APPLIED AND ENVIRONMENTAL MICROBIOLOGY, Feb. 2003, p. 779–786
Vol. 69, No. 2
0099-2240/03/$08.000 DOI: 10.1128/AEM.69.2.779–786.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Hydrogen-Dependent Oxygen Reduction by Homoacetogenic
Bacteria Isolated from Termite Guts
Hamadi I. Boga† and Andreas Brune*
Fachbereich Biologie, Mikrobielle Ökologie, Universität Konstanz,
D-78457 Konstanz, Germany
Received 18 June 2002/Accepted 13 November 2002
Although homoacetogenic bacteria are generally considered to be obligate anaerobes, they colonize the
intestinal tracts of termites and other environments that are not entirely anoxic in space or time. In this study,
we investigated how homoacetogenic bacteria isolated from the hindguts of various termites respond to the
presence of molecular oxygen. All strains investigated formed growth bands in oxygen gradient agar tubes
under a headspace of H2-CO2. The position of the bands coincided with the oxic-anoxic interface and depended
on the O2 partial pressure in the headspace; the position of the bands relative to the meniscus remained stable
for more than 1 month. Experiments with dense cell suspensions, performed with Clark-type O2 and H2
electrodes, revealed a large capacity for H2-dependent oxygen reduction in Sporomusa termitida and Sporomusa
sp. strain TmAO3 (149 and 826 nmol min1 mg of protein1, respectively). Both strains also reduced O2 with
endogenous reductants, albeit at lower rates. Only in Acetonema longum did the basal rates exceed the
H2-dependent rates considerably (181 versus 28 nmol min
1 mg of protein)1). Addition of organic substrates
did not stimulate O2 consumption in any of the strains. Nevertheless, reductive acetogenesis by cell suspen-
sions of strain TmAO3 was inhibited even at the lowest O2 fluxes, and growth in nonreduced medium occurred
only after the bacteria had rendered the medium anoxic. Similar results were obtained with Acetobacterium
woodii, suggesting that the results are not unique to the strains isolated