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In this study we aimed to identify small molecules with high affinity involved in the allosteric regulation of LV15553, a MarR member from Lactobacillus brevis ATCC367. Using high throughput screening, novobiocin was found to specifically bind LVIS553 with a KD = 33.8 ± 2.9 µM consistent with a biologically relevant ligand. Structure guided site-directed mutagenesis identified Lys9 as a key residue in novobiocin recognition. The results found in vitro were correlated in vivo. An increased tolerance to the antibiotic was observed when LVIS553 and the downstream putative transport protein LVIS552 were either expressed in a low copy plasmid in L. brevis or as a single copy chromosomal insertion in Bacillus subtilis. We provide evidence that LVIS553 is involved in the specific regulation of a new mechanism of tolerance to novnbiocin. [ABSTRACT FROM AUTHOR]

Hydrogen generated by reforming various hydrocarbons contains impurities such as carbon monoxide (CO) and carbon dioxide (CO 2) in varying concentrations. These impurities are known to poison the platinum and platinum alloy catalysts used in polymer electrolyte fuel cells (PEFCs) even at elevated temperatures. Amongst other approaches, pulsed oxidation for CO conversion has been proposed to enable usage of impure hydrogen fuel in PEFC applications. The present work evaluates the pulsed oxidation technique experimentally for practical implementation under high CO contamination levels. The implementation and effects of key operating parameters such as pulse width, current, and threshold potential for activation are systematically analyzed in terms of CO mitigation effectiveness. These parameters determine the extent of CO stripping and consequently the performance and energy conversion efficiency of the PEFC. Implementation of pulsing at set threshold potential rather than at fixed time intervals is shown to improve performance recovery up to 95% of the baseline performance under pure hydrogen. Technical means of utilizing the electrical energy generated during pulsing are discussed and measured, indicating a boost in the overall energy efficiency of the cell. Extended duration testing shows the feasibility of this technique to sustain CO poisoning in PEFCs at practical current densities. Image 1 • Fuel cell operation on low-cost, CO-containing hydrogen is explored experimentally. • Pulsed oxidation of adsorbed CO is systematically evaluated at elevated temperature. • Energy conversion efficiency is calculated from the data with and without pulsing. • Fuel cell performance recovery up to 95% is demonstrated by tuning key parameters. [ABSTRACT FROM AUTHOR]