Figure 6.

Based on bioassays with O. lucimarinus CCE9901, a thiazole-related B1 precursor (or precursors) is abundant in coastal and open-ocean near-surface seawater. Data in (a) are from an incubation of surface seawater off La Jolla, CA, USA. SW+HMP data represent maximum O. lucimarinus CCE9901 yields from seawater plus HMP, and SW data represent yields from seawater alone. SW+HMP maximum yields were significantly higher than unamended samples, indicating the presence of a thiazole-related B1 precursor(s), at all time points except 13th August 6:30 (t-test, n=3, P<0.05). Black and white bars along the x axis indicate the light and dark periods of the incubation. Positive controls (+1 nM B1) yielded ~1.6–1.9 x 10⁷ cells ml⁻¹ at all time points, but are not plotted. Similar to results in (a), HMP addition to bioassays of 10 m N. Pacific, Line P station 26 seawater led to increased maximum yields (b). In contrast, HMP addition did not stimulate yields in bioassays of 2 m seawater from near the open-ocean N. Atlantic BATS station (c). Dashed horizontal lines in (b, c) represent the upper quantification limit of the CCE9901 bioassay; this threshold was not plotted in (a), as all values were below this threshold. Asterisks in (b, c) denote data that were significantly higher (t-test, n=3, P<0.05) than respective unamended SW controls. Additions of B1 or HMP were at a final concentration of 1 nM.