Effects of vitamin B12 concentration on chemostat cultured Synechococcus sp. strain PCC 7002

Publisher Website
Google Scholar
Abstract
The effects of vitamin B12 availability on the physiology of the cyanobacterium Synechococcus sp. strain PCC 7002 were examined in a continuous culture chemostat system. The availability of vitamin B12 within the system was demonstrated to control the cell density and cellular chlorophyll levels under nutrient-limiting conditions. Electron micrographs of vitamin B12 replete and vitamin B12 deficient cyanobacteria indicated that a reduction in vitamin B12 availability induced a loss of thylakoid integrity within the system. Polyacrylamide gel electrophoresis demonstrated that the expression of outer membrane proteins of 95, 70, and 34 kDa was enhanced during vitamin B12 limited growth. Cellular quotients were determined to be a minimum of 256 molecules of vitamin B12/cell to sustain a growth rate of 0.6/day. A comparison with eukaryotic plankton demonstrated that the vitamin B12 requirements of cyanobacteria may be more similar to those of chloroplasts than to those of the entire group of eukaryotic algae.Key words: chemostats, cellular quotients, cyanobacterial physiology, Synechococcus, vitamin B12.