Determination of tolerable levels of pH stress in cyanobacterium Spirulina sp.

Some microorganisms produce biopolymers from the polyhydroxyalkanoate group. Polyhydroxyalkanoates have mechanical properties similar to polyethylene and polypropylene, with the advantage that they are completely decomposed. Polymer polyhydroxybutyrate belongs to this group that accumulates under the conditions of stress inside the microorganism. The effect of pH stress (to increase the production of polyhydroxybutyrate) on the growth of cyanobacterium Spirulina sp. and tolerance to different levels of pH stress in this cyanobacteria was studied. Growth carve of samples were studied and measurement of protein, anthocyanin, malondialdehyde (MDA), phenol and flavonoid in controlled conditions (light and temperature) was performed in three replications. Treatments including pH of 10 (control), 6, 8 and 12 were considered. In general, changes of the growth curve for treatments with acidic medium were dropping compared to control and it was similar to control at pH=12. In all treatments, MDA levels showed meaningful changes and the amount of protein remained unchanged and the anthocyanin, phenol and flavonoid levels increased compared to control independently to treatments. According to the results of this study, although pH changes, in the long run, are readjusted and approach its optimum values again (about 10), they increase stress reactions in the short term. However, such short-term and temporary reactions cannot result in significant increases in defense reactions and subsequently, secondary compounds associated with stress, including polyhydroxybutyrate. Therefore, it seems that despite the stress occurrence at pH 6 and 12, the use of pH stress did not cause to increase polyhydroxybutyrate significantly

کلیدواژه ها:

Spirulina sp. ، pH ، Malondialdehyde ، Anthocyanin ، Phenol