The fish egg microbiome: diversity and activity against the oomycete pathogen Saprolegnia

Y. Liu

Prof. dr. F. Govers (promotor); Prof. dr. J.M. Raaijmakers (promotor); Dr. I. de Bruijn (co-promotor); Wageningen University, 13 June 2016, 170 pp.

The fish egg microbiome: diversity and activity against the oomycete pathogen Saprolegnia

Emerging oomycete pathogens increasingly threaten biodiversity and food security. This thesis describes the study of the microbiome of Atlantic salmon (Salmo salar L.) eggs and analyses of the effects of infections by the oomycete pathogen Saprolegnia on the microbial architecture. A low incidence of Saprolegniosis was correlated with a relatively high abundance and richness of specific commensal Actinobacteria. Among the bacterial community, the isolates Frondihabitans sp. 762G35 (Microbacteriaceae) and Pseudomonas sp. H6 significantly inhibited hyphal attachment of Saprolegnia diclina to live salmon eggs. Chemical profiling showed that these two isolates produce furancarboxylic acid-derived metabolites and a lipopeptide viscosin-like biosurfactant, respectively, which inhibited hyphal growth of S. diclina in vitro. Among the fungal community, the fungal isolates obtained from salmon eggs were closely related to Microdochium lycopodinum/Microdochium phragmitis and Trichoderma viride. Both a quantitative and qualitative difference in the Trichoderma population between Saprolegnia-infected and healthy salmon eggs was observed, which suggested that mycoparasitic Trichoderma species could play a role in Saprolegnia suppression in aquaculture. This research provides a scientific framework for studying the diversity and dynamics of microbial communities to mitigate emerging diseases. The Frondihabitans, Pseudomonas and Trichoderma isolates, and/or their bioactive metabolites, are proposed as effective candidates to control Saprolegniosis.