Division competence in Tetrahymena: Determination of minimum cell volume and rate of nutrient uptake
✍ Scribed by Anders Poul Andersen; Per Hellung-Larsen
- Publisher
- John Wiley and Sons
- Year
- 1989
- Tongue
- English
- Weight
- 495 KB
- Volume
- 41
- Category
- Article
- ISSN
- 0730-2312
No coin nor oath required. For personal study only.
✦ Synopsis
Cell volume and doubling time have been determined for exponentially growing Tetrahymena pyriformk cells in broth medium with and without glucose and in media made from these media by dilution with water. The cells tolerate media with dry weights from 105 down to 0.06 g/L. In the diluted media the cells have small volumes and the doubling time is increased.
When the cell volume increase per time per cell in a given medium is expressed as a function of the cell volume in this same medium, a direct proportionality is found. From this equation the minimum cell volume of division competence (MVDC) can be found. It is 2,100 pm3 for T. pyr~ormis at 28%.
The lag period resulting from an upshift of exponentially growing cells from diluted media to more concentrated media is a function of the initial and resulting cell volumes and MVDC.
The increase in cell volume per unit of time for a given cell depends on the dry weight of the medium. This parameter can be transformed to mass increase per cell surface area per time, which represents rate of nutrient uptake. When plotted against the dry weight of the media, a Michaelis-Menten-like curve is obtained with two K, values of 3.8 and 0.08 g/L with corresponding V, , values of 20 and 4 ng/cm2s.
The low K, value (0.08 g/L) indicates that Tetruhymena is able to take up nutrients from highly diluted media. The high value of V, , (20 n g / y ;s) increases the ability of growth in more concentrated media. Thus, the adaptabhty of Tetruhymena to regulate its growth rate on media with considerable differences in nutrient supply is partly explained.
Keywords: d l ~d d i ~p d m e d i a , ~~o l i c c e U s
Recently [l] we showed that T. pyrifmis, GL cells grown under different conditions have different cell-size and doubling times. For cells grown in broth medium or in aqueous dilutions of broth medium we found that the cell size decreases and the doubling time increases when the growth medium is diluted. Whereas starving cells get smaller and smaller towards a non-viable state, this is not the case with cells in strongly diluted media. Here we show that exponentially growing cells in broth media (with or without glucose) diluted several hundredfold all have about the same cell size and that