THE EFFECT OF SALINITY ON GROWTH AND AMINO-ACID-COMPOSITION IN THE MARINE DIATOM NITZSCHIA-PUNGENS

Nitzschia pungens f. multiseries and N. pungens f. pungens, isolated from two estuaries in Maritime Canada, were grown at various salinities (6 - 48 parts per thousand) and their growth rates and free amino acid compositions were determined. The optimal salinity range for growth of f. multiseries was 30 - 45 parts per thousand whereas that of f. pungens was 15 - 30 parts per thousand. At higher salinities there was increased production of a ninhydrin-positive compound, which was identified as the amino acid taurine. When f. multiseries was grown at a salinity of 48 parts per thousand and rapidly exposed to 15 parts per thousand, the concentration of taurine decreased markedly (from 61 to 7% of the total amino acids). The evidence indicates that taurine may serve to regulate the osmotic pressure of N. pungens f. multiseries, a role not previously assigned to taurine in a marine diatom.