FIG 4 .

Haptophyte maximum cell densities and cellular thiamin quotas. Maximum cell densities were attained at the onset of the stationary phase in (A) E. huxleyi and (B) Pavlova sp. under amendments ranging from 100 to 500 pM thiamin (black circles), HMP (blue circles), and AmMP (purple circles). Controls and treatments were performed in biological triplicates, and error bars (within circles) represent the SD. Treatments that are not significantly different from one another share the same letter. Note that in ocean seawater, the maximum reported thiamin and HMP concentrations are 400 pM (4) and 35 pM (2), respectively. (C) Thiamin cellular quotas in E. huxleyi obtained by the thiochrome chemical assays of cultured cells grown in either thiamin (black bars) or HMP (blue bars) amended medium or by calculation (Table 1).