Kuhl, Theresa (2017) The response of the Baltic Sea sponge Halichondria panicea upon challenge with Vibrio bacteria. (Master thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 69 pp.

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Abstract

Sponges (phylum Porifera) constantly encounter microbial cells, including potential pathogens, during their pumping activity, while harbour diverse and specific symbiotic microbial communities . However, how sponges detect and distinguish different microbes (e.g., symbionts vs food bacteria vs potential pathogens) remains unknown . I hypothesized that their innate immune system could be involved to provide specific recognition of microbes by ways of immune memory. I aimed to investigate potential pathways of bacteria recognition in sponges by adopting an experimental approach. First, an aquaculture flow through system for Baltic sponges was optimized. Then, sponges were challenged with either an autochthonous Vibrio strain isolated from the Baltic Sea (VB) or an exogenous Vibrio strain isolated from the Mediterranean Sea (VM). Sterile artificial seawater was used as control. The immune response of the sponge was monitored by ways of antimicrobial a ssays and differential gene expression analysis (e.g., RT qPCR of targeted gene hsp70 ). I expected a differentiated immune reaction of the sponge towards the two different bacteria strains. Moreover, under the hypothesis of immune memory , I expected a stro nger immune response in H. panicea against the exogenous Vibrio compared to the autochthonous Vibrio. Sponges were successfully kept in a flow through system with a suspension method according to Barthel & Theede 1986 )). Sampling occurred at two time points (6h and 24h). The antimicrobial assay showed the strongest immune reaction after 6 hours in form of a bigger halo diameter. The overall reaction was higher in the sponges treated with VM. The real time quantitative PCR (RT qPCR ) was optimized for actin (reference gene ) and h sp70 (target gene ) in H. panicea. The expression level of the heat shock protein Hsp70 was increased in the VM treatment. This study provides further insights in sponges’ immune reaction to varying bacterial strains suggesting specificity towards different bacteria in these basal metazoans.

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