Motility of the diplomonad fish parasite Spironucleus vortens through thixotropic solid media

Investigation of a series of nutrient-supplemented thixotropic gels at successive dilutions that impede the trajectories of a highly vigorous motile flagellated protist, Spironucleus vortens, provides insights into both its swimming characteristics and a means for its immobilization. The progress of movement of this organism through the solidified growth medium was monitored by the in situ reductive production of a formazan chromophore from a dissolved tetrazolium salt. The physical properties of the gels were measured using an Anton Paar rheometer. The test parameters and measurements included: angular frequency, complex viscosity, complex shear modulus, shear rate and rotational recovery. These rheological characteristics affected the forward velocity of the organism through the gels, during and after multiple resetting, information potentially useful for determination of the dynamic characteristics of flagellar movement and propulsion rates of the organism. Application to separation of single cells, individuals of distinct sizes or the differing species from mixed cultures of motile and non-motile organisms or less actively swimming species was evident. These applications can be used when isolating the parasite from the intestinal contents of its host or from faecal pellets.