Background: Nosema bombycis is a unicellular eukaryotic pathogen of the silkworm, Bombyx mori, and a hazard to the silkworm industry. Because of its long incubation period and horizontal and vertical transmission, it is a quarantine pathogen in sericulture. The microsporidian life cycle includes a dormant extracellular phase and intracellular proliferation phase. The proliferation period is the most active period of the microsporidian. This period lacks spore wall protection and may be the most

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... susceptible stage for control. Results: The N. bombycis protein (NBO_76g0014) was identified as a transmembrane protein and named NbTMP1. It is not homologous with proteins from other microsporidia and species. NbTMP1 has a transmembrane region of 23 amino acids at the N-terminus. Indirect immunofluorescence analysis (IFA) results suggest that NbTMP1 is secreted on the plasma membrane as the spores develop. Western blot and qRT-PCR analysis showed that NbTMP1 expressed in all development stages of N. bombycis in infected cells and in the silkworm midgut. Down-regulation of NbTMP1 expression resulted in significant inhibition of N. bombycis proliferation. Conclusions: We confirmed that NbTMP1 is a membrane protein of N. bombycis. Reduction of the transcription level of NbTMP1 significantly inhibited N. bombycis proliferation, and this protein may be a target for the selective breeding of N. bombycis resistant silkworm strains.