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Metabolic Changes in Giardia intestinalis during Differentiation

Timothy A. Paget, P. Timothy Macechko and Edward L. Jarroll
The Journal of Parasitology
Vol. 84, No. 2 (Apr., 1998), pp. 222-226
DOI: 10.2307/3284474
Stable URL: http://www.jstor.org/stable/3284474
Page Count: 5
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Metabolic Changes in Giardia intestinalis during Differentiation
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Abstract

The oxygen uptake rate and metronidazole (MTZ) sensitivity in Giardia spp. cysts is greatly reduced from that in trophozoites. Thus, this project was undertaken to assess when in the encystation process these phenomena occur. Oxygen uptake rates approximately doubled (from ~4.9 to 8.3 μ M O2 min-1 10-6 cells) during the first 5 hr into encystation. This increase was followed by a marked decrease to 2.3 μ M O2 min-1 10-6 by 12 hr. By 50 hr into encystation, oxygen uptake was 0.7 μ M O2 min-1 10-6 cells. Glucose stimulated oxygen uptake by 89% in trophozoites but did not demonstrably stimulate oxygen uptake in cells after 12 hr into encystment. Deoxy-D-glucose uptake dropped by more than an order of magnitude in encysting cells compared to nonencysting cells. In contrast, aspartate uptake remained relatively constant regardless of whether cells were encysting or not. This suggests that there is a change in the parasite's ability to transport glucose during cyst formation; a similar change in the parasite's ability to transport aspartate was not observed after 40 hr into encystation. MTZ inhibited oxygen uptake by 77% in trophozoites, but there was no detectable inhibition of oxygen uptake 8 hr after trophozoites were transferred to encystation medium. We propose that this resistance to MTZ may be due to a change in metabolic flux away from the pyruvate ferredoxin oxidoreductase pathway. Oxygen uptake by noninduced cysts increased exponentially during the 30 min following the induction of excystation. Likewise, MTZ sensitivity returned within 15 min after the induction of excystation, and by 30 min into excystation full sensitivity had returned.

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