A-3txf_sequence summary.xksx: Abundance of contigs or unique sequences for each biofilm samples from anodes in the MEC reactor Hodon Waterloo final_fasta_working.docx: Raw sequences with their identification numbers RNA S1_MEC.docx: Representative sequences with their ID number and taxonomy. This dataset is associated with the following publication: Santodomingo, J., H. Ryu, B. Dhar, and H. Lee. Ohmic resistance affects microbial community and electrochemical kinetics in a multi-anode microbial electrochemical cell. JOURNAL OF POWER SOURCES. Elsevier Science Ltd, New York, NY, USA, 331: 315-321, (2016).

This study assessed the conductivity of a Geobacter-enriched biofilm anode along with biofilm activity in a microbial electrochemical cell (MxC) equipped with two gold anodes (25 mM acetate medium), as different proton gradients were built throughout the biofilm. There was no pH gradient across the biofilm anode at 100 mM phosphate buffer (current density 2.38 A/m2) and biofilm conductivity (Kbio) was as high as 0.87 mS/cm. In comparison, an inner biofilm became acidic at 2.5 mM phosphate buffer in which approximately 80 μm of the inner biofilm anode was metabolically inactive. At this low phosphate buffer, Kbio significantly decreased by 0.27 mS/cm, together with declined current density of 0.64 A/m2. This work demonstrates that biofilm conductivity depends on metabolic activity of Geobacter in the conductive biofilm anode. The decreased Kbio at acidic environment implies the presence of multiple conduction-EET pathways in the biofilm anode. This dataset is associated with the following publication: Dhar, B., J. Sim, H. Ryu, H. Ren, J. Santodomingo, J. Chae, and H. Lee. Microbial Activity Influences Electrical Conductivity of Biofilm Anode. WATER RESEARCH. Elsevier Science Ltd, New York, NY, USA, 127: 230-238, (2017).

This study systematically assessed intracellular electron transfer (IET) and extracellular electron transfer (EET) kinetics with respect to anode potential (Eanode) in a mixed-culture biofilm anode enriched with Geobacter spp. High biofilm conductivity (0.96–1.24 mScm^-1) was maintained during Eanode changes from -0.2 to +0.2 V versus the standard hydrogen electrode (SHE), although the steady-state current density significantly decreased from 2.05 to 0.35 Am^-2 in a microbial electrochemical cell. Substantial increase of the Treponema population was observed in the biofilm anode at Eanode=+0.2 V, which reduced intracellular electron-transfer kinetics associated with the maximum specific substrate-utilization rate by a factor of ten. This result suggests that fast EET kinetics can be maintained under dynamic Eanode conditions in a highly conductive biofilm anode as a result of shift of main EET players in the biofilm anode, although Eanode changes can influence IET kinetics. This dataset is associated with the following publication: Dhar, B., H. Ryu, H. Ren, J. Santodomingo, J. Chae, and H. Lee. High Biofilm Conductivity Maintained Despite Anode Potential Changes in a Geobacter-Enriched Biofilm. ChemSusChem. Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, GERMANY, 9(24): 3485 –3491, (2016).

H2O2_COD_EPA: Measurements of hydrogen peroxide and COD concentrations for water samples from the MEC reactors. MEC_acclimation: raw data for current and voltage of the anode in the MEC reactor. This dataset is associated with the following publication: Sim, J., J. An, E. Elbeshbishy, R. Hodon, and H. Lee. Characterization and optimization of cathodic conditions for H2O2 synthesis in microbial electrochemical cells. Bioresource Technology. Elsevier Online, New York, NY, USA, 195: 31-36, (2015).

H2O2_COD_EPA: Measurements of hydrogen peroxide and COD concentrations for water samples from the MEC reactors. MEC_acclimation: raw data for current and voltage of the anode in the MEC reactor. This dataset is associated with the following publication: Sim, J., J. An, E. Elbeshbishy, R. Hodon, and H. Lee. Characterization and optimization of cathodic conditions for H2O2 synthesis in microbial electrochemical cells. Bioresource Technology. Elsevier Online, New York, NY, USA, 195: 31-36, (2015).

