Growth and Osmoregulation of Chaetoceros muelleri in Relation to Salinity

The growth and osmoregulation of Chaetoceros muelleri Lemmermann(Bacillariophyceae) were investigated as a function of salinity.This centric diatom grew well over a wide range of salinityand required concentrations of NaCl above 10 mM for growth.Using gas chromatography- mass spectroscopy (GC-MS) analysisof cell extracts, we demonstrated that the alga contains anisomer of cyclohexanetetrol. The level of this isomer increasedwith increasing salinity. Levels of free amino acids also increasedwith increasing salinity, and quantitative determination withan amino acid analyzer revealed that the level of glutamic acidincreased the most with increases in salinity. Levels of intracellularK⁺ and Cl^– also increased significantly with increasesin salinity. Thus, in C. muelleri, not only organic solutessuch as the cyclohexanetetrol isomer and glutamic acid, butalso inorganic solutes such as K⁺ and Cl^– contribute toosmoregulation. (Received November 7, 1994; Accepted April 10, 1995)