Cell Stress by Phosphate of Two Protozoa Tetrahymena thermophile and Tetrahymena pyriformis

摘要

Phosphorus is one of the bioelements most needed as a compound cell by living organisms. Phosphorus is involved in several pathologies: in human with bone and kidney diseases, in mammals with metabolism disorder (glucose, insulin style="font-family:Verdana;">··· style="font-family:Verdana;">), in microorganisms wh style="font-family:Verdana;">ose style="font-family:;" "=""> style="font-family:Verdana;"> phosphorus is involved in cell growth. Phosphorus has various forms including pyrophosphate, a by-product of multiple pathways of biosynthesis. Enzymes that hydrolyze pyrophosphate are called inorganic pyrophosphatases (PPases). Two major types of inorganic pyrophosphatases are distinguished: the soluble pyrophosphatases (sPPases) and the membrane pyrophosphatases (mPPases or H style="font-family:Verdana;">+ style="font-family:Verdana;">/Na style="font-family:Verdana;">+ style="font-family:Verdana;">-PPases). They play a key role in the control of intracellular inorganic pyrophosphate level and produce an important ions gradient (H style="font-family:Verdana;">+ style="font-family:Verdana;"> or Na style="font-family:Verdana;">+ style="font-family:Verdana;">) to the cells. In this work, we primarily focused on the physiological study in a phosphate-poor medium of two models style="font-family:Verdana;"> style="font-family:Verdana;">Tetrahymena thermophile style="font-family:Verdana;"> style="font-family:Verdana;"> and style="font-family:Verdana;"> style="font-family:Verdana;">Tetrahymena pyriformis style="font-family:Verdana;"> style="font-family:Verdana;">, following the mobility, the growth and the morphology of cells. Secondly, we evaluated the enzymatic activity of soluble and membrane pyrophosphatases in both species grown in the same complex medium. A decrease of cell growth is correlated with unusual morphologies and different mobility in the stress medium. The measurement of soluble and membrane inorganic pyrophosphatases activities also shows a decrease which illustrates the lack of phosphate found in the stress medium. Deficiency of phosphate is a limiting factor for protozoan growth. These results indicate that Tetrahymena can be used as style="font-family:Verdana;">a style="font-family:Verdana;">model of cellular stress and consist style="font-family:Verdana;">s style="font-family:;" "=""> style="font-family:Verdana;">of style="font-family:Verdana;">a target to study inorganic pyrophosphatases for a better understanding of phosphate cycle in higher organisms.