Acclimation of photosynthetic pigments and photosynthesis of the cyanobacterium Nostoc sp strain UAM 206 to combined fluctuations of irradiance, pH, and inorganic carbon availability

We analysed the combined effect of pH, irradiance, and inorganic carbon ava ilability on growth and pigment composition of the cyanobacterium Nostoc sp . strain UAM206, isolated from rice fields. This cyanobacterium contains ph ycoerythrin in its phycobilisomes and can show chromatic acclimation. Under inorganic carbon limitation, the growth rate of Nostoc sp. strain UAM206 w as affected by pH, but not by irradiance. Chlorophyll a phycoerythrin (PE), and phycocyanin (PC) contents were inversely correlated to irradiance. Chl orophyll a (Chla) content was not affected by pH; however, with increasing pH, phycocyanin, phycoerythrin, and allophycocyanin (APC) content increased . Inorganic carbon availability masked or decreased some of the effects of pH under inorganic carbon limitation; however, the significant effect of pH on the allophycocyanin contents was clearly independent of the inorganic c arbon availability. Analysis of our results indicates that elevation of ext ernal pH and available inorganic carbon results in an increase in the numbe r of phycobilisomes along with a decrease in their size (PC+PE/APC ratio), while irradiance mostly affects the size of the phycobilisome. Likewise, in creasing irradiance, pH, and available inorganic carbon results in an incre ase in the PSII/PSI ratio (APC/Chla ratio). Finally, Nostoc so. strain UAM2 06 seems able to acclimate its photosynthetic apparatus to variations of th e three studied environmental factors that are known to occur in rice field s.