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Algal-bacterial interactions: a study of Gymnodinium catenatum and its associated bacteria

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Albinsson, ME (2011) Algal-bacterial interactions: a study of Gymnodinium catenatum and its associated bacteria. PhD thesis, University of Tasmania.

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Abstract

Over the last decades, harmful algal blooms (HABs) have increased globally in both
frequency and extent, leading to intensified efforts to determine the primary factors
that are controlling the population and toxin dynamics of bloom-forming algal species.
One poorly understood factor in HAB ecology, yet shown to be of great importance,
is that of algal-bacterial interactions.
Efforts to investigate the relationships and mechanisms of interaction are often hindered
by the complex composition of the algal-associated bacterial communities,
wherefore this present study used simplified algal-bacterial experimental model systems.
The model systems are based on the toxin producing dinoflagellate Gymnodinium
catenatum and two of its associated bacteria, Marinobacter sp. DG879 and Alcanivorax
sp. DG881, both known to support growth and survival of G. catenatum in
culture. Using the experimental model systems, the work presented in this thesis examined
the growth dynamics of G. catenatum and its associated bacteria, and studied
the effect of bacteria on the toxicity of G. catenatum. The abundance of Alcanivorax
and Marinobacter genotypes associated with natural populations of G. catenatum in
the Derwent Estuary and D’Entrecasteaux Channel, south-east Tasmania was also
investigated.
This thesis demonstrates that the bacterial community is important for growth of G.
catenatum and showed that different bacteria, in particular Marinobacter sp. DG879,
have a significant effect on the growth dynamics and toxicity of G. catenatum laboratory
cultures. When grown with Marinobacter sp. DG879, G. catenatum was found
to remain viable in culture for a period longer than ever recorded, suggesting that
Marinobacter sp. DG879 produce a compound inducing a positive growth response
in G. catenatum, or that it plays a role in carbon recycling or nitrogen fixation. Toxin
analysis of the G. catenatum / Marinobacter sp. DG879 cultures revealed a toxin
profile significantly different to other analysed treatments containing different bacteria.
As the experimental design of the study sought to minimise genetic variation
among treatments, and with biotransformation generally operating on extracellular
toxins (this study focussed on intracellular toxins), the differing toxin profile seen in the G. catenatum with Marinobacter sp. DG879 is most likely a response to Marinobacter
sp. DG879 influencing toxin synthesis indirectly through its effect on
dinoflagellate physiology. The field studies also suggest that Marinobacter sp. may
have an important role in natural populations of G. catenatum, preceding G. catenatum
blooms.
With the use of molecular detection methods becoming more widespread, and with
more research on naturally occurring blooms, there is potential that specific elements
of the bacterial population, such as Marinobacter sp. DG879 could be employed as
indicator species of G. catenatum and other algal blooms, ultimately allowing for
early detection and management of potentially harmful blooms.

Item Type: Thesis (PhD)
Keywords: algal-bacterial interactions, algal toxicity, algal growth studies
Additional Information:

Copyright 2011 the Author

Date Deposited: 19 Sep 2011 05:57
Last Modified: 11 Mar 2016 05:53
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