Updated project metadata. Exoproteome from parasitic protists constitutes of extracellular proteins which play a fundamental role in multifactorial host-parasite interactions. Lytic factors, especially secreted proteases in extracellular milieu, are capable to modulate tissue invasion, thereby aggravating host susceptibility. Despite the important role of exoproteins during infection, exoproteomic data on Histomonas meleagridis are non-existent. The present study employed traditional 1D-in-gel-zymography (1D-IGZ) and micro-LC-ESI-MS/MS (shotgun proteomics), to scrutinize H. meleagridis exoproteomes, obtained from a clonal virulent and attenuated strains. Both strains were maintained as mono-eukaryotic monoxenic culture with Escherichia coli. We demonstrated active in vitro secretion kinetics of proteases by both parasites, with widespread proteolytic activity ranging from 17 kDa to 120 kDa. Based on protease inhibitor-susceptibility tests, a predominant repertoire of cysteine proteolysis was present in the parasite exoproteomes, with stronger activity from virulent H. meleagridis. Shotgun proteomics, aided by customized database, identified 176 proteins including actin, potential moonlighting glycolytic enzymes, lytic molecules such as pore-forming proteins (PFPs) and proteases like cathepsin-L like cysteine protease. To quantify the exoproteomic differences between the virulent and the attenuated H. meleagridis cultures, a sequential window acquisition of all theoretical spectra mass spectrometric (SWATH-MS) approach was applied. Surprisingly results showed most of the exoproteomic differences to be of bacterial origin, involving metabolism and locomotion. By deciphering such molecular signatures, novel insights into an inherent complex in vitro protozoan- bacteria relationship was elucidated.