PHYSIOLOGICAL CHARACTERIZATION OF SIX LIPID‐PRODUCING DIATOMS FROM THE SOUTHEASTERN UNITED STATES1

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Abstract
Six strains of diatoms from intertidal waters were isolated as part of the SERI Aquatic Species Program collection and screening effort: Amphiprora hyalina Greville, Cyclotella cryptica Reimann, Lewin & Guillard, Navicula acceptata Hustedt (two strains, NAVIC6 and NAVIC8), Navicula saprophila Lange‐Bertalot & Bonik, and Nitzschia dissipata (Kütz.) Grunow. Among numerous algal strains isolated as part of this collection effort, these six strains showed rapid growth and elevated lipid content in preliminary screening experiments and were chosen for further physiological characterization. N. dissipata grew most rapidly at 25°C, whereas the other five strains grew best at 30–35°C. Salinity tolerance varied among strains, with maximal growth occurring at the following conductivities: 10–60 mS.cm−1 (A. hyalina and N. acceptata NAVIC8), 10–35 mS.cm−1 (C. cryptica), 20–45 mS.cm−1 (N. acceptata NAVIC6), 10 mS.cm−1 (N. saprophila), and 20–35 mS.cm−1 (N. dissipata). The diatoms also differed in their utilization of nitrogen sources with A. hyalina growing optimally with either nitrate or urea; N. acceptata NAVIC6, with either nitrate or ammonium; C. cryptica, N. acceptata NAVIC8, and N. dissipata, with nitrate; and N. saprophila, with urea. Under optimal conditions, A. hyalina grew at 2.0 doublings. day−1; C. cryptica grew at 3.0 doublings. day−1. Each Navicula strain had a growth rate of 3.8 doublings. day−1, and N. dissipata grew at 2.6 doublings.day−1. All six strains had lipid contents in excess of 37% ashfree dry weight (AFDW) under nutrient‐limited conditions, with N. saprophila having the highest lipid content at 48% AFDW.