Abstract
Microalgae of the genus Prototheca (P.) are associated with rare but severe infections (protothecosis) and represent a potential zoonotic risk. Genotype (GT) 2 of P. zopfii has been established as pathogenic agent for humans, dogs, and cattle, whereas GT1 is considered to be non-pathogenic. Since pathogenesis is poorly understood, the aim of this study was to determine immunogenic proteins and potential virulence factors of P. zopfii GT2. Therefore, 2D western blot analyses with sera and isolates of two dogs naturally infected with P. zopfii GT2 have been performed. Cross-reactivity was determined by including the type strains of P. zopfii GT2, P. zopfii GT1, and P. blaschkeae, a close relative of P. zopfii, which is known to cause subclinical forms of bovine mastitis. The sera showed a high strain-, genotype-, and species-cross-reactivity. A total of 198 immunogenic proteins have been analyzed via MALDI—TOF MS. The majority of the 86 identified proteins are intracellularly located (e.g., malate dehydrogenase, oxidoreductase, 3-dehydroquinate synthase) but some antigens and potential virulence factors, known from other pathogens, have been found (e.g., phosphomannomutase, triosephosphate isomerase). One genotype-specific antigen could be identified as heat shock protein 70 (Hsp70), a well-known antigen of eukaryotic pathogens with immunological importance when located extracellularly. Both sera were reactive to glyceraldehyde-3-phosphate-dehydrogenase of all investigated strains. This house-keeping enzyme is found to be located on the surface of several pathogens as virulence factor. Flow-cytometric analysis revealed its presence on the surface of P. blaschkeae.
Highlights
Prototheca spp. are inconspicuous microorganisms that have remained poorly described despite their worldwide distribution
Visual Analysis of Western Blots In 2D-PAGE, proteins from Prototheca whole-cell extracts were evenly distributed over the selected pI range and well-resolved, as shown in Supplementary Material (Figure S1)
This suggest that antigen epitopes do not vary much between the Prototheca species and genotypes even though small differences are visible
Summary
Prototheca spp. are inconspicuous microorganisms that have remained poorly described despite their worldwide distribution These unicellular algae attracted our attention because of their ability to infect vertebrates with severe manifestations. Based on molecular analysis, they are classified as colorless green algae, closely related to Chlorella sp. They lack genes for photosynthesis and can use organic carbon sources in almost every environment, including fossil oils (Walker et al, 1975; Pore et al, 1983). P. wickerhamii, P cutis, P. zopfii, and P. blaschkeae are reported to cause infections in vertebrates, primarily mammals like household pets (cats and dogs), livestock (pigs and cattle) and humans (Pore and Shahan, 1988; Leimann et al, 2004; Camboim et al, 2011). One case of severe systemic infection due to P. blaschkeae has been reported so far (Thompson et al, 2009)
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