title: UV irradiation responses in Giardia intestinalis.
abstract: The response to ultraviolet light (UV) radiation, a natural stressor to the intestinal protozoan parasite Giardia intestinalis, was studied to deepen the understanding of how the surrounding environment affects the parasite during transmission. UV radiation at 10 mJ/cm(2) kills Giardia cysts effectively whereas trophozoites and encysting parasites can recover from UV treatment at 100 mJ/cm(2) and 50 mJ/cm(2) respectively. Staining for phosphorylated histone H2A showed that UV treatment induces double-stranded DNA breaks and flow cytometry analyses revealed that UV treatment of trophozoites induces DNA replication arrest. Active DNA replication coupled to DNA repair could be an explanation to why UV light does not kill trophozoites and encysting cells as efficiently as the non-replicating cysts. We also examined UV-induced gene expression responses in both trophozoites and cysts using RNA sequencing (RNA seq). UV radiation induces small overall changes in gene expression in Giardia but cysts show a stronger response than trophozoites. Heat shock proteins, kinesins and Nek kinases are up-regulated, whereas alpha-giardins and histones are down-regulated in UV treated trophozoites. Expression of variable surface proteins (VSPs) is changed in both trophozoites and cysts. Our data show that Giardia cysts have limited ability to repair UV-induced damage and this may have implications for drinking- and waste-water treatment when setting criteria for the use of UV disinfection to ensure safe water.
authors.affiliation: Department of Cell and Molecular Biology, Uppsala University, Uppsala, Sweden.
authors.forename: Elin
authors.initials: E
authors.lastname: Einarsson
authors.affiliation: Department of Cell and Molecular Biology, Uppsala University, Uppsala, Sweden.
authors.forename: Staffan G
authors.initials: SG
authors.lastname: Svärd
authors.affiliation: Department of Virology, Immunobiology and Parasitology, National Veterinary Institute, Uppsala, Sweden. Electronic address: Karin.troell@sva.se.
authors.forename: Karin
authors.initials: K
authors.lastname: Troell
mesh_terms: D000818:Animals; D001483:Base Sequence / Q000528:radiation effects; D001646:Bile / Q000469:parasitology; D002417:Cattle; D016000:Cluster Analysis; D004249:DNA Damage / Q000528:radiation effects; D004261:DNA Replication / Q000528:radiation effects*; D016054:DNA, Protozoan / Q000528:radiation effects*; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D015870:Gene Expression / Q000528:radiation effects; D016829:Giardia lamblia / Q000235:genetics / Q000528:radiation effects*; D006657:Histones / Q000378:metabolism; D010766:Phosphorylation; D016053:RNA, Protozoan / Q000302:isolation & purification / Q000528:radiation effects; D060888:Real-Time Polymerase Chain Reaction; D014158:Transcription, Genetic / Q000528:radiation effects; D014466:Ultraviolet Rays
chemical_list: D016054:DNA, Protozoan; D006657:Histones; D016053:RNA, Protozoan
keywords: Cysts; DNA replication; Giardia; Inactivation; Trophozoites; UV stress