Microbial and chemical diversity of tetrodotoxin producing marine animals

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Copyright: Chau, Rocky
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Abstract
Marine molluscs are known to employ a variety of defence systems to improve their survivability, such as the production of bioactive molecules. Recently, microbes have been identified as the true producers of these compounds. Similarly, tetrodotoxin (TTX) is hypothesised to have a bacterial origin, however, much controversy still exists. This thesis attempts to shed further light on the biosynthetic origins of TTX with a focus on Hapalochalaena sp. and Pleurobranchaea maculata. This thesis also investigates the potential for biosynthesis of other natural products by bacteria living in association with these marine molluscs. Culture-based studies attempting to isolate TTX-producing bacterium within Hapalochalaena sp. and P. maculata were unable to isolate any such strains. Furthermore, we attempted to replicate the production of TTX by published TTX-producing bacteria, however, TTX was unable to be detected in these strains via spectrometric methods. Nevertheless, culture-independent methods were able to identify four taxa that were strongly correlated to TTX-concentration in P. maculata. Further experiments, however, are required to isolate or characterise these strains. Molecular screening for natural product biosynthesis genes, putatively involved in the biosynthesis of TTX and other natural products, revealed many candidate bacteria. These experiments also identified a bacterium with significant biosynthetic potential, Pseudoalteromonas sp. HM-SA03. Members of Pseudoalteromonas are known to produce many bioactive compounds. Mining of the HM-SA03 genome identified a total of seven novel NRPS and PKS biosynthesis gene clusters. Bioinformatic analysis of these gene clusters revealed putative novel pathways for the assembly of bromoalterochromide, alteramide and pseudoalterobactin-like compounds. However, production of these compounds in laboratory-cultures of Pseudoalteromonas sp. HM-SA03 could not be confirmed by chemical studies. Nonetheless, chemical studies were able to identify the production of eight diketopiperazines. These bioactive molecules have been observed to function as cell-signalling molecules, and are proposed to function as such in the complex microbial community identified within the Hapalochalaena octopus. Taken together, these results indicate that marine molluscs are a rich source of biosynthetically potent microbes that deserve further attention for the elucidation of new natural products.
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Author(s)
Chau, Rocky
Supervisor(s)
Neilan, Brett A.
Kalaitzis, John A.
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Publication Year
2013
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty
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