ABSTRACT
As some single-celled microorganisms swim, they move back and forth across a curve, often a straight line, that describes their primary swimming direction. This curve could be a line joining
the initial point to the endpoint of the portion of the swimming track being analyzed. The swimming of spermatozoa is observed by placing them in liquid in a low flat dish, called a Makler cell, that fits on the stage of a phase-contrast microscope. This chapter provides mathemati cal models that might describe this swimming motion of different types of spermatozoa observed by Katz,38,39 Mahoney,50 Olds-Clarke,54 Robertson,57 Swanson,64 and the rabbit data of Young69-71 and suggests that the primary cross-track frequency and the organism’s swimming speed could serve as an identifier to keep track of an individual single-celled swimmer over a period of time while experiments concerning bioeffects of pharmaceuticals and other chemical stressors were being carried out. The term microorganism is used here to denote both an independent biosystem such as a protozoa and a single-celled swimmer such as a Makler-cell-confined spermatozoa. Computer analysis suggests that the theories of this chapter are valid for both human spermatozoa and rabbit spermatozoa; the analysis was carried out for human spermatozoa data provided by Katz38,39 and rabbit spermatozoa data provided by Young.69-71
The concept of using swimming microorganisms to assess toxicity is not new, as Noever53 and Silverman62 have worked with Tetrahymena swimming pattern alteration by toxins with a view toward eliminating or reducing the need for rabbit eye testing for ocular irritation, and Young69-71 has demonstrated that spermatozoa wobble motion changes are correlated with the presence of toxins. Prior work with phylum protozoa analyzed in the book of Hill32 has included the work of Loefer and Mefferd47,48 and others for the ciliate Tetrahymena, which was used in biotoxicity testing also by Noever52 53 and Silverman.60-62 Experimental work to a certain extent has focused on Tetrahymena pyriformis, regarded by many as the star performer of the phylum protozoa. The Ohio Science Workbook chapter by Silverman62 pointed out that if one added a toxin to a dish of Tetrahymena, the normal zig-zag swimming pattern changes; Silverman62 also pointed out that the most commonly observed changes are to a pattern of tight circles as though only the cilia on one side are functioning, or to marked decreases in swimming speed, or to conditions where two of the Tetrahymena stick together as though the toxin caused something to happen to their membrane. These observations are not mentioned in the other papers of Silverman,60,61 where statistics for a variety of toxins are given. In their 1952 letter to the editor Loefer and Mefferd47,48 describe pattern formation in swimming microorganisms by looking at a dense culture in a shallow medium. Loefer and Mefferd47,48 noted that horizontal swimming streams form a polygonal network with four or five streams meeting at nodes of the network and observed that at these nodes where the organisms meet, they fall to the bottom of the shallow medium and then swim upward to rejoin the horizontal streams. Loefer and Mefferd47,48 observed that under ideal circumstances, these patterns form in 10 s. Noever52,53 and other NASA scientists using a side-looking microscope and examining Tetrahymena thermophila observed that large populations of these creatures, being sensitive to gravity, formed interesting geometrical patterns that were altered or were completely broken up when chemical stressors were added. Recently Young69-71 published a paper that supports the thesis of this chapter, namely, that motion parame ters of spermatozoa can indeed be used as a test of biotoxicity. Young69-71 pointed out that a parameter called wobble, which is the curvilinear speed of the microorganism divided by the net speed along a best fitting straight line, seems to be related to toxicity. It appears from comparisons of model predictions to laboratory data that the wobble parameter used by Young69-71 could be very accurately computed with the methods of Cohoon14 for individual spermatozoa. Roberts and Berk56 used changes in normal chemoattraction of protozoa to test the toxicity of water. The correlation of swimming speed with fertilization by Holt, Moore, and Hillier34 and Olds-Clarke54 would also seem to support the thesis that swimming parameters and statistics could measure the chemical environment of spermatozoa and that keeping track of affected individual swimmers could help us advance the understanding developed by Austin,3 Berril,5 Chang,9 Dehehy,17 Dresdner,19 Goltz,28 Gwatkin,30 Kopf,42 Mack,49 Mahoney,50 Olds-Clarke,54 Robertson,57 and others of changes in motion occurring when the chemical environment of the spermatozoa is similar to that occurring during fertilization. This understanding might be improved by application of the electron microscopy methods used by Swanson64 after the motion has ceased, or by employment of the fluorescent probe methods used by Vasquez67 while the motion is still being observed in a Makler cell. If water pollutant levels cause observable changes in motion parameters, this could be used as a warning that these levels could be dangerous to humans.
