Observation of yeast cell movement and aggregation in a small-scale MHz-ultrasonic standing wave field (original) (raw)

Some physiological/morphological changes have been reported before, when suspended yeasts have been irradiated with well-defined ultrasonic standing, as well as propagating, plane waves around 2.2 MHz, as used in ultrasonic coagulation, e.g., for cell filtering. Thus we used yeast as a biological model to explore the reasons for both those morphology changes and some unusual macroscopic behaviour in the case of water-rich ethanol mixtures when used as carrier liquid. When the cells were suspended in 12% (v/v) ethanol-water mixture separation was greatly reduced; the yeast cells were not retained in the pressure nodal planes of the standing wave, but mixed turbulently through the separation system. How this behaviour alters the efficiency of retention/immobilisation was measured. As the viability of the yeast was decreased as well the morphology of the cells was examined using transmission electron microscopy. Two effects, according to the type of assessment, were evident; a disrupti...

The influence of ultrasound on a decrease of the number of colonies of microorganisms and chemical oxygen demand has been investigated. Oxidation of organic compounds proceeds according to the first order reaction during sonication and destruction of microorganisms proceeds according to the pseudo-second order process. A mathematical model of ultrasonic degradation of yeast aggregate was proposed.

Retention and manipulation of microbial cells through exploitation of ultrasonic forces has been reported as a novel cell immobilisation technique. The spatial ordering of yeast cells, within suspensions subjected to an ultrasonic standing wave field, was analysed for the first time. A technique, based on 'freezing' the spatial arrangement using polymer gelation was developed. The resultant gel was then sectioned and examined using microscopic techniques. Light Microscopy confirmed the presence of specific regions in the ultrasonic field, where the cells are organised into bands corresponding to the standing waves' pressure nodal planes. Computer Image Analysis measurement of several physical parameters associated with this cell distribution matched the values derived from the theoretical model. The spatial cell-cell re-arrangement within each band and uneven distribution along the nodal planes have been analysed by Scanning Electron Microscopy. These results complement ...

The principle of ultrasonically enhanced settling (UES) is successfully applied in biotechnology for filtration purposes, e.g. as cell-filter. Particles (biological cells) are concentrated in certain regions of a sonicated volume by an ultrasonic standing wave field (~2 MHz). Due to the dependence of the final settling velocity on the diameter of an object (Stoke's law), the agglomerates formed by sonication settle more quickly than single cells. This principle, which relies on a sufficiently large difference in mass densities of the particles and the host liquid, is also applicable to dispersed material lighter than the liquid. Up to now, no feasible solution was at hand when a suspension contained both heavier and lighter particles. For this demand, a novel setup, the UES dual-chamber separator, was tested on suspensions of yeast cells and oil droplets as a model system. Here the volume exposed to the standing wave field is divided into two parts by an ultrasonically transpare...