PHYSIOLOGICAL PROFILES OF SYNECHOCOCCUS (CYANOPHYCEAE) IN IRON-LIMITING CONTINUOUS CULTURES

We examined the physiology and biochemistry associated with the iron-l imited continuous culture of the halotolerant cyanobacterium Synechoco ccus PCC 7002. Biomass production, photosynthetic pigment levels, phot osynthetic efficiency, and the production of hydroxamate- and catechol -type siderophores are reported for cells grown over a range of availa ble iron concentrations. The relationship between the yield of Synecho coccus PCC 7002 in iron-limited chemostats and the concentration of av ailable iron was not linear. Synechococcus PCC 7002 expressed an induc ible physiological response that led to alterations either in the cell ular iron quotient or, more likely, in levels of available iron due to induced iron-scavenging processes. During iron limitation these cyano bacteria produced components consistent with the activation of a high- affinity iron transport system; both hydroxamate- and catecholtype sid erophores were detected. Iron-limited Synechococcus PCC 7002 also redu ced CO2 fixation rates from luxury levels to a rate that matched the c ellular growth rate, presenting interesting implications for oceanic c arbon flux models.