Interactions between bacteria and Saprolegnia parasitica, causal agent of Saprolegniosis in fish and amphibians

PO-24 Interactions between bacteria and Saprolegnia parasitica, causal agent of Saprolegniosis in fish and amphibians Yiying Liu EU-SAPRO (Marie Curie International Training Network), The Netherlands Saprolegniosis is a devastating oomycete disease of fish and amphibians and causes substantial economic and environmental damage in aquaculture and natural ecosystems. The predominant causal agents of Saprolegniosis are Saprolegnia parasitica and Saprolegnia declina. In our project, bacterial communities associated with fish eggs were characterized and tested for their ability to inhibit growth of these two oomycete pathogens. BOX-PCR analysis and 16S-rDNA sequencing revealed that the bacterial communities associated with salmon eggs are genetically diverse. Most of the bacterial isolates that inhibit hyphal growth of Saprolegnia were identified as Pseudomonas species. Subsequent in vitro assays showed that many of these antagonistic Pseudomonas strains produce biosurfactants and other extracellular bioactive compounds that cease or restrict Saprolegnia hyphal growth. Fungal strains that were associated with salmon eggs were identified by ITS-sequencing as Trichoderma and Microdochium species. The potential of the identified bacterial and fungal isolates to protect eggs from Saprolegnia infections is ongoing. Also the mechanisms, genes and bioactive compounds involved in inhibition of the growth and pathogenicity of Saprolegnia will be elucidated.