Investigation of the fumarate metabolism of the syntrophic propionate-oxidizing bacterium strain MPOB |
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Authors: | Bernardina L M Van Kuijk Elvire Schlösser Alfons J M Stams |
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Institution: | (1) Laboratory of Microbiology, Wageningen Agricultural University, Hesselink van Suchtelenweg 4, NL-6703 CT Wageningen, The Netherlands Tel. +31-317-483101; Fax +31-317-483829 e-mail: fons.stams@algemeen.micr.wau.nl, NL |
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Abstract: | The growth of the syntrophic propionate-oxidizing bacterium strain MPOB in pure culture by fumarate disproportionation into
carbon dioxide and succinate and by fumarate reduction with propionate, formate or hydrogen as electron donor was studied.
The highest growth yield, 12.2 g dry cells/mol fumarate, was observed for growth by fumarate disproportionation. In the presence
of hydrogen, formate or propionate, the growth yield was more than twice as low: 4.8, 4.6, and 5.2 g dry cells/mol fumarate,
respectively. The location of enzymes that are involved in the electron transport chain during fumarate reduction in strain
MPOB was analyzed. Fumarate reductase, succinate dehydrogenase, and ATPase were membrane-bound, while formate dehydrogenase
and hydrogenase were loosely attached to the periplasmic side of the membrane. The cells contained cytochrome c, cytochrome b, menaquinone-6 and menaquinone-7 as possible electron carriers. Fumarate reduction with hydrogen in membranes of strain MPOB
was inhibited by 2-(heptyl)-4-hydroxyquinoline-N-oxide (HOQNO). This inhibition, together with the activity of fumarate reductase with reduced 2,3-dimethyl-1,4-naphtoquinone
(DMNH2) and the observation that cytochrome b of strain MPOB was oxidized by fumarate, suggested that menequinone and cytochrome b are involved in the electron transport during fumarate reduction in strain MPOB. The growth yields of fumarate reduction
with hydrogen or formate as electron donor were similar to the growth yield of Wolinella succinogenes. Therefore, it can be assumed that strain MPOB gains the same amount of ATP from fumarate reduction as W. succinogenes, i.e. 0.7 mol ATP/mol fumarate. This value supports the hypothesis that syntrophic propionate-oxidizing bacteria have to
invest two-thirds of an ATP via reversed electron transport in the succinate oxidation step during the oxidation of propionate.
The same electron transport chain that is involved in fumarate reduction may operate in the reversed direction to drive the
energetically unfavourable oxidation of succinate during syntrophic propionate oxidation since (1) cytochrome b was reduced by succinate and (2) succinate oxidation was similarly inhibited by HOQNO as fumarate reduction.
Received: 18 March 1997 / Accepted: 10 November 1997 |
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Keywords: | Syntrophy Fumarate reduction Propionate oxidation Anaerobic growth Electron transport chain |
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