Genome ploidy in different stages of the Giardia lamblia life cycle
Article first published online: 20 DEC 2001
Volume 3, Issue 1, pages 55–62, January 2001
How to Cite
Bernander, R., Palm, J. E. D. and Svärd, S. G. (2001), Genome ploidy in different stages of the Giardia lamblia life cycle. Cellular Microbiology, 3: 55–62. doi: 10.1046/j.1462-5822.2001.00094.x
- Issue published online: 20 DEC 2001
- Article first published online: 20 DEC 2001
- Received 5 May 2000; revised 4 August, 2000; accepted 31 August, 2000.
The early diverging eukaryotic parasite Giardia lamblia is unusual in that it contains two apparently identical nuclei in the vegetative trophozoite stage. We have determined the nuclear and cellular genome ploidy of G. lamblia cells during all stages of the life cycle. During vegetative growth, the nuclei cycle between a diploid (2N) and tetraploid (4N) genome content and the cell, consequently, cycles between 4N and 8N. Stationary phase trophozoites arrest in the G2 phase with a ploidy of 8N (two nuclei, each with a 4N ploidy). On its way to cyst formation, a G1 trophozoite goes through two successive rounds of chromosome replication without an intervening cell division event. Fully differentiated cysts contain four nuclei, each with a ploidy of 4N, resulting in a cyst ploidy of 16N. The newly excysted cell, for which we suggest the term ‘excyzoite’, contains four nuclei (cellular ploidy 16N). In a reversal of the events occurring during encystation, the excyzoite divides twice to form four trophozoites containing two diploid nuclei each. The formation of multiple cells from a single cyst is likely to be one of the main reasons for the low infectious doses of G. lamblia.