Abstract
Saprolegnia parasitica is a pathogenic oomycete responsible for severe fish infections. Despite its low abundance in the cell wall of S. parasitica, chitin is essential for hyphal growth as the inhibition of its biosynthesis leads to highly reduced growth. Here we identified and characterized chitin synthases (CHS) from S. parasitica as potential targets for anti-oomycete drugs. Bioinformatics analyses allowed the identification of six different putative Chs genes in the genome of the pathogen. The total number of genes was confirmed by Southern blot analysis and their expression levels were determined by quantitative PCR. Four of the six Chs genes were expressed in the mycelium, while the two others exhibited undetectable levels of expression. The mycelium was highly sensitive to the addition of nikkomycin Z (NZ) in the culture medium, which led to a decreased amount of chitin in the cell wall by up to 40% in the conditions tested, and to the formation of abnormal branching structures in the hyphae. The presence of NZ increased the expression level of one of the genes, Chs3, suggesting that the corresponding product is compensating the disruption of chitin biosynthesis in the hyphae. In addition, the activity of isolated CHS was strongly inhibited by NZ in vitro. Altogether our data indicate the importance of CHS for the vegetative growth of S. parasitica and demonstrate that these enzymes represent promising targets for the control of diseases caused by oomycetes.
Highlights
The oomycete lineage includes highly destructive plant and animal pathogens (Latijnhouwers et al, 2003; Phillips et al, 2008)
Nikkomycin Z is a specific inhibitor of chitin synthases (CHS) and it was shown to inhibit the growth of the oomycete S. monoica (Guerriero et al, 2010)
To test whether this antibiotic has a similar effect in the growth of the devastating fish pathogen S. parasitica, the mycelium was grown in the presence of three different concentrations of nikkomycin Z (NZ)
Summary
The oomycete lineage includes highly destructive plant and animal pathogens (Latijnhouwers et al, 2003; Phillips et al, 2008). The species Saprolegnia parasitica is ubiquitous to all freshwater environments, and it infects wild and cultivated fish and crustaceans, causing the disease saprolegniosis This infection currently represents a severe threat to the aquaculture industry and to some wild populations of animals (Derevnina et al, 2016). Saprolegniosis has experienced a resurgence and it currently represents one Chitin Biosynthesis in Saprolegnia parasitica of the main threats to aquaculture (van West, 2006). It primarily affects the farming of salmonid species where it causes losses of tens of millions of euros per year in the major producing countries. There are no efficient and environmentally friendly disease control methods available against this pathogen, the urgent need to develop new management strategies
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