web.pdx.edu/~rueterj/algae_research/shift.htm

"Shift up/Shift down"

 

In some cases, algal cultures or natural samples of phytoplankton have been observed to change their metabolic rate on a longer time period than would be expected for adaptation to a change in the conditions. This

The terms "shift up" and "shift down" are used differently in the phytoplankton physiology and the microbial metabolism literature. In phytoplankton physiology, this term is used to specify and general shift in the rate of metabolism with no specific mechanism. The work on nutrient availalbility from upwelling is an example in which the phytoplankton have been described to be shifted up. In the microbial metabolism literature, "shift up/shift down" is a very specific term that has to do with the ability to synthesize new protein and in particular the amount of rRNA that the cell has.

Unbalanced growth

Shifts in metabolism can only be studied while cells are in the process of adapting, where the daughter cells are not equivalent to the mother cells. This process is

Research in my lab addressed this:

Nancy Unsworth examined the RNA content of cells grown on ammonium vs. nitrate. In this work we found that the effect of limitation by multiple factors was more than linear, i.e.that the simple model that describes limitation by several factors as simply shifting from one limitation to the other did not hold. Multiple limitation was more severe. The flip side of this finding is that when cells are relieved from multiple factor limitation, the ??

Abbas Sadeghi examined the effect of iron, light and nitrogen status on mRNA. In his Ph.D. thesis he addressed the importance of iron to the shift up/shift down phenomenon and made it clear that to study shift up/shift down without consideration of iron nutritional status could lead to misinterpretation of the cellular response.

Measurement:

Metabolic rate should be measured in terms of carbon uptake per cell carbon per time, nitrogen assimilation rate per cell nitrogen per time, or some other specific growth rate. Using different factors and then converting or using proxy measurement (such as chlorophyll) will not give an accurate information on shift up/shift down because the ratios can change, ie. C:N, chl:C, etc are not constant during unbalanced growth.

We have measured this using:

 

11/16/98 John Rueter