FEMS Microbiology Letters 83 (1991) 347-350 © 1991 Federation of European Microbiological Societies 0378-1097/91/$03.50 Published by Elsevier ADONIS 037810979100460A 347 FEMSLE 04653 Lithotrophic growth and hydrogen metabolism by Clostridium magnum Martin Bomar 1 Hans Hippe 2 and Bernhard Schink 1 l Lehrstuhl Mikrobiologie I der Eberhard-Karls-Uniuersitiit, Tiibingen, and 2 Deutsche Sammlung yon Mikroorganismen und Zellkulturen GrnbH, Braunschweig, F.R.G. Received 1 August 1991 Accepted 7 August 1991 Key words: Hydrogen metabolism; Homoacetogenesis; Clostridium magnum 1. SUMMARY Clostridium magnum, originally described as a non-autotrophic homoacetogenic bacterium, was found to be able to grow with H2/CO 2, formate, or methanol with stoichiometric acetate forma- tion, provided that the growth medium contained at least 0.025% (w/v) yeast extract. Hydrogen was also formed as a byproduct of glucose fer- mentation, and was consumed again after glucose consumption. Hydrogen formation from glucose was independent of growth conditions and reached similar maximal concentrations in min- eral media with or without ammonia added as well as in non-growing cultures or in the presence of carbon monoxide. 2. INTRODUCTION Homoacetogenic bacteria are characterized by their ability to use CO 2 as an electron acceptor in substrate oxidation, and to form acetate as a reduced fermentation product [1]. Most known homoacetogens can use hydrogen, formate, or other C 1 compounds as electron donors, and can exhibit an entirely autotrophic way of life [1-3]. Only Clostridium formicoaceticum [4] and C. magnum [5] were reported to be unable to utilize hydrogen as electron source. In the present com- munication we show that the latter bacterium exhibits active hydrogen metabolism during het- erotrophic or lithotrophic growth provided that the growth medium contains a minimum amount of yeast extract. Correspondence to: Present address: B. Schink, Fakult~it fiir Biologie der Universifiit Konstanz, Postfach 5560, D-7750 Konstanz, F.R.G. 3. MATERIALS AND METHODS Clostridium magnum strain WoBdP1, DSM 2767, was grown at 30 ° C in bicarbonate-buffered,