2377 - Microbiology(1998 144 2377-2406 Printed in Great...

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Microbiology (1998), 144, 2377-2406 Printed in Great Britain Biochemistry of methanogenesis : a tribute to Marjory Stephenson SPECIAL ~ LECTURE ~ Rudolf ~.Thauer 1998 Marjory Tel: +49 6421 178200. Fax: +49 6421 179209. e-mail : [email protected] Stephenson Prize Lecture Max-Planck-lnstitut fur terrestrische Mikrobiologie, Karl-von-Frisch-StraBe, D-35043 Marburq, and (Delivered at the 140th Ordinary Meeting. of the Laboratorium fur Mikrobiologie, Fachbereich Biologie, Philipps-Universitat, Karl-von-Frisch-StraBe, D-35032 Marburg, Germany Society for General I Microbiology, 31 March 1998) Keywords : methanogenesis and methanogenic archaea, methyl-coenzyme M reductase and its crystal structure, coenzyme F430, coenzyme M, coenzyme B Historical overview In 1933, Stephenson & Stickland (1933a) published that they had isolated from river mud, by the single cell technique, a methanogenic organism capable of growth in an inorganic medium with formate as the sole carbon source. 4HC00- + 4H’ + CH, + 3C0, + 2H,O AGO’ = - 144-5 kJ mol-’ Methane formation from formate was shown to occur in a stepwise manner, by the preliminary decomposition of formic acid into CO, and H, followed by a reduction of CO, by H,, suggesting that formate was not an intermediate in the reduction of CO, to methane. HCOO- + H+ -+ H, + CO, 4H,+CO, CH,+2H20 = - 3-5 kJ mol-’ = - 131 kJ mol-’ Cell suspensions of the micro-organism catalysed the reduction of methylene blue with H,, indicating that the methanogen contained an enzyme which activates mol- ecular hydrogen. H, 2e- + 2H+ E; = -414mV This enzyme had been discovered by Stephenson & Stickland (1931a) 2 years before in a number of bacterial species and was named by them ‘hydrogenase’. The paper by Stephenson & Stickland (1933a) is considered to mark the beginning of the modern era for study of methanogenesis (Wolfe, 1993). It is the first Except when otherwise noted, the free energy changes given for meth- anogenic reactions were calculated from the free energies of formation from the elements of the substrates and products with non-gaseous compounds at 1 M aqueous solution and gaseous compounds in the gaseous state at 1 atmosphere pressure (101 kPa). The free energy changes of formation were taken from Thauer eta/. (1977). report on the isolation in pure culture of a methanogen and the first study of an enzyme and of reactions involved in methanogenesis. Besides CO,, the cell suspensions of the methanogen isolated by Stephenson & Stickland (1933a) catalysed the reduction of carbon monoxide, formaldehyde (added as hexamethylenetetramine) and methanol to methane with H,, albeit at much lower rates than the reduction of CO,. It is significant that the cell sus- pensions did not yield methane from compounds of two or more carbon atoms. The cell suspensions did, however, slowly reduce sulphate with H, to H,S, a property not encountered by any other methanogen isolated since then. It therefore seems possible that, in spite of all efforts to purify it, the culture obtained by Stephenson & Stickland (1933a) was contaminated with one of the sulphate reducers abundantly present in the river mud (Stephenson & Stickland, 1931b) from which
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2377 - Microbiology(1998 144 2377-2406 Printed in Great...

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