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The microaerophilic flagellate Giardia intestinalis: oxygen and its reaction products collapse membrane potential and cause cytotoxicity

Lloyd, David, Harris, Janine C, Maroulis, Sarah, Biagini, Giancarlo A, Wadley, Robert B, Turner, Michael P and Edwards, Michael R 2000. The microaerophilic flagellate Giardia intestinalis: oxygen and its reaction products collapse membrane potential and cause cytotoxicity. Microbiology 146 (12) , 3109--3118. 10.1099/00221287-146-12-3109

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Abstract

Trophozoites of the microaerophilic flagellate parasitic protozoon Giardia intestinalis have only a limited capacity to detoxify O2. Thus, when exposed to controlled concentrations of dissolved O2 >8 μM, they gradually lose their ability to scavenge O2. In a washed cell suspension stirred under 10% air in N2 (equivalent to 25 μM O2), inactivation of the O2-consuming system was complete after 3·5 h; during this period accumulation of H2O2 (3 μmol per 106 organisms) and oxidation of cellular thiols to 16% of their initial level occurred. Under 20% air (50 μM O2), respiratory inactivation was complete after 1·5 h, and under air (258 μM O2), after 50 min. Loss of O2-consuming capacity was accompanied by loss of motility. Use of the fluorogen 2,7-dichlorodihydrofluorescein acetate indicated that intracellular H2O2 is produced at extranuclear sites. Flow cytometric estimation of the plasma membrane electrochemical potentials using bis(1,3-dibutylbarbituric acid) trimethine oxonol, DiBAC4(3), showed that values declined from −134 mV to −20 mV after 4·5 h aeration. Incubation of organisms with 60 μM H2O2 for 10 min gave partial collapse of plasma membrane potential and complete loss of O2 uptake capacity; motility and viability as assessed by DiBAC4(3) exclusion were completely lost after 1 h. Inactivation of the O2-consuming system and loss of viability were also observed on exposure to singlet oxygen photochemically generated from rose bengal or toluidine blue.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Biosciences
Publisher: Microbiology Society
ISSN: 1350-0872
Last Modified: 26 Feb 2020 09:30
URI: http://orca.cf.ac.uk/id/eprint/127983

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