Giardia lamblia is a common cause of diarrhea in humans and other mammals throughout the world. It can be distinguished from other Giardia species by light or electron microscopy. The two major genotypes of G. lamblia that infect humans are so different genetically and biologically that they may warrant separate species or subspecies designations. Trophozoites have nuclei and a well-developed cytoskeleton but lack mitochondria, peroxisomes, and the components of oxidative phosphorylation. They have an endomembrane system with at least some characteristics of the Golgi complex and encoplasmic reticulum, which becomes more extensive in encysting organisms. The primitive nature of the organelles and metabolism, as well as small-subunit rRNA phylogeny, has led to the proposal that Giardia spp. are among the most primitive eukaryotes. G. lamblia probably has a ploidy of 4 and a genome size of approximately 10 to 12 Mb divided among five chromosomes. Most genes have short 5′ and 3′ untranslated regions and promoter regions that are near the initiation codon. Trophozoites exhibit antigenic variation of an extensive repertoire of cysteine-rich variant-specific surface proteins. Expression is allele specific, and changes in expression from one vsp gene to another have not been associated with sequence alterations or gene rearrangements. The Giardia genome project promises to greatly increase our understanding of this interesting and enigmatic organism.

Biology of Giardia lamblia.

The genome of the eukaryotic protist Giardia lamblia, an important human intestinal parasite, is compact in structure and content, contains few introns or mitochondrial relics, and has simplified machinery for DNA replication, transcription, RNA processing, and most metabolic pathways. Protein kinases comprise the single largest protein class and reflect Giardia's requirement for a complex signal transduction network for coordinating differentiation. Lateral gene transfer from bacterial and archaeal donors has shaped Giardia's genome, and previously unknown gene families, for example, cysteine-rich structural proteins, have been discovered. Unexpectedly, the genome shows little evidence of heterozygosity, supporting recent speculations that this organism is sexual. This genome sequence will not only be valuable for investigating the evolution of eukaryotes, but will also be applied to the search for new therapeutics for this parasite.

https://science.sciencemag.org/content/sci/317/5846/1921.full.pdf

Genomic minimalism in the early diverging intestinal parasite Giardia lamblia.

The serum- and glucocorticoid-inducible kinase-1 (SGK1) is ubiquitously expressed and under genomic control by cell stress (including cell shrinkage) and hormones (including gluco- and mineralocort...

https://www.physiology.org/doi/pdf/10.1152/physrev.00050.2005

(Patho)physiological Significance of the Serum- and Glucocorticoid-Inducible Kinase Isoforms

To address the source of infection in humans and public health importance of Giardia duodenalis parasites from animals, nucleotide sequences of the triosephosphate isomerase (TPI) gene were generated for 37 human isolates, 15 dog isolates, 8 muskrat isolates, 7 isolates each from cattle and beavers, and 1 isolate each from a rat and a rabbit. Distinct genotypes were found in humans, cattle, beavers, dogs, muskrats, and rats. TPI and small subunit ribosomal RNA (SSU rRNA) gene sequences of G. microti from muskrats were also generated and analyzed. Phylogenetic analysis on the TPI sequences confirmed the formation of distinct groups. Nevertheless, a major group (assemblage B) contained most of the human and muskrat isolates, all beaver isolates, and the rabbit isolate. These data confirm that G. duodenalis from certain animals can potentially infect humans and should be useful in the detection, differentiation, and taxonomy of Giardia spp.

/pdf/triosephosphate-isomerase-gene-characterization-and-1zqdmycacr.pdf

Triosephosphate Isomerase Gene Characterization and Potential Zoonotic Transmission of Giardia duodenalis

The taxonomy, life cycle patterns and zoonotic potential of Giardia infecting mammals and birds have been poorly understood and controversial for many years. The development of molecular tools for characterising isolates of Giardia directly from faeces or environmental samples has made an enormous contribution to resolving these issues. It is now clear that the G. duodenalis morphological group is a species complex comprising a series of what appear to be largely host-adapted species, and at least two zoonotic species for which humans are the major host, but which are also capable of infecting other mammals. It is proposed that this new information be reflected in the redesignation of several species of Giardia described previously. The molecular epidemiological tools that are now available need to be applied in different endemic foci of Giardia transmission, as well as in outbreak situations, in order to understand better the frequency of zoonotic transmission as well as to develop more effective approaches to controlling giardiasis.

Variation in Giardia: implications for taxonomy and epidemiology.

