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UV irradiation responses in Giardia intestinalis
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Microbiology.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Microbiology.
2015 (English)In: Experimental parasitology, ISSN 0014-4894, E-ISSN 1090-2449, Vol. 154, 25-32 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2015. Vol. 154, 25-32 p.
Keyword [en]
UV stress, Giardia, Trophozoites, Cysts, Inactivation, DNA replication
National Category
Microbiology in the medical area
Identifiers
URN: urn:nbn:se:uu:diva-256984DOI: 10.1016/j.exppara.2015.03.024ISI: 000355640500005PubMedID: 25825252OAI: oai:DiVA.org:uu-256984DiVA: diva2:838493
Available from: 2015-06-30 Created: 2015-06-29 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Comparative Cell Biology in Diplomonads
Open this publication in new window or tab >>Comparative Cell Biology in Diplomonads
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The diplomonads are a diverse group of eukaryotic flagellates found in microaerophilic and anaerobic environments. The most studied diplomonad is the intestinal parasite Giardia intestinalis, which infects a variety of mammals and cause diarrheal disease. Less is known about Spironucleus salmonicida, a parasite of salmonid fish, known to cause systemic infections with high mortality.

We created a transfection system for S. salmonicida to study cellular functions and virulence in detail (Paper I). The system was applied to explore the mitochondrion-related organelle (MRO) in S. salmonicida. We showed that S. salmonicida possesses a hydrogenosome (Paper II) with a higher metabolic capacity than the corresponding MRO of Giardia, the mitosome. Evolutionary analysis of key hydrogenosomal proteins showed ancient origin, indicating their presence in the ancestral diplomonad and subsequent loss in Giardia. Annexins are of evolutionary interest since these proteins are found across all kingdoms. Annexin-like proteins are intriguingly expanded into multigene families in Giardia and Spironucleus. The annexins of S. salmonicida were characterized (Paper III) with distinct localizations to various cellular structures, including a putative adhesion structure anterior in the cell.

The disease-causing Giardia trophozoites differentiate into infectious cysts, a process essential for transmission and virulence of the parasite. Cysts are often spread via contaminated water and exposed to environmental stressors, such as UV irradiation. We studied the survival and transcriptional response to this stress factor (Paper IV) and results showed the importance of active DNA replication machinery for parasite survival after DNA damage. In addition, we studied transcriptional changes along the trajectory of encystation (Paper V), which revealed a coordinated cascade of gene regulation. This was observed for the entire transcriptome as well as putative regulators. Large transcriptional changes appeared late in the process with the majority of differentially regulated genes encoding hypothetical proteins. We studied the localizations of several of these to gain information of their possible function.

To conclude, the diplomonads are complex eukaryotic microbes with cellular processes adjusted to match their life styles. The work in this thesis has provided insight of their adaptations, differences and similarities, but also new interesting leads for future studies of diplomonad biology and virulence. 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. 84 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1303
Keyword
Giardia intestinalis, Spironucleus salmonicida, intestinal parasite, hydrogenosome, encystation, gene regulation, transfection, diplomonad, antigenic variation, annexin
National Category
Microbiology
Identifiers
urn:nbn:se:uu:diva-264541 (URN)978-91-554-9374-5 (ISBN)
Public defence
2015-12-04, A1:111a, BMC, Husargatan 3, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2015-11-12 Created: 2015-10-14 Last updated: 2015-11-13

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Einarsson, ElinSvärd, Staffan G.

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