Loss of endocytic capacity in aging Paramecium. The importance of cytoplasmic organelles

Evolutionary bioenergetics of ciliates

Understanding why various organisms evolve alternative ways of living requires information on both the fitness advantages of phenotypic modifications and the costs of constructing and operating cellular features. Although the former has been the subject of a myriad of ecological studies, almost no attention has been given to how organisms allocate resources to alternative structures and functions. We address these matters by capitalizing on an array of observations on diverse ciliate species and from the emerging field of evolutionary bioenergetics. A relatively robust and general estimator for the total cost of a cell per cell cycle (in units of ATP equivalents) is provided, and this is then used to understand how the magnitudes of various investments scale with cell size. Among other things, we examine the costs associated with the large macronuclear genomes of ciliates, as well as ribosomes, various internal membranes, osmoregulation, cilia, and swimming activities. Although a number of uncertainties remain, the general approach taken may serve as blueprint for expanding this line of work to additional traits and phylogenetic lineages.

Age-related total protein content of parental cells and total protein content of their exconjugant progeny in Paramecium primaurelia

Previous cytofluorometric analyses on Paramecium primaurelia, stock 90, provided information that cell inability or capacity to mate are correlated to variations in their total protein content (TPC). Besides, age-associated protein decrease was suggested to take place during the maturity period. This work follows the assumption that cells, conjugating early or late in their maturity, give rise to offspring showing a higher or a lower TPC, respectively, and that the TPC is in some way linked to the well known relation between increased age of conjugant cells and decreased length of immaturity period of their progeny. Isogenic parental lines of stock 90, maintained in exponential growth phase up to their clonal decline, were regularly allowed to mate at increasing fission ages during their maturity period, as long as they produced viable offspring. Firstly, cytofluorometrically measured TPC decreased in aging parental lines. It was subsequently found that exconjugant progeny derived from younger or older parents exhibit a higher or a lower TPC, respectively. Finally, a shortening of the immaturity period in progeny derived from parental cells of increased age is assumed to be related to the TPC variations.

Commitment to division in Paramecium: effect of nutrient level on the macronuclear DNA increment

In Paramecium, a fixed macronuclear DNA increment is associated with commitment to cell division. This study shows that this threshold DNA increment is about 70% of the final DNA increment in well-fed cells. The DNA increment is reduced when growth rate is decreased and decreases in parallel with growth rate to a minimum of 30% of the normal DNA increment. This minimum value is obtained when the growth rate is 20% of its normal level or lower. Further reduction in the growth rate produces no further reduction in the DNA increment. Following abrupt nutrient-level shifts, both the threshold DNA increment and the final DNA increment change progressively as the time of the shift is moved to later stages of the cell cycle. The threshold DNA increment is reset following nutrient-level shifts up to the point of commitment to division. These observations are consistent with the notion that the magnitude of the threshold DNA increment is strongly correlated with the rate of growth and is rapidly reset by factors which alter the growth rate. The implications of these observations for growth-driven regulation of the cell cycle are discussed.

Bioassay of environmental nickel dusts in a particle feeding ciliate

The ciliated protozoan Paramecium was used to quantitate cytotoxic and genotoxic effects of nickel particles. The biological response of these eukaryotic cells to pure nickel powder and iron-nickel powder was assayed and compared to the effect of the inorganic carcinogen nickel subsulfide. Cytotoxicity was determined by the percent survival of treated cells. Genotoxicity was indicated by significant increases in the fraction of nonviable offspring (presumed index of lethal mutations) found after self-fertilization (autogamy) in parents from the nickel-treated versus neutral control groups. The cells were exposed to the dusts and the biological effects determined. Only the nickel subsulfide consistently showed a significant increase in offspring lethality.

Studies on catalase, glutathione peroxidase and superoxidismutase activities in aging cells of Paramecium tetraurelia

The nature of the aging process has been the subject of considerable speculation. Now, some data indicate that free radical reactions going on continuously in the cells contribute to aging. Considering these data, we have investigated the activity of enzymes (catalase, glutathione peroxidase, superoxidismutase) present physiologically in the cell to limit to tolerable levels, the rate of free radicals or H2O2. These enzymes activities were assayed in Paramecium tetraurelia as clonal age increased. Catalase activity increases slightly during aging of paramecia, i.e. during maturity and senescence phases (20-150 fissions). No significant changes in glutathione peroxidase and superoxidismutase is found. Catalase activity was also assayed as a function of culture conditions. As the cells begin starving and the percentage of autogamous cells increases, catalase activity decreases. After autogamy, a large increase of catalase activity occurs during the sexual immaturity phase, i.e. during the first 20 fissions. By another way, H2O2 added in the culture medium (from 0 to 15 X 10(-5)M) causes an important increase of catalase activity (from 100 U.I. to 250 U.I.). The possible role of O-.2, OH. and H2O2 in aging is discussed.

Clonal aging in Paramecium tetraurelia. Absence of evidence for a cytoplasmic factor

Cells of Paramecium tetraurelia show clonal aging with characteristics comparable to the aging seen in tissue culture cell lines. An investigation is underway to determine the relative contributions, if any, of the cytoplasm and the macronucleus to the onset of senescence. Using a microinjection protocol, the importance of the cytoplasm to aging was tested. Cytoplasm was transferred from young cells into old cells to see if the mean age of death of the injected cell lines could be increased, compared with uninjected controls and sham injected controls. Cytoplasm from old cells was transferred into young cells to see if the mean age of death of the injected cell lines could be decreased, compared with sham injected and uninjected controls. In neither case was there any statistically significant change in mean ages of death. Furthermore, no changes can be demonstrated even with a protocol which transplanted 3 times the normal cytoplasmic volume. Thus, a cytoplasmic effect upon vegetative aging in P. tetraurelia cannot be demonstrated. Tests of a macronuclear influence are now underway.

