vaginosis and Prevotella bivia (Aroutcheva et al., 2001a). Consistent with this, Lactobacillus strains have been isolated from the human vaginal microbiota for probiotic use against vaginosis-associated pathogens (Reid & Burton, 2002; Reid et al., 2003) on the basis of their ability to produce high levels of hydrogen peroxide (Klebanoff et al., 1991; Hillier et al., 1992, 1993). Moreover, Pridmore et al. (2008) first reported for an

intestinal Lactobacillus that hydrogen peroxide contributes to the killing activity NVP-BGJ398 order of L. johnsonii NCC533 against serovar Typhimurium. Consistent with these reports, here, we observed that hydrogen peroxide concentration-dependently kills serovar Typhimurium, G. vaginosis and UPEC strains. Moreover, we report that lactic acid acts synergistically with hydrogen peroxide to kill G. vaginalis, S. typhimurium and UPEC more efficiently. The mechanism underlying the stimulatory effect of lactic acid observed could be related to the observation by Greenacre et al. (2006), who have reported that the lactic acid-induced acid tolerance response causes hydrogen peroxide sensitivity in serovar Typhimurium via the downregulation

of the OxyR regulon. A second mechanism could also be proposed, find more resulting from the permeabilizing effect of lactic acid on the gram-negative bacterial outer membrane (Alakomi et al., 2000), thus facilitating the passage of molecules across the membrane, and in turn increasing the killing effects of antimicrobial compounds (Niku-Paavola et al., 1999; Alakomi et al., 2000). “
“Candidatus Methylomirabilis oxyfera’; is a polygon-shaped bacterium Branched chain aminotransferase that was shown to have the unique ability to couple anaerobic methane oxidation to denitrification, through a newly discovered intra-aerobic pathway. Recently, the complete genome of Methylomirabilis oxyfera was assembled into a 2.7-Mb circular single chromosome by metagenomic sequencing. The genome of M. oxyfera

revealed the full potential to perform both methane oxidation and the conversion of nitrite via nitric oxide into oxygen and dinitrogen gas. In this study, we show by immunogold localization that key enzymes from both methane- and nitrite-converting pathways are indeed present in single M. oxyfera cells. Antisera targeting the particulate methane monooxygenase (pMMO) and the cd1 nitrite reductase (NirS) were raised and used for immunogold localization in both single- and double-labelling experiments. Our previous studies have shown that M. oxyfera does not develop pMMO-containing intracytoplasmic membranes as is observed in classical proteobacterial methanotrophs. Our results suggest that in M. oxyfera, the pMMO and NirS enzymes localized to the cytoplasmic membrane and periplasm, respectively. Further, double-labelling showed co-occurrence of pMMO and NirS in single M. oxyfera cells.