An Ultrastructural Study of Ingestion and Digestion in Tetrahymena pyriformis*

Abstract

SYNOPSIS. When the structures involved in digestive events in T. pyriformis are examined at the electron microscope level, some information is added to that long known from light microscopy. The food trapping mechanism consists of the three membranelles, undulating membrane, oral ribs, and a “valve” apparently closing the opening to the cytopharynx. Both of the latter structures are supported by microtubules. Fibers extend internally from the cytopharynx and are closely associated with the food vacuole as it forms. Clear vacuoles resembling pinocytic vacuoles appear to arise from differentiated areas of the pellicle and plasma membrane. These vacuoles may fuse with primary lysosomes. Hydrolases are thus contributed to the pinocytic vacuoles which may then fuse with food vacuoles. When first formed food vacuoles contain no hydrolases but may acquire them directly, from primary lysosomes or from pinocytic vacuoles. Digestion proceeds to completion in the food vacuole, at which time soluble food products are released to the cytoplasm. Undigested materials are lost through the cytopyge. In stationary growth phase cells autophagic vacuoles form containing mitochondria and other cellular particulates. Such vacuoles probably contain hydrolases when formed and they may receive others by fusion with primary lysosomes.

Particle production by planktonic ciliates1

“…Unlike copepods, which produce large, rapidly sinking, fecal pellets, ciliates release small amorphous fecal aggregates and purinoid-excretory bodies (e.g. Elliott and Clemmons 1966;Soldo et al 1978) which can be nearly the same size as the algal cells they engulf. These aggregates and excretory bodies remain suspended in the water and may be remineralized within the euphotic zone (Sieburth et al 1978;Antia et al 1980).…”

“…Fecal particles, which are not membrane-bound, are eliminated by ciliates (e.g. Elliott and Clemmons 1966;Hamilton and Preslan 1969). Although defecation has not been specifically studied in marine planktonic ciliates, Campbell (1927) recognized the presence of a cytopyge, which is used to eliminate fecal particles in the tintinnid Favella.…”

THE INFLUENCE OF THE MODE OF NUTRITION ON THE DIGESTIVE SYSTEM OF OCHROMONAS MALHAMENSIS

“…The absence of cytochemicallydetectable acid phosphatase activity in the vacuoles of cells in the osmotrophic medium is understandable since the cells obtain all essential nutrients by absorption and there is less requirement for digestive activity . As in T. pyriformis (15), the ingestion of particulate food results in increased acid phosphatase-staining in the food vacuoles. This clearly confirms the catabolic role of the large vacuoles in 0 .…”

“…The occurrence of acid phosphatase in digestive vacuoles has been demonstrated in many different types of protozoa (31) . Tetrahymena pyriformis forms few food vacuoles when cultured in an axenic, chemically-defined medium (38,39), whereas phagocytosis increases vacuolization (15) .…”

“…The merging of primary and secondary lysosomes with phagocytic vacuoles has been inferred from observations of T . pyriformis, kidney cells, and L fibroblast cells (15,22,40) .…”