Regulation of Nostoc Sp. Phycobilisome Structure by Light and Temperature

Nostoc sp. strain MAC cyanobacteria were green in color when grown in white light at 30 degrees C and contained phycobilisomes that had phycoerythrin and phycocyanin in a molar ratio of 1:1. Cells grown for 4 to 5 days in green light at 30 degrees C or white light at 39 degrees C turned brown and contained phycoerythrin and phycocyanin in a molar ratio of greater than 2:1. In addition to the change in pigment composition, phycobilisomes from brown cells were missing a 34.5-kilodalton, rod-associated peptide that was present in green cells. The green light-induced changes were typical of the chromatic adaptation response in cyanobacteria, but the induction of a similar response by growth at 39 degrees C was a new observation. Phycobilisomes isolated in 0.65 M phosphate buffer (pH 7) dissociate when the ionic strength or pH is decreased. Analysis of the dissociation products from Nostoc sp. phycobilisomes suggested that the cells contained two types of rod structures: a phycocyanin-rich structure that contained the 34.5-kilodalton peptide and a larger phycoerythrin-rich complex. Brown Nostoc sp. cells that lacked the 34.5-kilodalton peptide also lacked the phycocyanin-rich rod structures in their phycobilisomes. These changes in phycobilisome structure were indistinguishable between cells cultured at 39 degrees C in white light and those cultured at 30 degrees C in green light. A potential role is discussed for rod heterogeneity in the chromatic adaptation response.