Evolution and function of Eukaryotic-like Proteins (ELPs) from sponge symbionts

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Copyright: Reynolds, David
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Abstract
Sponges (phylum Porifera) are ancient metazoans that harbor a diverse range of microorganisms. Like other eukaryotic organisms, these microorganisms are symbiotic and are essential for the host s health and interaction with the environment. Although these symbiotic relationships are ubiquitous in sponges, our understanding of the mechanisms that drive and control these associations has been hampered by our inability to cultivate most host-associated microbes. Metagenomic sequencing has allowed us to obtain protein data from the symbiont community of six sponge species. One surprising finding in these metagenomic surveys was the presence and abundance of eukaryotic-like proteins (ELPs), in sponge symbionts and it is postulated that they play a role in symbiont host interactions. The aims of this study were therefore, to characterize the full range of ELPs in sponge symbionts, compare their phylogenetic relationships and understand their mode of action. All sponge microbiomes investigated were significantly more abundant in ELPs when compared to seawater samples. Bioinformatic analyses showed that the ELPs have the ability to be excreted from the symbiont and that ELPs have diverse associations with secondary domains. Phylogenetic analysis of ELPs showed that each symbiont community possesses divergent and specific sets of proteins for each ELP class. Evidence was found that some ELPs are related to sponge derived sequences, supporting a scenario of horizontal gene transfer between host and symbionts. ELPs were then recombinantly expressed in Escherichia coli and exposed to Acanthamoeba castellanii, which is functionally analogous to the phagocytic cells in the sponges. Phagocytosis assays with E. coli containing two ELP classes (AR and PQQ), showed a significantly higher percentage of amoeba containing bacteria and average number of intracellular of bacteria per amoeba when compared to negative controls. These results indicate that ELPs from sponge symbionts can modulate host cell functions, and specifically phagocytosis. The results herein support the notion that ELPs have evolved in sponge symbionts to modulate the behaviour of their host. These findings provide a possible explanation of how sponge symbionts communicate with their host and maintain a symbiotic relationship
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Author(s)
Reynolds, David
Supervisor(s)
Thomas, Torsten
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Publication Year
2012
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Thesis
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Masters Thesis
UNSW Faculty
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