Giardia intestinalis, a eukaryote without hydrogenosomes, produces hydrogen

• Published in: Microbiology (Society for General Microbiology) Vol. 148; no. 3; pp. 727 - 733
• Main Authors: Lloyd, David, Ralphs, James R, Harris, Janine C
• Format: Journal Article
• Language: English
• Published: Reading Soc General Microbiol 01-03-2002; Society for General Microbiology
• Subjects: Anaerobiosis; Animals; Biochemistry. Physiology. Immunology. Molecular biology; Biological and medical sciences; Culture Media; Fundamental and applied biological sciences. Psychology; Giardia intestinalis; Giardia lamblia - enzymology; Giardia lamblia - growth & development; Giardia lamblia - ultrastructure; Hydrogen - metabolism; Hydrogenase - genetics; Hydrogenase - metabolism; Mass Spectrometry; Microscopy, Confocal; Molecular Sequence Data; Organelles - ultrastructure; Protozoa; Characterization; Hydrogenase; Protozoa; Giardia lamblia; Enzyme; Hydrogen; Diplomonadida; Biosynthesis; Oxidoreductases; Mass spectrometry; Hydrogenosome
• ISSN: 1350-0872; 1465-2080
• DOI: 10.1099/00221287-148-3-727

Microbiology (BIOSI 1, Main Building), Cardiff University, PO Box 915, Cardiff CF10 3TL, Wales, UK 1
Author for correspondence: David Lloyd. Tel: [phone]. Fax: [phone]. e-mail: LloydD{at}cardiff.ac.uk
The microaerophilic flagellated protist Giardia intestinalis , the commonest protozoal agent of intestinal infections worldwide, is of uncertain phylogeny, but is usually regarded as the earliest branching of the eukaryotic clades. Under strictly anaerobic conditions, a mass spectrometric investigation of gas production indicated a low level of generation of dihydrogen (2 nmol min -1 per 10 7 organisms), about 10-fold lower than that in Trichomonas vaginalis under similar conditions. Hydrogen evolution was O 2 sensitive, and inhibited by 100 µM metronidazole. Fluorescent labelling of G. intestinalis cells using monoclonal antibodies to typical hydrogenosomal enzymes from T. vaginalis (malate enzyme, and succinyl-CoA synthetase and ß subunits), and to the large-granule fraction (hydrogenosome-enriched, also from T. vaginalis ) gave no discrete localization of epitopes. Cell-free extracts prepared under anaerobic conditions showed the presence of a CO-sensitive hydrogenase activity. This first report of hydrogen production in a eukaryote with no recognizable hydrogenosomes raises further questions about the early branching status of G. intestinalis ; the physiological characterization of its hydrogenase, and its recently elucidated gene sequence, will aid further phylogenetic investigations.
Keywords: early branching eukaryotes, diplomonads, membrane inlet mass spectrometry, hydrogenase