Trophozoites of Giardia ardeae were obtained from the great blue heron (Ardea herodias) and established in axenic culture using the TYI-S-33 medium. The generation time in culture for G. ardeae was 22-25 hr, which was 3-fold longer than for Giardia duodenalis (WB strain). A morphological comparison of trophozoites in the original intestinal isolate to those grown in culture revealed that they were identical for the following characteristics: a pyriform-shaped body, a ventral adhesive disc with a deep notch in the posterior border, teardrop-shaped nuclei, pleomorphism in median body structure ranging from a round-oval appearance (Giardia muris type) to that of a clawhammer (G. duodenalis type), and a single caudal flagellum on the right side (as viewed dorsally) with the left one being rudimentary. Analysis of the chromosomal migration patterns was performed by orthogonal-field-alternation gel electrophoresis and demonstrated that the pattern for G. ardeae was distinctly different from that for G. duodenalis (Portland 1-CCW strain). Bacterial symbionts were seen attached to trophozoites in the original isolate but could not be detected in cultured trophozoites using scanning electron microscopy, fluorescence light microscopy using the Hoechst 33258 dye for DNA localization, or by standard microbiological techniques using nonselective media for growing aerobic or anaerobic bacteria. This study demonstrated that avian-derived Giardia could be grown in axenic culture; based on morphological criteria and chromosomal migration patterns, that G. ardeae should be considered a distinct species; and that rationale for determining Giardia spp., based on median body structure alone, should no longer be considered adequate for classification at the species level.

Axenic culture and characterization of Giardia ardeae from the great blue heron (Ardea herodias).

Giardia spp.: distribution of contractile proteins in the attachment organelle.

A method for the isolation of Giardia trophozoites based on their ability to attach to warm surfaces has been developed. Mucosal scrapings were obtained from the small intestine of rats infected with Giardia and suspended in Hanks' balanced salt solution (HBSS). Trophozoites were concentrated by centrifugation and allowed to attach to the surfaces of polystyrene petri dishes incubated at 37 C. Incubation temperature significantly affected the recovery of trophozoites. After attachment at 37 C, trophozoites were separated from contaminating intestinal debris by incubation at cold temperature. The trophozoites detach at 4 C, whereas the intestinal debris remain adherent. Then the detached trophozoites were isolated by reattachment at 37 C. Examination by scanning electron microscopy revealed a marked reduction in contamination of attached trophozoites and dish surfaces after the use of cold temperature detachment and reattachment at 37 C. Viability of trophozoites as measured by erythrosin-B dye exclusion, remained above 90% up to 120 min after isolation. This method of isolation facilitates the recovery of this protozoan directly from small intestine for morphological and experimental study.

Isolation and purification of Giardia trophozoites from rat intestine

Giardia sp. trophozoites were isolated directly from the small intestines of rats and permitted to ach to polystyrene Petri dishes incubated attached trophozoites were treated in vitro with various agents which inhibit cell motility (cytochalasin-B, low Ca-, colchicine) and metabolism (iodoacetic acid, 2,4- dinitrophenol) and chemotherapeutic agents (quinacrine-HCl, metronidazole). Trophozoite attachment was sensitive to cytochalasin-B, low Ca-, iodoacetate, and quinacrine-HCl. Contractile proteins (actin, myosin) have been demonstrated previously in the periphery of the ventral disc. The effect of cytochalasin-B and low Ca++ concentrations on trophozoite attachment is consistent with the suggested role of contractile proteins in the mechanism of attachment. The effect of iodoacetate suggests that energy for attachment is derived from glycolysis. The effect of quinacrine-HCl on attachment was rapid (< 10 min with 10.0 ,ug/ml). Its mode of action on attachment is not understood. Trophozoites of the genus Giardia attach to the brush border of the host's intestinal epithe- lium by a specialized organelle called the ventral disc. Giardia muris has been reported to cause

Effect of cytochalasin-B, low Ca++ concentration, iodoacetic acid, and quinacrine-HCl on the attachment of Giardia trophozoites in vitro.

We have shown that cysts of the genus Spironucleus share many common morphological features with Giardia cysts including: 2-4 nuclei, flagellar axonemes, a distinct cyst wall, and they even display the same immunostaining as Giardia cysts when labeled with antibodies specific for Giardia cyst wall. A direct comparison of Spironucleus muris and Giardia microti cysts has revealed that cysts of S. muris are significantly smaller than cysts of G. microti. At the ultrastructural level, the cyst walls are similar in fibrillar appearance, but the width of the S. muris cyst wall is significantly less than that of G. microti. The cysts of S. muris also differ from G. microti in that they contain a striated rootlet fiber, flagellar sheath, and numerous glycogen rosettes. Characteristic features of Giardia include the adhesive disc and median body. Although the cysts of Spironucleus and Giardia are similar in appearance, these unique morphological features can be used to distinguish between the 2 protozoa and should be employed in the detection of Giardia cysts in water samples. Giardiasis is the most common waterborne

Dennis E. Feely

Papers

Axenic culture and characterization of Giardia ardeae from the great blue heron (Ardea herodias).

Giardia spp.: distribution of contractile proteins in the attachment organelle.

Isolation and purification of Giardia trophozoites from rat intestine

Effect of cytochalasin-B, low Ca++ concentration, iodoacetic acid, and quinacrine-HCl on the attachment of Giardia trophozoites in vitro.

A comparison of Giardia microti and Spironucleus muris cysts in the vole: an immunocytochemical, light, and electron microscopic study.