[Growth and synchronization of cell division in the alga Bumilleriopsis filiformis]

1. Axenic cultures of Bumilleriopsis were cultivated in mineral medium under continuous illumination and diluted every two days. The growth has been calculated to be 0.50 log10/day units at the optimum temperature of 23 to 24° C. 2. In liquid medium one cell normally divides into 2(n) daughter cells (=aplanospores). Under our culture conditions generally 8 and 16 daughter cells are produced by one Bumilleriopsis cell within 48 h. 3. Bumilleriopsis filiformis is the first Xanthophycean species to be synchronized. Light-dark changes induce some synchronization, but a high percentage of simultaneous division and rapid completion of a cell division burst is brought about most effectively by cycles composed of strong light/dim light/temperature changes (LS-T). With the most effective combination tested, i.e. 33 h of white 15000 lux light followed by 15 h of white 3000 lux (dim) light at temperatures of 24° in the first and 19° C in the second light phase (=33:15 h/15000:3000 lux/24:19° C), 96% of the cells divide synchronously. The burst occurs in such a manner that, on an average, 50% of the cells have divided 38 h after the start of the cycle. These synchronizing conditions were maintained up to 30 cycles without interruption (=continuous synchronization). 4. Cell wall formation is observed (by staining mother cells with methylene blue) 1 to 2 h before the cells divide completely and their daughter cells are released.