An axenic cyclostat of Prochlorococcus PCC 9511 with a simulator of natural light regimes

A cyclostat was designed for growing the oceanic oxyphotobacterium Prochlor ococcus PCC 9511. Culture of this organism, known to be difficult to grow, was mastered for a large volume. Prochlorococcus grew well and axenic condi tions were maintained for up to 15 days. We designed an illumination system allowing a smooth bell-shaped irradiance curve reaching almost 1000 mu mol quanta m(-2) s(-1) to be obtained. Cell division was strongly synchronised under these illumination conditions, which were close to those found at lo w latitude in the upper layer of ocean. The described device is particularl y well suited to make experiments requiring up to 6 L per day of well synch ronised, exponentially-growing Prochlorococcus culture.