Nitzschia navis-varingica

N. navis-varingica is a pennate diatom capable of producing the amnesic shellfish poisoning toxin domoic acid (Kotaki et al. 2000).

Cells yellow-brown, with two chloroplasts, one at each end. Cells lanceolate in valve view, 45-55 microns long and 9-11 microns wide, in girdle view rectangular, slightly indented in the middle. Pervalvar axis wider than the transapical axis. Interstriae 26-30 per 10 microns, raised above the striae externally. Each stria with a single row of circular areolae (3-4 in 1 micron). Raphe raised on a distinct keel, with the margins of the raphe slit extended as lips that flap outward distally. Wall of the raphe canal perforated by areolae and bearing longitudinal silica ridges. Raphe divided by a central nodule and subtended by more or less equidistant, distinct fibulae numbering 10-12 per 10 microns. A pattern of vermiform ridges present on the mantle. The cingular bands open and ornamented with wartlike structures. Valvocopula with 2-3 rows of areolae, copulae with 1-2 rows of areolae, or with or without scattered areolae.

Toxin-producing cultures of N. navis-varingica were isolated from a shrimp-culture pond in Vietnam and produced 1.7 pg of domoic acid per cell (Kotaki et al. 2000). Domoic acid production started in late exponential phase and reached a maximum during early stationary phase. Domoic acid levels decreased in axenic cultures (0.9 pg domoic acid per cell). A Vietnamese isolate had a maximum specific growth rate of 0.51 ± 0.02 per day and an upper pH limit for growth of 9.7-9.8 in the laboratory (100 micromolar photons m-2s-2 and 15 deg; Lundholm et al. 2004).

The average cell volume of a Vietnam isolate was 5427 ± 196 cubic microns (Lundholm et al. 2004).