Carbon-supported binary PtRu electrocatalysts were prepared by coimpregnation using ethanolic solutions of Pt(NH 3 ) 2 (NO 2 ) 2 as the Pt source, various Ru sources [RuCl 3 , Ru 3 (CO) 12 , and RuNO(NO 3 ) x ], and carbon black by thermal decomposition under reducing conditions, and their structure, morphology, and electrocatalytic properties were investigated. X-ray diffraction analysis and high resolution scanning electron microscopy indicated that the use of Cl-free Ru sources, i.e., Ru 3 (CO) 12 or RuNO(NO 3 ) x , afforded highly dispersed and uniform PtRu nanoparticles. Surface area measurements conducted by electro-oxidation of preadsorbed carbon monoxide indicated that the use of Ru 3 (CO) 12 as the Ru source yielded high surface area catalysts. In terms of the surfacearea specific current density (current density normalized by the specific surface area of PtRu metal obtained from preadsorbed CO electro-oxidation measurements), the electrocatalytic activity of Pt(NH 3 ) 2 (NO 2 ) 2 -Ru 3 (CO) 12 and Pt(NH 3 ) 2 (NO 2 ) 2 -RuNO(NO 3 ) x were equal. PtRu/C electrocatalysts prepared from ethanolic solutions of Pt(NH 3 ) 2 (NO 2 ) 2 -Ru 3 (CO) 12 resulted in high mass-specific activity toward methanol oxidation, with mass-specific current density as high as 159 mA mg Ϫ1 Pt at 500 mV. The efficiency of PtRu/C electrodes is discussed based on the significance of the use of Cl-free Ru sources.

We devised a single-batch fermentation system to simulate human colonic microbiota from fecal samples, enabling the complex mixture of microorganisms to achieve densities of up to 1011 cells/mL in 24 h. 16S rRNA gene sequence analysis of bacteria grown in the system revealed that representatives of the major phyla, including Bacteroidetes, Firmicutes, and Actinobacteria, as well as overall species diversity, were consistent with those of the original feces. On the earlier stages of fermentation (up to 9 h), trace mixtures of acetate, lactate, and succinate were detectable; on the later stages (after 24 h), larger amounts of acetate accumulated along with some of propionate and butyrate. These patterns were similar to those observed in the original feces. Thus, this system could serve as a simple model to simulate the diversity as well as the metabolism of human colonic microbiota. Supplementation of the system with several prebiotic oligosaccharides (including fructo-, galacto-, isomalto-, and xylo-oligosaccharides; lactulose; and lactosucrose) resulted in an increased population in genus Bifidobacterium, concomitant with significant increases in acetate production. The results suggested that this fermentation system may be useful for in vitro, pre-clinical evaluation of the effects of prebiotics prior to testing in humans.

This study investigated the effect of various prebiotics (indigestible dextrin, α-cyclodextrin, and dextran) on human colonic microbiota at a dosage corresponding to a daily intake of 6 g of prebiotics per person (0.2% of dietary intake). We used an in vitro human colonic microbiota model based on batch fermentation starting from a faecal inoculum. Bacterial 16S rRNA gene sequence analysis showed that addition of 0.2% prebiotics did not change the diversity and composition of colonic microbiota. This finding coincided with results from a clinical study showing that the microbiota composition of human faecal samples remained unchanged following administration of 6 g of prebiotics over seven days. However, compared to absence of prebiotics, their addition reduced the pH and increased the generation of acetate and propionate in the in vitro system. Thus, even at such relatively low amounts, prebiotics appear capable of activating the metabolism of colonic microbiota.

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Significance and Impact of the Study: A novel bioelectrochemical method can activate the methanogenesis of M. thermautotrophicus by controlling the redox potential in culture conditions at À0Á8 V, which is a difficult potential to achieve by conventional methods (e.g. by adding reducing agents). This study provides useful insights for the application of a bioelectrochemical system in industrial processes involving methanogens, such as in anaerobic digesters. AbstractTo investigate the precise effect of the redox potential on the methanogenesis of the hydrogenotrophic methanogen Methanothermobacter thermautotrophicus by using an electrochemical redox controlling system without adding oxidizing or reducing agents. A bioelectrochemical system was applied to control the redox conditions in culture and to measure the methane-producing activity of M. thermautotrophicus at a constant potential from +0Á2 to À0Á8 V (vs Ag/ AgCl). Methane production and growth of M. thermautotrophicus were 1Á6 and 3Á5 times increased at À0Á8 V, compared with control experiments without electrolysis, respectively, while methanogenesis was suppressed between +0Á2 and À0Á2 V. A clear relationship between an electrochemically regulated redox potential and methanogenesis was revealed.