ORIGINAL PAPER Hydrogen as an energy source for the human pathogen Bilophila wadsworthia Sofia M. da Silva Æ Sofia S. Venceslau Æ Cla ´udia L. V. Fernandes Æ Filipa M. A. Valente Æ Ine ˆs A. C. Pereira Received: 13 September 2007 / Accepted: 29 November 2007 / Published online: 9 December 2007 Ó Springer Science+Business Media B.V. 2007 Abstract The gram-negative anaerobic gut bacte- rium Bilophila wadsworthia is the third most common isolate in perforated and gangrenous appendicitis, being also found in a variety of other infections. This organism performs a unique kind of anaerobic respi- ration in which taurine, a major organic solute in mammals, is used as a source of sulphite that serves as terminal acceptor for the electron transport chain. We show here that molecular hydrogen, one of the major products of fermentative bacteria in the colon, is an excellent growth substrate for B. wadsworthia. We have quantified the enzymatic activities associated with the oxidation of H 2 , formate and pyruvate for cells obtained in different growth conditions. The cell extracts present high levels of hydrogenase activity, and up to five different hydrogenases can be expressed by this organism. One of the hydrogenases appears to be constitutive, whereas the others show differential expression in different growth conditions. Two of the hydrogenases are soluble and are recognised by antibodies against a [FeFe] hydrogenase of a sulphate reducing bacterium. One of these hydrogenases is specifically induced during fermentative growth on pyruvate. Another two hydrogenases are membrane- bound and show increased expression in cells grown with hydrogen. Further work should be carried out to reveal whether oxidation of hydrogen contributes to the virulence of B. wadsworthia. Keywords Bilophila wadsworthia Á Hydrogen Á Hydrogenase Á Formate dehydrogenase Á Gut bacteria Introduction A complex and dynamic population of microorgan- isms colonises the human intestinal tract, and this microflora has a pronounced impact on human physiology (Backhed et al. 2005; Guarner 2006). Gut microbial activity has several important conse- quences for health, namely in recovery of energy, in defence against pathogens, in proper development of the gut, as well as maturation of the immune system (Kelly et al. 2005; Mazmanian and Kasper 2006), by influencing the expression of host genes that partic- ipate in fundamental physiological functions. On the other hand, there is evidence suggesting that an inappropriate immune response to colonic bacteria may result in inflammatory bowel diseases (Guarner 2005; Macdonald and Monteleone 2005), and several of these bacteria may behave as opportunistic patho- gens, if they can penetrate other tissues, originating infectious processes. The diversity of the gut bacterial community is starting to be unravelled, with the majority of species belonging to novel and uncultured S. M. da Silva Á S. S. Venceslau Á C. L. V. Fernandes Á F. M. A. Valente Á I. A. C. Pereira (&) Instituto de Tecnologia Quı ´mica e Biolo ´ gica, Universidade Nova de Lisboa, Apartado 127, 2781-901 Oeiras, Portugal e-mail: ipereira@itqb.unl.pt 123 Antonie van Leeuwenhoek (2008) 93:381–390 DOI 10.1007/s10482-007-9215-x