Cellular and clonal aging in the suctorian protozoan Tokophrya infusionum

Quantitative methods for the study of aging in single organisms of the suctorian protozoan Tokophrya infusionum are described. New cell lines are initiated by metamorphosis of a ciliated embryo to form a sessile adult. The life history of adult cells consists of a sequence of age-related stages, culminating in cessation of reproduction and feeding, and eventual death. Lifespans of single cells were measured and were found to range rather widely about a mean, even when the cells compared were closely related within a single lineage. Variation appears to be inherent in the aging process in Tokophrya. Clones of Tokophrya undergo a gradual deterioration on a scale many times longer than the lifespan of individual cells. Lifespans of individual cells were determined when each of two clones were relatively young and later when their reproductive vigor had begun to decline. In both cases, the lifespan of individual cells were strikingly reduced in the old, as opposed to the young clones. The two types of senescence are thus experimentally separable, but nonetheless coupled phenomena. The similarity of aging in Tokophrya to that of other protozoa, fungi, and tissue culture cells is described and possible mechanisms are discussed.

Bioassay of genotoxic effects of environmental particles in a feeding ciliate

The ciliated protozoan, Paramecium, can be used to quantitate cytotoxic and genotoxic effects of ingested complex environmental particles. Cytotoxicity is quantitated by the increased proportion of treated versus control cells which do not retain their capacity for normal cell replication. Genotoxic effects are assessed by the increased fraction of nonviable offspring from treated versus control parent cells after the self-fertilization process of autogamy. Since these cells ingest nonnutrient respirable-sized particles, biological activity of intracellular extraction of dusts and fly ash can be compared before and after extraction with polar and nonpolar solvents. Previous studies indicated that coal fly ash was mutagenic in these eukaryotic cells. Mutagenicity of coal fly ash was not detectable after extraction with a concentration of HCl known to remove nonmatrix trace elements. These results suggested that this ciliate bioassay might be a detector of mineral mutagens. Fine particles of the carcinogenic nickel compounds, alpha-nickel subsulfide, and beta-nickel sulfide were compared for their biological activity in this bioassay. Both nickel compounds were ingested by the ciliates and induced heritable damage in the progeny of the treated parent cells.

Nucleolar changes in aging and autogamous Paramecium tetraurelia

A significant loss in nucleolar volume density (proportion of nuclear volume occupied by nucleoli) occurs in the macronucleus as clonal age increases, which suggests an age-correlated loss of ribosomal RNA synthesizing capacity. In the macronuclear fragments of cells undergoing autogamy, however, a significant gain in nucleolar volume density takes place.

Mutagenicity of fly ash particles in Paramecium

Paramecium, a protozoan that ingests nonnutritive particulate matter, was used to determine the mutagenicity of fly ash. Heat treatment inactivated mutagens that require metabolic conversion to their active form but did not destroy all mutagenicity. Extraction of particles with hydrochloric acid, but not dimethyl sulfoxide, removed detectable mutagenic activity.

Mutagenicity of coal fly ash: a new bioassay for mutagenic potential in a particle feeding ciliate

The use of the established mutagenesis assay in Paramecium as a prescreen for hazardous environmental particles is described. Since these protozoans ingest particles of the size respired by animals and man, the biological effects of the respirable fraction of fly ash particles were monitored in particle-feeding eukaryotic cells. Fly ash from coal combustion was utilized for these studies and was found to be mutagenic. The effects of physical and chemical treatment of the particle mutagenicity provided evidence for both heat-stable, heat-labile and acid extractable mutagenic agents.

Age-dependent modifications in membrane lipids: lipid composition, fluidity and palmitoyl-CoA desaturase in Tetrahymena membranes

The membrane lipid composition of Tetrahymena pyriformis NT-I was observed to change in a manner markedly dependent on the progress of culture age. The pellicular, mitochondrial and microsomal membranes were isolated from cell harvested at various growth phases (I, early exponential; II, mid-exponential; III, late exponential; IV, early stationary; V, late stationary) and their lipid composition was analyzed by thin-layer and gas-liquid chromatography. Although the phospholipid composition varied somewhat among membrane fractions, the most general age-dependent alteration was a considerable decrease in the content of phosphatidylethanolamine accompanied by a small increase in phosphatidylcholine. The 2-aminoethylphosphonolipid, enriched in the surface membrane pellicle, did not undergo a consistent change. As for fatty acid composition the most notable variation occurred in unsaturated fatty acids; a great increase in oleic and linoleic acids and a compensatory decrease in palmitoleic acid. This resulted in an augmented unsaturation of the overall phospholipid fatty acid profile of the aged membranes. The age-associated drastic decline in the palmitoleic acid content in membrane phospholipids could be accounted for by the markedly lowered activity of palmitoyl-CoA desaturase. The microsomes from the early exponential phase cells possess a 4-fold higher activity of the desaturase as compared to that of the late stationary phase microsomes. The decreased desaturase activity associated with the culture age was also reflected in the corresponding decrease in the conversion rate of [14C]palmitate to [14C]palmitoleate in cells labelled in vivo. The ESR spectra of the spin-labeled phospholipids extracted from the pellicular and microsomal membranes have led to the suggestion that these types of membrane would become more fluid with the age of growth.

Physiological dissection of various effects of ruthenium red dye on Paramecium cells

Polycationic dye ruthenium red, but not alcian blue, if externally applied to Paramecium cells quickly inhibits their phagocytosis. Ruthenium red combined with the cell surface diminishes frequency and duration of ciliary reversals and gradually inactivates the Ca++ gating mechanism. This effect persists for 1-3 after ruthenium red removal from the culture medium.