Figure 1.

Representative growth curves of Prochlorococcus under ambient and elevated CO₂. (a) Cell density (cells ml⁻¹) versus time (days) of Prochlorococcus (VOL4, MIT9312) in co-culture with Alteromonas (EZ55) at 400 p.p.m. (black circles) or 800 p.p.m. (white squares) CO₂. Growth statistics are in Table 1. (b) Cell density of Prochlorococcus (VOL4, MIT9312) over consecutive transfers (indicated by ‘T’) in co-culture with Alteromonas (EZ55). The asterisk indicates addition of streptomycin rendering Prochlorococcus axenic, the dashed line indicates the limit of detection and the numbers are exponential growth rate constants (day⁻¹) calculated from growth curves.