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At least 631 records · Page 35Linked to original sources
PubMed1997

Analysis of expressed sequence tags (ESTs) of the parasitic protozoa Entamoeba histolytica.

A directional cDNA library constructed from mRNA of the trophozoite of Entamoeba histolytica HM-1:IMSS strain was used for the generation of expressed sequence tags (ESTs). From 5' ends of the distinct cDNA clones, 105 ESTs were obtained. Of these, 30 clones (29%) were previously known E. histolytica genes. Forty-five clones (42%) had matches with entries for other organisms in the databases. These new E. histolytica genes constituted a broad range of transcripts distributed among cytoplasmic structural and regulatory proteins, enzymes, nuclear and other proteins, and proteins of unknown function. Thirty clones (29%) had no significant database matches and thus potentially represent E. histolytica-specific genes. These data of E. histolytica genes identified by nucleotide sequencing indicate the value of the adoption of genome sequencing strategies for the rapid increase in knowledge of organisms causing dysentery and liver abscess.

Animals↗
PubMed2000

Sensitivity of trypanosomatid protozoa to DFMO and metabolic turnover of ornithine decarboxylase.

alpha-Difluoromethylornithine (DFMO), the specific and irreversible inhibitor of ornithine decarboxylase (ODC), was able to induce the arrest of proliferation in Leishmania mexicana and ODC-transformed Trypanosoma cruzi cultures grown in a semi-defined medium essentially free of polyamines. Conversely, Crithidia fasciculata and Phytomonas 274 were not affected by the inhibitor. The drug-resistance of Crithidia and Phytomonas was neither caused by an impairment of DFMO uptake nor by a decrease of the enzyme affinity for the inhibitor. We were also able to rule out the possibility of ODC overexpression in the drug-tolerant parasites. The measurements of ODC metabolic turnover indicated that the enzymes from Crithidia and Phytomonas have a short half-life of 20-40 min, while ODC from Leishmania and transgenic Trypanosoma cruzi are rather stable with a half-life longer than 6 hours. Analyses of polyamine internal pools under different growth conditions have shown that DFMO was able to markedly decrease the levels of putrescine and spermidine in all parasites, but the depletion of spermidine was higher in trypanosomatids containing an ODC with slow turnover. Our results suggest that in these parasites cultivated in the presence of the drug, spermidine might decrease below critical levels needed to maintain trypanothione concentrations or other conditions essential for normal proliferation.

Animals↗
PubMed1995

The effects of cadmium on the successional stages of a freshwater protozoa community.

Microcosms containing protozoan were used to observe the differential effects of cadmium on the successional stages of a community. After 7, 14, and 21 days, 500 micrograms/liter cadmium was added. Some environmental parameters such as pH, conductivity, and nutrient levels affect metal toxicity. The effect of cadmium on diversity, density, and biomass was evident 48 hr after the addition of the metal. The pollutant caused a transition period in each treatment, of a different duration, followed by a recovery of the community. In both the control and the treatments, trophic structure was defined by bacterivore-detritivore, nonselective, and photoautotroph organisms.

Animals↗
PubMed1997

Seasonal changes in whole-cell metal levels in protozoa of activated sludge.

In this study the authors quantify, and correlate, whole-cell elemental levels of vorticellids in activated sludge, over a 1-year period, and Aspidisca cicada and Opercularia coarctata on one sampling date. The aim was to determine the extent, and seasonal variation, of metal uptake and/or accumulation, to give new information regarding the fate and dynamics of the cellular elements, and to determine how they are related to each other over time and between species, in an environment exposed to high levels of heavy metals. Samples of activated sludge were collected monthly, and whole-cell elemental levels of vorticellids determined by scanning electron microscopy electron probe X-ray microanalysis (XRMA). Positive intersample correlations were found between phosphorus and three elements, sulfur, potassium, and iron. Potassium and calcium levels correlated positively with sulfur levels. Iron levels were positively correlated with potassium levels. Levels in A. cicada sampled from activated sludge were also compared with the same species grown in vitro, previously isolated from the same sewage treatment works. The level of cellular elements varies considerably with time, and between species from the same environment. Vorticellids could tolerate varying levels of aluminum, copper, iron, and zinc. Decreased iron levels were associated with decreased phosphorus and potassium levels.

Animals↗
PubMed1999

Toxicity and bioaccumulation of cadmium in marine protozoa communities.

The behavior of cadmium in a protozoan community was analyzed in order to obtain new data concerning the toxicity and bioaccumulation of this heavy metal. For this purpose, microcosms with different concentrations of the pollutant (without cadmium, 500 microg Cd.l-1 and 1000 microg Cd.l-1) were used. Protozoans bioaccumulated 8. 74-283 microg Cd.g-1 dry weight, representing an accumulation capacity of 15.53-69.59 times more than that of bacteria. The addition of cadmium caused a significant reduction in protozoan density, whereas bacterial abundance was not affected.

Animals↗
PubMed1987

Longevity in the protozoa.

In ciliates there are examples of cells which have different proliferation potential in the macronucleus. Those species with limited macronuclear proliferation potential require sex to activate the reserve nucleus. In terms of the capital investment theory, some ciliates invested in their spare nucleus without loss of their original potential, while others accumulated debts and needed the reserve account to maintain life. Other cells neglected maintenance of their reserve account and failed unless their venture capital account was not a self-sustaining venture. Sex provided access to the reserve account and had to occur before deterioration of the reserve account. The question is not when cellular immortality was lost, but rather when immortality was partitioned from a mortal segment. The separation provided the option both for senescence and evolution in multicellular organisms. In colonial flagellates, separation of cells with infinite and finite cell lifespan potential occurred in some species, while in others the separation did not involve loss of immortality. In colonial flagellates, sex did not become an obligate stage. The immortal cells are haploid and could not accumulate damage and live (in contrast with the diploids in the ciliated protozoans). The present theory predicts that differences between species or cells with infinite versus finite lifespan potential may reveal differences in the critical determinants of longevity. Senescence could arise as an accident, as well as a design of nuclear differentiation. Cells therefore may have a much greater reserve for totipotency than would be predicted if they were assumed to lose immortality simply by the act of differentiation.

Aging↗
PubMed1976

Manganese in the shell of Centropyxis (Rhizopodea: Protozoa).

The proteinaceous shells of Centropyxis hirsuta contain a relatively high concentration of manganese in an amorphous state. The concentrations of manganese fill the alveoli which are characteristic of the shell structure. Observations based on cultured animals and subsequently examined by X-ray diffraction, a solid state energy dispersive X-ray analyser, and an analytical electron microscope, lead to the conclusions that manganese is selectively absorbed by Centropyxis hirsuta and deposited in the shell.

Amoeba↗