation was confirmed by the electrochemical studies by the significant decrease in charge transfer resistance (R ct) and the surface analysis of FTIR and SEM analysis were confirmed the seaweeds inhibit the biofilm. MEPP and MEST revealed the existence of organic and bioactive compounds like N, S, O blocks the electron transfers during the biofilm formation on a metal surface and thus inhibits corrosion rate. The study concluded seaweed extracts act as mixed-type of inhibitors, thus effectivley inhibit the biofilm formation and are easily accessible at low cost, eco-friendly. [ABSTRACT FROM AUTHOR]