Spontaneous chromosome rearrangements in the protozoan Giardia lamblia: estimation of mutation rates.
Subcloned lines of the WB strain of Giardia lamblia contain polymorphic ribosomal RNA (rRNA) encoding chromosomes (Le Blancq et al., Nucl. Acids Res. 1991, 19, 4405-4412). We show that in a continuously propagated culture of G.lamblia trophozoites the proportion of trophozoites with rearranged rRNA encoding chromosomes gradually increases, consistent with the high mutation rate of about 1% per cell per division cycle. This conclusion is based on the finding in one experiment that after about 8 division cycles 20% of the population consisted of independent mutants, while after approximately 100 division cycles 87.5% of the population were independent mutants. In a second experiment, approximately 38% and 71.5% of the trophozoites were independent mutants after approximately 9 and approximately 100 division cycles, respectively. The data show that the genome of the WB strain of G.lamblia has a highly recombinogenic phenotype. Extensive karyotype heterogeneity has also been observed among recently isolated G.lamblia strains obtained from a defined geographic area (Korman et al., J. Clin. Invest. 1992, 89, 1725-1733) suggesting that a high mutation rate might also occur in vivo.
Le Blancq
S M
SM
Department of Genetics and Development, College of Physicians and Surgeons, Columbia University, New York, NY 10032.
Korman
S H
SH
Van der Ploeg
L H
LH
D000818:Animals; D002875:Chromosomes / Q000378:metabolism*; D015342:DNA Probes / Q000235:genetics; D016054:DNA, Protozoan / Q000378:metabolism*; D004275:DNA, Ribosomal / Q000378:metabolism*; D016521:Electrophoresis, Gel, Pulsed-Field; D016829:Giardia lamblia / Q000235:genetics*; D008433:Mathematics; D009154:Mutation / Q000235:genetics; D012335:RNA, Ribosomal / Q000235:genetics; D011995:Recombination, Genetic / Q000235:genetics*
D015342:DNA Probes; D016054:DNA, Protozoan; D004275:DNA, Ribosomal; D012335:RNA, Ribosomal