Ultrastructural Aspects of the Somatic Cortex and Contractile Vacuole of the Ciliate,Ichthyophthirius multifiliis Fouquet1

The trophont stage in the life cycle of Ichthyophthirius multifiliis was studied in the electron microscope. Surface ridges contain up to 24 ridge microtubules, disposed as a ribbon. Kinetosomes show the classic morphology of 9 triplets of microtubules. Associated with each kinetosome is a kinetodesmal fibril, originating in proximity to triplets 5, 6, and 7, and having a 30 nm periodicity; 3 to 5 postciliary microtubules, originating between triplets 8 and 9; and up to 3 transverse microtubules, originating at triplet 4, as well as a parasomal sac. Each cell is partially enclosed by a system of 3 “unit” membranes: the outer limiting membrane, and the outer and inner alveolar membranes. The last two membranes define the alveolar sac. Mucocysts, each with a dense core, are present in large numbers. The contractile vacuole system includes the contractile vacuole, associated tubules and vesicles, injection canals, a discharge canal, and a pore. Microtubules abound in the walls of the contractile vacuole, injection and discharge canals, and in the region of the pores, where both ring and radial microtubular arrangements are noted. The ultrastructure suggests that I. multifiliis is more closely related to Tetrahymena pyriformis than to Paramecium aurelia.     

An analysis of clutch-size in New World passerine birds

Variation in clutch-size among New World passerine birds was analysed with respect to four variables: body-mass, geographic latitude, the frequency of nest predation, and the structure of the nest. Data were analysed separately by averaging traits at three taxonomic levels: species, genus, and subfamily. Allometric scaling with body-mass did not account for significant variation in clutch-size regardless of the taxonomic level of analysis. Latitudinal effects on clutch-size were highly significant at all taxonomic levels. For species building small-pensile nests and open-cup nests, nest predation had a significant partial effect on clutch-size, with latitude held constant. When nest predation and latitude were held constant, clutch-size was significantly different among species building small-pensile nests, open-cup nests, and domed nests. These results suggest that New World passerine clutch-size is related to at least three variables: latitudinal effects, nest predation, and nest structure.     

AN AUTOMATED METHOD FOR QUANTIFYING THE L-ALANINE TRIGGER OF BACILLUS SUBTILIS SPORE GERMINATION AND COMPETITIVE INHIBITION BY D-ALANINE

We developed an automated method for studying the germination kinetics of Bacillus subtilis spores using a microtiter plate (MP) reader. Phosphate buffer supplemented with L-alanine was used to isolate the germination phase as determined by decrease in optical density (OD₆₃₀). Using a standard 96-well MP, L-alanine triggered germination kinetics were measured by automatic OD measurement every 3 min until the maximum OD₆₃₀ change (OD₆₃₀) was determined. When OD₆₃₀ values were plotted against L-alanine concentration on a double reciprocal plot, a straight line (R²= 0.98) was produced. The addition of D-alanine to the medium demonstrated classical competitive inhibition on double reciprocal plots. A 3-dimensional representation of the untransformed data showed the response surface nature of competitive inhibition. The method automates the tedious task of determining loss of refractility associated with spore germination under defined conditions so that inhibitors to germination can be studied. Since 96 OD₆₃₀ determinations can be done simultaneously in small volumes (200 μL) extensive data can be generated about inhibitors using relatively small spore crops in a single, short (1.4 h) incubation.