Untersuchungen zum Argininstoffwechsel bei Mycobacterium bovis ...

7. Summary
Michael Sürken
101
Studies on the arginine metabolism of Mycobacterium bovis BCG in vitro and
in a model of infection
The causative agent of tuberculosis, Mycobacterium tuberculosis, is able to persist in
its host for years under microaerobic or even anaerobic conditions, even though it is
considered to be an obligate aerobe organism. In the genome sequence of M.
tuberculosis, a gene with homology to arcA of Pseudomonas aeruginosa was
annotated. This gene encodes an arginine deiminase, an enzyme that is part of a
pathway (the arginine deiminase pathway, ADI-Pathway) in P. aeruginosa, enabling it
to grow under anaerobic conditions. In a previous study, arcA- deletion mutants in M.
tuberculosis and M. bovis BCG had been constructed (RÖHKER 2003).
The aim of the present study was to characterize the arginine deiminase in vitro and
to determine whether further enzymes of the ADI-Pathway are active in M.
tuberculosis and M. bovis BCG. Furthermore, it was examined if a deletion of the
arcA-gene in M. bovis BCG leads to attenuation in vivo.
In the in vitro examinations of this study, the arcA deletion mutants of M. tuberculosis
and M. bovis BCG were compared to the wildtype strains under anaerobic and
aerobic conditions. Under aerobic conditions, growth with arginine as the sole
nitrogen source was analysed. All strains grew under these conditions and no
differences in growth between mutants and wildtype strains were observed.
Under anaerobic conditions, the ∆arcA mutants were not able to produce ammonia
from arginine, in contrast to the wildtype strains. The mutant strains regained this
ability by complementation with the arcA-gene of M. tuberculosis. Thus, it can be
concluded that arcA in M. tuberculosis and M. bovis BCG mediates arginine
deiminase activity. These results also show that the activity mediated by arcA is only
present under anaerobic conditions.
Besides ammonia, citrulline is another product of the arginine deiminase reaction.
Incubated with Citrulline as the sole nitrogen source under anaerobic conditions, the
∆arcA mutants produced ammonia in comparable rates to the wildtype strains. This