Nitrogen nutrition and changes in amino acid pools of Cyanidium caldarium

Abstract

Cells of Cyanidium caldarium grown in batch under conditions of excess ammonium or nitrate contained respectively 11.2 and 11.7 μmol glutamate/ml packed cell volume (pcv). Glutamate was the dominant amino acid, and represented 40–43.3% of the total amino acid concentration; other amino acids detected, occurring at a lower level with respect to glutamate, were glutamine, aspartate, serine and alanine. Citrulline and 5-amino levulinic acid were also found. Cells grown in a chemostat under conditions of nitrogen limitation contained glutamate, aspartate, serine and alanine at concentrations equivalent to that of the above cells, but contained traces of other nitrogen compounds. Addition of ammonium or nitrate to N-limited cells caused a transient decrease in the concentration of glutamate, a rapid increase of glutamine and a substantial increase of other compounds. However, on adding ammonium to cells, glutamine rose abruptly during 60 min, attaining a concentration of 33 μmol/ml pcv, after which it decreased slightly; on adding nitrate to cells, by contrast, glutamine rose during a period of 30 min, attaining a value of 9.5 μmol/ml pcv, then decreased slightly to 4.3 μmol/ml pcv during 120 min; after this time, however, it remained constant around this value for the subsequent 210 min of incubation. After 48 hr of incubation under excess nitrate or ammonium, however, glutamine and other nitrogen compounds exhibited similar levels to those occurring in batch grown cells.