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J. Bacteriol., Dec 1996, 6895-6903, Vol 178, No. 23
ER Rocha, T Selby, JP Coleman and CJ Smith
Survival of Bacteroides fragilis in the presence of oxygen was dependent on
the ability of bacteria to synthesize new proteins, as determined by the
inhibition of protein synthesis after oxygen exposure. The B. fragilis
protein profile was significantly altered after either a shift from
anaerobic to aerobic conditions with or without paraquat or the addition of
exogenous hydrogen peroxide. As determined by autoradiography after
two-dimensional gel electrophoresis, approximately 28 newly synthesized
proteins were detected in response to oxidative conditions. These proteins
were found to have a broad range of pI values (from 5.1 to 7.2) and
molecular weights (from 12,000 to 79,000). The hydrogen peroxide- and
paraquat- inducible responses were similar but not identical to that
induced by oxygen as seen by two-dimensional gel protein profile. Eleven of
the oxidative response proteins were closely related, with pI values and
molecular weights from 5.1 to 5.8 and from 17,000 to 23,000, respectively.
As a first step to understanding the resistance to oxygen, a
catalase-deficient mutant was constructed by allelic gene exchange. The
katB mutant was found to be more sensitive to the lethal effects of
hydrogen peroxide than was the parent strain when the ferrous iron chelator
bipyridyl was added to culture media. This suggests that the presence of
ferrous iron in anaerobic culture media exacerbates the toxicity of
hydrogen peroxide and that the presence of a functional catalase is
important for survival in the presence of hydrogen peroxide. Further, the
treatment of cultures with a sublethal concentration of hydrogen peroxide
was necessary to induce resistance to higher concentrations of hydrogen
peroxide in the parent strain, suggesting that this was an inducible
response. This was confirmed when the bacterial culture, treated with
chloramphenicol before the cells were exposed to a sublethal concentration
of peroxide, completely lost viability. In contrast, cell viability was
greatly preserved when protein synthesis inhibition occurred after peroxide
induction. Complementation of catalase activity in the mutant restored the
ability of the mutant strain to survive in the presence of hydrogen
peroxide, showing that the catalase (KatB) may play a role in oxidative
stress resistance in aerotolerant anaerobic bacteria.
Copyright © 1996, American Society for Microbiology
Oxidative stress response in an anaerobe, Bacteroides fragilis: a role for catalase in protection against hydrogen peroxide
Department of Microbiology and Immunology, School of Medicine, East Carolina University, Greenville, North Carolina, USA.
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