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Abstract:
Gutless oligochaetes belonging to the phyla Annelida are found widely distributed in various
habitats around the world. These worms are unique from other gutless worms because in addition
to lacking a gut, mouth and anus they also lack execratory organs. They are therefore dependent
on their symbionts for nutrition as well as waste management. In this study species of gutless
oligochaetes, Olavius spp., from siliceous sediments near sea-grass beds off the coast of the
island of Elba, Italy were investigated.
Three species of Olavius spp. worms have been identified on Elba; Olavius algarvensis, Olavius
ilvae and one yet to be described species. The two main species, O. algarvensis and O. ilvae
harbor sulfur-oxidizing and sulfate-reducing symbionts. Under oxic conditions, the sulfur-
oxidizing gammaproteobacterial symbionts are able to use oxygen as an electron acceptor and
reduced sulfur as an electron donor for fixation. Inorganic carbon fixation rates have been
investigated and calculated for Olavius spp. worms from tracer incubations by Bergin (2009).
Transfer of fixed carbon (
13
C) from symbionts to symbiont-free host tissue was also investigated
with nanoSIMS but could not be shown by Bergin (2009). Due to wide variability between
individuals, a large number of worms would need to be investigated from tracer incubations to
reach a conclusion. Because nanoSIMS is a time consuming method, another method that would
allow analyzing large number of samples within a relatively shorter time was needed.
In this master’s thesis, tracer incubations were done on Olavius spp. worms to analyze the uptake
of labeled inorganic carbon over incubations times. Parallel unlabeled incubations for measuring
of dissolved inorganic carbon concentrations were also set up. Microautoradiography was tested
as an alternative method for analyzing two aspects; (i) where in the worms carbon was being
fixed and (ii) whether there was transfer into central parts of the worms.
After tracer incubation experiments, worms were observed to have taken up label from the
medium. There was an increase in the concentration of dissolved inorganic carbon in the
incubation medium. Microautoradiography revealed that label was mostly located on sections of
the worm where the symbionts were located.The results of this thesis show and confirm the findings of Bergin (2009) that the Gamma 1
symbionts of Olavius spp. worms fix carbon when transferred from hypoxic incubations to oxic
incubations, without an external sources of energy. The net increase in dissolved inorganic
carbon concentration also suggested that more respiration than fixation took place under the
given conditions. Although it was not possible to see transfer from the microautoradiography,
these experiments revealed important improvements that could be done for the optimization of
the method.