REGULATION OF PHOSPHATASE ACTIVITY IN CHROOCOCCID- IOPSIS ISOLATES FROM TWO DIVERSE HABITATS: EFFECT OF LIGHT, PH AND TEMPERATURE.

Abstract: Phosphomonoeaterase (PMEase) and phosphodiesterase (PDEase) activity was studied in the cyanobacterial cultures of Chroococcidiopsis isolated from two diverse cryptoendolithic habitats of Antarctic and Arizona. Because this organism is found within the rocks it appears that phosphorus metab-olism by alkaline phosphatase activity is a key factor to sustain growth of these organisms in that state, there being no other source of external P except in bound form in the rocks. The main findings in this paper show that specific pH and temperature regulate the PMEase and PDEase activities studied with different substrates in isolated of Chroococcidiopsis 1 and 2 although values were vastly different. The pH and tem-perature optima for phosphatase activity (PMEase and PDEase) of Chroococcidiopsis 1 and 2 were 9.5, 20 °C and 8.5, 40 °C respectively. It needs mentioning here that although the pH optimum for the enzyme activities in the Antarctic rock samples was the same i.e. 9.5 there was a striking difference in the tem-perature optimum in which maximum activity of both enzymes were recorded at 5 °C. A very crucial role of light and dark conditions were important for the enzyme activity and differed to a significant extent when compared with naturally occurring organisms in the Antarctic rocks. Low light fluxes of about 8 µmol photon m-2s-1 showed higher PMEase and PDEase activity then total dark conditions in the Chroococcidiopsis-1 culture. However under natural conditions when this organism is found within th