A biofilm anode acclimated with acetate, acetate+methane, and methane growth media for over three years produced a steady current density of 1.6-2.3 mA/m^2 in a microbial electrochemical cell (MxC) fed with methane as the sole electron donor. Geobacter was the dominant genus for the bacterial domain (93%) in the biofilm anode, while methanogens (Methanocorpusculum labreanum and Methanosaeta concilii) accounted for 82% of the total archaeal clones in the biofilm. A fluorescence in situ hybridization (FISH) image clearly showed a biofilm of bacteria and archaea, supporting a syntrophic interaction between them for performing anaerobic oxidation of methane (AOM) in the biofilm anode. Measured cumulative coulombs correlated linearly to the methane-gas concentration in the range of 10% to 99.97% (R^2 ≥ 0.99) when the measurement was sustained for at least 50 min. Thus, cumulative coulombs over 50 min. could be used to quantify the methane concentration in gas samples. This dataset is associated with the following publication: Gao, Y., H. Ryu, B. Rittmann, A. Hussain, and H. Lee. Quantification of the methane concentration using anaerobic oxidation of methane coupled to extracellular electron transfer. Bioresource Technology. Elsevier Online, New York, NY, USA, 241: 979-984, (2017).

A biofilm anode acclimated with acetate, acetate+methane, and methane growth media for over three years produced a steady current density of 1.6-2.3 mA/m^2 in a microbial electrochemical cell (MxC) fed with methane as the sole electron donor. Geobacter was the dominant genus for the bacterial domain (93%) in the biofilm anode, while methanogens (Methanocorpusculum labreanum and Methanosaeta concilii) accounted for 82% of the total archaeal clones in the biofilm. A fluorescence in situ hybridization (FISH) image clearly showed a biofilm of bacteria and archaea, supporting a syntrophic interaction between them for performing anaerobic oxidation of methane (AOM) in the biofilm anode. Measured cumulative coulombs correlated linearly to the methane-gas concentration in the range of 10% to 99.97% (R^2 ≥ 0.99) when the measurement was sustained for at least 50 min. Thus, cumulative coulombs over 50 min. could be used to quantify the methane concentration in gas samples. This dataset is associated with the following publication: Gao, Y., H. Ryu, B. Rittmann, A. Hussain, and H. Lee. Quantification of the methane concentration using anaerobic oxidation of methane coupled to extracellular electron transfer. Bioresource Technology. Elsevier Online, New York, NY, USA, 241: 979-984, (2017).

Background The metallo-β-lactamases are Zn(II)-containing enzymes that hydrolyze the β-lactam bond in penicillins, cephalosporins, and carbapenems and are involved in bacterial antibiotic resistance. There are at least 20 distinct organisms that produce a metallo-β-lactamase, and these enzymes have been extensively studied using X-ray crystallographic, computational, kinetic, and inhibition studies; however, much is still unknown about how substrates bind and the catalytic mechanism. In an effort to probe substrate binding to metallo-β-lactamase L1 from Stenotrophomonas maltophilia, nine site-directed mutants of L1 were prepared and characterized using metal analyses, CD spectroscopy, and pre-steady state and steady state kinetics. Results Site-directed mutations were generated of amino acids previously predicted to be important in substrate binding. Steady-state kinetic studies using the mutant enzymes and 9 different substrates demonstrated varying Km and kcat values for the different enzymes and substrates and that no direct correlation between Km and the effect of the mutation on substrate binding could be drawn. Stopped-flow fluorescence studies using nitrocefin as the substrate showed that only the S224D and Y228A mutants exhibited weaker nitrocefin binding. Conclusions The data presented herein indicate that Ser224, Ile164, Phe158, Tyr228, and Asn233 are not essential for tight binding of substrate to metallo-β-lactamase L1. The results in this work also show that Km values are not reliable for showing substrate binding, and there is no correlation between substrate binding and the amount of reaction intermediate formed during the reaction. This work represents the first experimental testing of one of the computational models of the metallo-β-lactamases.