Researches on the Intestinal Protozoa of Monkeys and Man. I. General Introduction, and II. Description of the whole Life-History ofEntamoeba histolyticain Cultures

Abstract

A pure strain of Entamoeba histolytica has been isolated and cultivated, and an attempt has been made to study and describe its whole life-history in detail.This strain (K. 28 c) was derived from the dysenteric dejecta of a kitten experimentally infected per os by means of typical cysts from the faeces of a monkey (Macacus sinicus). It has now been under continuous cultivation for about 20 months (220 serial subcultures), and its development in vitro has been uniform throughout.Methods have been devised, and are here described, whereby any desired stage in the life-history of this strain—amoebae, cysts, and all intermediate stages (including encystation and excystation)—can be readily procured in vitro at will.Detailed study has shown that the trophic amoebae multiply in cultures by simple binary fission only, as they do in their natural hosts. Their mode of division is briefly described.Encystation also occurs in vitro just as it does in the bowel, with formation of characteristic precystic amoebae and the final production of typical quadrinucleate cysts.Excystation has been carefully studied, and it has been found that a single quadrinucleate, amoeba escapes from each cyst through a minute perforation in its wall. An account is given of this remarkable process, which has not been described previously.The 4-nucleate excysted (metacystic) amoeba has been found to produce a new generation of trophic forms by a complicated series of nuclear and cytoplasmic divisions, which are described in detail for the first time. The final result of this subdivision is the production of eight uninucleate amoebulae by each quadrinucleate amoeba hatched from a cyst.These amoebulae are young trophic amoebae, and not gametes or conjugants. No sexual phenomena of any sort have been observed during the metacystic itages: and the life-history of E. histolytica, as visible in vitro, is thus wholly sexual.A development similar to that here described in the case of Strain K. 28 c has been found to occur in many other cultivated strains of E. histolytica— including a strain isolated directly from man, and a human strain experiaentally implanted in a monkey (M. sinicus) and recovered therefrom in pure culture. There are therefore good reasons for concluding that the development were described is not abnormal, and that it is probably closely parallel to that which occurs naturally inside man.

Atypical ploidy cycles, Spo11, and the evolution of meiosis

“…The parasitic amoebae Entamoeba histolytica and E. invadens also produce quadrinucleate cysts, and also infect the alimentary canal of vertebrates, but are very distantly related to Giardia, being members of the Amoebozoa rather than excavates [29,30]. The whole infective lifecycle of E. histolytica has been examined in detail with no convincing reports of meiosis [31]. The expression of Spo11, along with other meiotic genes, is induced during nutritional stress and encystment [32,33], and homologous recombination also occurs under these conditions [33].…”

Study of Dientamoeba fragilis Jepps & Dobell I. Electronmicroscopic Observations of the Binucleate Stages II. Taxonomic Position and Revision of the Genus*

“…6-9, 11, 15); (c) the proximal segments of the periodic filaments (PF) that overlie the atractophores (Figs. 7, 10-15); and (d) the part of the Golgi complex (PB) applied to the periodic and atractophore part of the polar complex (Figs 10,12,14,. 19).…”

Radiosensitivity of Entamoeba histolytica cysts

“…After staining with iodine, most of Dhe cysts were seen to be uninucleated but there was usually a satisfactory number of quadrinucleated cysts as well. Dobell (1928) has stated that only mature (i.e., quadrinucleated) cysts can excyst. Since cyst suspensions were precious and often contained barely enough cysts to work wit'h, the practice of Rees et al (1950) of discarding harvests showing less than 50 % quadrinucleated cysts was not followed.…”