EFFECTS OF VITAMIN-B-12 CONCENTRATION ON CHEMOSTAT CULTURED SYNECHOCOCCUS SP STRAIN PCC-7002

The effects of vitamin B-12 availability on the physiology of the cyan obacterium Synechococcus sp. strain PCC 7002 were examined in a contin uous culture chemostat system. The availability of vitamin B-12 within the system was demonstrated to control the cell density and cellular chlorophyll levels under nutrient-limiting conditions. Electron microg raphs of vitamin B-12 replete and vitamin B-12 deficient cyanobacteria indicated that a reduction in vitamin B-12 availability induced a los s of thylakoid integrity within the system. Polyacrylamide gel electro phoresis demonstrated that the expression of outer membrane proteins o f 95, 70, and 34 kDa was enhanced during vitamin B-12 limited growth. Cellular quotients were determined to be a minimum of 256 molecules of vitamin B-12/cell to sustain a growth rate of 0.6/day. A comparison w ith eukaryotic plankton demonstrated that the vitamin B-12 requirement s of cyanobacteria may be more similar to those of chloroplasts than t o those of the entire group of eukaryotic algae.