ELISA absorbance cut-off method affects malaria sporozoite rate determination in wild Afrotropical Anopheles

ABSTRACT. Malaria sporozoite infection rates in a mixed species group of 244 Anopheles gambiae Giles sensu lato and 115 An. funestus Giles wild female mosquitoes were compared using three methods to determine cutoff absorbance values for positivity of a Plasmodium falciparum Welch enzyme-linked immunosorbent assay (ELISA). Positive controls were based on P. falciparum circumsporozoite protein. As negative controls, four wild male Anopheles were included on each microtitre plate; tests were repeated on four consecutive days for each plate.
Infection rates were estimated at 13.1–22.8% using the mean absorbance value of negative controls plus three standard deviations, 11.7–12.8% using double the mean and 12.5–13.6% using the fixed cut-off value of 0.20 (allowing for 20% variation in negative control absorbance values).
Observed agreement for positivity or negativity among samples tested four times was 98.6% for the 2× mean method, 97.2% for the fixed cut-off 0.20 value, but only 82.7% for the mean +3 SD method. It was concluded that the 2× mean cut-off method is most reliable for field studies. P. falciparum sporozoite rates of 12.2% in An. funestus and 11.9% in An. gambiae s. l . were thus determined on the basis of the 2× mean cut-off method.
This comparative evaluation demonstrates that vector infectivity rates can be seriously over-estimated from sporozoite ELISA tests, by as much as 87% in one case considered here, depending on the absorbance cut-off method applied for negative controls.     

A Multi-Unit Sampling System and Its Use in the Characterization of Ultradian and Infradian Growth in Tetrahymena*

SYNOPSIS. A multi-unit automatic sampling device for investigation of microbial growth under a wide variety of conditions is described. The kinetics of asynchronous population growth for batch cultures of Tetrahymena pyriformis (W) at several temperatures show that there are 2 distinct growth phases: an exponential ultradian growth phase that is strongly temperature dependent and a non-stationary growth phase, the infradian phase, that shows little or no temperature dependence over the range from 15–27 C.     

Phylogenetic Position of Amblyospora Hazard & Oldacre (Microspora: Amblyosporidae) Based on Small Subunit rRNA Data and Its Implication for the Evolution of the Microsporidia

ABSTRACT. Sequences of the small subunit rRNA genes of Amblyospora californica and an Amblyospora sp. from Culex salinarius were determined. These sequences were compared phylogenetically with 16 other microsporidia. The results suggest Amblyospora forms a sister taxon to the rest of the microsporidia examined. The basal position of Amblyospora is discussed with respect to the evolution of microsporidian life cycles. These sequences represent the longest microsporidian small subunit rRNA genes sequenced to date, 1,359 and 1,358 bp, respectively. Structural features and GC content (49% for both) are comparable to those of other microsporidia which have been sequenced.     

Tropical zooplankton: phenotypic and spatial analyses of polymorphic Ceriodaphnia cornuta (Crustacea: Cladocera)

SUMMARY. 1. The predation-balanced polymorphism of Ceriodaphnia cornuta (a small-eyed horned form and a large-eyed unhorned form) in Lake Gatun, Panama, is re-examined approximately 12 years after the original study (Zaret, 1972a). We consider morphological variability, distribution and fecundity of the population inhabiting Laboratory Bay.
2. The two morphological characters emphasized by Zaret, eye size and horn length, are studied in detail. The C. cornuta population exhibits wide, yet continuous variation; coefficients of variation are 28% or eye diameter and range from 114% to 136% for horn and spine lengths. Phenotypic variation in the population is characterized by: (1) negative correlations between spine lengths and eye size; (2) positive correlations among spines from different body regions (anterior horn, lateral spines, and tail spine); and (3) weak correlations between body length and spine lengths.
3. While the horned and unhorned forms continue to coexist in Laboratory Bay. the frequencies of horned forms have increased in the open water areas since the time of the original study. The increase in horned form frequencies may be due to changes in fish predation intensity. Did vertical distribution patterns of the forms remain very similar to each other.
4. In contrast to previous laboratory findings, egg ratio calculations from field samples revealed similar clutch sizes for the horned and unhorned forms. The egg development time of the horned form, however, was found to be approximately 30% longer than that of the unhorned form, perhaps because of increased moulting difficulties produced by the presence of spines.     

Transmission and Scanning Electron Microscopy of the Evaginative Budding Process in Heliophrya sp. (Ciliata,Suctoria)1

ABSTRACT. A sessile, tentacle-bearing protozoon, Heliophrya sp. (Suctoria, Ciliata), reproduces asexually by evaginative budding to form a ciliated swarmer, which begins metamorphosis to the adult form within 30 min of its release from the parent cell. Morphological features of embryogenesis were investigated using transmission and scanning electron microscopy and found to correspond, with certain exceptions, to the few previous reports concerning evaginative budding in suctorians. Following invagination of a portion of the pellicle to form an embryonic cavity within the parent cell, numerous kinetosomes, apparently formed de novo, organize into rows which surround the embryonic cavity and eventually develop cilia that project into the cavity. When the cavity is complete, its walls are extruded through an opening in the parent cell surface. Parent cell cytoplasm streams into the incipient swarmer, thus supplying it with at least the minimum requirement of all cytoplasmic organelles. The ciliated swarmer remains attached to its parent cell for several minutes before it detaches. A complete pellicle is formed in both parent and swarmer prior to detachment. The numerous mitochondria underlying the parent cell pellicle in the vicinity of the attachment area suggest that cross wall formation is an energy-dependent process.     

Potassium-Ammonium Uptake Interactions in Tobacco Seedlings

Short-term (< 12 h) uptake experiments were conducted with6–7-week-old tobacco (Nicotiana tabacum L. cv. Ky 14)seedlings to determine absorption interactions between K⁺ andNH₄⁺. At equal solution concentrations (0.5 mol m^–3) netK⁺ uptake was inhibited 30–35% by NH₄⁺ and NH₄⁺ uptakewas decreased 9–24%. Removal of NH₄⁺ resulted in completerecovery in K⁺ uptake rate, but NH⁴⁺ uptake rate did not recoverwhen K⁺ was removed. In both cases, inhibition of the uptakerate of one cation saturated as the concentration of the othercation was increased up to 0.5 mol m^–3. The relative effectof K⁺-NH₄⁺ interactions was not altered when Cl- was replacedwith SO₄^2–, but the magnitudes of the uptake rates wereless in the absence of Cl-. The V_max for NH₄⁺ uptake was reducedfrom 128 to 105 µmol g^–1 dry wt. h^–1 in thepresence of 0.5 mol m^–3 K⁺ and the K_m for NH₄⁺ doubledfrom 12 to 27 mmol m^–3 in the presence of K⁺. The resultsof these K⁺-NH₄⁺ experiments are interpreted as mixed-noncompetitiveinteractions. However, an enhanced efflux of K⁺ coupled to NH₄⁺influx via an antiporter cannot be ruled out as contributingto the decrease in net K⁺ uptake. Key words: Nicotiana tabacum, K⁺, NH₄⁺, Uptake interactions     

Fusion <Emphasis Type="Italic">in vitro</Emphasis> of Membranes from Animal Cells

THE biological implications of membrane fusion are of general importance and several publications deal with the theoretical and practical aspects of this phenomenon^1–3. In this report, we describe experiments on the in vitro association or fusion of membranes. Because fusion was observed under physiological conditions it is possible that similar interactions also occur in vivo.