Glossina spp. harbour three symbiotic bacteria: Wigglesworthia glossinidia, on
which the fly depends for the production of essential B vitamins; Wolbachia spp.,
which may be involved in causing reproductive anomalies and Sodalis glossinidius,
which as yet has not been shown to have any positive input on the fly but may be
involved in susceptibility to trypanosome infection. The current work focuses on the
biological and molecular aspects of S. glossinidius but also examines the prevalence
of Wolbachia spp. in wild tsetse populations
One of the current theories is that the number of S. glossinidius present when the
tsetse takes its first blood meal may be an important factor in determining
susceptibility to infection. Therefore, the quantification of the number of
S.glossinidius bacteria present in tsetse may provide an insight into this mechanism.
Utilising quantitative PCR, the levels ofS. glossinidius were quantified and it was
found that the bacterial population size is dynamic over the developmental course of
S. glossinidius is one of the few insect symbionts that can be cultured in vitro. The in
vitro culture of this bacterium has been optimised in this work, reducing the time
taken for isolation of S. glossinidius by seven days. The growth pattern of S.
glossinidius was measured and used to evaluate the effect of stress conditions on the
bacterium. It was found that iron was an essential nutrient for the growth of this
bacterium and the growth of S. glossinidius was found to be inhibited in irondeficient medium. S. glossinidius was also found to synthesise siderophores in
response to these growth conditions.
The prevalence ofS. glossinidius was analysed in wild flies, with significant
differences being found both between different tsetse species and between individual
species sampled from different countries. Laboratory colonies, however, exhibit S.
glossinidius prevalences of 100% which this work has shown may be due to the
horizontal transmission through urophagous behaviour during blood meals. The
prevalence of Wolbachia spp. was seen to change over time, with the infection
sweeping into one population sampled. This may suggest that Wolbachia spp. causes
reproductive abnormalities in the tsetse as it is known to do in other insects.
It is concluded that the horizontal transmission of S. glossinidius is likely to account
for the ubiquity of this symbiont in laboratory colonies of tsetse and may have
adversely influenced the studies performed to date on this bacterium.