Role of Riboflavin and Certain Amino Acids in the Excystment of Schizopyrenus russelli*

SYNOPSIS. A simple medium, consisting of riboflavin and a mixture of L-glutamic acid, L-tryptophan, L-isoleucine, L-serine, and L-proline has been shown to induce rapid and mass scale excystment in Schizopyrenus russelli. Whereas percentage excystment was found to depend on the concentration of riboflavin and amino acids, more than 80% of cysts were found to excyst within 4 hr, when adequate amounts of these were supplied. Several individual amino acids, particularly L-glutamic acid, L-tryptophan, and L-proline, also supported considerable excystment, but riboflavin was always indispensable.     

Correlation of Encystment and Division in Schizopyrenus russelli*

SYNOPSIS. Schizopyrenus russelli, a free-living soil ameba, grows and encysts in the presence of bacteria. The encystment occurs with decline in the division rate. This is accompanied by incorporation of [U-¹⁴C] glucose into cyst cellulose. The degree of multiplication (but not of encystment) is a function of bacterial concentration. Berenil, a trypanocidal drug, while allowing excystment, completely inhibited multiplication of emerged amebae and their encystment. Addition of this drug after 24 hr, when amebae had gone into a phase of active division failed to check encystment, although it still inhibited further multiplication of the amebae. The findings suggest that a phase of cell division may be a prerequisite for encystment.     

Correlation of encystment and division in Schizopyrenus russelli.

Schizopyrenus russelli, a free-living soil ameba, grows and encysts in the presence of bacteria. The encystment occurs with decline in the division rate. This is accompanied by incorporation of [U-14C] glucose into cyst cellulose. The degree of multiplication (but not of encystment) is a function of bacterial concentration. Berenil, a trypanocidal drug, while allowing excystment, completely inhibited multiplication of emerged amebae and their encystment. Addition of this drug after 24 hr, when amebae had gone into a phase of active division failed to check encystment, although it still inhibited further multiplication of the amebae. The findings suggest that a phase of cell division may be a prerequisite for encystment.     

Ultrastructural Changes During Encystment of Schizopyrenus russelli*

Ultrastructural changes associated with the encystment of Schizopyrenus russelli have been studied by electron microscopy. Before encystment small “black bodies” appear in the cytoplasm and later migrate toward the periphery. The outer cyst wall is secreted at this stage as a thin discontinuous layer which thickens and subsequently becomes continuous. Concomitant with this, the endoplasmic reticulum surrounds the mitochondria. The inner cyst wall later appears as a multilayered structure which presumably is cast off from the plasma membrane. Between the inner and outer layers of the cyst wall, there is a middle, less electron-dense layer wherein extruded cytoplasmic material is found embedded at certain places.     

Isolation,Structure and Composition of Cyst Wall of Schizopyrenus russelli*

SYNOPSIS. A procedure is described for the isolation of cyst wall of Schizopyrenus russelli free of cytoplasmic material. It has 27.3% protein, 37.5% carbohydrate (of which 13.1% is cellulose), and 15.1% lipids. Sialic acid is absent. It has a relatively electrondense inner thick layer and a less electron-dense outer thin layer. The space between the 2 layers is 25 nm in younger cysts and 2.5 μ in fully mature cysts. This space is filled with a fibrillar spongy material likely to be cellulose.     

Changes in the Levels of Some Macromolecules and Certain Enzyme Activities in Excysting Schizopyrenus russelli

SYNOPSIS. Changes in macromolecular content and certain enzyme levels have been studied during excystment of Schizopyrenus russelli. Protein, RNA and DNA increase with the onset of excystment, the increase being more marked in the first 2 hr than later. Cellulose content is considerably decreased as the trophozoites start emerging from the cysts. There is no significant change in glycogen content. Enzyme activities of glutamic oxalacetic transaminase and ribonuclease increase while those of aldolase and isocitric dehydrogenase decrease as excystment proceeds.     

Action of Ultraviolet Radiation on Excystment and Concomitant Macromolecular Syntheses in Schizopyrenus russelli*

SYNOPSIS. Excystment of Schizopyrenus russelli was associated with increase in DNA, RNA, and protein. Both excystment and these macromolecular increases were sensitive to ultraviolet radiation. The effect of UV was partly reversed by incubation in the dark at 28 C, but not at 4 C. Excystment from cysts preincubated in the excystment medium (before UV treatment) was relatively resistant to radiation.