THE DNA CONTENT OF TROPHOZOITES AND CYSTS OF GIARDIA-LAMBLIA BY MICRODENSITOMETRIC QUANTITATION OF FEULGEN STAINING AND EXAMINATION BY LASER-SCANNING CONFOCAL MICROSCOPY

We investigated direct measurement of the DNA content of the parasitic intestinal flagellate Giardia lamblia through quantitation by Feulgen microspectrophotometry and also by visualization of Feulgen-stained D NA chromosomes within dividing cells by laser scanning confocal micros copy. Individual trophozoites of Giardia (binucleate) contained 0.144 +/- 0.018 pg of DNA/cell or 0.072 pg DNA/nucleus. Giardia lamblia cyst s (quadranucleate) contained 0.313 +/- 0.003 pg DNA or 0.078 pg DNA/nu cleus. The genome size (C) value per nucleus ranged between 6.5-7.1 x 10(7) sp for trophozoites and cysts, respectively Confocal microscopic examination of Giardia trophozoites undergoing binary fission reveale d five chromosome-like bodies within each nucleus. Further information about genome size and DNA content within different Giardia species ma y help to clarify the pivotal role of these primitive eukaryotic cells in evolutionary development.