The effect of acidity at limited irradiance on survival, growth, pigment composition and ammonium liberation of soil cyanobacterium Nostoc sp., collected from paddy-fields of Golestan province

Cyanobacterium Nostoc sp. can be considered as an interesting microorganism for the ability of excretion buffering compounds. With respect to possible applied potential of this strain, this ability has been studied under limited irradiance. Soil samples were collected from paddy-fields during one year. At the first step, different acidities (pHs 5,7,9) were studied under limited carbon dioxide condition. Results showed that in all treatments, organism tends to enter logarithmic phase of growth until third day, but acidic condition cause sharp decline on growth after this. Highest specific growth rate belong to alkaline condition (pH 9). For the next step, two alkaline condition near to pH 9 (pHs 8.5 and 9.5), were selected to compare. Results showed that specific growth rate was significantly less than pH 9, and even continuous aeration couldn’t be able to enlarge specific growth rate. Pigment composition can be rearranged at different acidities and phycobilisome systems cause viability and growth under acidity fluctuations and limited irradiance in addition of low carbon dioxide concentration. Ammonium liberation showed the highest rate at pH 5 and day two too.