Two thermotolerant cyanobacterial strains N9DM I and N9DM II were collected from Tuwa geothermal spring, Panchmahal, Gujarat, India, from different wells having temperature 30 +/- 2 degrees C and 55 +/- 2 degrees C respectively. Analysis of 16S rRNA gene sequence revealed that both the strains were nearest neighbour of Oscillatoria sp. In addition to high temperature tolerance Oscillatoria N9Dm sp. changes phycobilisome rod pigmentation as exposed to various temperatures. Oscillatoria N9DM sp. produces phycoerythrin (PE) and phycocyanin (PC) at 30 +/- 2 degrees C and 55 +/- 2 degrees C, respectively whereas at intermediate temperature (42 +/- 2 degrees C) it produced phycoerythrocyanin (PEC). Moreover reverted cultures (normally grown at 55 +/- 2 degrees C but now sub-cultured and grown at 30 +/- 2 degrees C) started producing PE. Furthermore, Oscillatoria N9DM sp. produced PE, PC and PEC in white, red and yellow light respectively and it showed direct correlation to different proteins produced at various temperatures. To best of our knowledge, this is the first report describing correlation of temperature and its effect on the phycobiliprotein production. This study for the first time also tried to explain that thermo-adaptation might have been evolved along with complementary chromatic adaptation (CCA) in certain thermotolerant cyanobacteria where fluctuation of temperature was prevalent throughout the year. (C) 2012 Elsevier Ltd. All rights reserved.