The host-pathogen interface : Characterising putative secreted proteins of the honeybee pathogen Nosema ceranae ( Microsporidia ).

Abstract

Microsporidia are obligate intracellular eukaryotic parasites related to fungi, possessing greatly reduced genomic and cellular components. The microsporidian Nosema ceranae threatens honeybee (Apis mellifera) populations. Nosemosis has a complex epidemiology affected by host, pathogen and environmental factors. Although a draft of the N. ceranae genome has been published, the molecular basis underpinning pathogenicity is not known. The lack of established culturing techniques and a tractable genetic system necessitates use of model systems for both host and parasite such as Saccharomyces cerevisiae. I hypothesise effectors essential to disease progression exist amongst N. ceranae secretome genes. In this study I have started characterising these genes using a combination of established and novel techniques for studying microsporidia proteins including bioinformatics, heterologous expression in S. cerevisiae, and the genome-wide analysis platform of Synthetic Genetic Arrays. This effort has yielded new insights into N. ceranae secreted proteins which lack similarity to known sequences. I identified N. ceranae protein NcS77 as a candidate effector implicated in targeting host nuclear pores. NcS50 and NcS85 co-localise with ERG6 a marker for lipid droplets (an organelle known to be targeted by another obligate intracellular pathogen Chlamydia trachomatis) when expressed in S. cerevisiae. N. ceranae polar tube proteins (PTP) induce filament formation when expressed in S. cerevisiae and PTP2 co-localises with the cell wall. Interestingly this phenotype is replicated by another secreted protein which may infer a common function. Together these data contribute to knowledge on N. ceranae pathology bringing us closer to understanding the disease and ultimately lead the way to mitigation.