Effects of temperature and sulfide on freshwater cyanobacteria isolated from a sulfur spring in the western ghat forests of Karnataka

Abstract

The study deals with the effect of different temperature regimes on the growth, photosynthetic and phycobilin pigment contents in some cyanobacterial species isolated from sulfur spring in the Western Ghats of Karnataka. In the present study four isolates from sulfur spring namely, Leptolyngbya purpurascens, Planktolyngbya limnetica, Scytonema bohnerii and Calothrix fusca were selected for the study. The study noticed that all the four isolated species of sulfur spring showed proper growth up to temperature 45oC (p<0.01). Interestingly, it was also noticed that all the four species showed moderate growth up to 50oC, while Scytonema bohnerii has tolerated up to 65oC, where it showed proper growth up to 50oC. Planktolyngbya limnetica showed slight growth up to 60oC, Leptolyngbya purpurecens exhibited the growth up to 55oC. Similarly, Calothrix fusca showed growth up to 50oC. The species namely, Leptolyngbya purpurecens, Planktolyngbya limnetica and Calothrix fusca did not show any growth below 25oC temperature. Scytonema bohnerii does not exhibited sustainable growth below 30oC. In the study, sulfur spring isolates produced higher carotenoids at the temperature between 40 and 45oC. In this study the effect of sulfide (Na2S) on their growth, photosynthetic ability and heterocyst frequency was also determined. It was observed that sulfide (Na2S) content at a particular concentration (50 to 55 ppm) significantly increased their growth, pigment production and also heterocyst numbers. But it was also observed that after 55 ppm. of sulfide concentration, there was a slight decline in the growth indicating that sulfide at higher concentration becomes toxic to that species, hence growth was inhibited.